Volume-outcome relationship in severe operative trauma surgery: A retrospective cohort study using a Japanese nationwide administrative database.
The relationship between hospital case volume and in-hospital mortality, often referred to as the volume-outcome relationship, has been studied in various types of surgery. Despite its usefulness in policymaking, it has not been reported in operative trauma surgery. This study aimed to identify the volume-outcome relationship in severe operative trauma surgery. A retrospective cohort study was conducted using a risk adjustment method based on the International Classification of Diseases 10th Revision Codes in a Japanese nationwide administrative database. Patients discharged from July 1, 2010, to March 31, 2015, who underwent severe operative trauma surgery, defined as having a mortality rate equal to or greater than 10%, were included. A logistic regression model with random effects was used for analysis. Annual hospital case volume was categorized into 4 groups: <6 (reference group), 6 to 11, 12 to 17, and ≥18. Subgroup analysis on head and torso trauma surgery was conducted. The study population consisted of 18,382 patients from 964 hospitals. Overall mortality was 19.7%. The adjusted odds ratio for mortality did not reduce significantly in the higher hospital case volume category. Subgroup analysis revealed that the adjusted odds ratio reduced significantly in the subgroup of torso surgery (<6 cases/y [reference] vs ≥6 cases/y; adjusted odds ratio, 0.55; 95% confidence interval, 0.42-0.73), but not in the operative head trauma surgery subgroup. A volume-outcome relationship was not identified in severe operative trauma surgery but was observed in the operative torso trauma surgery subgroup.