Abstract
Background The impact of intensive care unit (ICU) case volume on the mortality and medical costs of sepsis has not been fully elucidated. We hypothesized that ICU case volume is associated with mortality and medical costs in patients with sepsis in Japan. Methodology This retrospective nationwide study used the Japanese administrative data from 2010 to 2017. The ICU volume categorization into quartiles was performed according to the annual number of sepsis cases. The primary and secondary outcomes were in-hospital mortality and medical costs, respectively. A mixed-effects logistic model with a two-level hierarchical structure was used to adjust for baseline imbalances. Fractional polynomials were investigated to determine the significance of the association between hospital volume and clinical outcomes. Subgroup and sensitivity analyses were performed for the primary outcome. Results Among 317,365 sepsis patients from 532 hospitals, the crude in-hospital mortality was 26.0% and 21.4% in the lowest and highest quartile of sepsis volume, respectively. After adjustment for confounding factors, in-hospital mortality in the highest quartile was significantly lower than that of the lowest quartile (odds ratio = 0.829; 95% confidence interval = 0.794-0.865; p < 0.001). Investigations with fractional polynomials revealed that sepsis caseload was significantly associated with in-hospital mortality. The highest quartile had higher daily medical costs per person compared to the lowest quartile. Subgroup analyses showed that high-volume ICUs with patients undergoing mechanical ventilation, vasopressor therapy, and renal replacement therapy had a significantly low in-hospital mortality. The sensitivity analysis, excluding patients who were transferred to other hospitals, demonstrated a result consistent with that of the primary test. Conclusions This nationwide study using the medical claims database suggested that a higher ICU case volume is associated with lower in-hospital mortality and higher daily medical costs per person in patients with sepsis.