title: The relationship between patient volume and mortality in American trauma centres: a systematic review of the evidence.
abstract: OBJECTIVE
  To synthesise published and unpublished findings examining the relationship between institutional trauma centre volume or trauma patient volume per surgeon and mortality.
  
  
  BACKGROUND
  Evidence on the relationship between patient volume and survival in trauma patients is inconclusive in the literature and remains controversial.
  
  
  METHODS
  A literature search was performed to identify studies published between 1976 and 2013 via MEDLINE (Pubmed) and the Cumulative Index to Nursing and Allied Health Literature (EbscoHost) as well as footnote chasing. Abstracts from appropriate conferences and ProQuest Dissertations and Theses were also searched. Inclusion criteria required studies to be original research published in English that examined the relationship between mortality and either institutional or per surgeon volume in American trauma centres. We employed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Statement checklist and flowchart. The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach was employed to rate the quality of the evidence.
  
  
  RESULTS
  Of 1392 studies reviewed, 19 studies met defined inclusion criteria; all studies were retrospective. The definition of volume was heterogeneous across the studies. Patient population and analysis methods also varied across the studies. Sixteen studies (84%) examined the relationship between institutional trauma centre volume and mortality. Of the 16 studies, 12 examined the volume of severely injured patients and eight examined overall trauma patient volume. High institutional volume was associated with at least somewhat improved mortality in ten of 16 studies (63%); however, nearly half of these studies found only some subpopulations experienced benefits. In the remaining six studies, volume was not associated with any benefits. Four studies (25%) analysed the impact of surgeon volume on mortality. High volume per surgeon was associated with improved mortality in only one of four studies (25%).
  
  
  CONCLUSIONS
  The studies were extremely heterogeneous, thus definitive conclusions cannot be drawn regarding optimal volume before a clear advantage in survival is observed. A prospective study defining volume as a continuous variable is warranted to support current admission criteria for American trauma patients.
authors.affiliation: Trauma Research Department, Swedish Medical Department, Englewood, CO 80113, United States.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Caputo
authors.affiliation: Trauma Research Department, Swedish Medical Department, Englewood, CO 80113, United States.
authors.forename: Kristin M
authors.initials: KM
authors.lastname: Salottolo
authors.affiliation: Trauma Services Department, Swedish Medical Center, Englewood, CO 80113, United States.
authors.forename: Denetta Sue
authors.initials: DS
authors.lastname: Slone
authors.affiliation: Trauma Services Department, St. Anthony Hospital, Lakewood, CO 80228, United States; Rocky Vista University, Parker, CO 80134, United States.
authors.forename: Charles W
authors.initials: CW
authors.lastname: Mains
authors.affiliation: Trauma Research Department, Swedish Medical Department, Englewood, CO 80113, United States; Rocky Vista University, Parker, CO 80134, United States. Electronic address: dbaror@ampiopharma.com.
authors.forename: David
authors.initials: D
authors.lastname: Bar-Or
mesh_terms: D005260:Female; D017052:Hospital Mortality; D006801:Humans; D008297:Male; D017063:Outcome Assessment, Health Care; D011050:Policy Making; D016019:Survival Analysis; D014193:Trauma Centers / Q000458:organization & administration / Q000706:statistics & numerical data*; D015599:Trauma Severity Indices; D014481:United States; D014947:Wounds and Injuries / Q000401:mortality*
keywords: Mortality; Patient caseload; Patient volume; Systematic review; Trauma centre; Volume outcome relationship; Volume per surgeon