NURSING ASSESMENT. NURSING DIAGNOSIS. PLANNING NURSING CARE.
INTERVENTIONS FOR CLIENTS WITH FLUID, ELECTROLYTE, AND ACID-BASE IMBALANCES
NURSING ASSESSMENT
Assessment is the first step in the nursing process and includes systematic collection, verification, organization, interpretation, and documentation of data for use by health care professionals. The accompanying display presents the essential elements of the assessment process. Effective planning of client care depends on a complete database and accurate interpretation of information. Incomplete or inadequate assessment may result in inaccurate conclusions and incorrect nursing interventions. Proper collection of assessment data directs decision-making activities of professional nurses.
The goal of assessment is the collection and analysis of data that are used in formulating nursing diagnoses, identifying outcomes and planning care, and developing nursing interventions. This chapter discusses the purpose of assessment, types of assessment, and the use of data in the assessment process.
PURPOSE OF ASSESSMENT
The purpose of assessment is to establish a database concerning a client’s physical, psychosocial, and emotional health in order to identify health promoting behaviors as well as actual and/or potential health problems. The American Nurses Association (ANA), in its Standards of Clinical Nursing Practice (1998), supports the use of the nursing process and outlines the essential components of assessment in this process (see the accompanying display). Through assessment, the nurse determines the client’s functional abilities and the absence or presence of dysfunction. The client’s normal routine for activities of daily living and lifestyle patterns are also assessed. Identification of the client’s strengths provides the nurse and other members of the treatment team information about the skills, abilities, and behaviors the client has available to promote the treatment and recovery process. Some examples of client strengths are family support, intelligence, spiritual beliefs, and coping skills (how previous problems have been solved). The assessment phase also offers an opportunity for the nurse to form a therapeutic interpersonal relationship with the client. During assessment, the client is provided an opportunity to discuss health care concerns and goals with the nurse.
TYPES OF ASSESSMENT
The type and scope of informatioeeded for assessment are usually determined by the health care setting and needs of the client (see Figure 6-1).
Three types of assessment are comprehensive, focused, and ongoing. Although a comprehensive assessment is most desirable in initially determining a client’s need for nursing care, time limitations or special circumstances may dictate the need for abbreviated data collection, as represented by the focused assessment.
The assessment database can then be expanded after the initial focused assessment, and data should be updated through the ongoing assessment process.
COMPREHENSIVE ASSESSMENT
A comprehensive assessment is usually completed upon admission to a health care agency and includes a complete health history to determine current needs of the client. This database provides a baseline against which changes in the client’s health status can be measured and should include assessment of physical and psychosocial aspects of the client’s health, the client’s perception of health, the presence of health risk factors, and the client’s coping patterns.
FOCUSED ASSESSMENT
A focused assessment is an assessment that is limited in scope in order to focus on a particular need or health care problem or potential health care risks. Focused assessments are not as detailed as comprehensive assessments and are often used in health care agencies in which short stays are anticipated (e.g., outpatient surgery centers and emergency departments), in specialty areas such as labor and delivery, and in mental health settings or for purposes of screening for specific problems or risk factors (e.g., well-child clinics). See the accompanying display for sample questions used to assess a client experiencing labor.
ONGOING ASSESSMENT
Systematic follow-up is required when problems are identified during a comprehensive or focused assessment. An ongoing assessment is an assessment that includes systematic monitoring and observation related to specific problems. This type of assessment allows the nurse to broaden the database or to confirm the validity of the data obtained during the initial assessment. Ongoing assessment is particularly important when problems have been identified and a plan of care has been implemented to address these problems.
Systematic monitoring and observations allow the nurse to determine the response to nursing interventions and to identify any emerging problems.
The nurse delivering care to a client at home uses ongoing assessment. In the home, the nurse often has to direct the client to provide information relevant to the current problem, as the client may have a tendency to spend a lot of time telling stories of past medical problems and treatment, as opposed to providing information relevant to the situation at hand (Humphrey, 1994). Use of specific questions will be most helpful in eliciting specific information (see the accompanying display).
DATA COLLECTION
The nurse must possess strong cognitive, interpersonal, and technical skills in order to elicit appropriate information and make relevant observations during the data collection process. This process often begins prior to initial contact between the nurse and the client, primarily through the nurse’s review of biographical data and medical records. Upon meeting the client, the nurse continues data collection through interview, observation, and examination. A variety of sources and methods are used in compiling a comprehensive database.
TYPES OF DATA
Client data include information that the client communicates concerning perceptions of his or her own health status, as well as specific observations made by the nurse.
These two types of information are referred to as subjective and objective data.
Subjective data are data from the client’s point of view and include feelings, perceptions, and concerns. The data (also referred to as symptoms) are obtained through interviews with the client. They are called subjective because they rely on the feelings or opinions of the person experiencing them and cannot be readily observed by another.
Objective data are observable and measurable (quantitative) data that are obtained through observation, standard assessment techniques performed during the physical examination, and laboratory and diagnostic testing.
These data (also called signs) can be seen, heard, or felt by someone other than the person experiencing them. Assessments that are comprehensive and accurate include both subjective and objective data.
SOURCES OF DATA
A comprehensive database should include data from every possible source (see the accompanying display). The client should always be considered the primary source of information; however, other sources should not be overlooked.
The client’s family and significant others can also provide useful information, especially if the client is unable to verbalize or relate information. In addition, other health care professionals who have cared for the client may contribute valuable information. Medical records should also be reviewed, including the medical history and physical examination; results of laboratory and diagnostic tests and various health care professionals should also be consulted.
Pertinent literature should be investigated in order to pursue relevant information and plan appropriate nursing interventions. Written standards are valuable sources of data for comparison, for example, a standard table of infant growth to determine if an infant’s weight and height are withiormal growth range. Another valuable source of data is knowledge about the client’s normal parameters of functioning. The nurse’s knowledge based on experience is another important source of data.
METHODS OF DATA COLLECTION
The nurse collects information through the following methods: observation, interview, health history, symptom analysis, physical examination, and laboratory and diagnostic data. These approaches require systematic use of assessment skills that are discussed below.
OBSERVATION
The nurse uses the skill of observation to carefully and attentively note the general appearance and behavior of the client. These observations occur whenever there is contact with the client and include factors such as client mood, interactions with others, physical and emotional responses, and any safety considerations.
Observation helps the nurse determine the client’s status, both physical and mental. By carefully watching the client, the nurse can detect nonverbal cues that indicate a variety of feelings, including presence of pain, anxiety, and anger. Observational skills are essential in detecting the early warning signs of physical changes (e.g., pallor and sweating).
INTERVIEW
An interview is a therapeutic interaction that has a specific purpose. The purpose of the assessment interview is to collect information about the client’s health history and current status in order to make determinations about the client’s health needs. Effective interviewing depends on the nurse’s knowledge and ability to skillfully elicit information from the client using appropriate techniques of communication. Observation of nonverbal behavior during the interview is also essential to effectivem data collection.
INTERVIEW PREPARATION
The interview is more productive if the nurse has an opportunity to prepare for the interaction. Such preparation includes review of the client’s medical records, conversations with other health care team members (e.g., personnel in emergency departments or long-term care facilities), and research of the presenting medical diagnosis. This information can be useful in obtaining the client’s relevant history and formulating a current needs assessment.
INTERVIEW STAGES
Since the assessment interview often occurs at the beginning of a nurse-client relationship, it is helpful to begin the process with an orientation phase. During this period introductions are made, rapport is established, and roles are defined. The nurse interviews for a variety of reasons throughout the nurse-client relationship, including data collection, teaching, exploration of the client’s feelings or concerns, and provision of support.
The first few minutes of the nurse-client meeting may give an indication of the type of interviewing needed, so it is important that the nurse exhibit good listening skills as the relationship leads into the interview process.
There are three phases to an interview: introduction, working, and closure.
INTRODUCTION
The introduction stage of the interview establishes the goals for the interaction. The primary goal of the assessment interview is the collection of data about the client. In this phase of the interview, the purpose and use of the data collection should be discussed. For example, the nurse might state, “I need to ask you a few questions and talk to you for a few minutes about your health so that we can better plan your care.”
Adequate time and privacy should be allowed for the interview so that the client feels free to share any information that may be relevant. The nurse should also inform the client about the approximate duration of the interview.
The client is more likely to respond freely if the interview environment provides comfort and privacy and if rapport exists between the client and the nurse. The nurse should sit (if possible), establish eye contact with the client, and listen attentively. It is the nurse’s responsibility to note nonverbal messages that can indicate that the client is uncomfortable, tired, or preoccupied with other matters. If this situation occurs, it might be necessary to complete the interview at a later time.
For example, if the client is guarding an incision and verbalizing discomfort or is extremely anxious about an impending procedure, only essential data are collected and the comprehensive interview is postponed until immediate needs have been met.
WORKING
The working stage of the interview focuses on the details of data collection. The scope of the assessment interview depends on the type of assessment to be conducted (e.g., comprehensive or focused). The interview may be structured and formal (used in situations when a large amount of information needs to be obtained) or unstructured and informal (used in interactions that focus on a specific area of concern to the client). The nurse should be familiar with the specific assessment format used by the health care agency so that attentionn can be focused toward the client rather than the form itself. The interview generally begins with questions about biographical and other nonthreatening information.
The client’s reason for seeking health care is also addressed early in the working phase. The depth of the majority of questions that the nurse will ask the client depends on the data collection model used by the health care agency. Information is usually gathered from the general to the specific, with details about intimate or potentially embarrassing topics reserved until later in the interview.
The Nursing Checklist provides guidelines for interview preparation.
Techniques used during the interview will be determined by the setting and purpose of the interview. A comprehensive interview that seeks to identify problems and concerns is facilitated by open-ended questions, while an interview that focuses on specific details about a presenting problem will be facilitated by direct, closed questions. For example, an emergency setting would likely employ more direct, closed questions, while admission to a long-term care facility might require greater use of open-ended questions.
Closed questions are questions that can be answered briefly or with one-word responses. For example, the question “Have you been in the hospital before?” is a closed question that can easily be answered by a one-word response. Questions about the dates of and reasons for the hospitalizations are also closed questions that require brief answers.
Open-ended questions are questions that encourage the client to elaborate about a particular concern or problem. For example, the question “What led to your coming here today?” is open-ended and allows the client flexibility in response. Both closed and open-ended questions can be effective in collecting information.
CLOSURE
Closure is established in the introduction phase when approximate time parameters are set. As the interview session is concluding, the nurse should indicate this fact by stating that almost all the informatioeeded has been obtained or that the time for the interview is almost over. This action allows the client an opportunity to present any other relevant information and it avoids surprises when the interview terminates.
During the closure phase, the nurse summarizes what was covered or accomplished during the interview and requests validation of perceptions with the client. If the nurse or the client feels that additional time is needed for further exploration of specific points discussed during this session, plans can be made for future interviews.
HEALTH HISTORY
A primary focus of the data collection interview is the health history. The health history is a review of the client’s functional health patterns prior to the current contact with a health care agency. While the medical history concentrates on symptoms and the progression of disease, the nursing health history focuses on the client’s functional health patterns, responses to changes in health status, and alterations in lifestyle. The health history is also used in developing the plan of care and formulating nursing interventions.
DEMOGRAPHIC INFORMATION
Personal data including name, address, date of birth, gender, religion, race/ethnic origin, occupation, and type of health plan/insurance should be included. This information may be useful in helping to foster understanding of a client’s perspective.
REASON FOR SEEKING HEALTH CARE
The client’s reason for seeking health care should be described in the client’s own words. For example, the statement “fell off four-foot ladder and landed on right shoulder; unable to move right arm” is the client’s actual report of the event that precipitated his or her need for health care. The client’s perspective is important because it explains what is significant about the event from the client’s point of view. It is also important to determine the time of the onset of symptoms as well as a complete symptom analysis.
PERCEPTION OF HEALTH STATUS
Perception of health status refers to the client’s opinion of his or her general health. It may be useful to ask clients to rate their health on a scale of 1 to 10 (with 10 being ideal and 1 being poor), together with the clients’ rationale for their rating score. For example, the nurse may record a statement such as the following to represent the client’s perception of health: “Rates health a 7 on a scale of 1 (poor) to 10 (ideal) because he must take medication regularly in order to maintain mobility, but the medication sometimes upsets his stomach.”
PREVIOUS ILLNESSES, HOSPITALIZATIONS, AND SURGERIES
The history and timing of any previous experiences with illness, surgery, or hospitalization are helpful in order to assess recurrent conditions and to anticipate responses to illness, since prior experiences often have an impact on current responses.
CLIENT/FAMILY MEDICAL HISTORY
The nurse needs to determine any family history of acute and chronic illnesses that tend to be familial. Health history forms will frequently include checklists of various illnesses that the nurse can use as the basis of the questions about this aspect. The client should be instructed that family history refers to blood relatives. It is also helpful to indicate who the relative is in relation to the client (e.g., mother, father, sister).
IMMUNIZATIONS/EXPOSURE TO COMMUNICABLE DISEASE
Any history of childhood or other communicable diseases should also be noted. In addition, a record of current immunizations should be obtained. This is particularly important with children; however, records of immunizations for tetanus, influenza, and hepatitis B can also be important for adults. If the client has traveled out of the country, the time frame should be indicated in order to determine incubation periods for relevant diseases. The client should also be asked about potential exposure to communicable diseases, such as tuberculosis, or to human immunodeficiency virus (HIV).
ALLERGIES
Any drug, food, or environmental allergies should be noted in the health history. In addition to the name of the allergen, the type of reaction to the substance should also be noted.
