Coagulation Measurement and Optimisation in Cardiac Surgery

Coagulation is a complex physiological balancing mechanism that maintains haemostasis when blood vessels are injured. A hypercoaguable state as seen in early sepsis, cancer or pregnancy can cause arterial and/or venous obstruction with disruption of blood-flow and end organ damage. Similarly a hypocoaguable state can cause catastrophic haemorrhage and lead to death. Up to 20% of all blood transfusions in the USA are related to cardiac surgery (1). The pathogenesis of coagulopathy in this patient group is multifactorial: patients are older (2), and more complex and this is reflected in the number of redo surgeries and the concomitant use of agents such as clopidogrel, aspirin, coumarin anticoagulants and heparins. Also cardiopulmonary bypass activates the coagulation system with an initial hypercoaguable state and platelet activation, followed by factor and platelet consumption. Hypothermia, acidosis, hypocalcaemia and the dilutional effects of circuit priming all increase the risk of bleeding (3). Platelet transfusion per se in the perioperative period has been associated with an increased risk of serious adverse events (4). Indeed both red cell and platelet transfusion have been shown to have a negative risk-adjusted effect on health-related quality of life after cardiac surgery (5). The haemostatic status of a patient undergoing cardiopulmonary bypass can change very quickly because of haemorrhage or the use of high dose heparin or protamine and as such blood component administration in cardiac surgery can often be empiric. This is compounded by the limited utility of the standard coagulation tests, which have a slow turnaround time in a setting where there can be rapid changes in coagulation status. All patients presenting for cardiac surgery will be anticoagulated in the perioperative period, either for cardiac or non-cardiac reasons, and an appropriate balance needs to be struck between minimising perioperative blood loss and use of homologous blood products, and avoiding pathological thrombosis. Coagulation status can be measured by means of laboratory tests or near-patient tests (also referred to as point-of-care tests). Effective use and interpretation of these tests can guide physicians and surgeons alike in the use of medications and homologous blood products and timely intervention of surgery to optimise patient outcomes. Indeed, the thromboelastogram (TEG), a point-of-care test, should discriminate “surgical” from “medical” causes of bleeding in this population thus reducing unnecessary transfusions and allowing timely return to the operating room for definitive treatment. The TEG will also