Sequestration of Platelets Prior to Bypass Reduces Bleeding After Cardiac Surgery

Overview

Excessive bleeding is common after cardiac surgery. This may result in patients receiving a blood transfusion or suffering the life-threatening complication of cardiac tamponade. Tamponade is when excessive bleeding compresses the heart and prevents it from pumping properly. A major reason for the bleeding is the damage done to platelets by the cardiopulmonary bypass (CPB) machine. Often patients receive platelets and plasma from blood donors to try to reduce the bleeding post-operatively. The investigators plan to take platelets and plasma from patients before they are damaged. They would then return these 'undamaged' sequestered platelets to the patients after the bypass machine is no longer needed. Therefore, the investigators' primary question is whether platelet sequestration would reduce the bleeding problems that occur following cardiac surgery. They will evaluate bleeding problems using thromboelastography, which provides a comprehensive assessment of both how blood clots form and their strength. If sequestration reduces bleeding problems following cardiac surgery then it may reduce the chance of patients receiving blood products from donors. Although donated blood is thoroughly tested, its use does expose patients to the risk of transfusion errors, blood borne infections and reactions. Avoiding its use would be very desirable.

Hypothesis: Patients undergoing repeat median sternotomy or requiring prolonged cardiopulmonary bypass (CPB) often develop a coagulopathy at the end of surgery. We propose sequestering plasma and platelets from these patients prior to CPB and thus prior to the dilution and platelet damage that occurs with CPB. We hypothesise that if these plasma and platelets are stored properly during CPB, and administered at the end of the operation, they will reduce any coagulopathy and the associated bleeding. Study population: Patients undergoing repeat median sternotomy, mitral valve repair, double valve operations, aortic surgery, or combined valve and coronary artery surgery. Exclusion criteria will include those with anaemia, thrombocytopenia, unstable angina, anti-platelet therapy within the previous seven days, known or symptomatic cerebrovascular disease, known disorders of haemostasis, aprotinin sensitivity and pregnancy. Intervention: Patients will be randomised by a closed envelope technique to receive platelet/plasma sequestration or not. Patients randomised to undergo sequestration will have 14 mL/Kg blood taken. The blood will be separated into red cells and platelets/plasma. Anaemia would be prevented by returning the processed red blood cells to the patient. We will store platelets at 20-24°C/room temperature on a platelet rocker according to guidelines from the National Blood Service. Assessment of coagulation: Patients' coagulation status will be evaluated before and after surgery. Four methods will be employed to comprehensively assess the coagulation system: platelet counts and conventional clotting studies; heparin levels; thromboelastography; and platelet function analyser.