Treatment of the Patient with Decreased Extracellular Fluid Volume

In mild depletion states, treatment of the underlying disorder and replacement of normal dietary salt and water intake are sufficient to correct deficits. When blood pressure and tissue perfusion are compromised or the oral route of replacement cannot be used, intravenous fluid administration is required. The use of intravenous fluids is reviewed in more detail in Chapter 5 and only general guidelines are discussed here.

The amount and rate of repletion depend on the clinical situation. Cerebral perfusion and urine output are used as markers of tissue perfusion. Response of blood pressure and pulse to postural changes are adequate

• TABLE 2-4. Manifestations of Extracellular Fluid Volume (Total-Body Sodium) Depletion



Increased thirst

Orthostatic fall in blood pressure

Weakness and apathy

Orthostatic rise in pulse


Decreased pulse volume

Muscle cramps

Decreased jugular venous pressure


Dry skin and decreased sweat


Dry mucous membranes


Decreased skin turgor

noninvasive indicators of ECF volume status. Response to a rapid infusion of normal saline or direct measures of cardiovascular pressures are also used.

Fresh-frozen plasma and packed red cells are the most effective initial intravascular volume expander because they remain within the intravascular space. Increased cost and potential infectious complications limit their use. Isotonic sodium chloride (normal saline) is an effective volume expander. Its space of distribution is confined to the ECF. Because of its widespread availability, low cost, and lack of infectious complications normal saline is often used when rapid increases in ECF volume are required. Five percent dextrose in water (D5W) is a poor intravascular volume expander. Once the glucose is metabolized, which happens quickly, the remaining water is distributed in total-body water. It should never be used to expand the intravascular space as only approximately 8% of the administered volume remains intravascular.

Depending on the source of sodium loss, other electrolyte deficiencies may also need to be corrected. Potassium is lost with gastrointestinal causes such as diarrhea or vomiting. Magnesium may be deficient with thiazide diuretic use and diarrheal illnesses.

  • 1. Total-body sodium determines ECF volume. Sodium depletion is synonymous with ECF volume depletion.
  • 2. Sodium depletion results from kidney, skin, or gastrointestinal tract losses.
  • 3. If the kidney is the source of sodium loss, urine sodium concentration exceeds 20 mEq/L.
  • 4. Urine sodium concentration is less than 20 mEq/L or FENa is less than 1% if losses are from skin or gastrointestinal tract and the kidneys are responding appropriately.
  • 5. Renal sodium loss is caused by intrinsic kidney disease or external influences on the kidney.
  • 6. Treatment of the underlying disorder and replacement of normal dietary salt and water intake are sufficient to correct deficits with mild sodium depletion. Intravenous fluid administration is required when blood pressure and tissue perfusion are compromised or oral replacement cannot be used.
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