title: Effect of plasma-to-RBC ratios in trauma patients: a cohort study with time-dependent data*.
abstract: BACKGROUND
  A widespread approach today is to transfuse bleeding trauma patients with RBC concentrates and plasma at a 1:1 ratio. This regime is supported by a range of observational studies showing lower mortality in bleeding patients receiving equal volumes of plasma and RBCs. The rationale for this practice is still unclear with several studies failing to show any survival benefits of increased plasma use, perhaps due to a failure to account for the timing of transfused units.
  
  
  OBJECTIVE
  To study the association between plasma-to-RBC ratios and risk of death in trauma patients, using appropriate methods.
  
  
  METHODS
  In a retrospective cohort study, we assembled data on 741 transfused trauma patients at a large trauma center. Measures of transfusion therapy were assessed entirely time dependently, and relative risk of death was compared between patients receiving low to high plasma-to-RBC ratio (< 0.85 vs > 0.85).
  
  
  RESULTS
  In the time-dependent analyses, we saw no significant association between a low plasma ratio and the risk of death. However, age more than 75 years, injury severity score greater than 33, Glasgow Coma Scale less than 8, and systolic blood pressure lower than 90 mm Hg were all significantly associated with increased risk of death. Conversely, when the analyses were conducted with conventional methods, a strong protective effect of high plasma ratios was seen.
  
  
  CONCLUSIONS
  The key finding in our study is the strikingly different results produced by time-dependent analyses and the conventional analyses when studying survival and plasma-to-RBC ratio, supporting recent claims that prior studies showing benefit of high plasma ratios might have suffered from survival bias. There is a great need for further studies on the subject to enable improvements in treatment of massively bleeding trauma patients.
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden. marit.halmin@ki.se
authors.forename: Märit
authors.initials: M
authors.lastname: Halmin
authors.forename: Fredrik
authors.initials: F
authors.lastname: Boström
authors.forename: Olof
authors.initials: O
authors.lastname: Brattström
authors.forename: Joachim
authors.initials: J
authors.lastname: Lundahl
authors.forename: Agneta
authors.initials: A
authors.lastname: Wikman
authors.forename: Anders
authors.initials: A
authors.lastname: Östlund
authors.forename: Gustaf
authors.initials: G
authors.lastname: Edgren
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D016913:Blood Component Transfusion; D001794:Blood Pressure; D015331:Cohort Studies; D004906:Erythrocyte Count; D017707:Erythrocyte Transfusion; D005260:Female; D015600:Glasgow Coma Scale; D006470:Hemorrhage / Q000401:mortality*; D006801:Humans; D015601:Injury Severity Score; D019934:International Normalized Ratio; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D010949:Plasma; D010953:Plasma Volume; D012189:Retrospective Studies; D013548:Sweden / Q000453:epidemiology; D013599:Systole; D014193:Trauma Centers; D014947:Wounds and Injuries / Q000097:blood / Q000401:mortality*; D055815:Young Adult