Lewis: Medical-Surgical Nursing, 9th Edition
Chapter 17
Fluid, Electrolyte, and Acid-Base Imbalances
KEY POINTS

HOMEOSTASIS
· Body fluids and electrolytes play an important role in maintaining a stable internal environment of the body.
· A number of adaptive responses keep the composition and volume of body fluids and electrolytes within the narrow limits of normal to maintain homeostasis and promote health.
· Many diseases and their treatments have the ability to affect fluid and electrolyte balance and alter homeostasis.

WATER CONTENT OF BODY
· Water is the primary component of the body, accounting for approximately 60% of the body weight in the adult.
· The two major fluid compartments in the body are intracellular fluid (ICF), or inside the cells, and extracellular fluid (ECF), or outside the cells. ECF is composed of interstitial fluid, plasma, and transcellular fluids. ELECTROLYTES
· Electrolyte composition varies between the ECF and ICF, though the overall concentration of the electrolytes is approximately the same in the two compartments.
· The measurement of electrolytes is important in evaluating electrolyte balance, as well as in determining the composition of electrolyte preparations. MECHANISMS CONTROLLING FLUID AND ELECTROLYTE MOVEMENT
· Many different processes are involved in the movement of electrolytes and water between the ICF and ECF. Some of these include simple diffusion, facilitated diffusion, and active transport. Two forces drive water movement: hydrostatic pressure and osmotic pressure.
· Osmotic pressure is the amount of pressure required to stop the osmotic flow of water. Measuring osmolality is important because it indicates the water balance of the body.
· The tonicity of the fluid surrounding cells affects them. Fluids with the same osmolality as the cell are isotonic. Solutions in which the solutes are less concentrated than the cells are hypotonic; those with solutes more concentrated than cells or an increased osmolality are hypertonic.
· Hydrostatic pressure is the force within a fluid compartment and is the major force that pushes water out of the vascular system at the capillary level.
· Oncotic pressure (colloidal osmotic pressure) is osmotic pressure exerted by colloids in solution. The major colloid in the vascular system contributing to the total osmotic pressure is protein.

FLUID MOVEMENT IN CAPILLARIES
· The amount and direction of fluid movement between the interstitium and the capillary is determined by the interaction of (1) capillary hydrostatic pressure, (2) plasma oncotic pressure, (3) interstitial hydrostatic pressure, and (4) interstitial oncotic pressure.
· When capillary or interstitial pressures are altered, fluid may abnormally shift from one compartment to another, resulting in edema or dehydration. FLUID SPACING
· Fluid spacing describes the distribution of body water.
· First spacing describes the normal distribution of fluid in the ICF and ECF compartments.
· Second spacing refers to an abnormal accumulation of interstitial fluid (i.e., edema).
· Third spacing occurs when fluid accumulates in a portion of the body and it cannot be exchanged easily with the rest of the ECF (e.g., burns, blisters).

REGULATION OF WATER BALANCE
· Water balance is maintained by water intake and excretion.
· An intact thirst mechanism is important for fluid balance. The patient who cannot recognize or act on the sensation of thirst is at risk for fluid deficit and hyperosmolality.
· An increase in plasma osmolality or a decrease in circulating blood volume stimulates antidiuretic hormone (ADH) secretion.
· Glucocorticoids and mineralocorticoids secreted by the adrenal cortex help regulate both water and electrolytes. Aldosterone, a mineralocorticoid, has potent sodium-retaining and potassium-excreting capability.
· The kidneys are the primary organs for regulating fluid and electrolyte balance. o Kidneys regulate water balance through adjustments in urine volume. o With severely impaired renal function, the kidneys cannot maintain fluid and electrolyte balance, resulting in edema and electrolyte imbalances.
· Insensible water loss, which is invisible vaporization from the lungs and skin, assists in regulating body temperature.
· The older adult experiences normal physiologic changes that increase his or her susceptibility to fluid and electrolyte imbalances. Functional changes may occur that affect the ability to obtain fluids independently.

