Transfusion medicine handbook

6. Special Circumstances

6.13 Cardiopulmonary Bypass

Cardiopulmonary bypass usually impairs haemostatic mechanisms and, as a result, bleeding complications may be severe. The effect is especially pronounced for patients who have been on prolonged bypass for more than 2 hours, in ‘redo’ operations or with surgery for infective endocarditis. A number of mechanisms are involved including haemodilution, effects on platelet function, reduced levels of coagulation factors, intraoperative heparin anticoagulation, induced hypothermia, acidosis, hyperfibrinolysis and preoperative anticoagulation or antiplatelet therapy.

Routine laboratory tests of coagulation do not accurately predict the full nature and clinical importance of the haemostatic defect. Intra-operative point-of-care testing with an activated clotting time (ACT) assay, together with viscoelastic global assessments of coagulation using whole blood thromboelastography (TEG) or thromboelastometry (TEM), is often being used alongside PT/APTT and fibrinogen results.

Platelet transfusion is indicated if there is diffuse microvascular bleeding despite heparin reversal with protamine sulphate, in combination with either platelets < 100 x 10⁹/L or suspected platelet dysfunction. In the presence of non-surgical bleeding, FFP and cryoprecipitate may help to correct prolonged clotting times, improve haemostasis and reduce transfusion requirements. The routine use of FFP, cryoprecipitate or platelets at the end of bypass does however not reduce transfusion requirements.

Tranexamic acid is commonly used as an antifibrinolytic and has been shown to reduce red cell transfusion requirement. 

Red cell components for cardiac bypass surgery and ECMO
NZBS policy on the provision of red cell components, including whole blood, for use in recipients undergoing cardiopulmonary bypass surgery and ECMO is as follows:

• For paediatric patients less than 20 kg, resuspended red cells less than 5 days old will normally be made available for paediatric patients as a replacement for blood loss. Where possible, whole blood less than 2 days old will be provided for the purpose of bypass circuit priming.
• For adults and paediatric patients weighing 20kg or over, standard red cell components will be provided.