Introduction

Bleeding and the need for transfusion of allogeneic blood products are common during and after cardiothoracic surgery. Despite advances in operative techniques, approximately one third of elective coronary artery bypass grafting procedures require allogeneic blood. As a result, cardiac surgery alone accounts for 10% to 25% of all blood transfused per year within the United States. Although it may be life saving, transfusion of blood components also has associated risks. Before initiating allogeneic transfusion, the expected benefits of a transfusion must therefore be weighed against these risks.

Mechanisms of bleeding in cardiac surgery

A multitude of reasons explain why patients bleed in the context of cardiac surgery. Initially, it is helpful to characterize bleeding as either surgical or coagulopathic in nature. This distinction sounds simple, but is often difficult and is dependent on several factors, including patient characteristics, the operative procedure, surgical technique and the need for transfusion itself.

Surgical causes of excessive bleeding after cardiac surgery account for 50% to 70% of bleeding events. Suggested standard criteria that generally indicate surgical bleeding and mandate surgical exploration can be defined.

The presence of haemodynamic instability (e.g. tamponade) is also important in the decision-making process. In an effort to identify patients requiring surgical reexploration earlier, some units use a blood loss nomogram. This methods allows better visualization of bleeding trends and comparison with other patients operated on at the same institution. Reexploration must be considered if haemorrhage rate crosses several centile lines, or if the blood loss exceeds the 95th centile for two consecutive hours.