Abstract
Patients undergoing cardiac surgery with cardiopulmonary bypass are at risk of increased blood loss and transfusion requirements. Contact of blood with the surgical wound and the artificial surfaces of the extra-corporeal circuit results in a coagulopathy. Haemodilution during cardiopulmonary bypass also aggravates the reduction of haemostatic factors even further. On the other hand, systemic anticoagulation using high dose unfractionated heparin challenges the adequate anticoagulant monitoring. The most frequently used test to monitor systemic anticoagulation is the whole blood activated clotting time. This has, however, proven not be a reliable test. Other haemostatic assays have their own advantages and disadvantages, but tools to monitor anticoagulation and haemostasis adequately during and after cardiopulmonary bypass are to date lacking and/or show only a weak association with clinical bleeding. Viscoelastic whole blood techniques (TEG/ROTEM) have emerged as alternatives to the routine coagulation tests, and could be more suitable for providing information about the different phases of the blood clotting. Platelet function tests give more information about the presence of platelet dysfunction one, which is a major cause of bleeding after cardiac surgery. Likewise, thrombin generation tests reflect much, if not all, of the overall function of the blood clotting system. Further research of the applicability and added values of the viscoelastic whole blood tests and the thrombin generation tests in the cardiac surgical patient undergoing cardiopulmonary bypass is warranted. Simplicity in performing the test, preferably point-of-care, and rapid availability of the results, should thereby be the primary focus for targeted haemostatic interventions.
Highlights
During cardiopulmonary bypass (CPB) for cardiac surgery, contact of blood with the surgical wound and the artificial surfaces of the extra-corporeal circuit leads to haemostatic disturbances and triggers an angry defense reaction [1,2]
These infusions lead to a state of dilution coagulopathy while there is a significant fall in clotting factors [3]
All these factors are predictive for an increased risk of excessive perioperative blood loss and subsequent transfusion requirements [7,8]
Summary
Cardiac surgical patients undergoing CPB are typically anticoagulated using a very high dose of unfractionated heparin. This is the only anticoagulant that brings about an immediate effect and, that can be monitored bedside by a point-of-care test. Unfractionated heparin is neutralized by protamine at the end of the procedure [10]. The primary anticoagulant action of heparin appears to result from its binding with antithrombin (AT). The predominant action of AT is inactivation of factor IIa (thrombin) and factor Xa [11]. Following activation of AT, heparin is released and becomes available for interaction with other AT molecules. Decreased heparin responsiveness is often attributed to AT deficiency. Besides binding with AT, heparin may bind Measuring the real anticoagulant effect of heparin is complicated and depends on many variables which determine the patients sensitivity to heparin, such as: 1) the availability of AT; 2) the binding of heparin to proteins (such as albumin and glycosamineglycans) in the bloodstream [12]; 3) the binding of heparin to endothelium [11]; and 4) platelets: both the release of platelet factor 4 and platelets themselves are heparin neutralizing [13]
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