Cardiopulmonary bypass

The primary function of the cardiopulmonary bypass (CPB) machine is maintaining systemic perfusion while the heart is under manipulation, its chambers are open or it suffers severe dysfunction. The CPB circuit consists of a reservoir, blood pump, oxygenator, heat exchanger, arterial filter, cardioplegia delivery device and cannulae, interconnected by various sized tubing.Venous cannula re-direct venous blood away from the pulmonary circulation towards the venous reservoirs. A blood (roller or centrifugal) pump impulses blood volume forward through a membrane oxygenator and it allows rapid transfusion of oxygenated blood into the systemic circulation. The CPB flow needs to be enough to maintain an adequate cardiac output, which is normally achieved maintaining a flow of 2.2 litres/minute/m2 and a mean arterial pressure over 65 mmHg. The mortality and neurological complications after cardiac surgery are similar using either normothermic or hypothermic CPB. However, slow rewarming after hypothermia has been shown to reduce neurocognitive dysfunction. Before separation from CPB, good team communication is essential. A safety checklist that includes optimal temperature, heart rhythm, de-airing, acid-base status, ventilation, electrolytes and patient position should be applied. If heparin was used to maintain anticoagulation, it can be reverted with protamine after the patient is stable off-CPB. Some patients require inotropic or mechanical support to be ‘weaned’ from CPB.