Fluid, Electrolyte, and Acid-Base Balance

Fluid, Electrolyte, and Acid-Base Balance
Chapter 42 Fluid, Electrolyte, and Acid-Base Balance Fluid surrounds all the cells in the body and is also inside cells. Body fluids contain electrolytes such as sodium and potassium; they also have a certain degree of acidity. Fluid, electrolyte, and acid-base balances within the body maintain the health and function of all body systems. In this chapter, you will learn how the body normally maintains fluid, electrolyte, and acid-base balance. The characteristics of body fluids influence body system function because of their effects on cell function. These characteristics include the fluid amount (volume), concentration (osmolality), composition (electrolyte concentration), and degree of acidity (pH). All of these characteristics have regulatory mechanisms that keep them in balance for normal function. You also will learn how imbalances develop; how various fluid, electrolyte, and acid-base imbalances affect patients; and ways to help patients maintain or restore balance safely. Copyright © 2017, Elsevier Inc. All Rights Reserved.

Fluid Balance [Review Figure 42-1, Body fluid compartments, with students.] [Shown is Figure 42-2: Effects of isotonic, hypotonic, and hypertonic solutions. (From Hall JE: Guyton and Hall textbook of medical physiology, ed 13, Philadelphia, 2016, Saunders.)] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Fluid Balance (Cont.) Fluid balance consists of Fluid intake
Fluid distribution Fluid output Antidiuretic hormone Renin-angiotensin-aldosterone system Atrial natriuretic peptide Fluid homeostasis is the dynamic interplay of three processes: fluid intake and absorption, fluid distribution, and fluid output. To maintain fluid balance, fluid intake must equal fluid output. Because some of the normal daily fluid output (e.g., urine, sweat) is a hypotonic salt solution, people must have an equivalent fluid intake of hypotonic sodium-containing fluid (or water plus foods with some salt) to maintain fluid balance (intake equal to output). Fluid intake occurs orally through drinking but also through eating because most foods contain some water. Food metabolism creates additional water. Average fluid intake from these routes for healthy adults is about 2300 mL, although this amount can vary widely depending on exercise habits, preferences, and the environment. Other routes of fluid intake include intravenous (IV), rectal (e.g., enemas), and irrigation of body cavities that can absorb fluid. [Review Table 42-1, Laboratory Normal Values for Adults, with students.] [Review Table 42-2, Healthy Adult Average Fluid Intake and Output, with students.] The term fluid distribution means the movement of fluid among its various compartments. Fluid distribution between the extracellular and intracellular compartments occurs by osmosis. Fluid distribution between the vascular and interstitial portions of the extracellular fluid (ECF) occurs by filtration. [Shown is Figure 42-3: Osmosis moves water through semipermeable membrane. (From Patton KT, Thibodeau GA: Anatomy and physiology, ed 9, St Louis, 2016, Mosby.)] [Review Figure 42-4, Capillary filtration moves fluid between vascular and interstitial compartments, with students.] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Fluid Balance (Cont.) Thirst
An important regulator of fluid intake when plasma osmolality increases Thirst-control mechanism is located within the hypothalamus in the brain Thirst, the conscious desire for water, is an important regulator of fluid intake when plasma osmolality increases (osmoreceptor-mediated thirst) or the blood volume decreases (baroreceptor-mediated thirst and angiotensin II– and III–mediated thirst). The thirst-control mechanism is located within the hypothalamus in the brain. Osmoreceptors continually monitor plasma osmolality; when it increases, they cause thirst by stimulating neurons in the hypothalamus. [Shown is Figure 42-5: Stimuli affecting thirst mechanism.] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Case Study Robert is a junior nursing student assigned to Mrs. Reynolds. He has cared for other patients with gastrointestinal problems but never one with fluid and electrolyte problems. Robert plans his care by reviewing Mrs. Reynolds’ chart and her health care provider’s orders. [Ask students: What will Robert discover about the patient based on her history? Discuss: The patient’s history reveals that she is at risk for a fluid and electrolyte imbalance from a gastrointestinal (GI) disturbance and continued use of a diuretic.] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Fluid Balance (Cont.) Fluid output
Normally via skin, lungs, GI tract, kidneys Influenced by Antidiuretic hormone (ADH) Renin-angiotensin-aldosterone system (RAAS) Atrial natriuretic peptides (ANPs) Fluid output normally occurs through four organs: the skin, lungs, GI tract, and kidneys. The GI tract plays a vital role in fluid balance. Approximately 3 to 6 L of fluid moves into the GI tract daily and then returns again to the ECF. The average adult normally excretes only 100 mL of fluid each day through feces. However, diarrhea causes a large fluid output from the GI tract. The kidneys are the major regulator of fluid output because they respond to hormones that influence urine production. When healthy adults drink more water, they increase urine production to maintain fluid balance. If they drink less water, sweat a lot, or lose fluid by vomiting, their urine volume decreases to maintain fluid balance. These adjustments primarily are caused by the actions of antidiuretic hormone (ADH), the renin-angiotensin-aldosterone system (RAAS), and atrial natriuretic peptides (ANPs). ADH regulates the osmolality of the body fluids by influencing how much water is excreted in urine. It is synthesized by neurons in the hypothalamus that release it from the posterior pituitary gland. ADH circulates in the blood to the kidneys, where it acts on the collecting ducts. People normally have some ADH release to maintain fluid balance. More ADH is released if body fluids become more concentrated. Factors that increase ADH levels include severely decreased blood volume (e.g., dehydration, hemorrhage), pain, stressors, and some medications. The RAAS regulates ECF volume by influencing how much sodium and water are excreted in urine. It also contributes to regulation of blood pressure. Aldosterone circulates to the kidneys, where it causes resorption of sodium and water in isotonic proportion in the distal renal tubules. Removing sodium and water from the renal tubules and returning it to the blood increases the volume of the ECF. To maintain fluid balance, normally some action of the RAAS occurs. ANP also regulates ECV by influencing how much sodium and water are excreted in urine. Cells in the atria of the heart release ANP when they are stretched (e.g., by an increased ECV). ANP is a weak hormone that inhibits ADH by increasing the loss of sodium and water in the urine (see Fig. 42-6, C). Thus ANP opposes the effect of aldosterone. [Shown is Figure 42-6: Major hormones that influence renal fluid excretion. A, Antidiuretic hormone (ADH). B, Aldosterone. C, Atrial natriuretic peptide (ANP).] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Fluid Balance (Cont.) Fluid intake Fluid distribution
Thirst regulates fluid intake ~2300 mL/day Fluid distribution Extracellular and intracellular Vascular and interstitial Hormonal Influences Antidiuretic hormone Renin-angiotensin-aldosterone mechanism Atrial natriuretic peptides Fluid output Through kidneys, skin, lungs, and GI tract Insensible loss Sensible loss [This slide summarizes the components of fluid balance.] Copyright © 2017, Elsevier Inc. All Rights Reserved. 7

Quick Quiz! 1. A patient is diaphoretic and has an oral temperature of 104° F. These are classic signs of: A. ADH deficit. B. extracellular fluid loss. C. insensible water loss. D. sensible water loss. Answer: D Copyright © 2017, Elsevier Inc. All Rights Reserved.