For example, a client may report that he or she developed a rash or became short of breath. This reaction should be recorded. Clients may report an “allergy” to a medication because they developed an upset stomach after ingesting it, which the nurse will recognize as a side effect that would not necessarily preclude administration of the drug in the future.
CURRENT MEDICATIONS
All medications currently taken, both prescription and over-the-counter, are to be recorded by name, frequency and dosage. Remind clients that this information should include medications such as birth control pills, laxatives, and nonprescription pain relief medications. Ask which, if any, herbal preparations the client uses. Patterns related to caffeine and alcohol intake and use of tobacco or recreational drugs should also be explored.
Use of alternative/complementary treatment methods, including herbals, is ofteot shared by health care consumers. Some clients fear rejection or ridicule when divulging such information with health care providers. The nurse uses a sensitive, nonjudgmental approach when assessing for the client’s use of all healing practices.
DEVELOPMENTAL LEVEL
Knowledge of developmental level is essential for considering appropriate norms of behavior and for appraising the achievement of relevant developmental tasks.
Any recognized theory of growth and development can be applied in order to determine if clients are functioning within the parameters expected for their age group.
For example, if the nurse uses Erikson’s stages of psychosocial development, validation of an adult client attaining the developmental task of generativity versus stagnation can be validated by the nurse’s statement, such as “client prefers to spend time with his family; very involved in children’s school activities.”
PSYCHOSOCIAL HISTORY
Psychosocial history refers to assessment of dimensions such as self-concept and self-esteem as well as usual sources of stress and the client’s ability to cope.
Sources of support for clients in crisis, such as family, significant others, religion, or support groups, should be explored.
SOCIOCULTURAL HISTORY
In exploring the client’s sociocultural history, it is important to inquire about the home environment, family situation, and client’s role in the family. For example, the client could be the parent of three children and the sole provider in a single-parent family.
The responsibilities of the client are important data through which the nurse can determine the impact of changes in health status and thus plan the most beneficial care for the client.
ACTIVITIES OF DAILY LIVING
The activities of daily living is a description of the client’s lifestyle and capacity for self-care and is useful both as baseline information and as a source of insight into usual health behaviors. This database should include the following areas:
Nutrition: Includes type of diet and foods eaten and fluids consumed regularly, food preparation, the size of portions, and the number of meals per day. Food preferences and dislikes, as well as the client’s need for assistance in food preparation or eating should also be determined.
Elimination: Includes both urinary and bowel elimination frequency and patterns. Any recent changes or problems in these patterns should be noted.
Rest/sleep: Includes the usual number of hours of sleep, number of hours of sleep needed to feel rested, sleep aids used, and the time within the day or night when sleep usually occurs. Any bedtime rituals (especially with children) should also be noted.
Activity/exercise: Includes types of exercise and patterns in a typical day or week. If assistance is needed with activities such as walking, standing, or meeting hygienic needs, this information should be noted.
REVIEW OF SYSTEMS
The review of systems (ROS) is a brief account from the client of any recent signs or symptoms associated with any of the body systems. This allows the client an opportunity to communicate any deviations from normal that have not been otherwise identified. The review of systems relies on subjective information provided by the client rather than on the nurse’s own physical examination.
When a symptom is encountered, either while eliciting the health history or during the physical examination of the client, the nurse should obtain as much information as possible about the symptom. Relevant data include:
• Location: The area of the body in which the symptom (such as pain) can either be pointed to or described in detail.
• Character: The quality of the feeling or sensation (e.g., sharp, dull, stabbing).
• Intensity: The severity or quantity of the feeling or sensation and its interference with functional abilities. The sensation can be rated on a scale of 1 (very little) to 10 (very intense).
• Timing: The onset, duration, frequency, and precipitating factors of the symptom.
• Aggravating/alleviating factors: The activities or actions that make the symptom worse or better.
PHYSICAL EXAMINATION
The purpose of the physical examination is to make direct observations of any deviations from normal and to validate subjective data gathered through the interview.
Baseline measurements are obtained, and physical examination techniques are used to gather objective data.
BASELINE DATA
Baseline data collection is the systematic organization of observations obtained during the physical examination that forms the basis for comparison and evaluation to establish the status of a client at a given point in time.
Measurement of height, weight, and vital signs (temperature, pulse, respirations, and blood pressure) is important for comparison with future measurements in order to judge the significance of any changes (progress or regression) over time.
ASSESSMENT TECHNIQUES
The physical examination incorporates the use of visual, auditory, tactile, and olfactory senses and the use of systematic assessment techniques. The use of visual, auditory, and tactile senses will be described with each of the specific assessment techniques. In addition, olfaction (sense of smell) is helpful in detecting characteristic odors as well as those associated with altered health states.
For example, presence of infection is sometimes first detected by the change in the characteristic odor of body fluids or drainage. The four assessment techniques used in physical examination are inspection, palpation, percussion, and auscultation.
INSPECTION
Inspection involves careful visual observation. The client is observed first from a general point of view and then with specific attention to detail. For example, the nurse first observes for patterns of skin lesions and then focuses on the specific characteristics of individual lesions. Instruments such as a penlight and otoscope are often used to enhance visualization.
Effective inspection requires adequate lighting and exposure of the body parts being observed. Beginning nurses often feel self-conscious or embarrassed using the technique of inspection; however, most become comfortable with the technique over time. Nurses must also be sensitive to the client’s feelings of embarrassment with the use of inspection and respond to this situation by discussing the technique with the client and using measures such as draping in order to increase the client’s comfort level.
PALPATION
Palpation uses the sense of touch to assess texture, temperature, moisture, organ location and size, vibrations and pulsations, swelling, masses, and tenderness. Palpation requires a calm, gentle approach and is used systematically, with light palpation preceding deep palpation and palpation of tender areas performed last.
The technique of palpation uses the hands and fingers in different ways for assessment of:
• Temperature: Best detected using the dorsal (back) surface of the hand
• Texture, pulses, and swelling: Best detected using fingertips
• Vibration: Best detected with the base of the fingers
• Shape and consistency of organs or masses: Best detected by grasping organ or mass between fingertips
PERCUSSION
Percussion uses short, tapping strokes on the surface of the skin to create vibrations of underlying organs. It is used for assessing the density of structures or determining the location and the size of organs in the body. Structures with relatively more air (such as the lungs) produce louder, deeper, and longer sounds with ercussion than more dense, solid structures (such as the liver), which produce softer, higher, and shorter sounds.
AUSCULTATION
Auscultation involves listening to sounds in the body that are created by movement of air or fluid. Areas most often auscultated include the lungs, heart, abdomen, and blood vessels. Although direct auscultation is sometimes possible, a stethoscope is usually employed in order to channel the sound.
LABORATORY AND DIAGNOSTIC DATA
Results of laboratory and diagnostic tests can be useful objective data as these values often serve as defining characteristics for various altered health states; these can also be helpful in ruling out certain suspected problems.
For example, diabetic clients who are poorly controlled on diet and/or medication will usually have an elevated blood glucose level. The pattern of these types of variations is useful in determining a plan of care. In addition, the effectiveness of nursing and medical interventions and progress toward health restoration are often monitored through laboratory and diagnostic test data.
DATA VERIFICATION
Data verification is the process through which data are validated as being complete and accurate. Once the nurse completes the initial data collection, the data are reviewed for inconsistencies or omissions. This process is particularly important if data sources are considered unreliable. For example, if a client is confused or unable to communicate, or if two sources provide conflicting data, it is necessary for the nurse to seek further information or clarification. Data verification is done by examining the congruence between subjective and objective data.
For example, a client might exhibit nonverbal expressions of pain (e.g., guarding a part of the body, facial grimacing) but verbally deny feeling pain. The nurse would need to consider possible reasons for this discrepancy in findings and collect more information before formulating conclusions or planning care.
Findings should also be compared with norms. Any grossly abnormal findings should be rechecked and confirmed.
DATA ORGANIZATION
After data collection is completed and information is validated, the nurse organizes, or clusters, the information together in order to identify areas of strengths and weaknesses. This process is known as data clustering. How data are organized depends on the assessment model used.
ASSESSMENT MODELS
An assessment model is a framework that provides a systematic method for organizing data. The use of a model helps to ensure comprehensive and organized data collection. A guiding framework also provides direction for decision making about nursing diagnoses. A number of nursing and nonnursing models are used to assist with organization of data. This section describes only a few of the many assessment models available to nurses.
NURSING MODELS
Nursing models have been developed to focus on a wide range of human responses to alterations in health status. These models typically include psychosocial, sociocultural, and behavioral data as well as biophysical data.
Nursing models may offer the advantage of organizing information in a mode that more easily allows transition from data collection to nursing diagnoses.
NONNURSING MODELS
Nursing, of course, neither exists nor functions in a vacuum. Nursing uses related health concepts from other disciplines, some of which are discussed next.
BODY SYSTEMS MODEL
Approaching data collection by examining body systems is sometimes referred to as the “medical model,” since it is frequently used by physicians to investigate presence or absence of disease. This method organizes data collection according to the organ and tissue function in various body systems (e.g., cardiovascular, respiratory, gastrointestinal). Although nurses often use this method as well, the body systems model does not facilitate the formulation of nursing diagnoses. In addition, psychosocial aspects of the client’s status are ofteeglected with resultant fragmentation of care.
HIERARCHY OF NEEDS
Abraham Maslow’s hierarchy of needs proposes that an individual’s basic needs (physiological) must be met before progressing to higher-level needs. Maslow’s framework can be used to prioritize needs. Use of a hierarchy of needs model requires initial assessment of all physiological needs, followed by assessment of higher-level needs.
Using Maslow’s theory, a person’s needs should be addressed in the following order:
First: Physiologic needs—the basic survival needs, such as food, water, and oxygen.
Second: Safety and security needs—both physical (e.g., protection from bodily harm) and psychological (e.g., security and stability) needs.
Third: Need for love and belonging—humans have an innate need to be a part of a group, and to feel accepted by others.
Fourth: Self-esteem needs—individuals need to feel they are valued and worthwhile.
Fifth: Self-actualizatioeeds—the need to function at one’s optimal level, and to be personally fulfilled.
DATA INTERPRETATION
Data clustering facilitates recognition of patterns, and determination of further data that are needed. Data interpretation is necessary for identification of nursing diagnoses.
DATA DOCUMENTATION
Accurate and complete recording of assessment data are essential for communicating information to other health care team members. In addition, documentation is the basis for determining quality of care and should include appropriate data to support identified problems.
INTERVENTIONS FOR CLIENTS WITH FLUID, ELECTROLYTE, AND ACID-BASE IMBALANCES
Homeostasis
The human body functions best when certain conditions are kept within a narrow range of normal. One area extremely important for homeostasis is maintenance of the body’s normal fluid volume and composition. Water is the most common substance in the body. It is needed to deliver dissolved nutrients, electrolytes, and other substances to all organs, tissues, and cells. Changes in body fluid in terms of either the amount of water or the concentration of electrolytes can affect the functioning of all cells, tissues, and organs. For proper physiologic function, the volume of all body fluids and the types and amount of dissolved substances must be carefully regulated.
Fluid Compartments
The body’s fluid is contained within three compartments: cells, blood vessels, and the tissue space (space between the cells and blood vessels). To understand this concept, visualize cars on a freeway. The cars represent cells; the lanes represent the blood vessels, and the space between the cars in the lanes represents the tissue space. The freeway itself is the body. Just as traffic is ongoing and continuous, fluids move constantly from one compartment to another to accommodate the cell’s metabolic needs Specific terms are used in describing compartmentalized body fluid. The prefixes (see the accompanying display) used with the root words for the compartments that contain the body fluid give meaning to the following terms:
• Intracellular fluid: within the cell
• Intra vascular fluid: within blood vessels
• Interstitial fluid: between cells; fluid that surrounds cells
There are two types of body fluid: intracellular (ICF) and extracellular (ECF).
Because intravascular and interstitial fluid are outside the cells, these fluids are extracellular. Key terms used in explaining the movement of molecules in body fluids are:
• Solute: Substance dissolved in a solution
• Solvent: Liquid that contains a substance in solution
• Permeability: Capability of a substance, molecule, or ion to diffuse through a membrane (covering of tissue over a surface, organ, or separating spaces)
• Semipermeable: Selectively permeable (All membranes in the body allow some solutes to pass through the membrane without restriction but will prevent the passage of other solutes). Cells have permeable membranes that allow fluid and solutes to pass into and out of the cell. Permeability allows the cell to acquire the nutrients it needs from extracellular fluid to carry on metabolism and to eliminate metabolic waste products.
Filtration
Filtration is the movement of fluid through a cell or blood vessel membrane because of hydrostatic pressure differences on both sides of the membrane. Basically, filtration depends on differences in water volume exerting pressure against confining walls.
All fluid has weight. The overall weight of a fluid is related to the amount of fluid present in the confined space. Water molecules in a confined space constantly press outward against the confining walls or boundaries. Hydrostatic pressure is the force exerted by water molecules against the confining walls of a space. This pressure is caused by the weight of fluid against the walls. Hydrostatic pressure may be thought of as “water-pushing” pressure, because it is a force that moves water outward from a confined space through a membrane
Physiologic Activity
Water is the largest component of any body fluid. The amount of water in any body fluid compartment is a main factor in determining the hydrostatic pressure of that compartment. The proportion of water present in a fluid is inversely related to the viscosity (thickness) of that fluid. Thus more water and less solute results in decreased viscosity, and less water with more solute results in increased viscosity. Blood, a viscous fluid (more viscous than water), is confined within the blood vessels. Blood has hydrostatic pressure because of its weight and volume and also because the heart is pumping blood into the arterial circulation. The hydrostatic pressures of two fluid compartments can be compared whenever a permeable (porous) membrane separates the two compartments. If the hydrostatic pressure is the same in both fluid compartments, a state of equilibrium exists for hydrostatic pressure. If the hydrostatic pressure is not the same in both compartments, a state of disequilibrium.
