Dose response of intravenous heparin on markers of thrombosis during primary total hip replacement

Background Thrombogenesis in total hip replacement (THR) begins during surg ery on the femur. This study assesses the effect of two doses of unfraction ated intravenous heparin administered before femoral preparation during THR on circulating markers of thrombosis. Methods: Seventy-five patients undergoing hybrid primary THR were randomly assigned to receive blinded intravenous injection of either saline or 10 or 20 U/kg of unfractionated heparin after insertion of the acetabular compon ent. Central venous blood samples were assayed for prothrombin F1+2 (F1+2), thrombin-antithrombin complexes (TAT), fibrinopeptide A (FPA), and D-dimer , Results: No changes in the markers of thrombosis were noted after insertion of the acetabular component. During surgery on the femur, significant incr eases in all markers were noted in the saline group (P < 0.0001), Heparin d id not affect D-dimer or TAT. Twenty units per kilogram of heparin signific antly reduced the increase of F1+2 after relocation of the hip joint (P < 0 .001), Administration of both 10 and 20 U/kg significantly reduced the incr ease in FPA during implantation of the femoral component (P < 0.0001). A fo urfold increase in FPA was noted in 6 of 25 patients receiving 10 U/kg of h eparin but in none receiving 20 U/kg (P = 0.03). Intraoperative heparin did not affect intra- or postoperative blood loss, postoperative hematocrit, o r surgeon's subjective assessments of bleeding. No bleeding complications w ere noted. Conclusions: This study demonstrates that 20 U/kg of heparin administered b efore surgery on the femur suppresses fibrin formation during primary THR. This Ending provides the pathophysiologic basis for the clinical use of int raoperative heparin during THR.