Fluid Imbalances ECF imbalances Osmolality imbalances
Volume Osmolality Osmolality imbalances Hypernatremia, “water deficit”; hypertonic Hyponatremia, “water excess”; hypotonic Clinical dehydration ECV deficit and hypernatremia combined If disease processes, medications, or other factors disrupt fluid intake or output, imbalances sometimes occur. For example, with diarrhea, fluid output is increased, and a fluid imbalance (dehydration) occurs if fluid intake does not increase appropriately. Two major types of fluid imbalances are known: volume imbalances and osmolality imbalances. Volume imbalances are disturbances of the amount of fluid in the extracellular compartment. Osmolality imbalances are disturbances of the concentration of body fluids. Volume and osmolality imbalances may occur separately or in combination. With an extracellular fluid volume (ECV) imbalance, too little (ECV deficit) or too much (ECV excess) isotonic fluid is present. ECV deficit and excess are abnormal volumes of isotonic fluid, manifested as sudden changes in body weight and changes in markers of vascular and interstitial volume. ECV deficit is present when isotonic fluid is insufficient in the extracellular compartment. Remember that a lot of sodium is found in normal ECF. With ECV deficit, output of isotonic fluid exceeds intake of sodium-containing fluid. Because ECF is both vascular and interstitial, signs and symptoms arise from lack of volume in both of these compartments. [Review Table 42-3, Fluid Imbalances, with students.] ECV excess occurs when too much isotonic fluid is found in the extracellular compartment. Intake of sodium-containing isotonic fluid has exceeded fluid output. For example, when you eat more salty foods than usual and drink water, you may notice that your ankles swell or rings on your fingers feel tight, and you gain 2 lbs (1 kg) or more overnight. These are manifestations of mild ECV excess. In an osmolality imbalance, body fluids become hypertonic or hypotonic, and this causes osmotic shifts of water across cell membranes. Osmolality imbalances are called hypernatremia and hyponatremia. An osmolality imbalance body fluids become hypertonic or hypotonic, which causes osmotic shifts of water across cell membranes. The osmolality imbalances are called hypernatremia and hyponatremia. Hypernatremia, also called water deficit, is a hypertonic condition. One of two general causes make body fluids too concentrated: loss of relatively more water than salt, or gain of relatively more salt than water. When the interstitial fluid becomes hypertonic, water leaves cells by osmosis, and they shrivel. Signs and symptoms of hypernatremia are those of cerebral dysfunction, which arise when brain cells shrivel. Hyponatremia, also called water excess or water intoxication, is a hypotonic condition. It arises from gain of relatively more water than salt or loss of relatively more salt than water. The excessively dilute condition of interstitial fluid causes water to enter cells by osmosis, causing the cells to swell. Signs and symptoms of cerebral dysfunction occur when brain cells swell. ECV deficit and hypernatremia often occur at the same time; this combination is called clinical dehydration. The ECV is too low, and the body fluids are too concentrated. Clinical dehydration is common with gastroenteritis or other causes of severe vomiting and diarrhea when people are not able to replace their fluid output with enough intake of dilute sodium-containing fluids. Signs and symptoms of clinical dehydration are those of both ECV deficit and hypernatremia. [Shown is Figure 42-7: Fluid volume and osmolality imbalances.] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Electrolyte Balance Intake and absorption Distribution Output
Plasma concentrations of K+, Ca2+, Mg+, and phosphate (Pi) are very low compared with their concentrations in cells and bone. Concentration differences are necessary for normal muscle and nerve function. Output Urine, feces, and sweat Vomiting, drainage, and fistulas You can best understand electrolyte balance by considering the three processes involved in electrolyte homeostasis: electrolyte intake and absorption, electrolyte distribution, and electrolyte output. [Review Table 42-4, Electrolyte Intake and Absorption, Distribution, and Output, with students.] Plasma concentrations of K+, Ca2+, Mg2+, and phosphate are very low compared with their concentrations in cells and bone. Intake comes from foods and beverages. Some substances enhance or hinder electrolyte absorption. Although sodium is an electrolyte, it is not included here because serum sodium imbalances are the osmolality imbalances discussed previously. Electrolyte output occurs through normal excretion in urine, feces, and sweat. Output also occurs through vomiting, drainage tubes, and fistulas. When electrolyte output increases, electrolyte intake must increase to maintain electrolyte balance. Similarly, if electrolyte output decreases, as with oliguria, electrolyte intake must also decrease to maintain balance. Copyright © 2017, Elsevier Inc. All Rights Reserved.

Electrolyte Imbalances
Potassium (K+) Hypokalemia Hyperkalemia Calcium (Ca2+) Hypocalcemia Hypercalcemia Magnesium (Mg2+) Hypomagnesemia Hypermagnesemia [Hypernatremia and hyponatremia were discussed with osmolality imbalances.] [Ask students: Use your knowledge of word origins to analyze the terms on the slide. Discuss: -emia means blood condition; hyper- means excessive; hypo- means deficient; and the three word roots (kal, calc, and magnes) represent the three elements potassium, calcium, and magnesium.] Factors such as diarrhea, endocrine disorders, and medications that disrupt electrolyte homeostasis cause electrolyte imbalances. Electrolyte intake greater than electrolyte output or a shift of electrolytes from cells or bone into the ECF causes plasma electrolyte excess. Electrolyte intake less than electrolyte output or shift of electrolyte from the ECF into cells or bone causes plasma electrolyte deficit. Hypokalemia is abnormally low potassium concentration in the blood. Hypokalemia results from decreased potassium intake and absorption, a shift of potassium from the ECF into cells, and an increased potassium output. Common causes of hypokalemia from increased potassium output include diarrhea, repeated vomiting, and use of potassium-wasting diuretics. People who have these conditions need to increase their potassium intake to reduce their risk of hypokalemia. Hypokalemia causes muscle weakness, which becomes life threatening if it includes respiratory muscles and potentially life-threatening cardiac dysrhythmias. [Review Table 41-5, Electrolyte Imbalances, with students.] Hyperkalemia is abnormally high potassium ion concentration in the blood. Its general causes are increased potassium intake and absorption, shift of potassium from cells into the ECF, and decreased potassium output. People who have oliguria (decreased urine output) are at high risk of hyperkalemia from the resultant decreased potassium output unless their potassium intake also decreases substantially. Understanding this principle helps you remember to check urine output before you administer IV solutions containing potassium. Hyperkalemia can cause muscle weakness, potentially life-threatening cardiac dysrhythmias, and cardiac arrest. Hypocalcemia is abnormally low calcium concentration in the blood. The physiologically active form of calcium in the blood is ionized calcium. Total blood calcium also contains inactive forms that are bound to plasma proteins and small anions such as citrate. Factors that cause too much ionized calcium to shift to bound forms cause symptomatic ionized hypocalcemia. People who have acute pancreatitis frequently develop hypocalcemia because calcium binds to undigested fat in their feces and is excreted. This process decreases absorption of dietary calcium and increases calcium output by preventing resorption of calcium contained in GI fluids. Hypocalcemia increases neuromuscular excitability, which is the basis for its signs and symptoms. Hypercalcemia is abnormally high calcium concentration in the blood. Hypercalcemia results from increased calcium intake and absorption, shift of calcium from bones into the ECF, and decreased calcium output. Patients with cancer often develop hypercalcemia because some cancer cells secrete chemicals into the blood that are related to parathyroid hormone. When these chemicals reach the bones, they cause shift of calcium from bones into the ECF. This weakens bones, and the person sometimes develops pathological fractures (i.e., bone breakage caused by forces that would not break a healthy bone). Hypercalcemia decreases neuromuscular excitability, the basis for its other signs and symptoms, the most common of which is lethargy. Hypomagnesemia is abnormally low magnesium concentration in the blood. Its general causes include decreased magnesium intake and absorption, shift of plasma magnesium to its inactive bound form, and increased magnesium output. Signs and symptoms are similar to those of hypocalcemia because hypomagnesemia also increases neuromuscular excitability. Hypermagnesemia is abnormally high magnesium concentration in the blood. End-stage renal disease causes hypermagnesemia unless the person decreases magnesium intake to match the decreased output. Signs and symptoms are caused by decreased neuromuscular excitability, with lethargy and decreased deep tendon reflexes being most common. Copyright © 2017, Elsevier Inc. All Rights Reserved.

Case Study (Cont.) Mrs. Reynolds’ physician has admitted her for observation and has obtained a blood sample for electrolyte levels, complete blood count (CBC), and an electrocardiogram (ECG). Orders include nothing by mouth, an IV infusion of 0.9% saline at 125 mL/hr, intake and output (I&O) recordings, and vital signs every 4 hours, in addition to daily weights. [Ask students: What assessment activities do you anticipate Robert will perform? Discuss: Ask Mrs. Reynolds to describe her nausea and what accompanying signs and symptoms she is experiencing. Conduct an examination of GI and urinary function. Assess her vital signs. Assess Mrs. Reynolds’ skin and mucous membranes for indicators of dehydration. Evaluation her laboratory vales and electrocardiogram (ECG) results.] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Acid-Base Balance Acid production, buffering, and excretion interplay to create balance Acids release hydrogen (H+) ions; bases (alkaline substances) take up H+ ions Degree of acidity is reported as pH pH scale: 1.0 (very acid) to 14.0 (very base) pH of 7.0 is neutral; normal arterial blood is 7.35 to 7.45 Maintaining pH within this normal range is very important for optimal cell function Normal acid-base balance is maintained with acid excretion equal to acid production. Acids release hydrogen (H+) ions; bases (alkaline substances) take up H+ ions. The more H+ ions that are present, the more acidic is the solution. If the pH goes outside the normal range, enzymes within cells do not function properly; hemoglobin does not manage oxygen properly; and serious physiological problems occur, including death. Laboratory tests of a sample of arterial blood called arterial blood gases (ABGs) are used to monitor a patient’s acid-base balance. [Review Table 42-6, Arterial Blood Gas Measures, with students.] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Acid-Base Balance (Cont.)
Acid production CO2 +H2O ↔ H2CO3 ↔ H+ + HCO3− Carbon dioxide + water ↔ Carbonic acid ↔ Hydrogen ion + Bicarbonate Production: Cellular metabolism constantly creates two types of acids: carbonic acid and metabolic acids. Cells produce carbon dioxide (CO2), which acts as an acid in the body by converting to carbonic acid. Metabolic acids are any acids that are not carbonic acid. They include citric acid, lactic acid, and many others. [Shown is Figure 42-8: Acid production and excretion.] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Acid buffering Buffers are pairs of chemicals that work together to maintain normal pH of body fluids HCO3− + H+ ↔ H2CO3 Bicarbonate + Hydrogen ion ↔ Carbonic acid H2CO3 ↔ H+ + HCO3− Carbonic acid ↔ Hydrogen ion + Bicarbonate Buffering: If too many free H+ ions are present, a buffer takes them up, so they no longer are free. If too few are present, a buffer can release H+ ions to prevent an acid-base imbalance. Buffers work rapidly—within seconds. All body fluids contain buffers. The major buffer in ECF is the bicarbonate (HCO3−) buffer system, which buffers metabolic acids. It consists of a lot of bicarbonate and a small amount of carbonic acid (normally a 20:1 ratio). Addition of H+ released by a metabolic acid to a bicarbonate ion makes more carbonic acid. Now the H+ is no longer free and will not decrease the blood pH. If too few H+ ions are present, the carbonic acid portion of the buffer pair will release some, increasing the bicarbonate, again returning pH to normal. Other buffers include hemoglobin, protein buffers, and phosphate buffers. Cellular and bone buffers also contribute. Buffers normally keep the blood from becoming too acid when acids that are produced by cells circulate to the lungs and kidneys for excretion. Copyright © 2017, Elsevier Inc. All Rights Reserved.