This means that the two compartments have a gradient, or graded difference, of hydrostatic pressure: one compartment has a higher hydrostatic pressure than the other. Because the human body constantly seeks equilibrium, a gradient across a cell membrane causes forces to rearrange the distribution of substances on both sides of the membrane until an equilibrium is reached. In most instances, substances move or are rearranged from the greater amount of pressure or concentration to the lesser amount. Thus when a hydrostatic pressure gradient exists between two fluid compartments, fluid from the compartment with the higher hydrostatic pressure moves through (filters) the membrane into the compartment with the lower hydrostatic pressure. This filtration continues only as long as the hydrostatic pressure gradient exists. An equilibrium is reached when enough fluid leaves one compartment and enters the other compartment to make the hydrostatic pressure in both compartments equal.
When the two compartments are in equilibrium for hydrostatic pressure, a gradient no longer exists between them. Although water molecules may be exchanged evenly back and forth between two compartments in equilibrium, no net filtration of fluid occurs. In equilibrium, neither compartment gains or loses water molecules, and the hydrostatic pressure in both compartments remains the same.
Clinical Function and Significance
Blood pressure is a hydrostatic filtering force measured in millimeters of mercury (mm Hg). It moves whole blood from the heart to tissue areas where filtration can occur. Filtration is important for the exchange of water, nutrients, and waste products when blood arrives at the tissue capillaries.
One factor that determines whether or not fluid leaves the blood vessels and enters the tissue spaces (interstitial fluid) is the difference between the hydrostatic pressure of the fluid in the capillaries and that of the fluid in the interstitial tissue spaces. The lining of the capillaries is only one cell layer thick. Therefore the “wall” that holds blood in the capillaries is thin.
Large spaces (pores) between the cells in the capillary membrane help water filter freely through capillary membranes in either direction if a hydrostatic pressure gradient is present
Figure • The process of filtration. (©
Compartment A has more water molecules and greater hydrostatic pressure than does compartment B.
Water molecules move down the hydrostatic pressure gradient from compartment A through the permeable membrane into compartment B, which has a lower hydrostatic pressure. Enough water molecules have moved down the hydrostatic pressure gradient from compartment A into compartment В that both sides now have the same amount of water and the same amount of hydrostatic pressure. An equilibrium of hydrostatic pressure now exists between the two compartments, and no further net movement of water will occur.
Edema (tissue swelling) can develop as a result of changes iormal hydrostatic pressure gradients, such as in clients with right-sided congestive heart failure. In this condition, the volume of blood in the right side of the heart increases greatly because the right ventricle is too weak to pump blood efficiently into the pulmonary blood vessels. As blood volume accumulates, blood backs up into the venous system, and venous hydrostatic pressure rises. The increased venous pressure causes capillary hydrostatic pressure to increase until it is higher than the hydrostatic pressure in the interstitial spaces. Excess filtration of fluid from the capillaries into the interstitial tissue spaces occurs, resulting in the formation of visible edema.
Diffusion
Diffusion is the free movement of particles (solute) across a permeable membrane down a concentration gradient, that is, from an area of higher concentration to an area of lower concentration. Diffusion controls the movement of particles in solution across various body membranes.
Figure: The process of diffusion.
A. A small lump of sugar is placed in a beaker of water, its molecules dissolve and begin to diffuse outward. B., C. The sugar molecules continue to diffuse through the water from an area of greater concentration to an area of lesser concentration. D. Over a long period of time, the sugar molecules are evenly distributed throughout the water, reaching a state of equilibrium. Example of diffusion in the human body: Oxygen diffuses from an alveolus in a lung, where it is in greater concentration, across the capillary membrane, into a red blood cell, where it is in lesser concentration.
Physiologic Activity
The diffusion of particles into and out of cells and fluid compartments occurs via brownian motion, the kinetic energy of molecular motion. Brownian motion is the vibration of single molecules caused by electrons orbiting at the core of each molecule. Such motion produces totally random movement of molecules, which causes molecules to move and bump into each other within a confined space. These collisions cause a temporary increase in the speed of movement. As a result of the collisions, molecules in a solution spread out evenly through whatever space is available. They move from an area of higher concentration of molecules to an area of lower concentration until equal concentrations are present in all areas. The number of collisions is related to the concentration of molecules in a confined space. Spaces with many molecules have more collisions and faster molecule motion than spaces with fewer molecules.
A concentration gradient exists when two areas have different concentrations of the same type of molecules. Brownian motion of the molecules causes them to move down the concentration gradient. As a result of brownian motion, any membrane that separates two areas is struck repeatedly by molecules. When the molecule strikes a pore in the membrane that is large enough for it to pass through, diffusion occurs. The likelihood of any single molecule colliding with the membrane and going through a pore is much greater on the side of the membrane with a higher molecule concentration. The speed of diffusion is directly related to the degree of concentration difference between the two sides of the membrane.
The degree of concentration difference is usually referred to as the steepness of the gradient: The larger the concentration difference between the two sides, the steeper the gradient. Diffusion is more rapid when the concentration gradient is steeper (just as a ball rolls downhill more rapidly when the hill is steep than when the hill is nearly flat). The greater the difference in concentration, the more rapidly diffusion occurs from the area of higher concentration to the area of lower concentration. Diffusion of solute particles continues through the membrane as long as a concentration gradient exists between the two sides of the membrane. When the concentration of solute is the same on both sides of the membrane, an equilibrium exists and an equal exchange (not a net movement) of solute continues.
Clinical Function and Significance
Diffusion is important in the transport of gases and in the movement of most electrolytes, atoms, and molecules through cell membranes. Unlike capillary membranes, which permit the diffusion of most small-sized substances down a concentration gradient, cell membranes are selective. They permit the movement of some substances and inhibit the movement of other substances. Some molecules cannot move across a cell membran. “downhill” gradient exists, because the membrane is impermeable (not porous) to that molecule. Thus the concentration gradient is maintained permeability and special transport systems cause differences in the concentrations of specific substances from one fluid compartment to another.
For example, under normal conditions the fluid outside of the cells, the extracellular fluid (ECF), contains almost ten times more sodium ions than the fluid inside the cell, the intracellular fluid (ICF).
This extreme concentration difference results from the relative impermeability of the cell membrane to sodium and from a special “sodium pump” that moves any extra sodium out of the cell “uphill” against its concentration gradient and back into the ECF.
In some instances diffusion cannot occur without assistance, even down steep concentration gradients, because of membrane selectivity. A clinical example is the fact that even though the concentration of glucose is much higher in the ECF than in the ICF (creating a steep gradient for glucose), glucose cannot cross most cell membranes without the help of insulin. When insulin is present in the ECF, it binds to insulin receptor sites on cell membranes, which makes the membranes much more permeable to glucose. Glucose can then cross the cellular membrane down its concentration gradient until either an equilibrium of glucose concentration is created or insulin binding decreases.
Diffusion across a cell membrane that requires the assistance of a transport system or membrane-altering system (e.g., insulin) is called facilitated diffusion or facilitated transport. Because this type of transport occurs down a concentration gradient and requires no energy from the cell, it is a form of diffusion.
Osmosis
Osmosis is the process by which only water molecules (solvent) move through a selectively permeable membrane. For osmosis to occur, a membrane must separate two fluid compartments, at least one of which must contain a solute that cannot move through the membrane. (The membrane is therefore impermeable to this solute.) A concentration gradient of this solute must also exist. If the membrane were permeable to this solute, then the solute would diffuse through the membrane down its concentration gradient until the concentrations of solute were equal on both sides of the membrane. Because the membrane is impermeable to the solute, these particles cannot cross the membrane, but water molecules can.
Physiologic Activity
For the fluid compartments to have equal concentrations of solute, the water molecules must move down their concentration gradient from the side with the higher concentration of water molecules (and thus a lower concentration of solute molecules) to the side with the lower concentration of water molecules (and thus a higher concentration of solute molecules). This movement continues until both compartments contain the same proportions of solute to solvent. The more dilute (less concentrated) fluid contains proportionately fewer solute molecules and more water molecules than the more concentrated fluid. Thus water moves by osmosis down its concentration gradient from the area of more dilute solute to the area of more concentrated solute until a new equilibrium is achieved. At this point, the concentrations of solute in the fluid compartments (the proportion of solute to solvent) on both sides of the membrane are equal, even though the total numbers of solute and volume of water may be different. This equilibrium is achieved by the movement of water molecules rather than the movement of solute molecules. Factors that determine whether and how fast osmosis occurs include the overall concentration of particles (solute) in solution, how easily the solute dissolves in water (solubility), and the amount of membrane available for osmosis.
Concentration of solute
The concentration of particles in body fluids is expressed in milliequivalents per liter (mEq/L), millimoles per liter (mmol/L), and milliosmoles per liter (mOsm/L). Osmoles and milliosmoles are used to describe the total concentration of solute particles (including electrolytes) contained in a solution. The number of milliosmoles present in body fluids can be expressed as either osmolarity or osmolality.
Osmolarity is the number of milliosmoles in a liter of solution; osmolality is the number of milliosmoles in a kilogram of solution. The normal osmolarity value for plasma and other body fluids ranges from 270 to 300 mOsm/L.
The body functions best when the osmolarity of the fluids in all compartments is approximately 300 mOsm/L. Many mechanisms work to keep the solute concentration close to optimum levels. When all body fluids have this solute concentration, the osmotic pressures (water-pulling) of the various fluid compartments are essentially equal, and no net water movement occurs. In such a situation, the body fluids are said to be isosmotic to each other. Another term with essentially the same meaning is isotonic (sometimes called nor-motonic).
Examples of specific intravenous (IV) solutions with overall concentrations of specific substances equaling 270 to 300 mOsm/L include 0.9% sodium chloride in water and Ringer’s lactate in water. Because these solutions are isotonic (or isosmotic) to plasma, their addition to plasma does not change the osmolarity or osmotic pressure of the plasma.
Fluids with osmolarities (solute concentrations) greater than 300 mOsm/L are hyperosmotic, or hypertonic, compared with isosmotic fluids. Hyperosmotic fluids have a greater osmotic pressure than do isosmotic fluids and tend to pull water from the isosmotic fluid compartment into the hyperosmotic fluid compartment until an osmotic balance is achieved. Fluids with osmolarities of less than 270 mOsm/L are hypo-osmotic, or hypotonic, compared with isosmotic fluids. Hypo-osmolar fluids have a lower or smaller osmotic pressure than isosmotic fluids. As a result, water tends to be pulled from the hypo-osmotic fluid compartment into the isosmotic fluid compartment until an osmotic balance is achieved.
Solubility of solute
Solubility refers to the degree to which a solute dissolves or dissociates completely in water. Solubility is directly related to osmotic pressure: The greater the solubility of the solutes in a fluid, the higher the osmotic pressure of that fluid.
Amount of available membrane
Side A has more solute molecules than does side B, even though the number of water molecules is the same on both sides. Thus side A has a greater osmotic (water pulling) pressure than does side B.
Movement of water occurs by osmosis toward side A because it has greater osmotic pressure. The membrane is not permeable to the solute molecules, so the actual number of solute molecules on side A and side В does not change. Only the water molecules move, because the membrane is not permeable to the solute molecules.Enough water molecules have moved from side В into side A that the actual concentration of solute is now the same on both sides, with a ratio of water to solute of 2:1. An equilibrium of osmotic pressure now exists between the two compartments, and no further net movement of water molecules or solute molecules will occur.
Clinical Function and Significance
Osmosis and filtration act together in capillary fluid dynamics to regulate both extracellular and intracellular fluid volumes. The thirst mechanism is an excellent example of the importance of osmosis in maintaining homeostasis. Thirst results from the activation of cells in the hypothalamus of the brain that respond to changes in extracellular fluid (ECF) osmolarity. These cells are so sensitive to changes in ECF osmolarity that they are called osmoreceptors. When a person loses body water, such as through excessive sweating during prolonged heavy exercise, ECF volume is decreased and os-molarity is increased (hypertonic conditions exist). The cells in the thirst center shrink as water moves from the cells into the hypertonic ECF. The shrinking of these cells stimulates a person’s awareness of thirst and increases the urge to drink. The person will usually drink enough fluid to replace the water lost through sweating and restore the ECF osmolarity to normal. After the ECF volume and osmolarity return to normal levels, the osmoreceptors return to their normal size and no longer send stimulatory messages.
ACTIVE TRANSPORT
Definition
A cell must use extra energy to move a substance across the cell membrane against a concentration gradient (uphill). This type of movement is called active transport because the cell must make active efforts for net movement to occur. Because of its energy demands and uphill movement, active transport is sometimes called “pumping,” and the mechanisms are known as membrane pumps.
Physiologic Activity
Active transport systems, or pumps, are usually located in the cell membrane and act as “gatekeepers” to maintain special environments inside cells. Some active transport pumps can carry more than one substance across the membrane at the same time. The sodium-potassium pump is an example of a common active transport system that simultaneously moves two substances in opposite directions against concentration gradients.
Sodium tends to diffuse slightly down its concentration gradient into the intracellular fluid (ICF) because it has such a high extracellular fluid (ECF) concentration compared with its ICF concentration. Similarly, because potassium has such a high concentration inside the cells compared with its concentration in ECF, it tends to diffuse slightly down its concentration gradient into the ECF. The action of the sodium-potassium pump moves the extra sodium out of the cell and returns the lost potassium back into the cell. The sodium-potassium pump requires the use of cellular energy. The energy for this process usually comes from breaking a high-energy bond (~P), which occurs when a phosphate group is split off from an adenosine triphosphate (ATP) molecule. The functioning of active transport pumps depends on the presence of adequate cellular ATP.
