RESPIRATORY AND METABOLIC ACID-BASE CHANGES DURING CARDIOPULMONARY BYPASS IN MAN

Twenty-two patients undergoing open-heart surgery with cardiopulmonarybypass have been studied to define acid-base changes associatedwith anaesthesia, bypass, hypothermia and recovery. The maintenanceof normal pH during the operation, or the inclusion of a periodof normothermia before cooling, had no measurable effect onthe postoperative acid-base state or clinical course as comparedwith the usual routine of bypass in respiratory alkalosis andwith immediate cooling. Lactate and pyruvate increased slowlythroughout anaesthesia and bypass to combined levels not exceeding5 m.equiv/1. Rapid metabolic acid-base shifts of at least equalmagnitude, not due to lactic or pyruvic acids, were apparentlyassociated mainly with temperature changes. Acidosis has notbeen found severe enough to need routine administration of bicarbonateat any stage.