Thirty-seven studies were included in the review (n=12,421 patients): 13 RCTs and 24 observational studies. Trial sample size ranged from 18 to 4,546 patients (median=94). Follow-up varied from one day to 68 months (median seven days). The quality of evidence was deemed low to very low: five trials used allocation concealment; six blinded patients; and one had adequate randomisation. High levels of survival bias were noted in some observational studies.
Compared with lower plasma ratios, there was a statistically significantly reduced risk of mortality in patients who underwent surgery with massive transfusion with higher plasma ratios (OR 0.38, 95% CI 0.24 to 0.60, I2=85%; 10 studies).
Compared with control, plasma had a statistically significantly increased risk of acute lung injury (OR 2.32, 95% CI 1.46 to 3.71, I2=38%; seven studies) and a statistically significantly reduced risk of multi-organ failure (OR 0.40, 95% CI 0.26 to 0.60, I2=0%; four studies).
There was no statistically significant difference in mortality in patients who underwent surgery without massive transfusions (seven studies). There was no statistically significant difference between groups in trials in patients with liver disease (three studies).
Sensitivity analysis did not explain the high levels of heterogenity in massive transfusion mortality.