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Transfusion of blood to the patient is still possible through the arterial cannula following cessation of CPB. The venous cannula is removed when the patient is stable and the process of reversing heparin with protamine is due to commence. Some surgeons leave the venous purse-string suture untied but snared to enable rapid re- insertion of a cannula for emergent return to CPB if required. Prior to protamine administration cardiotomy suction is stopped to avoid clotting within the bypass circuit. The protamine should be administered slowly due to its propensity for causing systemic vasodilatation and pulmonary vasoconstriction. Transfusion of residual blood from the pump is usually required to support cardiac filling during protamine administration; generally boluses of 100 ml are given, titrated against MAP and CVP, PA or LA pressures and direct observation of the heart. The aortic cannula is typically removed when protamine administration is completed, the patient is stable, and there is no further requirement for transfusion of residual blood via the CPB machine. The two purse-string sutures on the aorta are tied to secure the cannulation site. The remainder of the blood in the bypass circuit can be retained for transfusion by the anesthetist directly or it can be processed through a cell-salvage device to maximize the red cell concentration of this “pump blood.” After transfusion a further dose of protamine may be administered to counteract the heparin in the pump blood. Transition from CPB to physiological circulation is more often than not an uneventful process. In some circumstances, particularly when operating on patients with severely impaired ventricular function, or if there has been a long ischemic period during the procedure, weaning from CPB may require measures to be taken to support the circulation. Such measures are discussed in Chapter 8.