[The significance of exogenous sodium uptake in the perioperative homeostasis of the water and electrolyte balance].

In 13 surgical patients who underwent abdominal surgery of moderate degree it has been shown that postoperative sodium substitution of normal range (1.5 m eq/kg bw. .24 h) led to hyponatremia and aldosteronism with Na+ and water retention. Aldosteronism was strongly correlated to increased activity of the renin-angiotensin-system, both anteceded by restriction of the extracellular space and expansion of total body water. These were controlled by a high sodium input (5 m eq/kg bw. .24 h) without changing the volume infusion, which is demonstrated by suppressed renin and aldosterone secretion rates, improved diuresis and subsequent reduction of total body water in favor of a preserved functional extracellular space. In order to avoid inadequate fluid redistribution it seems reasonable to meet the patient's postoperative sodium requirements by increased sodium input.