Clinical Function and Significance
Cells use active transport to regulate cell volume and to control the intracellular concentration of many substances. All cells function best when their internal environments are maintained separately from the changes occurring in the extracellular fluid (ECF) environment.
A clinical example of what occurs when active transport fails is what results from tissue hypoxia (decreased oxygen supply in the body). Without adequate oxygen, ATP cannot be produced in sufficient amounts. Without ATP, the sodium-potassium pump cannot remove the extra sodium ions that have diffused from the ECF into the cell. The increased sodium concentration inside the cell increases the osmolarity and the osmotic pressure of the fluid inside the cell. Water moves into the cell in response to the increased osmotic pressure, causing the cell to swell and perhaps to lyse (break open) and die if oxygen is not provided.
CAPILLARY DYNAMICS
The circulatory system delivers nutrients and removes wastes at the tissue level. The important blood vessels for nutrient waste exchange are the thin-walled, porous capillaries. Nutrient delivery and waste removal depend on fluid movement in the capillary. Fluid movement at the capillary level is dynamic not only because it is continuous but also because the homeostasis of plasma and interstitial fluid volumes must be maintained. Opposing processes must occur for nutrients to move into tissue spaces, for wastes to move into circulation, and for the fluid volumes of both the vascular and tissue spaces to be maintained.
During these processes, some fluid with nutrients must leave the capillary and enter the interstitial (tissue space) fluid compartment for a short period, which temporarily expands the interstitial fluid volume. The nutrients in the interstitial fluid are taken up by the cells through various membrane transport processes. Water may be exchanged between the intracellular compartment and the interstitial compartment, but under normal circumstances there is no net change in water volume. Metabolic wastes created in the cells are moved into the interstitial fluid. These waste products and any extra fluid in the interstitial space must be returned via the capillary to the systemic circulation. If there were no way to return the fluid originally lost into the interstitial compartment back to the blood, the blood volume would be depleted to the point of circulatory failure, and the interstitial fluid compartment would greatly expand.
Capillary Forces Influencing Fluid Movement
Forces at the capillary level permit capillary fluid loss to be followed by a return of fluid to the capillary so that a near-equilibrium of fluid distribution is maintained at the capillary tissue level. The near-equilibrium is based on the fact that the forces tending to move fluid out from the capillary at the arterial end are nearly equal to the forces tending to move fluid from the interstitial compartment back into the capillary at the venous end.
Blood flowing from the arterial end of the capillary to the venous end is controlled by the following:
* Hydrostatic pressure of the blood
* Dynamic ejection of the blood from the left ventricle of the heart
* Patency or openness of the capillaries
The blood entering the arterial end of the capillary has a blood pressure, or a capillary (plasma) hydrostatic pressure (PHP), of about and permeable, and the usual tissue hydrostatic pressure is low. These factors create a natural tendency for filtration of fluid from the blood outward into the tissue spaces. The fluid portion of the blood, along with most of the smaller substances dissolved in the blood, filters through the capillary membrane into the tissue spaces. Through this process, nutrients and other essential substances can reach the cells.
If net filtration as a result of plasma hydrostatic pressure were the only force or factor involved at this level, blood volume would be progressively lost from circulation and would appear in the tissues. Fortunately, other mechanisms that favor the reabsorption of tissue fluid into the capillaries are also part of capillary dynamics. These mechanisms are plasma osmotic pressure and tissue hydrostatic pressure.
Osmosis (of water) through the capillary membrane (in either direction) occurs in response to differences in the concentrations of osmotically active substances in the capillary blood and tissue fluid. Tissue osmotic pressure (TOP) tends to draw fluid out of the capillary. Plasma osmotic pressure(POP) in the capillary tends to keep fluid in the capillary and draw fluid from the interstitial space into the capillary. Under normal conditions, osmotic pressure in capillary plasma is greater than osmotic pressure in tissue because there is a higher concentration of proteins in the blood than in the interstitial fluid.
Because the capillary membrane is highly impermeable to proteins, it does not allow blood proteins to pass freely through it into the tissue space. Therefore blood proteins remain in the capillary and add to the osmotic pressure. The specific type of osmotic pressure exerted by plasma proteins is called colloidal oncotic pressure because it is caused by the presence of proteins (colloidal substances) rather than by dissociated ions such as sodium (crystalloid substances). The average colloidal oncotic pressure in capillary blood is about
Blood pressure (hydrostatic pressure) is greater than colloidal oncotic pressure at the arterial end of the capillary. Capillary hydrostatic pressure favors the filtration of fluid fromCapillary blood normally flows from the arterial end to the venous end:
Venous end of capillary
At the arterial end, the forces that tend to move fluid from the capillary into the tissue space are
Plasma hydrostatic pressure
Tissue osmotic pressure
Total forces moving fluid out =
At the arterial end, the forces that tend to move fluid from the tissue spaces into the capillary are
Tissue hydrostatic pressure
Plasma colloidal oncotic pressure
Total forces moving fluid in =
The total forces tending to move fluid out at the arterial end are
Plasma hydrostatic pressure
Tissue osmotic pressure
Total forces moving fluid out =
At the venous end of the capillary, the forces that tend to move fluid from the tissue spaces back into the capillary are
Tissue hydrostatic pressure-
Plasma colloidal oncotic pressure
Total forces moving fluid in =
The total forces tending to move fluid out at the venous end are
Because the pressures tending to move fluid out of the capillary at the arterial end (
The capillary into the tissue spaces, and colloidal oncotic pressure favors the reabsorption of fluid from the interstitial space into the capillary. The difference between these two capillary pressures at the arterial end of the capillary indicates that the filtering force outward is greater than the reabsorbing force inward.arterial end of the capillary because the water lost from the capillary has diluted the solute concentration of the tissue fluid. As a result, forces favoring the return of water from the tissues into the capillary are greater than the forces favoring filtration, and some water returns from the interstitial space back into the capillary at the venous end.
Tissue Forces Influencing
Fluid Movement
Tissue forces also influence the movement of solutions at the capillary level. These forces are tissue hydrostatic pressure (THP) and tissue osmotic pressure (TOP), both of which are usually relatively small forces. In some diseases, however, these forces increase greatly and change capillary dynamics.
To determine the direction of fluid movement in any one area of the capillary, the forces that move fluid out from the capillary are compared with the forces that move fluid into the capillary. Two forces at the arterial end that move fluid out from the capillary are the plasma hydrostatic pressure (PHP) (normally about
Plasma hydrostatic pressure (PHP) decreases as blood flows through the length of the capillary. As filtration proceeds along the capillary, water is lost from the capillary, and the PHP gradually decreases. Therefore the pressures that create the outward filtration force (from the capillary into the interstitial fluid) decrease, whereas the pressures that create the inward reabsorption force (from the interstitial fluid into the capillary) remain the same. Eventually, the outward filtration pressures and the inward reabsorption pressures become equal.
Clinical Function and Significance
Finally, at the venous end of the capillary, the inward reabsorption forces exceed the outward filtration forces. The venous end of the capillary has a much lower hydrostatic pressure than does the arterial end. This decreased hydrostatic pressure has two causes:
• Because much of the water in the blood was filtered out of the capillary at the arterial end, the volume of water remaining in the blood at the venous end of the capillary is diminished.
Because the venous portion of the capillary is farther away from the heart than the arterial end, blood pressure is lower in the venous end.
At the venous end of the capillary, the hydrostatic pressure is low and the interstitial fluid (tissue) hydrostatic pressure is high (because water has moved from the arterial end of the capillary into the interstitial space). The colloidal osmotic pressure at the venous end of the capillary exceeds that at the arterial end because water has been lost, which increases the concentration of proteins. The tissue osmotic pressure at the venous end of the capillary is lower than at the Lymph
In most cases, not all of the fluid that leaves the capillary at the arterial end and enters the interstitial space is returned to the capillary at the venous end. A small amount remains in the tissues. If this situation is not balanced by another mechanism to return the fluid to the systemic circulation, blood volume would become depleted and the interstitial areas would constantly be edematous. Instead, this extra fluid leaking out from the capillaries is returned to the systemic circulation as lymph.
Lymph fluid is similar to blood plasma (from which it is formed) but contains far less protein. It is returned to the circulation by lymph vessels, or lymphatics. Lymphatics begin as small, thin-walled, vein-like vessels that join to form larger lymphatic vessels. Two large groups of lymphatic vessels connect the entire lymph system with the general circulatory system. The left thoracic lymph duct drains lymph from the abdomen, gastrointestinal tract, pelvis, lower extremities, left side of the thorax, left arm, and left side of the head and neck into the left subclavian vein at the point where it joins the left internal jugular vein. Lymph from the right arm, right side of the thorax, and right side of the head and neck drains into the right subclavian vein through three lymph ducts. Lymph nodes are situated along the lymphatic paths and filter the lymph fluid.
Lymphatics carry lymph fluid in one direction: toward the heart. Lymph flow is slower than blood flow because lymph has no pump and no direct connection between the arterial blood circulation and the lymphatic system. Lymph flow is enhanced by skeletal muscle contractions, intrathoracic pressure changes during breathing, and a peristalsis-like motion in the lymph vessels.
Hormonal Regulation of Fluid and Electrolyte Balance
The endocrine system helps to control fluid and electrolyte balance. Three hormones that help control these critical balances are aldosterone, antidiuretic hormone (ADH), and atrial natriuretic peptide (ANP).
ALDOSTERONE
Aldosterone is a hormone secreted by the adrenal cortex. Aldosterone secretion is stimulated by either a decreased sodium level in the extracellular fluid (ECF) or an increased sodium level in urine. Aldosterone directly influences sodium balance by preventing sodium loss. Because sodium in body fluids exerts osmotic (water-pulling) pressure, water attempts to follow sodium in physiologically proportionate amounts (Guyton & Hall, 2000). As a result of this sodium-water relationship, aldosterone secretion also indirectly regulates water balance.
In the kidney, blood is supplied to the nephrons via the afferent arteriole. Specialized cells (juxtaglomerular cells) inside the afferent arteriole near the nephron glomeralus are sensitive to changes in serum concentrations of sodium. This area of the afferent arteriole comes into direct contact with a specialized area of the distal convoluted tubule (the macula densa). Together, the juxtaglomerular cells and the macula densa form the juxtaglomerular complex. When this complex senses that actual serum sodium concentrations are lower thaormal or that the total blood volume is low, the macula densa stimulates juxtaglomerular cells to secrete renin.
Renin acts on an inactive plasma protein called an-giotensinogen, converting it to
ANTIDIURETIC HORMONE
Antidiuretic hormone (ADH), also known as vasopressin, is produced in the brain and stored in the posterior pituitary gland. The release of ADH from the posterior pituitary gland is controlled by the hypothalamus in response to changes in blood osmolarity. The hypothalamus contains specialized cells (osmoreceptors) that are sensitive to changes in blood osmolarity. Increased blood osmolarity, especially an increase in the concentration of plasma sodium, results in a slight shrinkage of these cells and triggers the hypothalamus to stimulate the posterior pituitary to release ADH.
ADH acts directly on kidney tubules and collecting ducts, making them more permeable to water. As a result, more water is reabsorbed by these tubules and returned to the circulation, which in turn decreases the osmolarity of the blood by making it more dilute. When blood osmolarity decreases, especially when the plasma sodium concentration is below normal, the osmoreceptors swell slightly and inhibit the release of ADH. Less water is reabsorbed and more is lost from the body in the urine. As a result, the amount of water in the extracellular fluid (ECF) decreases, bringing osmolarity to normal.
ATRIAL NATRIURETIC PEPTIDE
Atrial natriuretic peptide (ANP) is secreted by special cells that line the atria of the heart. It is secreted in response to increased blood volume and blood pressure. ANP binds to receptor sites in the collecting ducts of the nephrons, creating effects opposite those of aldosterone. Kidney reabsorption of sodium is inhibited at the same time that glomerular filtration is increased (Briggs et al., 1996). The outcome is increased output of urine with a high sodium content, which results in decreased circulating blood volume and decreased blood osmolarity.
Body Fluids
Fluids, especially water, make up about 55% to 60% of total adult body weight and can be divided into the extracellular fluid (ECF) and intracellular fluid (ICF). The ECF compartment accounts for approximately
A person’s age, gender, and ratio of lean mass to body fat influence the amount and distribution of body fluids. An older adult has less total body water than a younger adult. Because fat cells contain practically no water, an obese person has less total body water than a lean person of the same body weight.Decreased serum sodium concentration sensed by cells in afferent arterioleStimulates secretion of renin from juxtaglomerular complexAngiotensin I ReninBlood volume lowAngiotensin II constricts afferent arterioleBlood volume normal or highAngiotensin II constricts efferent arteriole Allows fluid to be removed, thus increasing the relative concentration of sodium in the blood Increases serum sodium level without further decreasing blood volume
WOMEN’S HEALTH CONSIDERATIONS
A woman of any age usually has less total body water than does a man of similar size and age. This difference exists because men generally have more muscle mass than women and because women have a higher percentage of body fat. Differences in muscle mass and percentage of body fat are partly a result of the influence of sex hormones. These differences in fat to lean body weight may be responsible for some of the differences seen in women’s and men’s responses to drugs.
Body fluids allow cell nutrition and transport active molecules (e.g., hormones) that are important to the regulation of normal physiologic functions. Most physiologic processes occur only in a watery environment. Body fluids are constantly renewed, purified, and replaced as fluid balance is maintained through intake and output. The total amount of water within each fluid compartment is stable, but water moves continually among all compartments. Water is not static in any compartment but is exchanged constantly while maintaining a volume equilibrium. summarizes the key points regarding fluid and electrolyte balance.