FLUID AND ELECTROLYTE IMBALANCES
· Fluid and electrolyte imbalances are classified as either deficits or excesses. o Fluid volume deficit can occur with abnormal loss of body fluids (e.g., diarrhea, drainage, hemorrhage, and polyuria), inadequate intake, or a plasma-to-interstitial fluid shift. o Fluid volume excess may result from excessive intake of fluids, abnormal retention of fluids (e.g., heart failure, renal failure), or interstitial-to-plasma fluid shift.
· The goals of treatment in fluid imbalances are to correct the underlying cause and to restore fluid and electrolyte balance. SODIUM IMBALANCES
· Sodium is the major ECF cation and plays a major role in maintaining the concentration and volume of the ECF.
· Hypernatremia is an elevated serum sodium that may occur with water loss or sodium gain. o Symptoms include those of dehydration and any accompanying ECF volume deficit, such as postural hypotension, weakness, and decreased skin turgor. o Hypernatremia is treated by cause. With water deficits, volume is replaced. If sodium excess occurs, dilution is accomplished with sodium-free IV fluids.
· Hyponatremia is a low serum sodium level. Common causes include water excess from inappropriate use of sodium-free or hypotonic IV fluids. o Symptoms of hyponatremia are related to cellular swelling and are primarily manifested in the central nervous system. o In hyponatremia from water excess, fluid restriction is often the only treatment. If fluid loss is the cause, replacement with sodium-containing solutions is indicated.

POTASSIUM IMBALANCES
· Potassium is the major ICF cation and is the major factor in the resting membrane potential of nerve and muscle cells. Changes in potassium balance cause a number of clinical problems.
· Hyperkalemia is an elevated serum potassium level. o The most common cause is renal failure. Hyperkalemia is also common with massive cell destruction (e.g., burn or crush injury, tumor lysis); rapid transfusion of stored, hemolyzed blood; and catabolic states (e.g., severe infections). o The most clinically significant manifestations of hyperkalemia are disturbances in cardiac conduction. Other manifestations include cramping leg pain, followed by weakness or paralysis of skeletal muscles. o Monitor the electrocardiograph of all patients with hyperkalemia to detect potentially fatal dysrhythmias and monitor the effects of therapy. o The patient experiencing dangerous cardiac dysrhythmias should receive IV calcium gluconate.
· Hypokalemia is a low serum potassium level. o The most common causes are from abnormal losses from either the kidneys or the gastrointestinal tract. o Hypokalemia can cause potentially lethal ventricular dysrhythmias. Skeletal muscle weakness and paralysis, including the respiratory muscles, leading to shallow respirations and respiratory arrest, can occur. o Patients taking digoxin experience increased digoxin toxicity if their serum potassium level is low. o Treat hypokalemia by giving potassium chloride supplements and increasing dietary intake of potassium.

CALCIUM IMBALANCES
· The functions of calcium include transmission of nerve impulses, myocardial contractions, blood clotting, formation of teeth and bone, and muscle contractions.
· Calcium is present in the serum in three forms: free or ionized; bound to protein (primarily albumin); and bound with phosphate, citrate, or carbonate. The ionized form is the biologically active form.
· Hypercalcemia is an elevated serum calcium level. o Hyperparathyroidism causes two thirds of the cases. The remainder are caused by malignancy, especially from myeloma, breast, renal, or lung cancers. o Manifestations include decreased memory, confusion, disorientation, fatigue, muscle weakness, constipation, cardiac dysrhythmias, and renal calculi. o Treatment consists of promoting the excretion of calcium in urine by administering a loop diuretic and hydrating the patient with isotonic saline infusions.
· Hypocalcemia is a low serum calcium level. o The most common cause is a decrease in the production of parathyroid hormone. o Hypocalcemia causes increased muscle excitability resulting in tetany. o Observe a patient who has had neck surgery, particularly a thyroidectomy, for signs of hypocalcemia. o Treatment of hypocalcemia is usually oral or IV calcium supplementation.

PHOSPHATE IMBALANCES
· Phosphorus is a primary anion in the ICF and is essential to the function of muscle, red blood cells, and the nervous system.
· Hyperphosphatemia is an elevated serum phosphorus level. It is usually associated with acute or chronic renal failure. o Symptoms include neuromuscular irritability, tetany, and calcified deposits in soft tissues. o The primary management is treating the underlying cause.
· Hypophosphatemia is a low serum phosphorus level. o It most often occurs in a patient who is malnourished or has a malabsorption syndrome. o It is often asymptomatic. If symptoms occur, they are typically severe, requiring treatment with oral or IV phosphorus.

