Heart-lung bypass is the technique by which the functions of the heart and lungs are temporarily taken over by an external machine during open heart surgery, allowing the surgeon to operate on a still, empty heart. The heart is stopped using a cardioplegic solution, and blood is diverted from the right side of the heart, passed through an oxygenator (which adds oxygen and removes carbon dioxide), and returned to the arterial circulation via a pump. The entire circuit is known as a cardiopulmonary bypass (CPB) circuit.
Heart-lung bypass has made possible most of the major advances in cardiac surgery since it was first used clinically in 1953 by Dr John Gibbon. Operations that require the heart to be stopped and entered, such as open valve replacement, correction of congenital heart defects, coronary artery bypass grafting (CABG), and heart transplantation, all rely on heart-lung bypass. The bypass circuit maintains circulation to the brain and other organs while the heart is motionless.
Although heart-lung bypass has become routine in cardiac surgery, it does carry recognised risks. The passage of blood through the artificial circuit activates the immune system and produces a systemic inflammatory response. Microscopic air bubbles or particles (micro-emboli) can reach the brain and contribute to cognitive changes after surgery. Kidney function may be temporarily impaired. These risks are managed by the perfusionist (specialist technician who runs the bypass circuit) and by careful surgical technique.
Most patients spend a predictable time on bypass determined by the complexity of the procedure. After the heart is restarted and its function confirmed, the bypass circuit is gradually weaned off and circulation returns to normal. For detailed information on how the circuit works and its clinical implications, see Cardiopulmonary Bypass.
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