SOURCES OF FLUID INTAKE
Fluid intake is regulated through the thirst drive. Fluids enter the body primarily as liquids. Because solid foods contain up to 85% water, some fluid also enters the body as ingested solid foods. In addition, water is a by-product of cellular metabolism. This metabolic water accounts for about 300 mL of the daily water requirement. A rising plasma osmolarity or a decreasing plasma volume stimulates the sensation of thirst. Sensations such as mouth dryness or the thought that a person has not had a drink recently can trigger the thirst drive. An adult drinks an average of 1500 mL of fluid per day and obtains an additional 800 mL of fluid from ingested foods kidney is the most important and the most sensitive. Water loss via the kidney is closely regulated and is adjustable. The volume of urine excreted daily varies depending on the amount of fluid intake and the body’s need to conserve fluids.
The minimum amount of urine per day needed to dissolve and excrete toxic waste products is 400 to 600 mL. This minimal volume is called the obligatory urine output. If the 24-hour urine output falls below the obligatory output amount, wastes are retained and can cause lethal electrolyte imbalances, acidosis, and a toxic build up of nitrogen. This urine is maximally concentrated, with a specific gravity (the weight of the liquid compared with the weight of pure water) of 1.032 or higher and an osmolarity of at least 1200 mOsm/L.
Urine can also become very dilute, with a specific gravity of 1.005 and an osmolarity of 200 mOsm/L. Dilution can result from a large fluid intake and is reflected in a large volume of urine output. The ability of the kidneys to make either concentrated or very dilute urine helps to maintain fluid and electrolyte balance. With the influence of aldosterone, antidiuretic hormone (ADH), and atrial natriuretic peptide (ANP), the kidney is able to respond when extracellular fluid concentrations, volumes, or pressures change.
Other normal water loss occurs through the skin, the lungs, and the gastrointestinal tract. Additional water losses can occur via salivation, drainage from fistulas and drains, and gastrointestinal suction. “Measured by subtracting the amount returned from the amount instilled. Measurement is accurate only when these substances are excreted in liquid form.
Water loss from the skin, lungs, and stool — called insensible water loss because it cannot be controlled—can be significant. In a healthy adult, insensible water loss is about 15 to 20 mL/kg/day. Insensible water loss can increase dramatically in hypermetabolic states such as thyroid crisis, trauma, burns, states of extreme stress, and fever. For every degree Celsius of increase in body temperature, insensible water loss increases by 10%. Insensible water loss also increases when atmospheric conditions are hot and dry. Examples of clients at risk for increased insensible water loss include those undergoing mechanical ventilation and those with rapid respirations (tachypnea). Insensible water loss (not including sweat) is pure water and does not contain electrolytes. Therefore excessive amounts of insensible water loss result in a more hypertonic extracellular fluid (ECF) with a smaller volume. If this loss is not balanced by intake, the hypertonic ECF and accompanying dehydration can lead to hypernatremia (elevated serum sodium level).
Loss by sweating is variable and can reach a maximum rate of about 2 L/hr. Although it contains electrolytes, sweat is slightly hypotonic compared to plasma. The amount of sweating is regulated by the autonomic nervous system, body temperature, and blood flow in the skin. Water loss through stool is normally minimal. However, this loss can increase significantly with severe diarrhea or excessive fistula drainage. Clients with ulcerative colitis can experience a diarrheal fluid loss of several liters per day. Diarrheal fluid contains water, potassium, sodium, bicarbonate, and chloride. Thus, with diarrhea, hypotonic fluid containing some electrolytes is lost.
Electrolytes
Electrolytes, or ions, are substances in body fluids that carry an electrical charge. Cations are positively charged ions; anions are negatively charged ions. Body fluids are electrochemically neutral, which means that the number of positive ions is balanced by an equal number of negative ions. However, the distribution of ions differs in the extracellular fluid (ECF) and the intracellular fluid (ICF)
Most electrolytes have different concentrations in the ICF and ECF. This concentration difference helps maintain membrane excitability and transmit nerve impulses. The ranges of electrolyte concentration in these fluid compartments are extremely narrow. Thus even small changes in these concentrations can result in major pathologic alterations.
Electrolyte homeostasis is controlled by balancing the dietary intake of electrolytes with the renal excretion or reab-sorption of electrolytes. For example, the concentration of plasma potassium is maintained between 3.5 and 5.0 mmol/L. In theory, the potassium in common foods could greatly increase the ECF potassium concentration and lead to major problems. Usually, however, the excretion of potassium by the kidney keeps pace with potassium intake and prevents major changes in the concentration of plasma potassium.
SODIUM
Sodium (Na+) is the major cation in the extracellular fluid (ECF) and is the main factor responsible for maintaining ECF osmolarity. The activity of the sodium-potassium pump keeps the sodium concentration of the intracellular fluid (ICF) low (about 14 mmol/L) while maintaining high sodium concentrations in the plasma and other extracellular fluids. Maintaining this difference in sodium concentration is vital for the following physiologic functions:
Initiation of skeletal muscle contraction
• Initiation of cardiac contractions
• Transmission of nerve impulses
• Maintenance of ECF osmolarity Maintenance of ECF volume
• Maintenance of the kidney urine-concentrating system
The concentration of sodium in the ECF determines whether water is retained, excreted, or moved from one body compartment to another.
To maintain electrical balance, the concentration of sodium (a cation) within a body fluid must be matched by an equal concentration of anions (negatively charged substances). Each positive charge in the ECF must be balanced by a negative charge so the fluid does not carry either an overall positive or an overall negative charge. When this balance is present, a state of electroneutrality exists in that fluid. Changes in the concentration of plasma sodium seriously change fluid volume and the distribution of other electrolytes.
The normal concentration of plasma sodium ranges between 136 and 145 mEq/L or mmol/L. Sodium enters the body through the ingestion of many foods and fluids . The average dietary intake of sodium is about 6 to 12 g/day. Sodium is also stored deep within the kidney tissues and can be released to the ECF as needed. Despite great variations in sodium intake, the concentration of serum sodium usually remains within the normal range. Serum sodium balance is regulated by the kidney under the influences of aldosterone, antidiuretic hormone (ADH), and atrial natriuretic peptide (ANP).
Low serum sodium levels inhibit the secretion of ADH and ANP and stimulate aldosterone secretion. Together these actions increase serum sodium concentration by increasing kidney re-absorption of sodium and enhancing kidney loss of water.
High serum sodium levels inhibit aldosterone secretion and directly stimulate the secretion of ADH and ANP. Together these hormones cause an increase in kidney excretion of sodium and kidney reabsorption of water.
POTASSIUM
In contrast to sodium, potassium (K+) is the major cation of the intracellular fluid (ICF). The normal plasma concentration of potassium ranges from 3.5 to 5.0 mEq/L or mmol/L (see Table 11-5). The normal ICF concentration of potassium is about 140 mEq/L (mmol/L). Because of its high concentration inside cells, potassium has some control over intracellular osmolarity and volume. Keeping this large difference in potassium concentration between the ICF and the extracellular fluid (ECF) is critical for excitable tissues to generate action potentials and transmit impulses. Functions of potassium include the following:
• Regulation of protein synthesis Regulation of glucose use and storage
• Maintenance of action potentials in excitable membranes
Because potassium levels in the plasma and interstitial fluid are so low, any change in concentration is poorly tolerated by the body and seriously affects physiologic activities. For example, a decrease in plasma potassium of only 1 mEq/L (from 4 mEq/L to 3 mEq/L) is a 25% difference in total ECF potassium concentration. In contrast, a decrease in plasma sodium of 1 mEq/L (from 140 mEq/L to 139 mEq/L) is, overall, a much smaller change (less than 1%) in total ECF sodium concentration.
Potassium drifts out of cells down its concentration gradient into the ECF. Almost all foods contain potassium. Potassium intake averages approximately 2 to 20 g/day. Despite heavy potassium intake and the drifting of potassium from cellular storage sites into the ECF, the healthy body keeps plasma potassium levels within the narrow range of normal values required for physiologic function.
The primary controller of ECF potassium concentration is the sodium-potassium pump within the membranes of all body cells. This pump removes three sodium ions from the fluid inside the cell for every two potassium ions that it returns to the cell. In this way, the levels of both serum sodium and cellular potassium remain high.
Some potassium regulation also occurs through kidney function. The kidney is the excretory route for ridding the body of ECF potassium (80% of potassium removed from the body occurs via the kidney). Unlike sodium, no hormone has been identified that directly controls kidney reabsorption of potassium; thus the kidney does not conserve potassium directly.
CALCIUM
Calcium (Ca2+) is a mineral whose presence and functions are closely related to those of phosphorus and magnesium. Calcium is a divalent cation (an ion having two positive charges) that exists in the body in two forms: bound and ionized (unbound or free).
Bound calcium is usually connected to specific serum proteins, especially albumin. Ionized calcium is present in the blood and other extracellular fluid (ECF) as free calcium. Free calcium is the active form and must be kept within a narrow range in the ECF. The body functions best when plasma calcium concentrations are maintained between 9.0 and 10.5 mg/dL, or between 2.25 and 2.75 mmol/L. Because the concentration of calcium in the intracellular fluid (ICF) is low, calcium has a steep gradient between ECF and ICF. Calcium functions in many ways and in many specialized body systems, including the following:
• Enhances the activity of enzymes or reactions Increases skeletal muscle contraction
• Increases cardiac muscle contraction
• Regulates nerve impulse transmission
• Assists in blood clotting
• Provides bone strength and density
Calcium enters the body by dietary intake and absorption through the intestinal tract. Absorption of dietary calcium requires the active form of vitamin D. Calcium is stored in the bones. When both plasma calcium levels and stored calcium levels are adequate, intestinal absorption of dietary calcium is inhibited and urine excretion of excess calcium increases. When more plasma calcium is needed, parathyroid hormone (PTH) is secreted and released from the parathyroid glands. PTH causes serum calcium levels to increase in the following ways:
• Releasing free calcium from bone storage sites directly into the ECF (resorption)
• Stimulating vitamin D activation, thus increasing intestinal absorption of dietary calcium
• Inhibiting kidney excretion of calcium and stimulating kidney reabsorption of calcium
When excess calcium is present in plasma, secretion of PTH is inhibited and the secretion of thyrocalcitonin (TCT), a hormone secreted by the thyroid gland, is increased. TCT causes the plasma calcium level to decrease in the following ways:
• Inhibiting bone resorption of calcium
• Inhibiting activation of vitamin D, causing decreased gastrointestinal uptake of calcium
• Increasing kidney excretion of calcium in the urine
MAGNESIUM
Magnesium (Mg2+) is another mineral that forms a cation when dissolved in water. Adults have an average of
• Stimulating skeletal muscle contraction
• Participating in carbohydrate metabolism
• Activating adenosine triphosphate (ATP)
• Activating B-complex vitamins
• Enhancing deoxyribonucleic acid (DNA) synthesis
• Enhancing protein synthesis
Extracellular magnesium regulates blood coagulation and skeletal muscle contractility.
Magnesium is found in many foods, such as nuts, vegetables, fish, and whole grains. The daily magnesium requirement for adults is approximately 300 mg.
Although magnesium is similar to calcium in many respects and its presence in serum must be kept within a narrow range of normal values, little is known about its regulation. Magnesium is absorbed from the intestinal tract at the same place as calcium. The absorption of phosphorus inhibits magnesium absorption. Parathyroid hormone (PTH) stimulates the release of magnesium from bone in much the same way that it stimulates the release of calcium.
CHLORIDE
Chloride (Cl~) is the major anion of the extracellular fluid (ECF) and works with sodium in aintaining ECF osmotic pressure. Chloride is important in the formation of hydrochloric acid in the stomach. The normal plasma concentration of chloride ranges from 90 to 110 mEq/L or mmol/L.
Only a small amount of chloride is present inside the cells because negatively charged particles on the cell membrane repel chloride and prevent it from crossing the membrane. However, extracellular chloride can enter cells when exchanged for another anion that is leaving the cell. This situation, called a chloride shift, results in decreased concentrations of plasma chloride but no net body loss of chloride. Bicarbonate (HCO3) is the anion most commonly exchanged for chloride. Chloride enters the body through dietary intake. Because chloride (along with sodium, potassium, and many other minerals) is a part of a salt, most diets contain enough chloride to meet the normal needs of the body.
ASSESSMENT OF FLUID AND ELECTROLYTE BALANCE
History
One way of organizing history data to assess the client’s fluid and electrolyte status is to use Gordon’s Functional Health Patterns (Gordon, 2000). The patterns that most affect fluid and electrolyte status are the Nutritional-Metabolic The client’s nutritional history can often reveal a problem that affects fluid and electrolyte balance. The nurse obtains this information directly because the client may not understand the connection between dietary intake and the onset of fluid and electrolyte imbalances.
The guidelines for obtaining a thorough fluid and electrolyte history do not differ from those for assessing any other system; however, the information collected is more specific. For example, exact intake and output volumes are important, as are serial daily weights. The nurse may need to guide the client in accurately reporting the amount of fluid ingested and changes in urine patterns. The nurse also assesses the types of fluids and foods ingested to determine amount and osmolarity. Many clients do not consider solid food to contain liquid. Solid foods such as ice cream, gelatin, and ices are liquids at body temperature, and the nurse includes them when calculating fluid intake. Output fluids include losses not only through urine but also through perspiration, diarrhea, and insensible loss during fevers.
Older adults often use laxatives, which can disturb fluid and electrolyte balance. Misuse and overuse of these drugs can lead to serious imbalances.
