title: Hospital volume and patient outcomes after cholecystectomy in Scotland: retrospective, national population based study.
abstract: OBJECTIVE
  To define associations between hospital volume and outcomes following cholecystectomy, after adjustment for case mix using a national database.
  
  
  METHODS
  Retrospective, national population based study using multilevel modelling and simulation.
  
  
  METHODS
  Locally validated administrative dataset covering all NHS hospitals in Scotland.
  
  
  METHODS
  All patients undergoing cholecystectomy between 1 January 1998 and 31 December 2007.
  
  
  METHODS
  Mortality, 30 day reoperation rate, 30 day readmission rate, and length of stay.
  
  
  RESULTS
  We identified 59,918 patients who had a cholecystectomy in one of 37 hospitals: five hospitals had high volumes (>244 cholecystectomies/year), 10 had medium volumes (173-244), and 22 had low volumes (<173). Compared with low and medium volume hospitals, high volume hospitals performed more procedures non-electively (17.1% and 19.5% v 32.8%), completed more procedures laparoscopically (64.7% and 73.8% v 80.9%), and used more operative cholangiography (11.2% and 6.3% v 21.2%; χ(2) test, all P<0.001). In a well performing multivariable analysis with bias correction for a low event rate, the odds ratio for death was greater in both the low volume (odds ratio 1.45, 95% confidence interval 1.06 to 2.00, P=0.022) and medium volume (1.52, 1.11 to 2.08, P=0.010) groups than in the high volume group. However, in simulation studies, absolute risk differences between volume groups were clinically negligible for patients with average risk (number needed to treat to harm, low v high volume, 3871, 1963 to 17,118), but were significant in patients with higher risk. In models accounting for the hierarchical structure of patients in hospitals, those in medium volume hospitals were more likely to undergo reoperation (odds ratio 1.74, 1.31 to 2.30, P<0.001) or be readmitted (1.17, 1.04 to 1.31, P=0.008) after cholecystectomy than those in high volume hospitals. Length of stay was shorter in high volume hospitals than in low (hazard ratio for discharge 0.78, 0.76 to 0.79, P<0.001) or medium volume hospitals (0.75, 0.74 to 0.77, P<0.001). These differences were also only of clinical significance in patients at higher risk.
  
  
  CONCLUSIONS
  There is wide variation among hospitals in the management of gallstone disease and an association between higher hospital volume and better outcome after a cholecystectomy. The relative risk of death is lower in high volume centres, and although absolute risk differences between volume groups are significant for elderly patients and patients with comorbidity, they are clinically negligible for those at average risk.
authors.affiliation: Department of Clinical Surgery, University of Edinburgh, Royal Infirmary of Edinburgh, Edinburgh, UK. mail@ewenharrison.com
authors.forename: Ewen M
authors.initials: EM
authors.lastname: Harrison
authors.forename: Stephen
authors.initials: S
authors.lastname: O'Neill
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Meurs
authors.forename: Pang L
authors.initials: PL
authors.lastname: Wong
authors.forename: Mark
authors.initials: M
authors.lastname: Duxbury
authors.forename: Simon
authors.initials: S
authors.lastname: Paterson-Brown
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Wigmore
authors.forename: O James
authors.initials: OJ
authors.lastname: Garden
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D002763:Cholecystectomy / Q000706:statistics & numerical data*; D005260:Female; D005705:Gallbladder Diseases / Q000453:epidemiology / Q000473:pathology / Q000601:surgery*; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012606:Scotland / Q000453:epidemiology; D012959:Socioeconomic Factors; D016896:Treatment Outcome