title: Prevalence of survivor bias in observational studies on fresh frozen plasma:erythrocyte ratios in trauma requiring massive transfusion.
abstract: Observational studies on transfusion in trauma comparing high versus low plasma:erythrocyte ratio were prone to survivor bias because plasma administration typically started later than erythrocytes. Therefore, early deaths were categorized in the low plasma:erythrocyte group, whereas early survivors had a higher chance of receiving a higher ratio. When early deaths were excluded, however, a bias against higher ratio can be created. Survivor bias could be reduced by performing before-and-after studies or treating the plasma:erythrocyte ratio as a time-dependent covariate.We reviewed 26 studies on blood ratios in trauma. Fifteen of the studies were survivor bias-unlikely or biased against higher ratio; among them, 10 showed an association between higher ratio and improved survival, and five did not. Eleven studies that were judged survivor bias-prone favoring higher ratio suggested that a higher ratio was superior.Without randomized controlled trials controlling for survivor bias, the current available evidence supporting higher plasma:erythrocyte resuscitation is inconclusive.
authors.affiliation: Department of Anaesthesia and Intensive Care, The Chinese University of Hong Kong, Shatin, NT, Hong Kong SAR. hoamh@hotmail.com
authors.forename: Anthony M-H
authors.initials: AM
authors.lastname: Ho
authors.forename: Peter W
authors.initials: PW
authors.lastname: Dion
authors.forename: Janice H H
authors.initials: JH
authors.lastname: Yeung
authors.forename: John B
authors.initials: JB
authors.lastname: Holcomb
authors.forename: Lester A H
authors.initials: LA
authors.lastname: Critchley
authors.forename: Calvin S H
authors.initials: CS
authors.lastname: Ng
authors.forename: Manoj K
authors.initials: MK
authors.lastname: Karmakar
authors.forename: Chi W
authors.initials: CW
authors.lastname: Cheung
authors.forename: Timothy H
authors.initials: TH
authors.lastname: Rainer
mesh_terms: D015982:Bias; D017707:Erythrocyte Transfusion / Q000639:trends; D006801:Humans; D010949:Plasma; D015995:Prevalence; D012771:Shock, Hemorrhagic / Q000453:epidemiology* / Q000628:therapy*; D017741:Survivors