Meta-analysis of plasma to red blood cell ratios and mortality in massive blood transfusions for trauma.

BACKGROUND The current military paradigm for blood transfusion in major trauma favours high plasma:RBC ratios. This study aimed determine whether high plasma:red blood cell (RBC) ratios during massive transfusion for trauma decrease mortality, using meta-analysis of contemporaneous groups matched for injury severity score. METHODS A systemic review of the published literature for massive blood transfusions in trauma was performed. Patients were categorised into groups based on plasma:RBC transfusion ratios. Meta-analysis was only performed when there were no significant differences in Injury Severity Score (ISS) between ratio groups within studies. The main endpoint was 30-day mortality. RESULTS Six observational studies reporting outcomes for 1885 patients were included in this meta-analysis. Five studies were from civilian environments and one from a military setting. Ratio cut-offs at 1:2 were the most commonly reported, demonstrating a survival advantage with higher ratios (OR 0.49, 95% CI 0.31-0.80, p=0.004). Ratios≥1:2 showed a significant reduction in mortality compared to lower ratios (OR 0.56, 95% CI 0.40-0.78, p<0.001). Reducing the cut-off level was still protective (ratios between 1:2.5 and 1:4, OR 0.41), although the confidence interval was wide (0.16-1.00, p=0.05) and data heterogenous (I(2)=78%). Ratios of 1:1 were not proven to confer additional benefit beyond ratios of 1:2 (OR 0.50, 95% CI 0.37-0.68, p<0.001). CONCLUSIONS In groups matched for ISS, there was a survival benefit with high plasma:RBC resuscitation ratios. No additional benefits of 1:1 over 1:2 ratios were identified.