Preoperative evaluation and postoperative prediction of hemostatic function with thromboelastography in patients...

Patients who receive cardiac procedures, in particular "redo" ones, often suffer complications from massive bleeding, largely due to bypass-induced coagulopathies. Cardiopulmonary bypass (CPB) may cause damage of the blood components, both in terms of quality and quantity. In order to investigate the qualitative changes of blood constituents with special regard to coagulation resulting from the complex insult of previous cardiac surgery, thromboelastography (TEG) was used to analyze the whole clotting process.

Seventy-four patients who underwent cardiac surgery with CPB were prospectively studied. Of them, 32 patients received "redo" cardiac surgery. Blood samples for routine laboratory coagulation tests (RCT) and TEG examination were drawn before and after cardiopulmonary bypass. Clinically significant bleeding was defined if the chest tube drainage was greater than 100 ml/h for 3 consecutive h or greater than 300 ml in 1 h during the first 8 h after surgery. Prebypass and postbypass coagulation parameters were compared and the percentage of accuracy, false positive and false negative rate were deduced from calculation.

In the TEG tracings, preoperative alpha angle and maximum amplitude were significantly decreased in the "redo" group when compared with primary group, indicating less competent platelet function and platelet-fibrin interaction. Lower platelet count was also found by conventional coagulation tests in "redo" patients. Postoperatively, higher percentage of excessive hemorrhage was also noted in the "redo" group (42.8% vs. 27.5% in primary group). However, a much lower predictive accuracy was found in "redo" patients in comparison with primary cardiac patients (53.5% vs. 90%).

We concluded that thromboelastography failed to predict postoperative hemorrhage in "redo" cardiac patients and the graphic recordings derived could not be treated as a guide of transfusion therapy. We thought that inferior preoperative hemostatic status and severer coagulopathy might be responsible for the differences between "redo" and primary cardiac patients.