Sarah Bos

76 CHAPTER 5 thromboprophylactic strategies appear warranted. Notably, the current clinical practice appears suboptimal as a recent survey in the United States showed that although the vast majority of hepatobiliary surgeons would use thromboprophylaxis, many would delay heparin administration in patients with thrombocytopenia or a prolonged PT.(104) Also, only 14% of surveyed surgeons would continue prophylaxis after discharge. Nonetheless, awareness of the need for adequate postoperative pharmacologic thromboprophylaxis is increasing, leading to adaptations in clinical guidelines.(105) Similarly, optimal prevention of thrombotic events following liver transplant surgery requires clinical studies. Whereas we know that a prolonged PT, in this particular study displayed as an increase in international normalized ration (INR), following liver transplantation does not protect from thrombotic disease, it was recently shown that those patients that developed a venous thrombosis following liver transplantation had a significantly higher INR at day 7 after transplantation compared with those that did not develop a thrombotic event.(80) These results suggest that delayed liver function recovery forms a risk for VTE following liver transplantation, and reinforce the notion that thrombo- prophylaxis should not be withheld from patients with a prolonged PT. In liver transplantation, there is only one study that reports on the efficacy of pharmacological thromboprophylaxis to prevent systemic thrombosis using subcutaneous unfractionated heparin every 8 hours. The incidence of VTE in the non-heparin group was 3.5 versus 1% in the treated group.(84)In two other cohorts assessing incidence of VTE following liver transplantation, numbers on the use of prophylaxis were absent or only given when patients received anticoagulant treatment before surgery or when an intraoperative thrombectomy was performed.(80,81) Pharmacological thromboprophylaxis may also help to prevent early PVT or HAT, but to our knowledge, the effect of routine thromboprophylaxis on PVT or HAT has never been assessed in the post livertransplant population. Thromboprophylaxis has been shown to reduce the risk for PVT following partial hepatectomy,(106) suggesting a role for anticoagulation in post-transplant hepatic vessel thrombosis. HAT is traditionally believed to be a surgical complication,(78,107,108) although patient- and graft-related factors such as prior liver transplantation, prolonged cold ischemic time, prolonged operating time, low recipient weight, acute rejection, hemodynamic, infectious and immunological factors, have also been reported to contribute.(74,76,109) Nevertheless, there is increasing amounts of data suggesting that changes in the hemostatic system may contribute to the development of HAT as well.(54,76) Endothelial damage and activation of the hemostatic system can be the result of cytomegalovirus infection (CMV). Supported by the reported