Prevention

• having major surgery (especially orthopaedic) ^a
• likely to have poor mobility ^a
  • major trauma ^a
  • leg plaster cast ^a
  • spinal cord injury or spinal fracture ^a
  • stroke ^a
  • decompensated heart failure ^a
  • myocardial infarction or unstable angina ^a
• at increased risk for DVT
  • old ^a
  • active cancer having chemotherapy ^a
  • recurrent venous thromboembolism ^a
  • pregnant with thrombophilia ^{c d}

Why?

• Venous thromboembolism prophylaxis reduces deep vein thrombosis in all these groups.
• Heparin prophylaxis reduces deep vein thrombosis and pulmonary embolism, but increases the risk of having an episode of excessive bleeding or requiring a blood transfusion. ^a
• It reduces fatal PE without clearly increasing death from haemorrhage. ^a

Heparin prophylaxis reduces venous thromboembolism and fatal PE, but increases excessive bleeding

Patient	Treatment	Comparison	Outcome	CER	OR (95% CI)	NNT (95% CI)
undergoing general, orthopaedic or urologic surgery a	subcutaneous heparin	placebo	deep vein thrombosis	27%	0.68 (0.65 to 0.71)	15 (13 to 16)
			non-fatal pulmonary embolism	2.0%	0.40 (0.29 to 0.51)	83 (70 to 100)
			fatal pulmonary embolism	0.83%	0.64 (0.49 to 0.80)	340 (240 to 610)
			episodes of excessive bleeding or need for transfusion	3.8%	1.66 (1.55 to 1.77)	-43 (-51 to -37)
undergoing neurosurgery a	heparin	placebo	any bleeding at 30 days	2.9%	2.06 (1.12 to 3.77)	-34 (-230 to -18)

Heparin reduces venous thromboembolism in elderly patients with infection

Patient	Treatment	Comparison	Outcome	CER	RRR (95% CI)	NNT (95% CI)
elderly patients with infection a	heparin	nothing	non-fatal venous thromboembolism at 60 days	2.0%	38% (17% to 54%)	130 (83 to 340)

LMWH reduces venous thromboembolism in patients wearing leg plaster casts

Patient	Treatment	Comparison	Outcome	CER	RRR (95% CI)	NNT (95% CI)
below knee or cylindrical leg plaster cast a	LMWH	nothing	DVT at 19 days	4.3%	100%	23 (14 to 85)