Evaluation and treatment of cancer-related fluid deficits: volume depletion and dehydration.

Fluid deficits should be divided into two categories (dehydration and volume depletion) according to pathophysiology and into 3 categories (hyponatremic, hypernatremic, and isotonic) according to the plasma sodium concentration. Dehydration (total water deficit especially intracellular) is always hypernatremic, while volume depletion (intravascular water and sodium deficit) is either hyponatremic, hypernatremic, or isotonic. There are no clear clinical differences among the various categories, but a delay of capillary refill, tachycardia, and orthostatic hypotension are more common with early volume depletion. An Evans blue and mannitol test can be used to distinguish between hypernatremic volume depletion and dehydration. Careful clinical assessment and laboratory tests (especially serum sodium) are the key to diagnosis and effective management. According to the type (hypernatremic, hyponatremic, or isotonic), severity of fluid deficit, and associated symptoms, oral or parenteral fluid should be given along with treatment of the underlying cause. In hemodynamically compromised individuals with orthostatic hypotension and oliguria, replacement with isotonic saline until hemodynamic stabilization is crucial. Terminal hydration is still controversial. Important ethical principles govern clinical decision-making about hydration at the end of life.