title: Comparison of risk-adjusted survival in two Scandinavian Level-I trauma centres.
abstract: BACKGROUND
  Assessment of trauma-system performance is important for improving the care of injured patients. The aim of the study was to compare risk-adjusted survival in two Scandinavian Level-I trauma centres.
  
  
  METHODS
  This was an observational, retrospective study of prospectively-collected trauma registry data for patients >14 years from Karolinska University Hospital - Solna (KUH), Sweden, and Oslo University Hospital - Ullevål (OUH), Norway, from 2009-2011. Probability of survival (Ps) was calculated according to the Trauma and Injury Severity Score (TRISS) method. Risk-adjusted survival per patient was calculated by assigning every patient a value corresponding to gained or lost fractional life: Each survivor contributed a reward of 1-Ps and each death a penalty of -Ps. The sum of penalties and rewards, corresponding to the difference between expected and actual mortality, was compared between the centres. We present the data as excess survivors per 100 trauma patients.
  
  
  RESULTS
  There were 4485 admissions at KUH and 3591 at OUH. The proportion of severely injured patients was higher at OUH compared with KUH (Injury Severity Score [ISS] >15: 33.9 % vs. 21.1 %, p <0.001). OUH had a larger proportion of patients >65 years (16.0 % vs. 13.4 %, p <0.001) and greater comorbidity (ASA-PS ≥3: 14.6 % vs. 6.9 %, p <0.001) compared with KUH. The frequency of helicopter transport and presence of prehospital physicians was higher at OUH compared with KUH (27.6 % vs. 15.5 % and 30.5 % vs. 3.7 %, both p <0.001). Secondary admissions were 5.2-fold more common at OUH compared with KUH (p <0.001). There were no differences in 30-day mortality for severely injured patients (ISS >15). Risk-adjusted survival rate was higher at OUH than at KUH for primary (0.59 vs. 0.51) but lower for secondary (1.41 vs. 2.85) admissions (both p <0.001).
  
  
  CONCLUSIONS
  Adjustments for age as a continuous variable and comorbidity should be made when comparing risk-adjusted survival between hospitals, but this is not possible with the TRISS model. A survival prediction model that takes this into account may be a better choice for Scandinavian trauma populations. The current study could not rule out the influence of the system differences between the centres on risk-adjusted survival.
authors.affiliation: Division of Surgery, Department of Clinical Science, Intervention and Technology (CLINTEC), Karolinska Institute, Stockholm, Sweden. poya.ghorbani@karolinska.se.
authors.forename: Poya
authors.initials: P
authors.lastname: Ghorbani
authors.affiliation: Department of Anaesthesiology, Vestfold Hospital Trust, Tønsberg, Norway.|Norwegian Trauma Registry, Oslo University Hospital, Oslo, Norway.
authors.forename: Kjetil Gorseth
authors.initials: KG
authors.lastname: Ringdal
authors.affiliation: Norwegian Trauma Registry, Oslo University Hospital, Oslo, Norway.|Oslo University Hospital Trauma Registry, Oslo University Hospital, Oslo, Norway.|Department of Research and Development, Division of Emergencies and Critical Care, Oslo University Hospital - Ullevål, Oslo, Norway.
authors.forename: Morten
authors.initials: M
authors.lastname: Hestnes
authors.affiliation: Oslo University Hospital Trauma Registry, Oslo University Hospital, Oslo, Norway.|Department of Anaesthesiology, Division of Emergencies and Critical Care, Oslo University Hospital - Ullevål, Oslo, Norway.
authors.forename: Nils Oddvar
authors.initials: NO
authors.lastname: Skaga
authors.affiliation: Oslo University Hospital Trauma Registry, Oslo University Hospital, Oslo, Norway.|Department of Anaesthesiology, Division of Emergencies and Critical Care, Oslo University Hospital - Ullevål, Oslo, Norway.
authors.forename: Torsten
authors.initials: T
authors.lastname: Eken
authors.affiliation: Department of Medicine, Karolinska University Hospital - Solna, Stockholm, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Ekbom
authors.affiliation: Division of Surgery, Department of Clinical Science, Intervention and Technology (CLINTEC), Karolinska Institute, Stockholm, Sweden.
authors.forename: Lovisa
authors.initials: L
authors.lastname: Strömmer
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D012042:Registries; D012189:Retrospective Studies; D018570:Risk Assessment / Q000379:methods*; D015996:Survival Rate / Q000639:trends; D013548:Sweden / Q000453:epidemiology; D014193:Trauma Centers / Q000706:statistics & numerical data*; D015599:Trauma Severity Indices; D014949:Wounds, Nonpenetrating / Q000401:mortality*
keywords: Injury severity; Risk-adjustment; Scandinavia; TRISS; Trauma mortality