Acid excretion systems: lungs and kidneys Lungs excrete carbonic acid. Kidneys excrete metabolic acids. Excretion of carbonic acid When you exhale, you excrete carbonic acid in the form of CO2 and water. Excretion of metabolic acids The kidneys excrete all acids except carbonic acid. The body has two acid excretion systems: lungs and kidneys. The lungs excrete carbonic acid; the kidneys excrete metabolic acids. When you exhale, you excrete carbonic acid in the form of CO2 and water. If the PaCO2 (i.e., level of CO2 in the blood) rises, the chemoreceptors trigger faster and deeper respirations to excrete the excess. If the PaCO2 falls, the chemoreceptors trigger slower and shallower respirations, so more of the CO2 produced by cells remains in the blood and makes up the deficit. These alterations in respiratory rate and depth maintain the carbonic acid portion of acid-base balance. Sometimes people who have lung disease have difficulty with normal excretion of carbonic acid, which causes it to accumulate and make the blood more acid. The kidneys excrete all acids except carbonic acid. They secrete H+ into the renal tubular fluid, putting HCO3− back into the blood at the same time. If too many H+ ions are present in the blood, renal cells move more H+ ions into the renal tubules for excretion, retaining more HCO3− in the process. If too few H+ ions are present in the blood, renal cells secrete fewer H+ ions. Phosphate buffers in the renal tubular fluid keep the urine from becoming too acidic when the kidneys excrete H+ ions. If the kidneys need to excrete a lot of H+, renal tubular cells secrete ammonia, which combines with H+ ions in the tubules to make NH4+, ammonium ions. Buffering by phosphate and the creation of NH4+ turn free H+ ions into other molecules in the renal tubular fluid. This process enables metabolic acid excretion in urine without making urine too acidic. People who have kidney disease often have difficulty with normal excretion of metabolic acids. Copyright © 2017, Elsevier Inc. All Rights Reserved.

Quick Quiz! 2. The body’s fluid and electrolyte balance is maintained partially by hormonal regulation. Which of the following statements shows an understanding of this mechanism? A. “The pituitary secretes aldosterone.” B. “The kidneys secrete antidiuretic hormone.” C. “The adrenal cortex secretes antidiuretic hormone.” D. “The pituitary gland secretes antidiuretic hormone.” Answer: D Copyright © 2017, Elsevier Inc. All Rights Reserved.

Acid-Base Imbalances Types of acidosis: respiratory and metabolic
Types of alkalosis: respiratory and metabolic Respiratory acidosis Arises from alveolar hypoventilation Lungs unable to excrete enough CO2 Excess carbonic acid in the blood decreases pH. Respiratory alkalosis Arises from alveolar hyperventilation Lungs excrete too much CO2 Deficit of carbonic acid in the blood increases pH. People develop acid-base imbalances when their normal homeostatic mechanisms are dysfunctional or overwhelmed. The term acidosis describes a condition that tends to make the blood relatively too acidic. Because our cells produce two types of acid, two different types of acidosis have been identified: respiratory acidosis and metabolic acidosis. The term alkalosis describes a condition that tends to make the blood relatively too basic (alkaline). Two types of alkalosis are known: respiratory alkalosis and metabolic alkalosis. The body has compensatory mechanisms that limit the extent of pH change with acid-base imbalances. Compensation involves physiological changes that help normalize the pH but do not correct the cause of the problem. If the problem is a respiratory acid-base imbalance, only the lungs can correct the problem, but the kidneys can compensate by changing the amount of metabolic acid in the blood. If the problem is a metabolic acid-base imbalance, only the kidneys can correct the problem, but the lungs can compensate by changing the amount of carbonic acid in the blood. Thus, the kidneys compensate for respiratory acid-base imbalances; the respiratory system compensates for metabolic acid-base imbalances. These compensatory mechanisms do not correct the problem, but they assist the body to survive by moving the blood pH toward normal. However, if the underlying condition is not corrected, these compensatory mechanisms eventually will fail. Respiratory acidosis arises from alveolar hypoventilation; the lungs are unable to excrete enough CO2. The PaCO2 rises, creating an excess of carbonic acid in the blood, which decreases pH. The kidneys compensate by increasing excretion of metabolic acids in the urine, which increases blood bicarbonate. This compensatory process is slow, often taking 24 hours to show clinical effect and 3 to 5 days to reach steady state. Decreased cerebrospinal fluid (CSF) pH and intracellular pH of brain cells cause decreased levels of consciousness. [Review Table 42-7, Acid-Base Imbalances, with students.] Respiratory alkalosis arises from alveolar hyperventilation; the lungs excrete too much carbonic acid (CO2 and water). The PaCO2 falls, creating a deficit of carbonic acid in the blood, which increases pH. Respiratory alkalosis usually is short lived; thus the kidneys do not have time to compensate. When the pH of blood, CSF, and intracellular fluid increases acutely, cell membrane excitability also increases, giving rise to neurological symptoms such as excitement, confusion, and paresthesias. If the pH rises enough, central nervous system (CNS) depression can occur. Copyright © 2017, Elsevier Inc. All Rights Reserved.

Acid-Base Imbalances (Cont.)
Metabolic acidosis Arises from increase in metabolic acid or decrease in base (bicarbonate) Kidneys unable to excrete enough metabolic acids, which accumulate in the blood Results in decreased level of consciousness Metabolic alkalosis Arises from direct increase in base (bicarbonate) or decrease in metabolic acid Results in increased blood bicarbonate Metabolic acidosis occurs from an increase in metabolic acid or a decrease in base (bicarbonate). The kidneys are unable to excrete enough metabolic acids, which accumulate in the blood, or bicarbonate is removed from the body directly, as with diarrhea. In either case, the blood HCO3− decreases, and the pH falls. With an increase in metabolic acids, blood HCO3− decreases because it is used to buffer metabolic acids. Similarly, when patients have conditions that cause the removal of HCO3−, the amount of HCO3− in the blood decreases. To help identify the specific cause, health care providers and the laboratory calculate the anion gap, a reflection of unmeasured anions in plasma. You calculate anion gap by subtracting the sum of plasma concentrations of the anions Cl− and HCO3− from the plasma concentration of the cation Na+. When reviewing laboratory reports, check the reference values from the laboratory that measured the electrolyte concentrations. [Review Table 42-8, Anion Gap in Metabolic Acidosis, with students.] The abnormally low pH in metabolic acidosis stimulates the chemoreceptors, so the respiratory system compensates for the acidosis by hyperventilation. Compensatory hyperventilation begins in a few minutes and removes carbonic acid from the body. This process does not correct the problem, but it helps limit the pH decrease. Metabolic acidosis decreases one’s level of consciousness. Metabolic alkalosis occurs from a direct increase in base (HCO3−) or a decrease in metabolic acid, which increases blood HCO3− by releasing it from its buffering function. Common causes include vomiting and gastric suction. The respiratory compensation for metabolic alkalosis is hypoventilation. The decreased rate and depth of respiration allow carbonic acid to increase in the blood, as can be seen by an increased PaCO2. The need for oxygen may limit the degree of respiratory compensation for metabolic alkalosis. Because HCO3− crosses the blood-brain barrier with difficulty, neurological signs and symptoms are less severe or even absent with metabolic alkalosis. Copyright © 2017, Elsevier Inc. All Rights Reserved.

Nursing Knowledge Base
Use the scientific knowledge base in clinical decision making to provide safe, optimal fluid therapy. Apply knowledge of risk factors for fluid imbalances and physiology of normal aging when assessing older adults, knowing that this age group is at high risk for fluid imbalances. Ask questions to elicit risk factors for fluid, electrolyte, and acid-base imbalances. Perform clinical assessments for signs and symptoms of these imbalances. You will apply knowledge about fluid, electrolyte, and acid-base imbalance in many clinical settings. You will incorporate nursing and collaborative interventions to maintain or restore fluid and electrolyte balance. Skills and techniques for safe IV therapy are a vital area of the nursing knowledge base and the focus of much nursing research to support evidence-based practice. Copyright © 2017, Elsevier Inc. All Rights Reserved.

Critical Thinking Successful critical thinking requires a synthesis of knowledge, experience, information gathered from patients, critical thinking attitudes, and intellectual and professional standards. In the case of fluid, electrolyte, and acid-base balance, you integrate knowledge of physiology, pathophysiology, and pharmacology and previous experiences and information gathered from patients. Clinical judgments require you to anticipate the information necessary to analyze the data and make decisions regarding patient care. During assessment, consider all elements that build toward making an appropriate nursing diagnosis. Critical analysis of data enables an understanding of how fluid, electrolyte, and acid-base imbalances affect a specific patient and the patient’s family. In addition, critical thinking attitudes, such as accountability, discipline, and integrity, assist you in identifying appropriate nursing diagnoses and planning successful interventions. Professional standards such as the Infusion Nurses Society (INS) standards of practice provide valuable guidance for appropriate assessment. Copyright © 2017, Elsevier Inc. All Rights Reserved.

