In vitro bleeding time (PFA-100™) helps to identify patients with platelet dysfuction-dependent increased bleeding after coronary artery bypass grafting

Objectives

Platelet dysfunction and surgical bleeding are the most important causes of blood loss after cardiopulmonary bypass (CPB). The aim of this study was to find out whether there is a correlation between pre- and postbypass PFA-100 (Dade Diagnostika, GmbH, Germany) in vitro bleeding time and blood loss within the first 6 postoperative hours.

Methods

After local ethics committee approval, 110 consecutive patients scheduled for elective first time coronary artery bypass grafting (CABG) were enrolled. Platelet function was assessed using a PFA-100 analyzer with epinephrine-mediated platelet activation. The measurements were performed 15 min before skin incision and 15 min after protamine administration. Patients were classified as increased bleeders (blood loss >600 ml/6 hours) and normal bleeders (blood loss <600 ml/6 hours). PFA values greater than 180 s were considered abnormal.

Results

See Figure 1. Increased bleeding occurred in 28 patients and 82 had normal blood loss. Prebypass PFA values showed a sensitivity of 75% and a specificity of 65% for increased bleeding, whereas postbypass PFA values showed a sensitivity of 60% and a specificity of 41%. No patient required surgical re-exploration.

Conclusion

In this study, prebypass PFA values identified 75% of the patients with increased bleeding risk due to pre-existing (mainly drug-induced) platelet dysfunction. Postbypass PFA values, reflecting drug-induced and CPB-related platelet dysfunction as well as a combination of both, showed the same sensitivity and specificity problems as reported in previous studies. A differential diagnosis based exclusively on this point-of-care test appears to be, in presence of a mixed etiology, less reliable. However, our data suggest that, in addition to the classic differential diagnosis management of postoperative bleeding, the identification of increased bleeders with normal PFA values (false negative) may facilitate the decision for early surgical re-exploration. Also, the identification of increased bleeders with abnormal PFA values (true positive) may help to select patients who can benefit from administration of desmopressin or platelets. Therefore, routine use of PFA (with epinephrine-mediated platelet activation) may provide a useful additional information for the early differential diagnosis of increased bleeding after CBP.