Postoperative metabolic alkalosis following general surgery: its incidence and possible etiology

A prospective clinical study was performed on 293 patients, in order to elucidate the abnormalities in acid-base balance following general surgery. Six arterial blood gas and pH determinations were taken from each patient before surgery and on postoperative days zero, one, three, five and seven. A total of 1699 determinations were obtained. Although the majority of patients (87.5 per cent) had a normal acid-base balance before surgery, a postoperative metabolic alkalosis was seen in 50.5 per cent of the patients. However, there was an extremely low incidence of other postoperative acid-base abnormalities, apart from a transient increase in metabolic acidosis on the operative day. A significantly high mortality rate (32.3 per cent) was observed in 31 patients who had continuous metabolic alkalosis during the postoperative period. An excessive bicarbonate load resulting from the administration of fresh frozen plasma following surgery was strongly suggested as one of the major causes of postoperative metabolic alkalosis. Further investigation is required to elucidate the mechanism of the generation of metabolic alkalosis induced by the postoperative bicarbonate load in surgical patients.