Porth's Essentials of Pathophysiology, 4e

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Disorders of Fluid, Electrolyte, and Acid–Base Balance

C h a p t e r 8

Manifestations of Isotonic FluidVolume Deficit and Excess

TABLE 8-3

Fluid Volume Deficit

Fluid Volume Excess

AcuteWeight Loss (% body weight) Mild fluid volume deficit: 2% Moderate fluid volume deficit: 5% Severe fluid volume deficit: >8%

AcuteWeight Gain (% body weight) Mild fluid volume excess: 2% Moderate fluid volume excess: 5% Severe fluid volume excess: >8%

Signs of Compensatory Mechanisms Increased thirst Increased ADH: oliguria and high urine specific gravity Decreased Interstitial FluidVolume

Increased Interstitial FluidVolume

Decreased skin and tissue turgor Dry mucous membranes Sunken and soft eyeballs Depressed fontanel in infants DecreasedVascular Volume

Edema

IncreasedVascular Volume Full and bounding pulse

Postural hypotension Weak, rapid pulse Decreased vein filling

Venous distention

Pulmonary edema (severe fluid excess)

Hypotension and shock (severe deficit)

 Shortness of breath  Crackles  Dyspnea  Cough

ADH, antidiuretic hormone.

assessment of the degree of fluid deficit and adequate measures to resolve the deficit and treat the underlying cause are essential. Isotonic FluidVolume Excess Isotonic fluid volume excess, which represents an iso- tonic expansion of the ECF compartment with increases in both interstitial and vascular volumes, usually results from an increase in total body sodium that is accom- panied by a proportionate increase in body water. Although it can occur as the result of excessive sodium intake, it is most commonly caused by a decrease in sodium and water elimination by the kidney. Among the causes of decreased sodium and water elimination are disorders of renal function, heart failure, liver failure,

and corticosteroid hormone excess. A condition called circulatory overload results from an increase in blood volume; it can occur during infusion of intravenous fluids or transfusion of blood if the amount or rate of administration is excessive. Heart failure produces a decrease in the effective circulating volume and renal blood flow and a com- pensatory increase in sodium and water retention (see Chapter 20). Persons with severe congestive heart fail- ure maintain a precarious balance between sodium and water intake and output. Even small increases in sodium intake can precipitate a state of fluid volume excess and a worsening of heart failure. Liver failure (e.g., cirrho- sis of the liver) impairs aldosterone metabolism and decreases effective circulating volume and renal per- fusion, leading to increased salt and water retention.

FIGURE 8-9. Decreased tissue turgor in a 61-year-old male with severe volume depletion. Skin was pinched over anterior leg (A) and continued to be tented after 10 minutes (B) . (From de Vries Feyers C. Decreased tissue turgor. Images in medicine. N Engl J Med. Jan 27, 2011;364:e6. Copyright © 2011. Massachusetts Medical Society.)