Venous thromboembolism: prophylaxis: LMWH is more effective than heparin in surgical and orthopaedic patients.

Clinical bottom line (level 1a)

  1. In general surgical patients, low molecular weight heparin is better than unfractionated heparin for preventing deep vein thrombosis (NNT = 71 at unknown) and pulmonary embolism (NNT = 255 at unknown) .
  2. In orthopaedic surgery patients, LMWH is better than unfractionated heparin for preventing DVT (NNT = 15 at unknown) and PE (NNT = 44 at unknown) .
  3. The effect on major bleeding in both cases is unclear.
Nurmohamed et al: Lancet 1992; 340: 152-156
Expires May 2003

The study

Systematic review of randomised controlled trials of
  • Patients: undergoing general surgery (abdominothoracic or gynaecologic) or orthopaedic surgery (elective or traumatic hip surgery)
  • Intervention: low molecular weight heparin compared with unfractionated heparin
  • Outcome: venous thromboembolism and major bleeding


Articles found in English, French or German using MEDLINE, 1984 to April 1991 (search terms: none given) and search of Current Contents, lists of conference abstracts and bibliographies of relevant papers

Selection criteria: as above
Appraisal criteria: assessed by two independent reviewers using set criteria detailed in the text
Articles excluded if: studies with inadequate screening methods for DVT

seventeen general surgery trials (6878 patients) and six orthopaedic surgery trials (1294 patients)
There was no comment on heterogeneity.

The evidence

Outcome Time to outcome CER RR
(95% CI)		 NNT
(95% CI)
deep vein thrombosis (general surgery) unknown 230/3411
(6.74%)		 0.79
(0.65 to 0.95) 		71
(42 to 300)
pulmonary embolism (general) unknown 20/2843
(0.70%)		 0.44
(0.21 to 0.95) 		255
(180 to 2850)
major bleed (general) unknown 51/1966
(2.59%)		 1.01
(0.70 to 1.48) 		-3900
(NNT = 130 to infinity;
NNH = 80 to infinity)
deep vein thrombosis (orthopaedic) unknown 132/622
(21.2%)		 0.68
(0.54 to 0.86) 		15
(10 to 34)
pulmonary embolism (orthopaedic) unknown 24/582
(4.12%)		 0.43
(0.22 to 0.82) 		44
(32 to 139)
major bleed (orthopaedic) unknown 8/622
(1.29%)		 0.75
(0.26 to 2.14) 		-310
(NNT = 68 to infinity;
NNH = 105 to infinity)

Comments

  1. The meta-analysis combines disparate operations and types of LMWH- unclear how valid this is?
  2. These results suggest that high risk patients benefit more from LMWH.

Citation

  1. Nurmohamed MT, Rosendaal FR, Buller HR, et al: Low-molecular-weight heparin versus standard heparin in general and orthopaedic surgery: a meta-analysis. Lancet 1992; 340: 152-156
Contributor: Chris Ball and Clare Wotton, May 2000
Reviewer:

Clinical Question.
Patient undergoing surgery
Intervention or Exposure LMWH
Comparison unfractionated heparin
Outcome DVT or PE