MAGNESIUM IMBALANCES
· Magnesium plays an important role in many essential cellular processes.
· Hypermagnesemia is an elevated serum magnesium level. It usually occurs when a patient with renal insufficiency or failure has an increased magnesium intake. o Initial clinical manifestations include lethargy, drowsiness, and nausea and vomiting. With rising levels, deep tendon reflexes are lost, followed by somnolence, then respiratory and cardiac arrest. o Primary treatment focuses on prevention by avoiding magnesium-containing medications and foods. Severe symptoms require treatment with IV calcium.
· Hypomagnesemia, a low serum magnesium level, is associated with malnutrition states, such as fasting or starvation. It produces neuromuscular and CNS hyperirritability. o Clinical manifestations are related to neuromuscular and CNS irritability and include hyperactive deep tendon reflexes, tremors, seizures, and confusion. o Treatment involves replacing magnesium.

ACID-BASE IMBALANCES
· Patients with a number of clinical conditions frequently develop acid-base imbalances. You must always consider the possibility of acid-base imbalance in patients with serious illnesses.
· Normally the body has three mechanisms by which it regulates acid-base balance to maintain the arterial pH between 7.35 and 7.45. These mechanisms are the buffer system, the respiratory system, and the renal system.

Alterations in Acid-Base Balance
· Acid-base imbalances are classified as respiratory or metabolic. Respiratory imbalances affect carbonic acid concentrations; metabolic imbalances affect the base bicarbonate. · Respiratory acidosis (carbonic acid excess) occurs whenever there is hypoventilation. · Respiratory alkalosis (carbonic acid deficit) occurs whenever there is hyperventilation. · Metabolic acidosis (base bicarbonate deficit) occurs when an acid other than carbonic acid accumulates in the body or when bicarbonate is lost from body fluids. · Metabolic alkalosis (base bicarbonate excess) occurs when a loss of acid (prolonged vomiting or gastric suction) or a gain in bicarbonate occurs.
· Arterial blood gas (ABG) values provide valuable information about a patient’s acid-base status, the underlying cause of the imbalance, the body’s ability to regulate pH, and the patient’s overall oxygen status.
· In cases of acid-base imbalances, the clinical manifestations are generalized and nonspecific. The treatment is directed toward correction of the underlying cause.

ASSESSMENT OF FLUID, ELECTROLYTE, AND ACID-BASE IMBALANCES
· Assess for the specific clinical manifestations of fluid, electrolyte, and acid-base imbalances as presented throughout this chapter.
· Other health history data consist of assessment of past health history, medications, surgery or other treatments, and a review of systems using functional health patterns.
· There are no specific physical assessment findings to assess for fluid, electrolyte, and acid-base imbalances.
· Assessment of serum electrolyte values is the best starting point for identifying imbalances. Other useful tests include osmolality, glucose, BUN, creatinine, and specific gravity.

ORAL FLUID AND ELECTROLYTE REPLACEMENT
· In all cases, treatment is directed toward correction of the underlying cause.
· Mild deficits can be corrected using the appropriate oral rehydration or electrolyte solution.

INTRAVENOUS FLUID AND ELECTROLYTE REPLACEMENT
· Fluid replacement therapy is used to correct many fluid and electrolyte imbalances. The amount and type of solution used is determined by patient requirements and laboratory results.
· Hypotonic solutions, such as 5% dextrose in water and 0.45% NaCl, provide more water than electrolytes, diluting the ECF and producing movement of water from the ECF to the ICF.
· Administration of an isotonic solution, such as lactated Ringer’s and 0.9% NaCl, expands only the ECF. There is no net loss or gain from the ICF.
· A hypertonic solution initially increases the osmolality of the ECF and results in expansion of the ECF. It is used in the treatment of hypovolemia and hyponatremia.
· KCl, CaCl, MgSO4, and HCO3– are common additives to the basic IV solutions.
· Plasma expanders stay in the vascular space and increase the osmotic pressure.

Central venous access devices
· Central venous access devices (CVADs) are placed in large blood vessels. This permits frequent, continuous, rapid, or intermittent administration of IV fluids, complex medication treatments, vesicant agents, blood and blood products, and parenteral nutritional therapy.
· Three different methods are used to achieve central venous access: centrally inserted catheters, peripherally inserted catheters, or implanted ports.
· The major disadvantage of CVADs is an increased risk of systemic infection.
· Nursing management of CVADs includes assessment, dressing change and cleansing, injection cap changes, and flushing.