Nursing Process: Assessment
Through the patient’s eyes Nursing history Age: very young and old at risk Environment: excessively hot? Dietary intake: fluids, salt, foods rich in potassium, calcium, and magnesium Lifestyle: alcohol intake history Medications: include over-the-counter (OTC) and herbal, in addition to prescription medications Using a systematic approach in assessment enables you to help patients safely maintain or restore fluid, electrolyte, and acid-base balances. A patient’s fluid, electrolyte, or acid-base imbalance is sometimes so severe that it prevents initial discussion of his or her expressed needs, values, and preferences. However, when a patient is alert enough to discuss care, you need to elicit this information. Focus on the patient’s experience with fluid, electrolyte, or acid-base alterations and his or her perceptions of the illness. Ask about the patient’s greatest concerns regarding fluid status to build the basis for active partnership in planning, implementing, and evaluating patient-centered care. Clinical assessment begins with a patient history designed to reveal risk factors that cause or contribute to fluid, electrolyte, and acid-base imbalances. Ask specific, focused questions to identify factors that contribute to a patient’s potential imbalances. [Review Table 42-9, Risk Factors for Fluid, Electrolyte, and Acid-Base Imbalances, and Box 42-1, Nursing Assessment Questions, with students.] First, assess a patient’s age. An infant’s proportion of total body water (70% to 80% total body weight) is greater than that of children or adults. Infants and young children have greater water needs and immature kidneys (Hockenberry and Wilson, 2015). They are at greater risk for ECV deficit and hypernatremia because body water loss is proportionately greater per kilogram of weight. Children who are between the ages of 2 and 12 years frequently respond to illnesses with fevers of higher temperatures and longer duration than those of adults (Hockenberry and Wilson, 2015). At any age fever increases the rate of insensible water loss. Adolescents have increased metabolism and increased water production because of their rapid growth changes. Fluctuations in fluid balance are greater in adolescent girls because of hormonal changes associated with the menstrual cycle. Older adults experience a number of age-related changes that potentially affect fluid, electrolyte, and acid-base balances. [Review Box 42-2, Focus on Older Adults: Factors Affecting Fluid, Electrolyte, and Acid-Base Balance, with students.] Environment. Hot environments increase fluid output through sweating. Sweat is a hypotonic sodium-containing fluid. Excessive sweating without adequate replacement of salt and water can lead to ECV deficit, hypernatremia, or clinical dehydration. Ask patients about their normal level of physical work and whether they engage in vigorous exercise in hot environments. Do the patients have fluid replacements containing salt available during exercise and activity? Assess dietary intake of fluids; salt; and foods rich in potassium, calcium, and magnesium. Ask patients if they follow weight-loss diets. Starvation diets and those with high fat and no carbohydrate content often lead to metabolic acidosis. In addition, assess the patient’s ability to chew and swallow, which, if altered, interferes with adequate intake of electrolyte-rich foods and fluids. Take an alcohol intake history. Chronic alcohol abuse commonly causes hypomagnesemia, in part because it increases renal magnesium excretion. Obtain a complete list of your patient’s current medications, including OTC and herbal preparations, to assess the risks for fluid, electrolyte, and acid-base imbalances. Use a drug reference book or a reputable online database to check the potential effects of other medications. Ask specifically about the use of baking soda as an antacid, which can cause ECV excess because of its high sodium content that holds water in the extracellular compartments. For an individual who uses laxatives, ask about the consistency and frequency of stools. Multiple loose stools remove fluid and electrolytes from the body, thus causing numerous imbalances. [Review Box 42-3, Commonly Used Medications that Cause Fluid, Electrolyte, and Acid-Base Imbalances, with students.] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Nursing Process: Assessment (Cont.)
Medical history Recent surgery (physiological stress) Gastrointestinal output Acute illness or trauma Respiratory disorders Burns Trauma Chronic illness Cancer Heart failure Oliguric renal disease Patients who are very young or very old, whose I&O of fluid and/or electrolytes are not equal, or who have various chronic diseases or trauma are at high risk for fluid, electrolyte, and acid-base imbalances. Surgery causes a physiological stress response, which increases with extensive surgery and blood loss. On the second to fifth postoperative days, increased secretion of aldosterone, glucocorticoids, and ADH causes increased ECV, decreased osmolality, and increased potassium excretion. In otherwise healthy patients, these imbalances resolve without difficulty, but patients who have preexisting illnesses or additional risk factors often need treatment during this time period. Increased output of fluid through the GI tract is a common and important cause of fluid, electrolyte, and acid-base imbalances that requires careful assessment. Acute conditions that place patients at high risk for fluid, electrolyte, and acid-base alterations include respiratory diseases, burns, trauma, GI alterations, and acute oliguric renal disease. Many acute respiratory disorders predispose patients to respiratory acidosis. For example, bacterial pneumonia causes alveoli to fill with exudate that impairs gas exchange, causing the patient to retain carbon dioxide, which leads to increased PaCO2 and respiratory acidosis. Burns place patients at high risk for ECV deficit from numerous mechanisms, including plasma-to-interstitial fluid shift and increased evaporative and exudate output. The greater the body surface burned, the greater is the fluid loss. Hemorrhage from any type of trauma causes ECV deficit from blood loss. Some types of trauma create additional risks. For example, crush injuries destroy cellular structure, causing hyperkalemia by massive release of intracellular K+ into the blood. Head injury typically alters ADH secretion. It may cause diabetes insipidus (deficit of ADH), in which patients excrete large volumes of very dilute urine and develop hypernatremia. In contrast, head injury may cause the syndrome of inappropriate antidiuretic hormone (SIADH), in which excess secretion of ADH causes hyponatremia by retaining too much water and concentrating the urine. Chronic illness. Many chronic diseases create ongoing risks of fluid, electrolyte, and acid-base imbalances. In addition, the treatment regimens for chronic disease often cause imbalances. The specific fluid and electrolyte imbalances that occur with cancer depend on the type and progression of the cancer and treatment regimen. Many patients with cancer develop hypercalcemia when their cancer cells secrete chemicals that circulate to bones and cause calcium to enter the blood. Other fluid and electrolyte imbalances occur in cancer because some types of tumors cause metabolic and endocrine abnormalities. In addition, patients with cancer are at risk for fluid and electrolyte imbalances as a result of the side effects (e.g., anorexia, diarrhea) of chemotherapy, biological response modifiers, or radiation Patients who have chronic heart failure have diminished cardiac output, which reduces kidney perfusion and activates the RAAS. The action of aldosterone on the kidneys causes ECV excess and risk of hypokalemia. Most diuretics used to treat heart failure increase the risk of hypokalemia while reducing the ECV excess. Dietary sodium restriction is important with heart failure because Na+ holds water in the ECF, making the ECV excess worse. In severe heart failure, restriction of both fluid and sodium is prescribed to decrease the workload of the heart by reducing excess circulating fluid volume. Oliguria occurs when the kidneys have a reduced capacity to make urine. Some conditions, such as acute nephritis, cause a sudden onset of oliguria, whereas other problems, such as chronic kidney disease, lead to chronic oliguria. Oliguric renal disease prevents normal excretion of fluid, electrolytes, and metabolic acids, resulting in ECV excess, hyperkalemia, hypermagnesemia, hyperphosphatemia, and metabolic acidosis. The severity of these imbalances is proportionate to the degree of renal failure. Copyright © 2017, Elsevier Inc. All Rights Reserved.

