The influence of LMW heparin on the coagulation and fibrinolytic response to surgery.

The response of components of the coagulation and fibrinolytic systems has been examined in patients undergoing minor and major elective surgery and receiving or not receiving subcutaneously administered prophylactic low molecular weight (LMW) heparin. Blood samples were withdrawn pre-operation (PO), post-anaesthesia (PA), during operation (DO) and 24 hours post-operation. Release of plasminogen activator occurred post anaesthesia at a time when factor VIII components were unchanged or decreased. Induction of anaesthesia decreased plasminogen (p less than 0.005) fibrinogen (p less than 0.02) ATIII (p less than 0.002) and fast a2-antiplasmin (p less than 0.005). During operation plasminogen activator release reached a peak in association with a moderate increase in factor VIII components. Heparin treatment produced a prolongation of APTT at DO (p less than 0.05) and at 24hr (p less than 0.002) stages, this prolongation being apparently unrelated to its concentration but did not prevent the rise of factor VIII components observed at 24 hr (p less than 0.02). Prekallikrein (p less than 0.05) and antithrombin III levels (p less than 0.05) were significantly higher whereas fast a2-antiplasmin (p less than 0.002) was significantly lower at 24 hours in patients undergoing major operation and treated with heparin. Protein C levels fell significantly at 24 hours in the untreated patient (p less than 0.014) and in the heparin treated group the fall was greater than the control group (p less than 0.007). At 24 hours other haemostatic and fibrinolytic components were unaffected by heparin treatment.