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Prevention of Deep Vein Thrombosis after Elective Hip Surgery: A Randomized Trial Comparing Low Molecular Weight Heparin with Standard Unfractionated Heparin

Mark N. Levine, MD; Jack Hirsh, MD; Michael Gent, DSc; Alexander G. Turpie, MD; Jacques Leclerc, MD; Peter J. Powers, MD; Richard M. Jay, MD; and Jean Neemeh, MD
[+] Article and Author Information

Grant Support: In part by the Heart and Stroke Foundation of Ontario and the Medical Research Council of Canada.

Requests for Reprints: Mark Levine, MD, OCF Hamilton Centre, 711 Concession Street, Hamilton, Ontario, Canada L8V 1C3.

Current Author Addresses: Drs. Levine, Hirsh, and Gent: Hamilton Civic Hospitals Research Centre, 711 Concession Street, Hamilton, Ontario, Canada L8V 1C3.

Dr. Turpie: HGH-McMaster Clinic, Hamilton General Hospital, Hamilton, Ontario, Canada L8L 2X2.

Dr. Leclerc: Montreal General Hospital, 1650 Cedar Avenue, Montreal, Quebec, Canada H36 1A4.

Dr. Powers: St. Joseph's Hospital, 50 Charlton Avenue East, Hamilton, Ontario, Canada L8N 4A6.

Dr. Jay: Sunnybrooke Medical Centre, 2075 Bay view, Toronto, Ontario, Canada M4N 3M5.

Dr. Neemeh: Centre Hospitalier Sainte Jeanne D'Arc, 3570 St. Urbain Street, Montreal, Quebec, Canada H2X 2N8.


©1991 American College of PhysiciansAmerican College of Physicians


Ann Intern Med. 1991;114(7):545-551. doi:10.7326/0003-4819-114-7-545
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Objective: To determine the relative efficacy and safety of low molecular weight (LMW) heparin (Enoxaparin) compared with standard calcium heparin for the prevention of postoperative deep vein thrombosis in patients undergoing elective hip surgery.

Design: A double-blind, randomized, controlled trial.

Patients: Six hundred sixty-five consecutive patients undergoing hip replacement at five participating hospitals.

Interventions: Patients received either fixed-dose LMW heparin, 30 mg subcutaneously twice daily, or fixed-dose standard calcium heparin, 7500 units subcutaneously twice daily; both regimens were started 12 to 24 hours after surgery and continued for 14 days or until discharge if sooner.

Measurements: All patients had postoperative I-125-fibrinogen leg scanning and impedance plethysmography. If results of one or both tests were positive, then venography was done. Otherwise, venography was done between day 10 and day 14, or sooner if the patient was ready for discharge.

Results: Evaluable venograms were obtained in 258 of the 333 patients randomly assigned to receive LMW heparin and in 263 of the 332 patients assigned to receive calcium heparin. For patients with evaluable venograms, thrombosis was detected in 50 patients (19.4%) who received LMW heparin compared with 61 patients (23.2%) who received standard heparin (difference, - 3.8%; 95% CI, - 11.1% to 3.6%) (P > 0.2). Proximal deep vein thrombosis was detected in 5.4% of the patients receiving LMW heparin and in 6.5% of the patients receiving standard heparin (difference, - 1.1%; CI, - 5.2% to 3.3%) (P > 0.2). For the entire group of 665 patients, venous thrombosis occurred in 17.1% given LMW heparin and in 19.0% given standard heparin. Hemorrhagic complications occurred in 31 patients (9.3%) given standard heparin and in 17 patients (5.1%) given LMW heparin (difference, 4.2%; CI, 0.3% to 8.2%) (P = 0.035). The relative risk reduction was 45%. The rate of major bleeding in the standard heparin group was 5.7% compared with 3.3% in the LMW heparin group (difference, 2.4%; CI, - 1.0% to 5.4%) (P = 0.13). The relative risk reduction was 42%.

Conclusion: Low molecular weight heparin is significantly less hemorrhagic than standard unfractionated heparin; the difference in the rate of deep vein thrombosis, although not statistically significant (P > 0.2), favors the use of LMW heparin.

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