Other important areas of the client history include body weight changes, thirst or excessive drinking, exposure to hot environments, and the presence of other disorders, such as kidney or endocrine diseases (e.g., Cushing’s disease, Addi-son’s disease, diabetes mellitus, and diabetes insipidus). The nurse makes a general assessment of the client’s level of consciousness and mental status, because changes in mental status may support findings of imbalance. In such cases, the nurse may need to check the accuracy of historical data with family members.
Physical Assessment
Hydration is the normal state of fluid balance. A normally hydrated adult is alert and has moist eyes and mucous membranes, a urine output nearly the same as the amount of fluid ingested (with a urine specific gravity of approximately 1.015), and good skin turgor.
The nurse assesses skin turgor by pinching a fold of skin. This pinched fold should return immediately to its original shape after release. Decreased turgor, a sign of dehydration, is present when the fold remains in a pinched shape after being released and rebounds slowly (tenting).
Figure • Examining the skin turgor of an older client
The nurse can best assess skin turgor in body areas that contain little fat tissue, such as over the sternum, on the forehead, or on the back of the hand. An older person may have poor skin turgor because of the loss of tissue elasticity related to the aging process; thus a true state of hydration may be more difficult to assess in an older adult than in a younger adult. The best areas for assessing turgor in the older adult are over the sternum and on the forehead.
Skin hydration assessment also includes an examination for dryness. The mucous membranes and the conjunctiva are normally moist. An assessment of fluid balance always includes an examination of the eyes, nose, and oral mucous membranes. A dry, sticky, “cottony” mouth; the absence of tearing; weight loss; and decreased urine output all indicate an actual fluid volume deficit. A major criterion used in assessing fluid and electrolyte status is accurate measurement of fluid intake and output. Accurate assessment of actual fluid intake and output is the nurse’s responsibility, and volumetric measuring devices must be used.
Behavioral and neurologic assessments are included in fluid assessment because changes in fluid balance can result in an alteration of neurologic function. In hypertonic states, neuronal cell shrinkage may induce serious nervous system excitability and hyperactivity, and convulsions may occur. Another variable to assess is the degree of thirst, but this may be difficult to gauge in a confused older client. The nurse approximates insensible water loss (e.g., sweat) in every client. Special situations also require an assessment of fluid loss from other routes, including the following:
• Fluid losses from wounds
• Gastric or intestinal drainage
• Blood loss from hemorrhage
• Drainage of body secretions, such as bile and pancreatic juices, through fistulas
Electrolytes control the activity of excitable membranes, and electrolyte imbalances are associated with altered function of these membranes. Electrolyte assessment includes a complete neuromuscular assessment of muscle tone and strength, movement, coordination, and tremors. Assessment of other systems, including the cardiac system (heart rate, the strength of contractions, and the presence of dysrhythmias) and gastrointestinal system (peristalsis), may indicate changes of excitable membrane function.
Part of the nurse’s assessment focuses on changes from previous findings (including mental status, physical examination data, and laboratory data). Fluid and electrolyte imbalances can occur quickly; therefore the nurse must be familiar with the client’s baseline assessment data to detect any changes
Psychosocial Assessment
Psychosocial assessment related to fluid and electrolyte status includes both psychologic and cultural factors that might influence balance. Depressed clients may refuse fluids or forget to drink adequate fluids. Clients with bulimia or anorexia nervosa (eating disorders) may use laxatives to excess or may induce vomiting, resulting in fluid and electrolyte imbalances. The nurse also assesses social practices. For example, excessive alcohol or drug use may lead to fluid or electrolyte imbalance.
Diagnostic Assessment
Laboratory results are important in identifying specific fluid and electrolyte imbalances or disorders that alter fluid and electrolyte status. Other laboratory values that are helpful in assessing fluid and electrolyte status include blood urea nitrogen level (BUN), glucose concentration, creatinine level, pH, bicarbonate level, osmolarity, hemoglobin, and hematocrit.
The urine test results may be helpful in assessing fluid status. If a laboratory report is not available, the nurse can perform various tests using a dipstick to help determine fluid and electrolyte status, including detecting substances that should not be present in the urine, such as glucose, acetone, protein, and blood. Urine measurements such as pH and specific gravity also can be determined in this way.Lormal body functioning requires a proper balance of all body fluids. Many health problems can disrupt fluid intake or output, placing all clients at risk for some degree of fluid imbalance. Although most imbalances of fluid are accompanied by electrolyte imbalances, this chapter focuses only on client problems associated with fluid imbalances.
Overview
In dehydration, the body’s fluid intake is not sufficient to meet the body’s fluid needs, resulting in a fluid volume deficit. Three basic types of dehydration are possible Isotonic dehydration, in which water and dissolved electrolytes are lost in equal proportions
• Hypertonic dehydration, in which water loss is greater than electrolyte loss
• Hypotonic dehydration, in which electrolyte loss is greater than water loss
Dehydration is a clinical state rather than a disease and can be caused by many factors. Dehydration may be an actual decrease in total body water caused by either too little an intake of fluid or too great a loss of fluid. Dehydration also can occur without an actual decrease in total body water, such as when water shifts from the plasma into the interstitial space. This condition is called relative dehydration.
Pathophysiology
ISOTONIC DEHYDRATION
Isotonic dehydration is the most common type of fluid volume deficit. Problems caused by isotonic dehydration result from loss of plasma volume. Isotonic dehydration involves loss of isotonic fluids from the extracellular fluid (ECF) compartment, including both the plasma and the interstitial space. Because isotonic fluid is lost, plasma osmolarity remains normal. This type of dehydration does not cause a shift of fluids between compartments, so the intracellular fluid (ICF) volume remains normal. Isotonic dehydration decreases circulating blood volume (hypovolemia) and leads to inadequate tissue perfusion. Compensatory mechanisms attempt to maintain adequate tissue perfusion to vital organs in spite of decreased vascular volume
Isotonic dehydration has many causes. These include inadequate intake of fluids and solutes, fluid shifts between compartments, and excessive losses of isotonic body fluids.
HYPERTONIC DEHYDRATION
Hypertonic dehydration is the second most common type of fluid volume deficit. The problems caused by hypertonic dehydration result from changes in the concentrations of specific electrolytes.
Hypertonic dehydration occurs when water loss from the extracellular fluid (ECF) is greater than electrolyte loss. This water loss increases the osmolarity of the remaining plasma, making it hypertonic or hyperosmolar compared with normal ECF. The hyperosmolar plasma has an increased osmotic pressure that causes fluid to move from the intracellular fluid (ICF) into the plasma and interstitial fluid spaces. The fluid shift leads to cellular dehydration and shrinkage. The fluid shift also causes the plasma volume to increase to normal or greater thaormal levels.
Hypertonic dehydration is caused by the loss of any body fluid that is hypotonic (low osmolarity, or decreased concentration of solute particles compared with isotonic body fluid) or occurs when water loss is greater than electrolyte loss. Common causes of hypertonic dehydration are conditions such as excessive perspiration, hyperventilation, ketoacidosis, prolonged fevers, diarrhea, early-stage renal failure, diabetes insipidus, and ketoacidosis in the diuretic phase
HYPOTONIC DEHYDRATION
Hypotonic dehydration is the least common type of fluid volume deficit. The problems caused by hypotonic dehydration result from fluid shifts between compartments, causing a decrease in plasma volume.
Hypotonic dehydration involves excessive loss of sodium and potassium from the ECF. This loss leads to decreased osmolarity of the remaining ECF, making it hypotonic compared with normal ECF. The decreased ECF osmolarity lowers the osmotic pressure of plasma and interstitial fluids to below that of the fluid inside the cells, the ICE As a result of this difference in osmotic pressure, water moves from the plasma and interstitial spaces into the cells, creating a plasma volume deficit and causing the cells to swell. Cell swelling causes widespread problems and symptoms. Because brain cells are more sensitive to swelling than the cells of other tissues, neurologic problems usually occur with hypotonic dehydration. Hypotonic fluid also dilutes the normal electrolyte concentrations and causes sodium and potassium imbalances. Hypotonic dehydration is usually associated with chronic illness. Chronic renal failure, in which the kidneys waste sodium, leads to hypotonic dehydration. Chronic malnutrition and taking in excessive amounts of hypotonic fluids also cause hypotonic dehydration.
OTHER CHANGES. The nurse asks the client about changes in the tightness of clothing, rings, and shoes. A sudden decrease in tightness may indicate dehydration; an increase may reflect edema. Other related findings include the sensation of palpitations or lightheadedness on moving from a lying or a sitting position to a standing position (caused by orthostatic, or postural, hypotension).
The nurse asks about any abnormal or excessive fluid losses, such as perspiration, diarrhea, bleeding, vomiting, urination, salivation, and wound drainage. Other important information to collect includes chronic illnesses, recent acute illnesses, recent surgery, and medications.
The nurse asks specific questions about urine output, including the frequency and amount of voidings. The nurse also asks about the client’s usual fluid intake and the intake during the previous 24 hours. It is just as important to determine the types of fluids ingested as it is to determine the amount of fluids ingested, because fluids vary widely in osmolarity.
ILLNESSES
• Vomiting Diarrhea
• Burns Large, draining wounds
• Liver dysfunction Diabetes mellitus
• Diabetes insipidus Renal disease
• Hemorrhage Major venous obstruction
• Prolonged febrile state
Nurse also asks whether the client has recently engaged in strenuous physical activity and, if so, whether the activity took place in hot or dry environmental conditions.
PHYSICAL ASSESSMENT/CLINICAL MANIFESTATIONS
The clinical manifestations of dehydration depend on which fluid compartments lose fluid, although all body systems are affected to some degree. The most obvious and life-threatening clinical manifestations are seen when dehydration causes a decrease in the plasma volume.
RESPIRATORY MANIFESTATIONS.
The respiratory rate increases directly with the degree of fluid loss from plasma volume. The decreased blood volume is perceived by the body as decreased oxygen levels (hypoxia), and increased respiration is an attempt to maintain oxygen delivery.
INTEGUMENTARY MANIFESTATIONS.
Changes in skin may be useful indicators of hydration. The nurse assesses for changes in the skin and mucous membranes that may indicate dehydration, including skin color, moisture, skin turgor, and edema. In older clients this information is less reliable because of poor skin turgor resulting from the loss of elastic tissue and the loss of tissue fluids with aging. The nurse assesses skin turgor by noting the following:
• How easily the skin over the back of the hand and arm can be gently pinched between the thumb and the forefinger to form a “tent”
• How soon the pinched skin resumes its normal position after release
• Whether depressions (pits) remain in the skin after a fin ger is pressed firmly but gently (over the shin, over the sternum, and over the sacrum)
• How deep the depression is (in millimeters)
• How long the depression remains
In generalized dehydration, skin turgor is poor, with the tenting remaining for minutes after pinching the skin, and no skin depressions occur with gentle pressure. The skin appears dry and scaly. The nurse assesses skin turgor in an older adult by pinching the skin over the sternum, the forehead, or the abdomen because these areas more reliably indicate hydration (see Figure).
Figure Hand veins full and bulging in the dependent position (top). Hand veins collapsed (bottom).
As a person ages, the skin loses elasticity and tents on extremities even when the person is well hydrated. In dehydration, oral mucous membranes are not moist. They may be covered with a thick, sticky, pastelike coating and may have cracks and fissures. The surface of the tongue may have deep furrows.
NEUROLOGIC MANIFESTATIONS. Dehydration may cause changes in body temperature and mental status as the brain is less perfused. The client with dehydration typically has a low-grade fever. One cause of the fever is the constriction of blood vessels that occurs as a compensation for hypovolemia. The blood vessel constriction makes heat dissipation more difficult.
Fever can also cause dehydration. A client with a temperature greater than 102° F (39° C) for longer than 6 hours is especially at risk. Older adults, who normally have a body temperature range of 96° to 98° F (35.4° to 36.6° C), are at greater risk for dehydration during episodes of fever. Mental status changes are also common with dehydration. Chart 12-2 outlines how to assess mental status quickly.
RENAL MANIFESTATIONS. The volume and the composition of urine output indicate the hydration status of the renal system. The nurse monitors urine output, comparing total output with total fluid intake and daily weights. Accurate intake and output measurement is a major nursing responsibility. Urine output below 500 mL/day for any client without renal disease is cause for concern. A client with fluid imbalance is weighed each day at the same time and on the same scale. When possible, the client wears the same amount and type of clothing for each weigh-in. Metabolic weight loss (even in starvation) usually accounts for only about V2 pound of weight loss per day. Any weight loss in excess of this amount is considered fluid loss of health and possible treatment regimens. As dehydration worsens, psychosocial activities reflect abnormal functioning of the central nervous system. The client may become anxious, restless, lethargic, and confused. These behavioral changes are more obvious in hypertonic and hypotonic dehydration because of intracellular fluid (ICF) shifts in brain cells, resulting in shrinkage or swelling of the cells. If the conditions causing the dehydration continue, circulation to cerebral tissues becomes so impaired that delirium and coma can occur.
LABORATORY ASSESSMENT
No single laboratory test result confirms or rales out dehydration. Instead, a diagnosis of dehydration is based on laboratory findings along with presenting signs and symptoms. Laboratory findings depend on the type of dehydration present. Isotonic and hypotonic dehydration states with accompanying plasma volume deficits show hemoconcentration (elevated levels of hemoglobin, hematocrit, serum osmolarity, glucose, protein, blood urea nitrogen, and various electrolytes) because only the water is lost and other substances remain. Hemoconcentration is not present when dehydration is caused by hemorrhage, because loss of all blood and plasma products occurs. Specific urine laboratory values can help to confirm dehydration if the client does not have renal dysfunction. Usually the urine of the client with dehydration is concentrated, with a specific gravity greater than 1.030. Volume is decreased, and osmolarity is greatly increased. Usually the color is dark amber and a strong odor is evident.