Physical Assessment Daily weights Fluid intake and output (I&O)
Indicator of fluid status Use same conditions Fluid intake and output (I&O) 24-hour I&O: compare intake versus output Intake includes all liquids eaten, drunk, or received through IV Output = Urine, diarrhea, vomitus, gastric suction, wound drainage Laboratory studies Data gathered through a focused physical assessment validate and extend the information collected in the patient history. [Review Table 42-10, Focused Nursing Assessments for Patients with Fluid, Electrolyte, and Acid-Base Imbalances, with students.] Daily weights are an important indicator of fluid status. Each kilogram (2.2 lbs) of weight gained or lost overnight is equal to 1 L of fluid retained or lost. These fluid gains or losses indicate changes in the amount of total body fluid, usually ECF, but do not indicate a shift between body compartments. Weigh daily patients with heart failure and those who are at high risk for or who actually have ECV excess. Daily weights are also useful for patients with clinical dehydration or other causes of or risks for ECV deficit. Weigh the patient at the same time each day with the same scale after a patient voids. Calibrate the scale each day or routinely. The patient needs to wear the same clothes or clothes that weigh the same; if using a bed scale, use the same number of sheets on the scale with each weighing. Compare the weight of each day with that of the previous day to determine fluid gains or losses. Look at the weights over several days to recognize trends. Interpretation of daily weights guides medical therapy and nursing care. Teach patients with heart failure to take and record their daily weights at home and to contact their health care provider if their weight increases suddenly by a set amount (obtain parameters from their health care providers). Recognizing trends in daily weights taken at home is important. Research shows that patients who are hospitalized for decompensated heart failure often experience steady increases in daily weights during the week before hospitalization. Measuring and recording all liquid I&O during a 24-hour period is an important aspect of fluid balance assessment. Compare a patient’s 24-hour intake with the patient’s 24-hour output. The two measures should be approximately equal if the person has normal fluid balance. To interpret situations in which I&Os are substantially different, consider the individual patient. For example, if intake is substantially greater than output, two possibilities exist: The patient may be gaining excessive fluid or may be returning to normal fluid status by replacing fluid lost previously from the body. Similarly, if intake is substantially smaller than output, two possibilities are known: The patient may be losing needed fluid from the body and developing ECV deficit and/or hypernatremia or may be returning to normal fluid status by excreting excessive fluid gained previously. In most health care settings, I&O measurement is a nursing assessment. Some agencies require a health care provider’s order for I&O. If you want to measure I&O for a patient with compromised fluid status, check your agency policies to determine whether you can institute it or if you need a health care provider’s order. Fluid intake includes all liquids that a person eats (e.g., gelatin, ice cream, soup), drinks (e.g., water, coffee, juice), or receives through nasogastric or jejunostomy feeding tubes. IV fluids (continuous infusions and intermittent IV piggybacks) and blood components are also sources of intake. Water swallowed while taking pills and liquid medications counts as intake. A patient receiving tube feedings often receives numerous liquid medications, and water is used to flush the tube before and/or after medications. Over a 24-hour period, these liquids amount to significant intake and always are recorded on the I&O record. Ask patients who are alert and oriented to assist with measuring their oral intake, and explain to families that they should not drink from the patient’s water pitcher or eat from the patient’s meal trays. Fluid output includes urine, diarrhea, vomitus, gastric suction, and drainage from postsurgical wounds or other tubes. Record a patient’s urinary output after each voiding. Instruct patients who are alert, oriented, and ambulatory to save their urine in a calibrated insert, which attaches to the rim of the toilet bowl. Teach patients and families the purpose of I&O measurements. Teach them to notify the nurse or nursing assistive personnel (NAP) to empty any container with voided fluid, or show them how to measure and empty the container themselves and report the results appropriately. Accurate I&O facilitates ongoing evaluation of a patient’s hydration status. Review the patient’s laboratory test results and compare them with normal ranges to obtain further objective data about fluid, electrolyte, and acid-base balances. Serum electrolyte tests usually are performed routinely on any patient entering a hospital to screen for imbalances and serve as a baseline for future comparisons. [Review Figure 42-9, Critical thinking model for fluid, electrolyte, and acid-base balances assessment, with students.] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Case Study (Cont.) Mrs. Reynolds states that she has no appetite, is nauseous, and has been vomiting and has had diarrhea for 7 days. Bowel sounds are hyperactive in all four quadrants. The patient has had only two loose stools since midnight. She voids with difficulty, with dark yellow urine. Her 24-hour intake was 1850 mL; her output was 2200 mL (of which urine was only 1000 mL). Temperature 99.6° F; pulse 100 bpm; BP 110/60 mm Hg with no changes when standing. Respirations are 18 breaths per minute and nonlabored with bilateral breath sounds clear to auscultation. Robert observes that Mrs. Reynolds’ skin is dry, and turgor is decreased. Inspection of mucous membranes reveals that they are dry with thick, clear mucus. The patient’s weight of 143 lb is down 1 lb since admission. [Ask students: What conclusions can Robert draw from this information? Discuss.] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Measuring Urine Output
[Shown is Figure 42-10: Containers for measuring urine output.] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Case Study (Cont.) Mrs. Reynolds’ laboratory results:
Hematocrit 44% (suggesting hypovolemia) Potassium 3.6 mEq/L and sodium 138 mEq/L (both low normal because of prolonged vomiting and diarrhea) ECG showed normal sinus rhythm. [Ask students: What nursing diagnosis should Robert choose? Discuss.] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Nursing Diagnosis • Decreased cardiac output • Acute confusion
• Impaired gas exchange • Excess fluid volume • Risk for electrolyte imbalance • Deficient knowledge regarding disease management Risk for injury •Deficient fluid volume When caring for patients with suspected fluid, electrolyte, and acid-base imbalances, it is particularly important to use critical thinking to formulate nursing diagnoses. The assessment data that establish the risk for or the actual presence of a nursing diagnosis in these areas may be subtle, and patterns and trends emerge only when there has been astute assessment. Multiple body systems often are involved; careful clustering of defining characteristics leads to selection of the appropriate diagnoses. [Discuss with students how each diagnosis would be determined.] [Review, Box 42-4, Nursing Diagnostic Process: Deficient Fluid Volume Related to Loss of Gastrointestinal Fluids via Vomiting, with students.] In addition to the accurate clustering of assessment data, an important part of formulating nursing diagnoses is identifying the relevant causative or related factor. You choose interventions that treat or modify the related factor for the diagnosis to be resolved. Copyright © 2017, Elsevier Inc. All Rights Reserved.

Case Study (Cont.) Robert chooses this nursing diagnosis: Deficient fluid volume related to excessive diarrhea, vomiting, and use of potassium-wasting diuretic The goal he sets are: Mrs. Reynolds’ fluid volume will return to normal by time of discharge. Mrs. Reynolds will achieve normal electrolyte balance by discharge. [Ask students: What expected outcomes would Robert establish for these goals? Discuss.] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Quick Quiz! 3. A senior student nurse delegates the task of intake and output to a new nursing assistant. The student will verify that the nursing assistant understands the task of I&O when the nursing assistant states, A. “I will record the amount of all voided urine.” B. “I will not count liquid stools as output.” C. “I will not record a café mocha as intake.” D. “I will notate perspiration and record it as a small or large amount.” Answer: A Copyright © 2017, Elsevier Inc. All Rights Reserved.

Planning Goals and outcomes Setting priorities
Establish an individual patient plan of care for each nursing diagnosis Setting priorities The patient’s clinical condition determines which of the nursing diagnoses takes the greatest priority Teamwork and collaboration During the planning process use critical thinking to synthesize information from multiple resources. Ensure that the patient’s plan of care integrates both scientific and nursing knowledge and all of the information that you collected about the individual patient. If the patient’s medical condition is not dealt with in a timely manner, fluid, electrolyte, and acid-base balances will worsen. For example, if a patient experiences vomiting and diarrhea, this needs to be addressed immediately, especially if the patient is young, elderly, or chronically ill. Do not delegate administration of IV fluid and hemodynamic assessment to NAP. When the patient is stable, you can delegate daily weights, I&O, and direct physical care to NAP. Collaborative care may involve other services, including discharge planning, nutritional support, and pharmacy. Ongoing communication and consultation are important because the patient’s condition can change quickly. Begin discharge planning early for patients with acute or chronic fluid and electrolyte disturbances by anticipating the needs of the patient and family as they transition to another setting. In the hospital, collaboration with other members of the health care team ensures that care will continue in the home or long-term care setting with few disruptions. You ensure that therapeutic regimens established in one setting continue through completion at the next setting. [Review Figure 42-11, Critical thinking model for fluid, electrolyte, and acid-base balances planning, with students.] [Review Figure 42-12, Concept map for Mrs. Beck, with students.] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Case Study (Cont.) Fluid balance Electrolyte and acid-base balance
Urine output will equal intake of ~1500 mL in 2 days. Mucous membranes will be moist in 24 hours. Skin turgor will return to normal within 24 hours. Daily weights will not vary by more than 2 lbs over the next 2 days. Electrolyte and acid-base balance Serum electrolyte and blood counts will be within normal limits within 48 hours. Mrs. Reynolds will not have any nausea or vomiting in 24 hours. [Ask students: What additional expected outcome would be included? Discuss: Mrs. Reynolds will not have more than 1 stool a day in 3 days.] [Ask students: What interventions can you anticipate? Discuss.] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Implementation Health promotion Fluid replacement education
Teach patients with chronic conditions about risk factors and signs and symptoms of imbalances. Health promotion activities focus primarily on patient education. Teach patients and caregivers to recognize risk factors for developing imbalances and to implement appropriate preventive measures. Parents must understand that infants and children need to replace fluids when vomiting or diarrhea occurs. Adults, especially the elderly and the infirm, also need to replace fluids when increased perspiration occurs. Patients with chronic health alterations often are at risk for developing fluid, electrolyte, and acid-base imbalances. They need to understand their own risk factors and the measures to be taken to avoid imbalances. Teach patients with chronic diseases and their family caregivers the early signs and symptoms of the fluid, electrolyte, and acid-base imbalances for which they are at risk, and what to do if these occur. Copyright © 2017, Elsevier Inc. All Rights Reserved.

