Ten studies (1,748 participants: 913 in the aspirin groups and 835 in the control groups).
All studies were considered to be of a low quality.
Total postoperative blood loss (8 studies): aspirin significantly reduced blood loss compared with control (WMD 210 mL, 95% CI: 87, 333, p<0.001). Similar results were seen for the subgroup of randomised studies only (WMD 315 mL, 95% CI: 218, 413, p<0.001; based on 4 studies). There was moderate heterogeneity overall (I2=68.4%) and for the non-randomised studies (I2=58.3%), but not for the randomised studies (I2=0%). Subgroup analyses showed a greater blood loss with aspirin in earlier studies (before 1990).
Blood transfusion:aspirin use was associated with significantly increased packed red blood cell transfusion (WMD 0.65 units/patient, 95% CI: 0.19, 1.10, p=0.005; based on 5 studies; I2=63.6%) and significantly increased fresh frozen plasma transfusion (WMD 0.61 units/patient, 95% CI: 0.07, 1.16, p=0.03; based on 5 studies; I2=90.3%). Aspirin use was also associated with an increase in platelet transfusion, although this difference was not statistically significant (p=0.06). Subgroup analyses showed similar conclusions for aspirin when the analysis was restricted to the randomised studies.
Re-exploration for bleeding (9 studies):aspirin was associated with a higher rate of re-exploration for bleeding compared with control (RR 2.32, 95% CI: 1.31, 4.08, p=0.004; I2=0%). Similar results were seen in the subgroup of randomised studies.