Analysis
COMMON NURSING DIAGNOSES AND COLLABORATIVE PROBLEMS
The following are priority nursing diagnoses for clients with dehydration:
1. Deficient Fluid Volume related to excessive fluid loss or inadequate fluid intake
2. Decreased Cardiac Output related to decreased plasma volume
3. Impaired Oral Mucous Membrane related to inadequate oral secretions
The primary collaborative problem is Potential for Dys-rhythmias.
ADDITIONAL NURSING DIAGNOSES AND COLLABORATIVE PROBLEMS
In addition to the commoursing diagnoses and collaborative problems, clients with dehydration may have one or more of the following:
• Constipation related to decreased body fluids
• Risk for Injury (fall) related to orthostatic (postural) hypotension
• Deficient Knowledge related to medication regimen and preventive measures
• Risk for Impaired Skin Integrity related to deficiencies of interstitial fluid and inadequate tissue perfusion
• Ineffective Airway Clearance related to thick, tenacious secretions
• Potential for Hypovolemic Shock
Planning and Implementation
DEFICIENT FLUID VOLUME
PLANNING: EXPECTED OUTCOMES. The client with dehydration is expected to have body fluid levels restored to normal.
INTERVENTIONS. Management of dehydration aims to prevent further fluid losses and increase fluid compartment volumes to normal ranges.
FLUID MANAGEMENT. Diet therapy, oral rehydration therapy, and drug therapy are the methods of choice to manage fluid volume deficit (Chart 12-4).
DIET THERAPY. Mild to moderate dehydration is corrected with oral fluid replacement if the client is alert enough to swallow and can tolerate oral fluids. The nurse or assistive nursing personnel encourages and measures fluid intake. The specific type of fluid needed for replacement varies with the type of dehydration.
The client’s compliance in drinking oral replacement fluids can be enhanced by using fluids he or she enjoys and by carefully timing the intake schedule. Dividing the total amount of fluids needed by nursing shifts helps to meet fluid needs more evenly with less danger of overhydration. The conscious client is offered small volumes of fluids every hour to increase intake.
ORAL REHYDRATION THERAPY. Oral rehydration therapy (ORT) is the most cost-effective way to replace fluids for the client with dehydration. Specifically formulated solutions containing glucose and electrolytes cause water to be absorbed even when the client is vomiting or has diarrhea. Fluid losses from diarrhea are usually 2 to 3 L/day and should be replaced liter for liter, especially in older clients. A typical order might be “Resol
DRUG THERAPY. Drug therapy for dehydration is directed at restoring fluid balance and controlling the causes of dehydration. Whenever possible, fluids are replaced by the oral route. When dehydration is severe or life threatening, intravenous (IV) fluid replacement may be necessary. Calculation of how much fluid to replace is based on the client’s weight loss and clinical manifestations. The rate of fluid replacement depends on the degree of dehydration and the presence of pre-existing cardiac, pulmonary, or renal problems.
The type of fluid ordered by the health care provider varies with the type of dehydration and the client’s cardiovascular status. The desired outcomes of therapy are appropriate fluid replacement and normal volumes in all body fluid compartments. Usually the client receives IV infusions of water with whatever solutes (especially electrolytes) are determined necessary on the basis of laboratory values. Generally, isotonic dehydration is treated with isotonic fluid solutions, hypertonic dehydration is treated with hypotonic fluid solutions, and hypotonic dehydration is treated with hypertonic fluid solutions.
Drug therapy includes the use of medications to correct the cause of the dehydration. Antidiarrheal medications are ordered when excessive diarrhea causes dehydration. Antimicrobial therapy may be used in clients with bacterial diarrhea. Antiemet-ics to control vomiting may be necessary when excessive vomiting produces dehydration. Antipyretics to reduce body temperature are helpful when fever contributes to dehydration.*
DECREASED CARDIAC OUTPUT
PLANNING: EXPECTED OUTCOMES. The client with dehydration is expected to have cardiac output restored to normal levels and to maintain adequate oxygenation to vital organs.
INTERVENTIONS. Interventions of drug and oxygen therapy aim to increase circulating fluid volume, support compensatory mechanisms, and prevent complications.
DRUG THERAPY. Drug therapy to increase body fluid volume and prevent excessive fluid loss is the same as that for the client with fluid volume deficit. Drugs to increase venous return or improve cardiac contractility are used only when a cardiac problem also is present.
OXYGEN THERAPY. Oxygen is usually delivered by mask or nasal cannula to the client with dehydration. The nurse administers water-nebulized oxygen at the rate or amount specified by the health care provider’s order.
FLUID MONITORING. Monitoring vital signs and level of consciousness is important when caring for clients with dehydration (see Chart 12-4). The nurse or assistive nursing personnel monitors the pulse, blood pressure, pulse pressure, central venous pressure, respiratory rate, skin and mucous membrane color, and urine output at least every hour until the fluid imbalance is resolved.
CRITICAL THINKING CHALLENGE
When you take the client’s blood pressure in a sitting position and in a standing position, the systolic pressure is
• Is this finding supportive or nonsupportive of fluid volume deficit?
• What would you teach this client to avoid complications associated with this problem?
IMPAIRED ORAL MUCOUS MEMBRANE
PLANNING: EXPECTED OUTCOMES. The client with dehydration is expected to have less discomfort and remain free of complications.
INTERVENTIONS
ORAL HEALTH RESTORATION. Interventions include drug therapy, fluid replacement, and good oral hygiene, as well as the early diagnosis and prevention of complications.
DRUG THERAPY. Drug therapy to increase fluid volume and prevent fluid loss is the same as that discussed earlier for deficient fluid volume (p. 165). Saliva substitutes, such as Salivart, can reduce the sensation of mouth dryness. To prevent aspiration, the nurse does not use such agents in an unconscious client.
ORAL HYGIENE. Nursing actions to promote oral hygiene can increase the client’s comfort. The lips are kept clean and moist. The thick, sticky coating on the tongue and mouth during dehydration can be reduced with frequent mouth care. Mouth care includes gentle toothbrushing several times a day and rinsing hourly. The nurse teaches the client to avoid mouthwashes and swabs that contain alcohol or glycerin because these products dry the oral mucosa further and may cause more discomfort by stinging or burning open areas of the mucosa. Rinsing the mouth with dilute solutions of hydrogen peroxide two or three times per day is a good form of oral hygiene; however, when used more frequently, this treatment increases oral dryness. Tap water and normal saline rinses can be used safely as often as the client wishes.
PREVENTION OF COMPLICATIONS. A dry mouth can lead to the development of sores and fissures in the mucosa, providing a portal of entry for many pathogens. The thick, sticky coating also is an excellent breeding ground for microorganisms. A major complication of mouth dryness is a wide variety of oral infections. Chart 12-4 summarizes nursing interventions for mouth care.
POTENTIAL FOR DYSRHYTHMIAS
PLANNING: EXPECTED OUTCOMES. The client with dehydration is expected to maintain his or her normal cardiac rhythm.
INTERVENTIONS. Interventions are aimed at correcting the dehydration and recognizing dysrhythmias so that appropriate drug therapy can be initiated.
DRUG THERAPY. Drug therapy to increase body fluid volume and prevent excessive fluid loss is the same as that discussed earlier for deficient fluid volume (p. 165).
Elevated potassium or calcium levels can cause life-threatening dysrhythmias. Drug therapy to reduce these electrolytes may be ordered. If potassium levels are elevated, a combination of 20 units of regular insulin in 100 mL of 20% dextrose may be administered to promote movement of potassium from the blood into the intracellular fluid (ICF). Drugs such as etidronate (Didronel) and plicamycin (Mithracin) may be administered to reduce an elevated serum calcium level.
MONITORING. The nurse monitors the client for signs and symptoms of cardiac dysrhythmias every 15 minutes until he or she is fully rehydrated. The rate, rhythm, and quality of the apical pulse are assessed and compared with the client’s baseline measurements. The nurse further assesses for fatigue, chest discomfort or pain, and shortness of breath. Hand grasps and deep tendon reflexes are assessed, and changes from baseline are noted. Clients at risk for dysrhythmias are monitored using elec-trocardiography (ECG). The pattern may show tall T waves or a shortened ST segment. Any change from the client’s baseline ECG is reported to the physician immediately.
Interventions
The focus of therapy is to reduce the client’s body temperature and restore fluid volume. After determining a patent airway, the first priority is to cool the client. All clothing is removed. If possible, the client is taken immediately to an air-conditioned environment and placed in the position for shock with the legs elevated. If no air-conditioning is available, he or she is placed in the shade. Water is sprayed or poured on the client, and all surrounding personnel fan him or her. Ice packs are wrapped in cloth and positioned on the client’s groin, head, and armpits.
Oxygen is administered by mask or nasal cannula. At least one IV line is started with a large-bore needle. When available, cooled normal saline (0.9% sodium chloride) is administered intravenously. Depending on how high the client’s temperature is, cooled sterile saline may be administered by peritoneal lavage. Vital signs, including rectal temperature, are monitored every 15 minutes until the client responds to therapy. An indwelling catheter is placed so that output can be monitored accurately. Depending on the severity of the client’s condition, a pulmonary artery catheter may be needed to monitor hydration status. If interventions are started promptly, the client has a good chance for full recovery. Responses usually start to occur within half an hour. If vital signs remain poor in spite of intervention, extensive laboratory assessment may be needed to determine possible organ damage.
Overhydration
OVERVIEW
Overhydration, also called fluid overload, is an excess of body fluid. It is not an actual disease but rather a clinical sign of a physiologic problem in which fluid intake or retention is greater than the body’s fluid needs. Overhydration may be either an actual excess of total body fluid or a relative fluid excess in one or more fluid compartments. The three basic types of fluid volume excess are isotonic overhydration, hypotonic overhydration, and hypertonic overhydration . Most problems caused by overhydration are related to fluid volume excess in the vascular space or to dilution of specific electrolytes and blood components. Clinical manifestations vary with the type and degree of overhydration (Chart 12-6). The conditions leading to overhydration (fluid overload) are related to excessive intake or inadequate excretion of fluid.
POTASSIUM IMBALANCE
Hypokalemia
OVERVIEW
Because 98% of total body potassium (K+) is intracellular, minor changes in extracellular potassium levels cause major changes in cell membrane excitability and in other cellular processes.
Hypokalemia is a serum potassium level below 3.5 mEq/L (mmol/L). A relatively common electrolyte imbalance, hypokalemia is potentially life threatening because every body system can be affected.
Pathophysiology
Decreased serum potassium levels increase the difference in potassium concentration between the fluid inside the cells (intracellular fluid [ICF]), and the fluid outside the cells (extracellular fluid (ECF]). This increased difference reduces the excitability of cells. Consequently, the cell membranes of all excitable tissues, such as nerve and muscle, are less responsive to normal stimuli.
The severity of problems caused by hypokalemia is directly related to how rapidly the serum potassium level decreases. When the loss of extracellular potassium is gradual, cells adjust and intracellular potassium decreases in proportion to the ECF potassium level. In this situation, the potassium concentration difference between the two fluid compartments remains unchanged; symptoms of hypokalemia may not appear until the potassium loss is extreme. Rapid changes in extracellular potassium levels (representing a more rapid loss of potassium) cannot be compensated for quickly and result in dramatic changes in body function.
• Etiology
Hypokalemia may result either from an actual total body potassium loss or from the movement of potassium from the ECF to the ICF, causing a relative decrease in extracellular potassium level. Table 13-1 summarizes the common causes of hypokalemia.
Actual potassium depletion occurs when potassium loss is excessive or when potassium intake is not sufficient to match normal potassium loss. Relative hypokalemia occurs when total body potassium levels are normal but the potassium distribution between fluid compartments is abnormal. Conditions that increase the cellular uptake of potassium, leading to hypokalemia, include metabolic alkalosis and insulin administration.
COLLABORATIVE MANAGEMENT
Assessment
HISTORY
The nurse collects data from clients at risk as well as from those with actual hypokalemia.
AGE. Age is an important consideration because renal capacity to concentrate urine decreases with aging, which increases potassium loss. Moreover, older adults are more likely to use medications that promote potassium loss.
MEDICATION USE. The nurse asks the client about medication use, especially diuretics, corticosteroids, and beta-adrenergic agonists or antagonists. These drugs increase potassium loss through the kidneys. One of the most common causes of hypokalemia is the use and misuse of diuretics. In clients taking digoxin (Lanoxin, Novodigoxin^X hypokalemia increases the sensitivity of the myocardium to the drug and may result in digoxin toxicity, even when the dosage is within the therapeutic range.
The nurse asks whether the client is taking a prescribed potassium supplement, such as potassium chloride (KC1). The client may not be taking the potassium chloride as prescribed because of its unpleasant taste.
OTHER FACTORS. Any acute or chronic disease state may lead to hypokalemia. The client is asked about recent illnesses and medical or surgical interventions. A thorough diet history, including a typical day’s food and beverage intake, helps the nurse to identify clients at risk for hypokalemia.
PHYSICAL ASSESSMENT/CLINICAL MANIFESTATIONS
The clinical manifestations of hypokalemia are associated with the altered function of many systems Skeletal muscles become weak in response to hypokalemia, and a stronger stimulus is needed to begin muscle contraction. A client may be so weak that he or she is unable to stand. Hand-grasps are weak, and hyporeflexia (a decreased response to deep tendon reflex stimulation) may be noted. Severe hypokalemia can lead to flaccid paralysis. The nurse assesses the degree of muscle weakness and determines the client’s ability to perform activities of daily living (ADLs).
