Cardiopulmonary Bypass Copolymer Surface Modification Reduces neither Blood Loss nor Transfusions in Coronary Artery Surgery

We read with interest the recent publication by Südkamp et al. concerning the efficacy of a cardiopulmonary bypass (CPB) copolymer surface in modulating blood loss and transfusion requirements in low-risk cardiac surgery patients [1]. We and others have previously demonstrated that this surface (SMAR_xT™, Sorin Biomedical) has intrinsic thromboresistant properties; however, in our relatively small trial, no clinical benefits were detected [2]. In Südkamp's randomized controlled trial, blood loss and transfusion requirements were identical between the groups (SMAR_xT™ and control), and the authors concluded that this surface “does not appear to improve clinical outcome”. We believe that these results are misleading since the trial design obscured the ability to detect the benefit of this surface. It is unfortunate that aprotinin was administered to both groups, as it is entirely probable that the antifibrinolytic and platelet-sparing effects of SMA surfaces are identical to those of aprotinin [3] [4] [5]. Although aprotinin's use is commonplace, its use in low-risk coronary cases is not supported; thus, a trial design excluding this drug would have been ethically and scientifically sound. Therefore, all the authors can conclude is that the use of SMA surfaces confer no additional benefit to aprotinin therapy regarding bleeding and transfusion requirements. Future approaches to improving the outcome with CPB will likely involve a combination of an optimized biocompatible surface coupled with a complementary pharmaceutical agent. It now becomes the clinical scientist's responsibility to design the trials to pair off these options.

References

• 1 Südkamp M, Mehlhorn U, Reza Raji M. et al . Cardiopulmonary bypass copolymer surface modification reduces neither blood loss nor transfusions in coronary artery surgery.  Thoracic Cardiov Surg. 2002;  50 1-4
• 2 Rubens F D, Labow R S, Lavallee G R. et al . Hematologic evaluation of cardiopulmonary bypass circuits prepared with a novel block copolymer.  Ann Thorac Surg. 1999;  67 689-698
• 3 Wachtfogel Y T, Kucich U, Hack C E. et al . Aprotinin inhibits the contact, neutrophil, and platelet activation systems during simulated extracorporeal perfusion.  J Thorac Cardiovasc Surg. 1993;  106 1-9
• 4 Blauhut B, Gross C, Necek S, Doran J E, Spath P, Lundsgaard-Hansen P. Effects of high-dose aprotinin on blood loss, platelet function, fibrinolysis, complement, and renal function after cardiopulmonary bypass.  J Thorac Cardiovasc Surg. 1991;  101 958-967
• 5 van Oeveren W, Harder M P, Roozendaal K J, Eijsman L, Wildevuur C R. Aprotinin protects platelets against the initial effect of cardiopulmonary bypass.  J Thorac Cardiovasc Surg. 1990;  99 788-796