The relationship between annual hospital volume of trauma patients and in-hospital mortality in New York State.

Background: Several studies in the literature have examined the volume-outcome relationship for trauma, but the findings have been mixed, and the associated impact of the trauma center level has not been examined to date. The purposes of this study are to (1) determine whether there is a significant relationship between the annual volume of trauma inpatients treated in a trauma center (with "patients" defined in multiple ways) and short-term mortality of those patients, and (2) examine the impact on the volume-mortality relationship of being a Level I versus Level II trauma center.

Methods: Data from New York's Trauma Registry in 2003 to 2006 were used to examine the impact of total trauma patient volume and volume of patients with Injury Severity Score (ISS) of at least 16 on in-hospital mortality rates after adjusting for numerous risk factors that have been demonstrated to be associated with mortality.

Results: The adjusted odds of in-hospital mortality patients in centers with a mean annual volume of less than 2,000 patients was significantly higher (adjusted odds ratio = 1.46, 95% confidence interval, 1.25-1.71) than the odds for patients in higher volume centers. The adjusted odds of mortality for patients in centers with an American College of Surgeons-recommended annual volume of less than 240 patients with an ISS of at least 16 was 1.41 times as high (95% confidence interval, 1.17-1.69) as the odds for patients in higher volume centers. However, for both volume cohorts analyzed, the variation in risk-adjusted in-hospital mortality rate was greater among centers within each volume subset than between these volume subsets.

Conclusion: When considering the trauma system as a whole, higher total annual trauma center volume (2,000 or higher) and higher volume of patients with ISS ≥16 (240 and higher) are significant predictors of lower in-hospital mortality. Although the American College of Surgeons-recommended 1,200 total volume is not a significant predictor, hospitals in New York with ISS ≥16 volumes in excess of 240 also have total volumes in excess of 2,000. However, when considering individual trauma centers, high volume centers do not consistently perform better than low volume centers. Thus, despite the association between volume and mortality, we believe that the most accurate way to assess trauma center performance is through the use of an accurate, complete, comprehensive database for computing center-specific risk-adjusted mortality rates, rather than volume per se.