The volume-outcome relationship in severely injured patients: A systematic review and meta-analysis

BACKGROUND The volume-outcome relationship in severely injured patients remains under debate and this has consequences for the designation of trauma centers. OBJECTIVES The aim of this study was to evaluate the relationship between hospital or surgeon volume and health outcomes in severely injured patients. METHODS Six electronic databases were searched from 1980 up to January 30, 2018, to identify studies that describe the relationship between hospital or surgeon volume and health outcomes in severely injured patients (preferably Injury Severity Score above 15). Selection of relevant studies, data extraction, and critical appraisal of the methodological quality were performed by two independent reviewers. Pooled adjusted and unadjusted estimates of the effect of volume on in-hospital mortality, only in study populations with Injury Severity Score greater than 15, were calculated with a random-effects meta-analysis. A mixed effects linear regression model was used to assess hospital volume as continuous parameter. RESULTS Eighteen observational cohort studies were included. The majority (13 [72%] of 18) reported an association between higher hospital or surgeon volume and lower mortality rate. Overall, the quality of the included studies was reasonable, with insufficient adjustment as one of the most common limitations. Eight studies were included in the meta-analysis with a total of 222,418 patients. High hospital volume (>240 admitted severely injured patients per year) was associated with a lower risk of mortality (adjusted odds ratio, 0.85; 95% confidence interval, 0.76-0.94). Four studies were included in the regression model, providing a beta of-0.17 per 10 patients (95% CI,-0.27 to-0.07). There was no clear association between surgeon volume and mortality rates based on three available studies. CONCLUSION Our systematic overview of the literature reveals a modest association between high-volume centers and lower mortality in severely injured patients, suggest