Hospital Volume and Mortality in Acute Ischemic Stroke Patients: Effect of Adjustment for Stroke Severity

Objective: Stroke severity of 1 hospital is a crucial information when assessing hospital performance. We aimed to determine the effect of stroke severity in the association between hospital patient volume and outcome after acute ischemic stroke. Methods: Data from National Acute Stroke Quality Assessment in 2013 and 2014 were analyzed. Hospital patient volume was defined as the annual number of acute ischemic stroke patients who admitted to each hospital. Comparisons among hospital patient volume quartiles before and after adjusting age, sex, onset to arrival and stroke severity were made to determine the associations between hospital patient volume and mortality at 30 days, 90 days and 1 year. Assessments for the nonlinear associations, with treating hospital patient volume as a continuous variable, and the associations between hospital patient volume and quality of care were also made. Results: A total of 14,666 acute ischemic stroke patients admitted to 202 hospitals were analyzed. In the crude analysis, patients admitted to hospitals with lower patient volume showed higher mortality with a non-linear inverse association with a cut-off value of 227 patients/year. While the associations remained significant after adjusting age, sex and onset to arrival time (P's < .05), they disappeared when stroke severity was further adjusted (P's >. 05). In contrary, hospital patient volume showed a nonlinear positive association with a plateau for summary measures of quality indicators even after adjustments for covariates including stroke severity (P < .001). Conclusions: Our study implicates that stroke severity should be considered when assessing hospital performance regarding outcomes of acute stroke care.