Introduction

Methods

Results

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References

Abstract

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.

Introduction

Larger hospital patient volume generally correlates with better outcomes in various diseases or medical procedures. Previous studies showed that outcomes, which were mortality in most studies, were better in hospitals with larger patient volume than those with smaller one, and this relationship might be attenuated above a specific threshold. A study based on the Medicare claim data between 2004 and 2006 in the US reported that admission to higher-volume hospitals was associated with lower 30-day mortality for acute myocardial infarction, heart failure, and pneumonia, and there was a volume threshold, for example, 910 patients for acute myocardial infarction, above which a higher hospital patient volume had no impact on outcomes. However, another study based on the Get With The Guidelines-Heart Failure registry has reported that hospital patient volume was not associated with in-hospital and 30-day mortality but process measures in patients hospitalized with acute heart failure, which implicates that hospital patient volume would be a structure metric reflecting quality of hospital care rather than an outcome determinant. Similar results were replicated in stroke studies using large national databases. These studies showed an inverse relationship between hospital patient volume and mortality in acute stroke population as in other diseases. However, since it has been addressed that stroke severity is the most important prognostic factor for individual stroke patients and inclusion of a stroke severity measure in risk adjustment models for comparing hospital performance on outcomes is recommended, previous studies had their weakness of not including stroke severity in their multivariable models. Especially, previous studies showed that information on stroke severity is crucial for assessing one hospital’s performance, especially when mortality is used as an indicator of outcome. However, only 1 study from Denmark adjusted stroke severity for evaluating the effect of stroke patient volume on outcomes and reported that hospital patient volume was not associated with 30-day or 1-year mortality.