Thrombin and cardiopulmonary bypass – A paradigm for evaluation of the regulation of hemostasis

Thrombin generation and bleeding in cardiac surgery: a clinical narrative review

This narrative review discusses the role of thrombin generation in coagulation and bleeding in cardiac surgery, the laboratory methods for clinical detection of impaired thrombin generation, and the available hemostatic interventions that can be used to improve thrombin generation. Coagulopathy after cardiopulmonary bypass (CPB) is associated with excessive blood loss and adverse patient outcomes. Thrombin plays a crucial role in primary hemostasis, and impaired thrombin generation can be an important cause of post-CPB coagulopathy. Existing coagulation assays have significant limitations in assessing thrombin generation, but whole-blood assays designed to measure thrombin generation at the bed-side are under development. Until then, clinicians may need to institute therapy empirically for non-surgical bleeding in the setting of normal coagulation measures. Available therapies for impaired thrombin generation include administration of plasma, prothrombin complex concentrate, and bypassing agents (recombinant activated factor VII and factor eight inhibitor bypassing activity). In vitro experiments have explored the relative potency of these therapies, but clinical studies are lacking. The potential incorporation of thrombin generation assays into clinical practice and treatment algorithms for impaired thrombin generation must await further clinical development.

The Case for a Conservative Approach to Blood Transfusion Management in Cardiac Surgery

Limiting blood transfusion in cardiac operations is a well-meaning goal of perioperative care. Potential benefits include decreasing morbidity and limiting procedural costs. It is difficult to identify transfusion as the cause of adverse outcomes. The need for transfusion may identify a sicker patient population at greater risk for a worse outcome that may or may not be related to the transfusion. We reviewed the indications for and adverse effects of blood transfusion in patients undergoing cardiac procedures to provide a balanced approach to management of blood resources in this population. We reviewed current literature, including systematic reviews and practice guidelines, to synthesize a practice management plan in patients having cardiac operations. Several prospective randomized studies and large population cohort studies compared a postoperative restrictive transfusion policy to a more liberal policy and found very little difference in outcomes but decreased costs with a restrictive policy. Evidence-based practice guidelines and implementation standards provide robust intervention plans that can limit harmful effects of transfusion and provide safe and effective procedure outcomes. A restrictive transfusion policy seems to be safe and effective but does not necessarily provide better outcome in most patient cohorts. The implications of these findings suggest that many discretionary transfusions could be avoided. A subset of high-risk patients could undoubtedly benefit from a more liberal transfusion policy, but the definition of high risk is ill defined.