Do Platelet Inhibitors Increase Operative Blood Loss?

Abstract

Although platelet inhibitory therapy improves arterial graft patency, surgeons are anxious that preoperative administration may increase operative bleeding. We investigated the effect of platelet inhibitors on blood loss during femoral artery replacement in dogs.Thirty greyhounds were randomised to receive placebo, a thromboxane antagonist GR32191 25mg (Glaxo Group Research) or aspirin 150mg (ASA) plus dipyridamole 50mg (DPM) twice daily starting 48 hours prior to implanting a 6cm length of 6mm PTFE in the femoral artery using standardised incision, mobilisation and anastomosis with 6.0 prolene. All bleeding was collected in swabs which were then thoroughly washed in 2L heparinised saline. The erythrocytes were haemolysed by adding potassium cyanide and the haemoglobin concentration measured in a Coulter Haemoglobinometer (Coulter Electronics). Blood loss was calculated by comparison to 1:500 dilution of the same animal’s venous blood. The bleeding time of the arterial anastomosis was also recorded.The mean (± sem) blood loss was similar in all three groups tending to be slightly less with GR32191 and ASA ± DPM at 135125 and 115±121 mis respectively, compared to 152±129 mis on placebo (NS). Anastomosis bleeding time appeared to be prolonged at 390±131 secs by the thromboxane antagonist compared to 291±40 with placebo and 224±136 with ASA and DPM, but this difference did not achieve statistical significance. There was a significant correlation (r=0.53) between blood loss and anastomotic bleeding time (p<0.001).This method of measuring blood loss is easily applicable to patients and does not demonstrate any important tendency to increased bleeding with preoperative platelet inhibitors.