Simply put, the purpose of cardiopulmonary bypass (CPB) is to provide the cardiac or thoracic surgeon a surgical field that would otherwise be incompatible with life (or, at the very least, would incur unacceptable morbidity). More specifically, the goals of CPB are to 1) move volume (blood) 2) add oxygen to blood 3) remove CO2 from blood 4) manage temperature 5) provide a bloodless, immobile surgical field and 6) protect vital organs (not simply the heart).
Goals of Cardiopulmonary Bypass Circulate volume (blood) Oxygenate blood Remove CO2 from blood Manage temperature Provide a bloodless, stationary surgical field Organ protection
Despite the remarkable ability of CPB to meet these goals, it has major disadvantages, including a massive stress response, hemodiluation, loss of pulsatile blood flow, exposure of hematologic elements to inorganic surfaces with accompanying hematologic trauma.
Physiologic Derangements Associated With Cardiopulmonary Bypass Stress Response Hemodilution Loss of Pulsatile Flow Exposure of Hematologic Elements to Inorganic Surfaces
Technically, anytime blood is intentionally diverted around the heart and/or lungs, some form of cardiopulmonary bypass is being performed. Indeed, there are many varieties of cardiopulmonary bypass. Except when otherwise noted, the phrase “cardiopulmonary bypass” will refer to full cardiopulmonary bypass (as opposed to left heart bypass, for instance).