Hemodilution and Hematocrit on Cardiopulmonary Bypass: How Low Can We Go?

Since 1953 when Dr. John Gibbons, Jr. and colleagues first successfully used cardiopulmonary bypass to perform an open mitral comissurotomy, the technology of the cardiopulmonary bypass (CPB) circuit and the physiologic management of patients during extracorporeal circulatory support have undergone a tremendous evolution. Despite major technologic advances and half a century of experience with cardiopulmonary bypass, the pathophysiologic consequences of CPB remain significant. Efforts to study and identify factors that contribute to poor outcomes in patients undergoing CPB have yielded important information, but nevertheless definitive answers and consensus on optimal practices have been difficult to realize. In 2009, Murphy et al reviewed the existing evidence for management of physiologic variables including hematocrit during cardiopulmonary bypass. He concluded that a paucity of data prevents strong recommendations and that randomized clinical trials are critically needed.