RESPIRATORY MANIFESTATIONS. The respiratory system can be seriously affected by hypokalemia through the depression of the nerves and muscles needed for breathing. Weakness of the skeletal muscles of respiration results in shallow respirations. The nurse assesses the client’s breath sounds, ease of respiratory effort, color of nail beds and mucous membranes, and rate and depth of respiration. Respiratory status is assessed at least every 2 hours because respiratory insufficiency often accompanies hypokalemia and is a major cause of death.
CARDIOVASCULAR MANIFESTATIONS. Cardiovascular changes often accompany hypokalemia. The nurse assesses the cardiovascular system by first palpating the peripheral pulses. In the client with hypokalemia, the pulse is usually thready and weak. Palpation is difficult, and the pulse is easily blocked with light pressure. The pulse rate ranges from excessively slow to excessively rapid, depending on whether a dysrhythmia (irregular heartbeat), especially premature ventricular contraction (PVC), is present. The nurse measures blood pressure with the client in the lying, sitting, and standing positions because orthostatic (postural) hypotension accompanies hypokalemia.
NEUROLOGIC MANIFESTATIONS. The neurologic manifestations of hypokalemia include changes in mental status. The client may experience short-term irritability and anxiety followed by lethargy that progresses to confusion and coma as hypokalemia worsens. Severe hypokalemia decreases sensory awareness. For example, the client may not be able to identify mild sensations of pain, touch, heat, and cold.
GASTROINTESTINAL MANIFESTATIONS. Hypokalemia decreases smooth muscle contractions within the gastrointestinal system, which leads to decreased peristalsis. The affected client has hypoactive bowel sounds and may experience nausea, vomiting, constipation, and abdominal dis-tention. The nurse assesses distention by measuring abdominal girth. Bowel sounds are assessed in all four abdominal quadrants to determine the extent of decreased peristalsis. Severe hypokalemia can cause paralytic ileus (the absence of peristalsis).
PSYCHOSOCIAL ASSESSMENT. Behavioral changes caused by hypokalemia usually occur within a short period. Information about the client’s behavior may need to be obtained from close family members or friends, depending on the client’s condition.
The nurse collects data about the onset and duration of behavioral changes as well as their association with any other physical signs and symptoms. The client may be lethargic and unable to perform simple problem-solving tasks that require concentration, such as counting backward from 100 by threes. As hypokalemia progresses, the client may become increasingly confused, especially to time and place. In severe hypokalemia, coma may develop.
LABORATORY ASSESSMENT
Hypokalemia is confirmed by a serum potassium value below 3.5 mEq/L (mmol/L). However, this value alone does not determine whether potassium loss has occurred or whether potassium has moved from the blood into the cells.
OTHER DIAGNOSTIC ASSESSMENTS
The health care provider may order a baseline electrocardiogram (ECG) and continuous cardiac monitoring for a client with severe hypokalemia. Hypokalemia causes electrical conduction abnormalities in the heart, including ST-segment depression, flat or inverted T waves, and increased U waves. Dysrhythmias can result in death, particularly in older adults who are taking digoxin.
Analysis
COMMON NURSING DIAGNOSES AND COLLABORATIVE PROBLEMS
The following are priority nursing diagnoses for clients with hypokalemia:
1. Risk for Injury related to skeletal muscle weakness
2. Constipation related to smooth muscle atony
The primary collaborative problem is High Risk for Ineffective Breathing Pattern related to neuromuscular impairment.
ADDITIONAL NURSING DIAGNOSES AND COLLABORATIVE PROBLEMS
In addition to the commoursing diagnoses and collaborative problems, clients with hypokalemia may have one or more of the following:
• Impaired Physical Mobility related to skeletal muscle weakness
Planning and Implementation
RISK FOR INJURY
PLANNING: EXPECTED OUTCOMES.
The client with hypokalemia is expected to avoid injury and have a return to a normal seram potassium level.
INTERVENTIONS
ELECTROLYTE MANAGEMENT: HYPOKALEMIA. Interventions for hypokalemia aim to prevent potassium loss, increase seram potassium levels, and provide a safe environment for the client. Drug and diet therapies help to restore normal seram potassium levels.
DRUG THERAPY. Drag therapies for the treatment and prevention of hypokalemia include additional potassium and drugs to prevent potassium loss.
Potassium Supplements. Most potassium supplements are potassium chloride, potassium gluconate, potassium citrate, or a combination of these salts. The amount and the route of potassium replacement depend on the degree of potassium loss. A client with a seram potassium level of 3 mEq/L needs 100 to 200 mEq of potassium supplement; a client with a seram potassium level of 2.0 mEq/L needs 500 to 600 mEq (Tannen, 1996).
Potassium is given intravenously for severe hypokalemia. A dilution of no more than 1 mEq/10 mL of solution is recommended. The maximum recommended infusion rate is 5 to 10 mEq/hr; this rate is never to exceed 20 mEq/hr under any circumstances. Older clients may not be able to handle this rate. Because the rapid infusion of potassium can cause cardiac arrest, potassium is seldom given by intravenous (IV) push.
Potassium is a severe tissue irritant and is never administered as an intramuscular or subcutaneous injection. Tissues damaged by potassium can become necrotic and slough, leading to a loss of function and requiring reconstructive surgery. IV potassium solutions irritate veins and can cause phlebitis. The nurse checks the orders carefully to ensure that the client receives the correct amount of potassium. The IV site is assessed every 2 hours, and the client is asked whether he or she feels burning or pain at the site. The IV solution is stopped immediately if infiltration occurs.
Oral potassium preparations may be administered as liquids or solids. Potassium chloride has a strong, unpleasant taste that is difficult to mask. Because potassium chloride can cause nausea and vomiting, it should not be taken on an empty stomach.
Potassium-Sparing Diuretics. Diuretics that increase the renal excretion of potassium commonly cause hypokalemia. These classes of diuretics include high-ceiling (loop) diuretics (e.g., furosemide [Lasix, Furoside^], bumetanide [Bumex], and ethacrynic acid [Edecrin]) and the thiazide diuretics (chlorothiazide [Diuril], hydrochlorothiazide [Esidrix, HydroDIURIL, Urozide^], and quinethazone [Hydromox]). These drags are avoided in clients with actual hypokalemia and in those who are at risk for hypokalemia. A potassium-sparing diuretic may be appropriate for clients with hypokalemia who require diuretic therapy. Potassium-sparing diuretics increase urine output without increasing potassium excretion. Potassium-sparing diuretics include spironolactone (Aldactone, Novospiroton^), triamterene (Dyrenium), and amiloride (Midamor).
DIET THERAPY. The nurse consults with the dietitian in teaching the client how to increase dietary potassium intake. Eating foods that are naturally rich in potassium helps to restore normal potassium levels and prevent further loss. Table 11-7 lists the potassium content of common foods.
SAFETY MEASURES. For a client with muscle weakness from hypokalemia, the nurse uses safety measures, eliminates hazards, and assists with ambulation. Obstacles or slippery areas are removed from the ambulation path, and the client wears nonslip footgear. When ambulating with assistance, the client wears a gait belt around the waist.
INEFFECTIVE BREATHING PATTERN
PLANNING: EXPECTED OUTCOMES. The client with hypokalemia is expected to have a breathing pattern adequate to maintain gas exchange.
INTERVENTIONS. The nurse monitors the client’s respiratory rate and depth at least once per hour, noting in particular increased rate and decreased depth. The effectiveness of the respiratory muscles can also be determined by assessing the client’s ability to cough. The face, oral mu-cosa, and nail beds are examined for pallor or cyanosis. The nurse evaluates arterial blood gas values for hypoxemia (decreased blood oxygen concentration) and hypercapnia (increased arterial carbon dioxide concentration).
Hyperkalemia
OVERVIEW
Hyperkalemia is a serum potassium level greater than 5.0 mEq/L (mmol/L). Because the range of normal serum potassium values is narrow, even slight increases above normal values can have serious adverse effects on the physiologic function of excitable tissues, especially the heart.
Pathophysiology
An elevated serum potassium level decreases the potassium concentration difference between the intracellular fluid (ICF) and the extracellular fluid (ECF). This decreased difference increases cell excitability; as a result, excitable tissues respond to less intense stimuli and may even discharge spontaneously.
COLLABORATIVE MANAGEMENT
Assessment
The client’s age is an important factor because renal function decreases with aging. The nurse asks about chronic illnesses (particularly renal disease and diabetes mellitus), recent medical or surgical interventions, and urine output, including frequency and amount of voidings. The nurse also inquires about medication use, particularly potassium-sparing diuretics. A diet history is obtained to determine the intake of potassium-rich foods or the use of salt substitutes, many of which contain potassium.
The nurse collects data regarding symptoms related to hyperkalemia. The client is asked if he or she has experienced palpitations, skipped heartbeats, other cardiac irregularities, muscle twitching, weakness in the leg muscles, and unusual tingling or numbness in the hands, feet, or face. The nurse inquires about recent changes in bowel habits, especially diarrhea, colic, and explosive bowel movements.
PHYSICAL ASSESSMENT/CLINICAL MANIFESTATIONS
Cardiovascular changes are the most severe results of hyperkalemia and are the most common cause of death in clients with hyperkalemia (Chmielewski, 1998). Cardiac manifestations of hyperkalemia include bradycardia, hypotension, and electrocardiographic (ECG) changes of tall, peaked T waves, prolonged PR intervals, flat or absent P waves, and wide QRS complexes. As serum potassium levels rise, ectopic beats (beats generated outside the normal conduction system in the ventricles) may appear. Complete heart block, ventricular standstill, and ventricular fibrillation are major life-threatening complications of severe hyperkalemia. The neuromuscular response to hyperkalemia has two phases. Skeletal muscles twitch in the early stages of hyperkalemia, and the client may be aware of unusual nerve sensations (e.g., tingling and burning) that are followed by numbness in the hands and feet and around the mouth (paresthesia). As hyperkalemia progresses, muscle twitching changes to weakness followed by flaccid paralysis. The weakness ascends from the distal to the proximal areas and initially affects the muscles of the arms and legs. Trunk, head, and respiratory muscles are not affected until serum potassium levels reach lethal levels.
The smooth muscle of the gastrointestinal tract responds to hyperkalemia by increasing peristalsis. As a result, the client may experience diarrhea and spastic colonic activity.
Figure. ECG changes associated with hyperkalemia.
(Modified with permission from John M. Clochesy.)
The nurse listens to bowel sounds and observes stools. Bowel sounds are hyperactive, with frequent audible rushes and gurgles. Bowel movements may be frequent, watery, and explosive.
LABORATORY ASSESSMENT
A serum potassium value greater than 5.0 mEq/L confirms hyperkalemia. If hyperkalemia results from dehydration, levels of other serum electrolytes, hematocrit, and hemoglobin may be elevated. Hyperkalemia associated with renal failure is usually accompanied by elevated levels of serum creatinine and blood urea nitrogen, decreased blood pH, and normal or low hematocrit and hemoglobin levels.
Interventions
Electrolyte management:
Hyperkalemia.
Interventions for hyperkalemia are aimed at immediately reducing the serum potassium level. Drug therapy is useful for restoring normal potassium balance by eliminating potassium administration, enhancing potassium excretion, and promoting the movement of potassium from the extracellular fluid (ECF) into the cells. Monitoring the client’s response to intervention is another major nursing responsibility
Eliminating potassium administration by stopping infusions of potassium-containing IV solutions and by keeping the IV catheter open is useful in managing hyperkalemia. The nurse withholds oral potassium supplements, and a potassium-restricted diet is ordered.
Increasing potassium excretion can be effective in managing hyperkalemia if renal function is not impaired. The physician orders the administration of potassium-excreting diuretics, such as furosemide (Miekley, 1998). For a client with renal problems, drug therapy to increase potassium excretion includes cation exchange resins that promote gastrointestinal sodium absorption and potassium excretion, such as sodium polystyrene sulfonate (Kayexalate). However, it may take sodium polystyrene sulfonate many hours to reduce potassium levels. If potassium levels are dangerously high, additional measures, such as dialysis and ultrafiltration, are necessary.
Promoting the movement of potassium from the extracellular fluid (ECF) to the intracellular fluid (ICF) can help reduce serum potassium levels temporarily. Potassium movement from the ECF into the cells is enhanced by the presence of insulin. Insulin increases the activity of the membrane-bound sodium-potassium pump, resulting in the movement of potassium from the blood and other ECFs into the cell (Chmielewski, 1998). The physician may order IV fluids that contain substantial amounts of glucose and insulin to help decrease serum potassium levels (usually 100 mL of 10% to 20% glucose with 10 to 20 units of regular insulin). These IV solutions are hypertonic and are administered through a central venous catheter or in a vein with a high blood flow to avoid local vein inflammation. The nurse observes the client for signs and symptoms of hypokalemia and hypoglycemia during this therapy.
Cardiac monitoring can help to prevent lethal dysrhythmias and allow for the early recognition of signs and symptoms of the adverse response of cardiac muscle. The nurse compares recent ECG tracings with the client’s baseline tracings or with tracings obtained when the client’s serum potassium level was close to normal.
Health teaching is a key factor in the prevention of hyperkalemia and in the early detection of its life-threatening complications. The teaching plan for the client at risk for hyperkalemia includes diet, medications, and recognition of the signs and symptoms of hyperkalemia. Diet education includes knowledge of foods to avoid (those high in potassium) and permissible foods containing little potassium. The nurse instructs the client to examine the labels on medications and food packages to determine the potassium content and to avoid salt substitutes, which usually contain potassium.
