For deep venous thrombosis:
general surgery, 22 studies with 2,893 patients (adjusted total);
traumatic orthopaedic surgery, 10 studies with 898 patients (adjusted total);
elective orthopaedic surgery, 13 studies with 863 patients (adjusted total); and
high-risk medical patients, 8 studies with 527 patients (adjusted total).
For pulmonary embolism:
general surgery, 26 studies with 6,827 patients (adjusted total);
traumatic orthopaedic surgery, 11 studies with 998 patients (adjusted total);
elective orthopaedic surgery, 16 studies with 1,066 patients (adjusted total); and
high-risk medical patients, 9 studies with 555 patients (adjusted total).
Antiplatelet therapy led to reductions in the rates of deep venous thrombosis and pulmonary embolism, which were similar in most groups, and overall, were statistically significant.
The odds of deep vein thrombosis were reduced from 33.6% (control) to 24.8% (antiplatelet groups), benefiting 90 patients per 1,000 treated. The odds of pulmonary embolism were reduced from 2.7% (control) to 1.0% (antiplatelet groups) benefiting 17 patients per 1,000 treated. The proportional reductions for both deep venous thrombosis and pulmonary embolism were similar in general, traumatic orthopaedic and elective orthopaedic surgery, and high-risk medical patients.
Antiplatelet therapy led to lower death rates from pulmonary embolism (0.9% on control compared to 0.2% on antiplatelet, p=0.0001), but non significant higher rates of fatal bleeds and other deaths. Overall, there were fewer deaths on antiplatelet treatment (1.0% on control compared to 0.7% on antiplatelet, p>0.05), but this difference is not statistically significant. There was an excess of nonfatal major bleeds (3 per 1,000 patients) and other complications (reoperations, wound haematomas, or infections due to bleeding; 22 per 1,000 patients) among surgical patients treated with antiplatelet agents.
A comparison between aspirin alone and aspirin plus dipyridamole for treatment of deep venous thrombosis was noted to be statistically significant, but given the large numbers of comparisons made in these studies the importance of this result is questionable.
There was little information on the benefit of using antiplatelet agents in addition to heparin, but the available evidence suggested that the effects may be additive for the prevention of pulmonary embolism. The additional benefit for deep venous thrombosis was unclear.