Plasma tissue factor pathway inhibitor levels as a marker for postoperative bleeding after enoxaparin use in deep vein thrombosis prophylaxis in orthopedics and general surgery

Low-molecular-weight heparins (LMWH) are widely used as antithrombotic prophylactic pharmaceutical agents in orthopedic and general surgery. Their antithrombotic characteristics are expressed by plasma mediators such as anti-Xa, anti-IIa, and increased release of tissue factor pathway inhibitor (TFPI) from vascular endothelium. The purpose of this clinical research is to study the relation between plasma levels of these mediators and postoperative bleeding. Forty-one consecutive patients undergoing hip or knee arthroplasty (n = 36) and colectomy (n = 5) received the standard enoxaparin (a LMWH) dose preoperatively (general surgery) or immediately postoperatively (orthopedic surgery). Major bleeding was defined as a postoperative drop of greater than or equal to 5 g/dL) of hemoglobin. The authors observed that there was a linear relationship between an increase in free/total TFPI ratio levels and postoperative bleeding. When that ratio increased by >60%, the hemoglobin dropped to >5 g/dL (n = 17). This relationship between free/total TFPI ratio increase and postoperative bleeding was statistically significant (P < 0.001). Those who did not bleed (hemoglobin drop was less than 5 g/dL) (n = 24) had a ratio increase (if any) of less than 50%. However, the authors did not observe any statistical relationship between anti-Xa, anti-IIa, or prothrombin time and postoperative bleeding in patients receiving LMWH for deep vein thrombosis prophylaxis in orthopedic and general surgery patients. The authors recommend a pre- and postoperative ratio level measurement whenever major bleeding is anticipated, as adjustments of LMWH dose or frequency might be necessary.