Low-output syndrome as a complication of open-heart surgery in 85 patients

Low-output syndrome (LOS) was manifested after cardiopulmonary bypass in 33% of the patients undergoing mitral valve replacement in 12% of those submitted to aortic valve surgery, and in 16% of the patients on whom coronary artery bypass surgery was performed. It was also a frequent complication of multiple valve procedures, LOS was the commonest cause of hospital deaths after valve or coronary bypass surgery. The development and prognosis of LOS is dependent on several factors which may be related to the preoperative state, intraoperative events and postoperative treatment. Of these, one of the most important prognostic factors that emerged in this study was perfusion time. It was longest in the group of the 14 patients who died of myocardial failure on the operating table, shortest amongst the 28 patients who survived LOS, and of intermediate length for the 43 patients who died of LOS postoperatively. The differences between the groups were statistically significant. The mechanism of myocardial injury is reviewed. The incidence of various extracardiac complications increased during th postoperative course in proportion to the duration of LOS. Many of these complications resulted in a fatal outcome even when the patient was succesfully weaned from inotropic pharmacological support. There was more survivors in the group treated with dopamine than in the groups treated with isoproterenol or a combination of these drugs.