[Electrolyte balance in major abdominal surgery. IV. Water diuresis under anesthesia and surgery (author's transl)]

12 patients with major laparotomies were studied during anesthesia alone, during three hours of surgery and during the first two hours of recovery. We demonstrated a decrease in plasma potassium and plasma sodium concentration starting with anesthesia and development of a moderate metabolic acidosis. Plasma osmolality was stable during anesthesia and surgery, but slightly decreased in the early postoperative period. Urine formation and osmolar clearance as well as renal sodium and potassium excretion showed a rising tendency during operation, reaching their maximal values in the recovery room. Sodium balance was positive during and after surgery, and sodium retention amounted to about 75% of sodium infused. Urine-to-plasma-osmolality-ratio was 2,0 under anesthesia alone, decreased during surgery and reached control values in the recovery room. In 5 out of 12 patient studied we demonstrated a temporary water diuresis at different points of anesthesia and laparotomy and occasionally even in the postoperative period. This could be due to low plasma levels of ADH caused by relative hypervolemia in the absence of other stimuli of ADH-secretion.