Introduction: In recent years, different strategies have been proposed to reduce the interaction between blood and foreign material during cardiopulmonary bypass (CPB), such as binding of heparin to the material. More recently, a new approach has been proposed: phosphorylcholine (PC) coating, which mimics the main lipid head group of the natural cell membrane, known for its non-thrombogenicity. Up to now, some experience with PCcoated circuits is available . The purpose of this study was to investigate the effect of oxygenator coating with PC on blood coagulation in patients at high risk for bleeding.
Method: 42 patients were randomized to undergo cardiac operations with either a standard (AVANT, STD group) or a PC-coated (AVANT PHISIO, Dideco, Mirandola, Italy, PC group) membrane oxygenator. Only patients belonging to Hardy class IV for bleeding risk (combined procedure and redo valve surgery) were included. The coagulation process was assessed by standard laboratory assays, thromboelastography® (TEG) and platelet function analyser (PFA-100) tests.
TEG measures shear elastic modulus of whole blood samples during clot formation. In particular, clot haemostatic mechanical characteristics are assessed by maximum amplitude (MA) value.
PFA-100 is a system designed to measure platelet-related primary haemostasis. The platelet function is inversely related to the test duration (closure time, CT).
Coagulation analyses were performed at baseline (1), at the end of CPB (2) and at ICU arrival (3). PFA analyses were also performed at additional times. Statistical analyses for continuous data were performed by means of unpaired t-test and Mann-Whitney test for normally and nonnormally distributed data, respectively. Pearson's correlation test was performed to quantify the association between variables.
Results: Three patients with evident surgical bleeding were excluded from analyses. A good correlation was found between MA and platelet count (r = 0.7, P < 0.001). Patients belonging to PC group had a significantly lower reduction of MA from baseline than patients in STD group both at times 2 and 3, and a significantly lower increase of CT after protamine administration (see Figure). A good correlation was found between MA and platelet count (r = 0.7, P < 0.001).
Discussion: The most important consequence of CPB on blood coagulation and therefore on postoperative bleeding is platelet dysfunction. Our study shows that PC coating of the oxygenator contributes to a superior platelet preservation for patients with increased risk of bleeding. This finding was well demonstrated by the lower reduction in TEG parameter MA and by a decrease of PFA parameter CT using PC-coated oxygenator while STD increased.
1 Albes JM, Stohr IM, Kaluza M, et al. Physiological coagulation can be maintained in extracorporeal circulation by means of shed blood separation and coating. J Thorac Cardiovasc Surg