Implementation (Cont.)
Acute care Enteral replacement of fluids Restriction of fluids Parenteral replacement of fluids and electrolytes TPN Crystalloids (electrolytes) Colloids (blood and blood components) Acute care nurses administer medications and oral and IV fluids to replace fluid and electrolyte deficits or to maintain normal homeostasis; they also assist with restricting intake as part of therapy for excesses. Prevention and treatment of ECV deficit, hypernatremia, and electrolyte deficits are accomplished with enteral or parenteral administration of appropriate fluid. Enteral replacements. Oral replacement of fluids and electrolytes is appropriate as long as the patient is not so physiologically unstable that oral fluids cannot be replaced rapidly. Oral replacement of fluids is contraindicated when the patient has a mechanical obstruction of the GI tract, is at high risk for aspiration, or has impaired swallowing. Some patients unable to tolerate solid foods are still able to ingest fluids. Strategies to encourage fluid intake include offering frequent small sips of fluid, popsicles, and ice chips. Record one-half the volume of the ice chips in I&O measurement. Pay attention to each patient’s preferred temperature of oral fluids. Cultural beliefs regarding appropriate fluid temperature may interfere with fluid intake unless the fluid with the preferred temperature is available. [Review Box 42-5, Cultural Aspects of Care: Fluid Therapy, with students.] When replacing fluids by mouth in a patient with ECV deficit, choose fluids that contain sodium. Patients who have hyponatremia usually require restricted water intake. Patients who have very severe ECV excess sometimes have both sodium and fluid restrictions. Fluid restriction often is difficult for patients, particularly if they take medications that dry the oral mucous membranes or if they are mouth breathers. In acute care settings, fluid restrictions usually allot half the total oral fluids between 7 a.m. and 3 p.m., the period when patients are more active, receive two meals, and take most of their oral medications. Offer the remainder of the fluids during the evening and night shifts. Patients on fluid restriction need frequent mouth care to moisten mucous membranes, decrease the chance of mucosal drying and cracking, and maintain comfort. Fluid and electrolytes may be replaced through infusion of fluids directly into veins (intravenously) rather than via the digestive system. Parenteral replacement includes parenteral nutrition (PN), IV fluid and electrolyte therapy (crystalloids), and blood and blood component (colloids) administration. IV devices are called peripheral IVs when the catheter tip lies in a vein in one of the extremities; they are called central venous IVs when the catheter tip lies in the central circulatory system (e.g., in the vena cava close to the right atrium of the heart). Practice standard body fluid precautions when administering parenteral fluids. PN, also called total parenteral nutrition (TPN), is IV administration of a complex, highly concentrated solution containing nutrients and electrolytes that is formulated to meet a patient’s needs. Depending on their osmolality, PN solutions are administered through a central IV catheter (high osmolality) or peripherally (lower osmolality). Chapter 45 reviews principles and guidelines for PN administration, which is used when patients are unable to receive enough nutrition orally or through enteral feeding. [Shown is Figure 42-13: Central venous lines deliver intravenous fluid into superior vena cava near heart. CVAD, central venous access device.] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Intravenous Therapy IV therapy: crystalloids Types of solutions
Isotonic Hypotonic Hypertonic Caution: Too rapid or excessive infusion of any IV fluid has the potential to cause serious problems Vascular access devices The goal of IV fluid administration is to correct or prevent fluid and electrolyte disturbances. IVs allow direct access to the vascular system, permitting continuous infusion of fluids over a period of time. To provide safe and appropriate therapy to patients who require IV fluids, you need knowledge of the correct ordered solution, the reason the solution was ordered, the equipment needed, the procedures required to initiate an infusion, how to regulate the infusion rate and maintain the system, how to identify and correct problems, and how to discontinue the infusion. [Review Table 42-11, Intravenous Solutions, with students.] An IV solution may be isotonic, hypotonic, or hypertonic. Isotonic solutions have the same effective osmolality as body fluids. Sodium-containing isotonic solutions, such as normal saline, are indicated for ECV replacement to prevent or treat ECV deficit. Hypotonic solutions have an effective osmolality less than body fluids, thus decreasing osmolality by diluting body fluids and moving water into cells. Hypertonic solutions have an effective osmolality greater than body fluids. If they are hypertonic sodium-containing solutions, they increase osmolality rapidly and pull water out of cells, causing them to shrivel. The decision to use a hypotonic or hypertonic solution is based on the patient’s specific fluid and electrolyte imbalance. Additives such as potassium chloride (KCl) are common in IV solutions. A health care provider’s order is necessary if an IV is to have additives added. Administer KCl carefully because hyperkalemia can cause fatal cardiac dysrhythmias. Under no circumstances should it be administered by IV push (directly through a port in IV tubing). Verify that a patient has adequate kidney function and urine output before administering an IV solution containing potassium. Patients with normal renal function who are receiving nothing by mouth should have potassium added to IV solutions. The body cannot conserve potassium, and the kidneys continue to excrete potassium even when the plasma level falls. Without potassium intake, hypokalemia develops quickly. Vascular access devices (VADs) are catheters or infusion ports designed for repeated access to the vascular system. Peripheral catheters are for short-term use (e.g., fluid restoration after surgery and short-term antibiotic administration). Devices for long-term use include central catheters and implanted ports, which empty into a central vein. Remember that the term central applies to the location of the catheter tip, not to the insertion site. Peripherally inserted central catheters (PICC lines) enter a peripheral arm vein and extend through the venous system to the superior vena cava, where they terminate. Other central lines enter a central vein such as the subclavian or jugular vein or are tunneled through subcutaneous tissue before entering a central vein. Central lines are more effective than peripheral catheters for administering large volumes of fluid, parenteral nutrition (PN), and medications or fluids that irritate veins. Proper care of central line insertion sites is critical for the prevention of catheter-related bloodstream infections (CRBSIs). Review Box 42-6, Evidence-Based Practice: Preventing Central Line Associated Blood Stream Infections (CLABSI), with students.] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Intravenous Therapy (Cont.)
Equipment Vascular access devices (VADs), tourniquets, clean gloves, dressings, IV fluid containers, various types of tubing, and electronic infusion devices (EIDs), also called infusion pumps Initiating the intravenous line Regulating the infusion flow Correct selection and preparation of IV equipment assists in safe and rapid placement of an IV line. Because fluids infuse directly into the bloodstream, sterile technique is necessary. Organize all equipment at the bedside for an efficient insertion. IV equipment includes vascular access devices (VADs), tourniquet, clean gloves, dressings, IV fluid containers, various types of tubing, and electronic infusion devices (EIDs), also called infusion pumps. VADs that are short, peripheral IV catheters are available in a variety of gauges such as the commonly used 20 and 22 gauges. A larger gauge indicates a smaller-diameter catheter. A peripheral VAD is called an over-the-needle catheter; it consists of a small plastic tube or catheter threaded over a sharp stylet (needle). Once you insert the stylet and advance the catheter into the vein, you withdraw the stylet, leaving the catheter in place. These devices have a safety mechanism that covers the sharp stylet when withdrawing it to reduce the risk of needlestick injury. Needleless systems allow you to make connections without using needles, which reduces needlestick injuries. The main IV fluid used in a continuous infusion flows through tubing called the primary line. The primary line connects to the IV catheter. Injectable medications such as antibiotics are usually added to a small IV solution bag and “piggybacked” as a secondary set into the primary line or as a primary intermittent infusion to be administered over a 30- to 60-minute period. The type and amount of solution are prescribed by the patient’s health care provider and depend on the medication added and the patient’s physiological status. If an IV infusion is connected to an EID, use the tubing designated for that EID. For gravity-flow IVs (not using an EID), select tubing as described in the equipment list of Skill Add IV extension tubing to increase the length of the primary line, which reduces pulling of the tubing and increases a patient’s mobility in changing position. After you collect the equipment at the patient’s bedside, prepare to insert the IV line by assessing the patient for a venipuncture site. The most common IV sites are on the inner arm. As you assess a patient for potential venipuncture sites, consider conditions that exclude certain sites. Venipuncture is contraindicated in a site that has signs of infection, infiltration, or thrombosis. Venipuncture is a technique in which a vein is punctured through the skin by a sharp rigid stylet (e.g., metal needle). The stylet is partially covered either with a plastic catheter or a needle attached to a syringe. [Review Box 42-7, Focus on Older Adults: Protection of Skin and Veins During Intravenous Therapy, with students.] After initiating a peripheral IV infusion and checking it for patency, regulate the rate of infusion according to the health care provider’s orders. For patient safety avoid uncontrolled flow of IV fluid into a patient. You are responsible for calculating the flow rate (mL/hr) that delivers the IV fluid in the prescribed time frame. The correct IV infusion rate ensures patient safety by preventing too-slow or too-rapid administration of IV fluids. Electronic infusion devices (EIDs), also called IV pumps or infusion pumps, deliver an accurate hourly IV infusion rate. EIDs use positive pressure to deliver a measured amount of fluid during a specified unit of time (e.g., 125 mL/hr). Familiarize yourself with the brand of EID in use at your agency so you are able to set the flow rate accurately. Many EIDs have capabilities that allow for single- and multiple-solution infusions at different rates. Electronic detectors and alarms respond to air in IV lines, occlusion, completion of infusion, high and low pressure, and low battery power. Regardless of the device in use, monitor the patient regularly to verify correct infusion of IV fluids. Flexion of an extremity, particularly at the wrist or elbow, can decrease IV flow rate by compressing the vein. [Shown is Figure 42-14: Over-the-needle catheter for venipuncture, and Figure 42-15: Common IV sites. A, Inner arm. B, Dorsal surface of hand.] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Initiating IV Therapy Maintaining the system
Keeping system sterile and intact Involves (1) keeping the system sterile and intact; (2) changing IV fluid containers, tubing, and contaminated site dressings; (3) assisting a patient with self-care activities so as not to disrupt the system; and (4) monitoring for complications of IV therapy. The frequency and options for maintaining the system are identified in agency policies. An important component of patient care is maintaining the integrity of an IV line to prevent infection. Inserting an IV line under appropriate aseptic technique reduces the chances of contamination from the patient’s skin microflora. After insertion, the conscientious use of infection control principles, including thorough hand hygiene before and after handling any part of the IV system, and maintaining sterility of the system during tubing and fluid container changes, prevents infection. Always maintain the integrity of an IV system. Never disconnect tubing because it becomes tangled, or it might seem more convenient for positioning or moving a patient or applying a gown. If a patient needs more room to maneuver, use aseptic technique to add extension tubing to an IV line. However, keep the use of extension tubing to a minimum because each connection of tubing provides an opportunity for contamination. Never let IV tubing touch the floor. IV tubing contains needleless injection ports through which syringes or other adaptors can be inserted for medication administration. Clean an injection port thoroughly with 2% chlorhexidine (preferred), 70% alcohol, or povidone-iodine solution and let it dry before accessing the system. Protective devices designed to prevent movement or accidental dislodgment of a VAD are called catheter stabilization devices. These devices are available in many hospitals, and nurses decide whether or not to use them when starting an IV line. This is a patient safety issue. Movement of the VAD in a vein can cause phlebitis and infiltration; VAD dislodgment requires using another VAD at a new IV infusion site. Infusion Nurses Society (INS) standards indicate that use of these devices is preferable over taping when feasible. [Shown is Figure 42-16: Potential sites for contamination of vascular access device, and Figure 42-17: Catheter stabilization device.] [Review Skill 42-1, Initiating Intravenous Therapy, with students.] [Review Skill 42-2, Regulating Intravenous Flow Rate, with students.] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Initiating IV Therapy (Cont.)
Changing intravenous fluid containers, tubing, and dressings Assisting patient with self-care activities Complications Fluid overload, infiltration, extravasation, phlebitis, local infection, bleeding at the infusion site Discontinuing peripheral IV access Patients receiving IV therapy over several days require periodic changes of IV fluid containers. It is important to organize tasks so you can change containers rapidly before a thrombus forms in the catheter. Recommended frequency of IV tubing change depends on whether it is used for continuous or intermittent infusion. [Review Skill 42-3, Maintenance of Intravenous System, with students.] [Review Skill 42-4, Changing a Peripheral Intravenous Dressing, with students.] To prevent the accidental disruption of an IV system, a patient often needs assistance with hygiene, comfort measures, meals, and ambulation. A potentially dangerous complication of IV therapy is circulatory overload with IV solution, which occurs when a patient receives too-rapid administration or an excessive amount of fluids. Assessment findings depend on the type of IV solution that infuses in excess. A potentially dangerous complication of IV therapy is circulatory overload with IV solution, which occurs when a patient receives too-rapid administration or an excessive amount of fluids. Assessment findings depend on the type of IV solution that infuses in excess. [Review Table 42-12, Complications of Intravenous Therapy with Nursing Interventions, with students.] Infiltration occurs when an IV catheter becomes dislodged or a vein ruptures and IV fluids inadvertently enter subcutaneous tissue around the venipuncture site. When the IV fluid contains additives that damage tissue, extravasation occurs. [Review Table 42-13, Infiltration Scale, with students.] Phlebitis (i.e., inflammation of a vein) results from chemical, mechanical, or bacterial causes. Risk factors for phlebitis include acidic or hypertonic IV solutions; rapid IV rate; IV drugs such as KCl, vancomycin, and penicillin; VAD inserted in area of flexion, poorly secured catheter; poor hand hygiene; and lack of aseptic technique (Wallis et al., 2014). The typical signs of inflammation (i.e., heat, erythema [redness], tenderness) occur along the course of the vein. Phlebitis can be dangerous because blood clots (thrombophlebitis) form along the vein and in some cases cause emboli. This may cause permanent damage to veins. [Review Table 42-14, Phlebitis Scale, with students.] Routine changes of peripheral IV catheters to reduce infection are not recommended. Bleeding can occur around the venipuncture site during the infusion or through the catheter or tubing if these become disconnected inadvertently (see Table 42-12). Bleeding is more common in patients who receive heparin or other anticoagulants or who have a bleeding disorder (e.g., hemophilia or thrombocytopenia) Discontinue IV access after infusion of the prescribed amount of fluid; when infiltration, phlebitis, or local infection occurs; or if the IV catheter develops a thrombus at its tip. Copyright © 2017, Elsevier Inc. All Rights Reserved.

