Chapter 17: Fluid, Electrolyte, and Acid-Base Imbalances
Body fluids and electrolytes play an important role in homeostasis.
Many diseases and their treatments have the ability to affect fluid and electrolyte balance.
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 and extracellular.
The measurement of electrolytes is important to the nurse in evaluating electrolyte balance, as
well as in determining the composition of electrolyte preparations.
Osmolality is important because it indicates the water balance of the body.
In the metabolically active cell, there is a constant exchange of substances between the cell and
the interstitium, but no net gain or loss of water occurs.
The major colloid in the vascular system contributing to the total osmotic pressure is protein.
The amount and direction of movement between the interstitium and the capillary are
determined by the interaction of (1) capillary hydrostatic pressure, (2) plasma oncotic pressure,
(3) interstitial hydrostatic pressure, and (4) interstitial oncotic pressure.
If capillary or interstitial pressures are altered, fluid may abnormally shift from one
compartment to another, resulting in edema or dehydration.
Fluid is drawn into the plasma space whenever there is an increase in the plasma osmotic or
oncotic pressure. This could happen with administration of colloids, dextran, mannitol, or
First spacing describes the normal distribution of fluid in the intracellular fluid (ICF)
and extracellular fluid (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 from which it is not easily exchanged with the rest
of the ECF.
Water balance is maintained via the finely tuned balance of 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 will
stimulate antidiuretic hormone (ADH) secretion. Reduction in the release or action of
ADH produces diabetes insipidus.
Aldosterone is a mineralocorticoid with potent sodium-retaining and potassium-excreting
The primary organs for regulating fluid and electrolyte balance are the kidneys, lungs,
and gastrointestinal tract.
Insensible water loss, which is invisible vaporization from the lungs and skin, assists in
regulating body temperature.
With severely impaired renal function, the kidneys cannot maintain fluid and electrolyte
balance. This condition results in edema, potassium, and phosphorus retention, acidosis,
and other electrolyte imbalances.
Structural changes to the kidney and a decrease in the renal blood flow lead to a decrease
in the glomerular filtration rate, decreased creatinine clearance, the loss of the ability to
concentrate urine and conserve water, and narrowed limits for the excretion of water,
sodium, potassium, and hydrogen ions.
Fluid and electrolyte imbalances are commonly classified as deficits or excesses.
Fluid volume deficit can occur with abnormal loss of body fluids (e.g., diarrhea, fistula
drainage, hemorrhage, polyuria), inadequate intake, or a plasma-to-interstitial fluid shift.
The use of 24–hour intake and output records gives valuable information regarding fluid
and electrolyte problems.
Monitoring the patient for cardiovascular and neurologic changes is necessary to prevent
or detect complications from fluid and electrolyte imbalances.
Accurate daily weights provide the easiest measurement of volume status. Weight
changes must be obtained under standardized conditions.
Edema is assessed by pressing with a thumb or forefinger over the edematous area. The rates of infusion of IV fluid solutions should be carefully monitored.
The goal of treatment in fluid and electrolyte imbalances is to treat the underlying cause.
Is the major ECF cation.
An elevated serum sodium may occur with water loss or sodium gain.
o 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 first
manifested in the central nervous system (CNS).
Is the major ICF cation.
Factors that cause potassium to move from the ICF to the ECF include acidosis, trauma
to cells (as in massive soft tissue damage or in tumor lysis), and exercise.
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 Manifestations of hyperkalemia include cramping leg pain, followed by weakness