title: Meta-analysis of plasma to red blood cell ratios and mortality in massive blood transfusions for trauma.
abstract: 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.
authors.affiliation: Academic Department of Military Surgery & Trauma, Royal Centre for Defence Medicine, Birmingham, UK.
authors.forename: Aneel
authors.initials: A
authors.lastname: Bhangu
authors.forename: Dmitri
authors.initials: D
authors.lastname: Nepogodiev
authors.forename: Heidi
authors.initials: H
authors.lastname: Doughty
authors.forename: Douglas M
authors.initials: DM
authors.lastname: Bowley
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001315:Australia / Q000453:epidemiology; D001803:Blood Transfusion / Q000401:mortality / Q000706:statistics & numerical data*; D004906:Erythrocyte Count; D005060:Europe / Q000453:epidemiology; D005260:Female; D006470:Hemorrhage / Q000097:blood / Q000401:mortality / Q000628:therapy*; D006801:Humans; D015601:Injury Severity Score; D008297:Male; D008875:Middle Aged; D009656:North America / Q000453:epidemiology; D010949:Plasma; D010976:Platelet Count; D011446:Prospective Studies; D014947:Wounds and Injuries / Q000097:blood / Q000401:mortality / Q000628:therapy*; D055815:Young Adult