Blood Transfusion Blood component therapy = IV administration of whole blood or blood component Blood groups and types Autologous transfusion Transfusing blood Transfusion reactions and other adverse effects Blood transfusion, or blood component therapy, is the IV administration of whole blood or a blood component such as packed red blood cells (RBCs), platelets, or plasma. Objectives for administering blood transfusions include (1) increasing circulating blood volume after surgery, trauma, or hemorrhage; (2) increasing the number of RBCs and maintaining hemoglobin levels in patients with severe anemia; and (3) providing selected cellular components as replacement therapy (e.g., clotting factors, platelets, albumin). Caring for patients receiving blood or blood products transfusion is a nursing responsibility. You must be thorough in patient assessment, checking the blood product against prescriber’s orders, checking blood product against patient identifiers, and monitoring for any adverse reactions. Blood transfusions are never regarded as routine; overlooking any minor detail can have dangerous and life threatening events for a patient. Blood transfusions must be matched to each patient to avoid incompatibility. RBCs have antigens in their membranes; the plasma contains antibodies against specific RBC antigens. If incompatible blood is transfused (i.e., a patient’s RBC antigens differ from those transfused), the patient’s antibodies trigger RBC destruction in a potentially dangerous transfusion reaction. The most important grouping for transfusion purposes is the ABO system, which identifies A, B, O, and AB blood types. Determination of blood type is based on the presence or absence of A and B red blood cell (RBC) antigens. Individuals with type A blood have A antigens on their RBCs and anti-B antibodies in their plasma. Individuals with type B blood have B antigens on their RBCs and anti-A antibodies in their plasma. A person who has type AB blood has both A and B antigens on the RBCs and no antibodies against either antigen in the plasma. A type O individual has neither A nor B antigens on RBCs but has both anti-A and anti-B antibodies in the plasma. [Review Table 42-15, ABO Compatibilities for Transfusion Therapy, with students.] People with type O blood are considered universal blood donors because they can donate packed RBCs and platelets to people with any ABO blood type. People with type AB blood are called universal blood recipients because they can receive packed RBCs and platelets of any ABO type. Autologous transfusion (autotransfusion) is the collection and reinfusion of a patient’s own blood. Blood for an autologous transfusion most commonly is obtained by preoperative donation up to 6 weeks before a scheduled surgery (e.g., heart, orthopedic, plastic, or gynecological). A patient can donate several units of blood, depending on the type of surgery and his or her ability to maintain an acceptable hematocrit. Blood for autologous transfusion is also obtained at the time of surgery by normovolemic hemodilution or through blood salvage (e.g., during surgery for liver transplantation, trauma, or vascular and orthopedic conditions). After surgery blood is salvaged from drainage from chest tubes or joint cavities. Autologous transfusions are safer for patients because they decrease the risk of mismatched blood and exposure to bloodborne infectious agents. Transfusion of blood or blood components is a nursing procedure that requires an order from a health care provider. Patient safety is a nursing priority, and patient assessment, verification of health care provider’s order, and verification of correct blood products for the correct patient are imperative. Perform a thorough patient assessment before initiating a transfusion and monitor carefully during and after the transfusion. Assessment is critical because of the risk of transfusion reactions. Always check agency policy and procedures before initiating any blood therapy. For patient safety always verify three things: that blood components delivered are the ones that were ordered; that blood delivered to the patient is compatible with the blood type listed in the medical record; and that the right patient receives the blood. When administering a transfusion you need an appropriate-size IV catheter and blood administration tubing that has a special in-line filter. [Review Figure 42-18, Filling tubing for blood administration.] If a transfusion reaction is anticipated or suspected, obtain vital signs more frequently. [Review Table 42-16, Acute Adverse Effects of Transfusion, with students.] The transfusion rate usually is specified in the health care provider’s orders. When patients have a severe blood loss such as with hemorrhage, they often receive rapid transfusions through a central venous catheter. A blood-warming device often is necessary because the tip of the central venous catheter lies in the superior vena cava, above the right atrium. Rapid administration of cold blood can cause cardiac dysrhythmias. Patients who receive large-volume transfusion of citrated blood have high risk of hyperkalemia, hypocalcemia, hypomagnesemia, and metabolic alkalosis, so they need careful monitoring. Transfusion reaction is an immune system reaction to the transfusion that ranges from a mild response to severe anaphylactic shock or acute intravascular hemolysis, both of which can be fatal. When you suspect acute intravascular hemolysis, do the following: Stop the transfusion immediately. Keep the IV line open by replacing the IV tubing down to the catheter hub with new tubing and running 0.9% sodium chloride (normal saline). Do not turn off the blood and simply turn on the 0.9% sodium chloride (normal saline) that is connected to the Y-tubing infusion set. This would cause blood remaining in the IV tubing to infuse into the patient. Even a small amount of mismatched blood can cause a major reaction. Immediately notify the health care provider or emergency response team. Remain with the patient, observing signs and symptoms and monitoring vital signs as often as every 5 minutes. Prepare to administer emergency drugs such as antihistamines, vasopressors, fluids, and corticosteroids per health care provider order or protocol. Prepare to perform cardiopulmonary resuscitation. Save the blood container, tubing, attached labels, and transfusion record for return to the blood bank. Obtain blood and urine specimens per health care provider order or protocol. Another category of adverse transfusion effects is diseases transmitted by blood from infected donors who are asymptomatic. Symptoms of these conditions may arise long after the transfusion. Diseases transmitted through transfusions include hepatitis B and hepatitis C, human immunodeficiency virus (HIV) infection and acquired immunodeficiency syndrome (AIDS), and cytomegalovirus infection. In the United States all units of blood for blood banks undergo screening for HIV, hepatitis B and hepatitis C viruses, syphilis, and West Nile virus, which reduces the risk of acquiring these bloodborne infections. [Shown is Figure 42-18: Filling tubing for blood administration.] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Case Study (Cont.) Robert will administer IV fluids (0.9% normal saline) at 125 mL/hr. He will provide Mrs. Reynolds with an additional 480 mL of noncaffeinated oral fluids every 8 hours. He will administer as ordered bismuth subsalicylate (Pepto Bismol) for diarrhea. He will maintain accurate I&O measurements. He will weigh Mrs. Reynolds daily and monitor trends. He will teach Mrs. Reynolds and her family about specific dietary modification (potassium-rich foods). [Ask students: What are the rationales for these interventions? Discuss: Replacement of body fluid restores blood volume and normal serum electrolyte levels; an isotonic solution expands the body’s intravascular fluid volume without causing a fluid shift from one compartment to another. Pepto-Bismol is an antidiarrheal and is given to inhibit GI secretions, stimulate absorption of fluid and electrolytes, inhibit intestinal inflammation, and suppress the growth of Helicobacter pylori. I&O documents hydration and fluid balance for directing therapy. Daily weights provide reliable data on fluid balance. Furosemide (Lasix) is a potassium-wasting diuretic. The body does not store potassium, thus requiring dietary supplements rich in potassium.] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Interventions Interventions for electrolyte imbalances
Support prescribed medical therapies Aim to reverse the existing acid-base imbalance Provide for patient safety Interventions for acid-base imbalances Arterial blood gases In addition to the administration of prescribed medical therapies, nursing interventions may be performed to preserve or restore electrolyte imbalance. Teach patients the reasons for their therapies and the importance of balancing electrolyte I&O to prevent imbalances in the future. Nursing interventions to promote acid-base balance support prescribed medical therapies and aim at reversing the existing acid-base imbalance while providing for patient safety. Patients with acid-base imbalances often require repeated arterial blood gas (ABG) analysis. Determination of a patient’s acid-base status requires obtaining a sample of arterial blood for laboratory testing. ABG analysis reveals acid-base status and the adequacy of ventilation and oxygenation. A qualified RN or other health care provider draws arterial blood from a peripheral artery (usually the radial) or from an existing arterial line (see agency policy and procedures). Before an arterial blood draw, perform an Allen test, which assesses arterial circulation in the hand. When performing the Allen test, apply pressure to both the patient’s ulnar and radial arteries in the selected hand. The fingers to the hand should be pale and blanched, indicating a lack of arterial blood flow. Release the pressure on the ulnar artery and observe for color to return to the fingers and hand, which indicates that there is adequate circulation to the hand and fingers via the ulnar artery. The Allen test ensures that the patient will have adequate blood flow to the hand if the radial artery is damaged. If color does not return, do not perform radial artery puncture on that arm. After the ABG puncture, apply pressure to the puncture site for at least 5 minutes to reduce the risk of hematoma formation. A longer time is necessary if the patient takes anticoagulant medications. Reassess the radial pulse after removing the pressure. After obtaining the specimen, take care to prevent air from entering the syringe because this alters the blood gas values. To reduce oxygen usage by blood cells, submerge the syringe in crushed ice and transport it immediately to the laboratory. Copyright © 2017, Elsevier Inc. All Rights Reserved.

