The fluid problem in the critically ill.

Fluid therapy in the critically ill patient must be adjusted to accommodate continuing changes in the plasma volume, interstitial space, and intracellular space. During and after hemorrhagic shock, replacement of crystalloid is needed to replenish the plasma and interstitial spaces during operation and then interstitial and intracellular spaces after operation. Severe sepsis leads to a more pronounced expansion of the interstitial space than that of hemorrhagic shock. Continuing therapy after both hemorrhage and sepsis should be directed toward maintaining effective plasma volume and levels of hemoglobin while the interstitial and intracellular spaces return to normal. Concomitantly, effective circulatory volume must be guided by continuing changes in cardiac, pulmonary, and renal function.