Effect of Heparin on Activated Partial Thromboplastin Time in Patients Undergoing Gynecologic or Obstetric Surgery

The exaggerated prolongation of the activated partial thromboplastin time (APTT) by heparin prophylaxis for postoperative thromboembolism may cause bleeding complications. We examined the effects of various doses of unfractionated heparin on the APTT in patients who underwent a gynecologic or obstetric operation. A total of 68 patients who underwent a gynecologic operation (n = 47) or a cesarean section (n = 21) with risk factors for thromboembolism received a continuous intravenous infusion of unfractionated heparin (110–285 IU/kg/day) after surgery until the patient was mobilized the next day. A group of 61 postoperative patients who did not receive heparin served as controls. The APTT was measured in these 129 patients preoperatively and on postoperative day 1. A clinical deep vein thrombosis occurred in only 1 patient, who was in the control group. No bleeding complications occurred in any patient. The percent change in the APTT was significantly correlated with the dose of heparin administered (p < 0.001). Compared with the control group, the mean APTT was not prolonged in the patients who received heparin at 110–149 IU/kg/day. It was prolonged significantly in the patients who received heparin at greater than 150 IU/kg/day. An exaggerated prolongation of the APTT, defined as an APTT greater than 150% of the preoperative value, was found in 0 of 32 patients in the 110–149 IU/kg/day group, 1 of 28 patients (3.6%) in the 150–199 IU/kg/day group and 2 of 8 patients (25%) in the 200–285 IU/kg/day group. The continuous postoperative administration of intravenous heparin at less than 200 IU/kg/day does not result in an exaggerated prolongation of the APTT.