Implementation Restorative care Home intravenous therapy
Nutrition support Medication safety Medications OTC drugs Herbal preparations After experiencing acute alterations in fluid, electrolyte, or acid-base balance, patients often require ongoing maintenance to prevent a recurrence of health alterations. Older adults require special considerations to prevent complications from developing. IV therapy often continues in the home setting for patients requiring long-term hydration, PN, or long-term medication administration. Initiate patient referral for discharge planning to social series, counselor, or home care coordinator for assessment of patient and community resources. A home IV therapy nurse works closely with the patient to ensure that a sterile IV system is maintained and complications can be avoided or recognized promptly. [Review Box 42-8, Patient Teaching: Home Intravenous Therapy, with students.] Most patients who have had electrolyte disorders or metabolic acid-base imbalances require ongoing nutritional support. Depending on the type of disorder, fluid or food intake may be encouraged or restricted. Patients or family members who are responsible for meal preparation need to learn to understand nutritional content of foods and read the labels of commercially prepared foods. Numerous medications, OTC drugs, and herbal preparations contain components or create potential side effects that can alter fluid and electrolyte balance. Patients with chronic disease who are receiving multiple medications and those with renal disorders are at significant risk for imbalances. Once patients return to a restorative care setting, whether in the home, long-term care, or other setting, drug safety is very important. Patient and family education regarding potential side effects and drug interactions that can alter fluid, electrolyte, or acid-base balance is essential. Review all medications with patients, and encourage them to consult with their local pharmacist, especially if they wish to try a new OTC drug or herbal preparation. Copyright © 2017, Elsevier Inc. All Rights Reserved.

Case Study (Cont.) Robert’s nursing actions: Findings
Monitor electrolyte levels and daily weights. Inspect oral mucous membranes; assess skin turgor. Evaluate I&O trends during next 48 hours. Findings Serum electrolyte levels: potassium 4.0 mEq/L and sodium 140 mEq/L. Mucous membranes remain dry; skin turgor normal. Mrs. Reynolds’ 24-hour intake is 2800 mL, and output is 2200 mL with 1800 mL urine. Urine specific gravity is 1.025, and weight has returned to 143 lb. Robert is encouraged by Mrs. Reynolds’ progress. Robert discusses sources of potassium in the diet with Mrs. Reynolds and writes this documentation note: “Denies nausea and reports feeling better. No diarrheal stool since yesterday afternoon around 3 p.m. On inspection, oral mucosa remains dry, without lesions or inflammation. Skin turgor is normal. Bowel sounds are normal in all four quadrants, abdomen soft to palpation. IV of 0.9% normal saline is infusing in left cephalic vein in forearm at 40 mL/hr per MD order. No tenderness or inflammation at IV site. Is able to identify five food sources for potassium to include in the diet. Is resting comfortably, out of bed in a chair, ate all of breakfast. Will continue to monitor.” Copyright © 2017, Elsevier Inc. All Rights Reserved.

Evaluation Through the patient’s eyes Patient outcomes
Review with patients how well their major concerns regarding fluid, electrolyte, or acid-base situations were alleviated or addressed. Patient outcomes Evaluate the effectiveness of interventions using the goals and outcomes established for the patient’s nursing diagnoses. Evaluation of a patient’s clinical status is especially important if acute fluid, electrolyte, and/or acid-base imbalances exist. A patient’s condition can change very quickly, and it is important to recognize impending problems by integrating information about his or her presenting risk factors, clinical status, effects of the present treatment regimen, and potential causative agent. For evaluation, you need knowledge of how various pathophysiological conditions affect fluid, electrolyte, and acid-base balance; the effects of medications and fluids; and the patient’s presenting clinical status. Compare your current assessment findings with the previous patient assessment. For example, a patient’s hypokalemia demonstrates improvement when the serum potassium is increasing toward normal and the physical signs and symptoms of hypokalemia begin to disappear or lessen in intensity. Specifically, the patient’s heart rhythm becomes more regular, and normal bowel function returns. For patients with less acute alterations, evaluation likely occurs over a longer period of time. In this situation, evaluation may be more focused on behavioral changes (e.g., the patient’s adherence to dietary restrictions and medication schedules). Another important element of evaluation is the family’s ability to anticipate alterations and prevent problems from recurring. The patient’s level of progress determines whether the plan of care needs to continue or be revised. If outcomes are not achieved, the questions asked might include the following: “What difficulties are you having with measuring your I&O daily and keeping a record?” “What barriers are you experiencing to obtaining the potassium-rich foods you need?” “Are you continuing to have frequent loose stools or diarrhea?” “Have you purchased an antacid, or are you still using baking soda as an antacid?” [Review Figure 42-19, Critical thinking model for fluid, electrolyte, and acid-base balances evaluation, with students.] Copyright © 2017, Elsevier Inc. All Rights Reserved.

Fluid, Electrolyte, and Acid-Base Balance

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Fluid, Electrolyte, and Acid-Base Balance

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