Causes of edema in the intensive care unit.

Patients in emergencies necessitating treatment in the intensive care unit (ICU) often develop generalized gross edema. The usual scenario is that in the emergency situation characterized by hypotension and (impending) organ failure, large amounts of fluids are administered that subsequently cannot be excreted adequately, even if the emergency situation subsides to a more stable condition. Three main factors underlie the inadequate restoration of volume balance: (1) impaired edema mobilization, due to the negative influence on lymphatic flow of reduced muscle activity and increased central venous pressure by mechanical ventilation; (2) secondary renal sodium retention by circulatory impairment and hypotension caused by mechanical ventilation and by the cardiodepressant and vasodilatory effects of (endo-)toxemia; and (3) primary renal sodium retention by renal vasoconstriction and filtration impediment, due to a complex of systemic and intrarenal vasomodulator activation and intrarenal endothelitis, or acute renal failure. Edema itself, as far as impeding organ function and necessitating mechanical ventilation, may further perpetuate this difficult to handle and vicious circle.