Physiologic principles and clinical sequelae of cardiopulmonary bypass.

CPB has been a key element in the safe and effective practice of cardiac surgery since its inception more than 30 years ago. Refinements in the apparatus, methods of tissue preservation, and innovations in technique have lowered the morbidity and mortality rates from these procedures. Despite these factors, the pump-oxygenator apparatus itself and the processes of hemodilution, hypothermia, and anticoagulation, which are intrinsic to its operation, effect temporary physiologic derangements in organ system functions. Although all of these phenomena resolve spontaneously, some require treatment while others do not. Therefore, appropriate clinical management of this group of patients, must be based on an understanding of CPB techniques and the anticipated physiologic sequelae. Hypertension should mostly be controlled because high systemic vascular resistance exacerbates the tendency for bleeding and stresses fresh anastomoses. Volume, urine flow, and potassium loss must be monitored strictly and treatment initiated promptly. Cardiac dysfunction requires cautious, individualized pharmacologic, and sometimes mechanical support in the perioperative and postoperative periods. Laboratory values should never be treated routinely. CPB is not without intrinsic risk of serious clinical complication, and these must be anticipated after surgery. The potential for complication increases when CPB exceeds 2 hours and rises sharply when pump time is prolonged more than 3 to 4 hours. Excessive pump time exacerbates blood trauma, produces abnormal capillary membrane permeability, and predisposes the patient to tissue anoxia. The potential for embolism and pulmonary complications is increased. Permanent organ system damage can be avoided through strict attention to myocardial and tissue preservation, meticulous filtration, precise technique, and avoidance of prolonged extracorporeal circulation.