The impact of pediatric intensive care unit volume on mortality: A hierarchical instrumental variable analysis*

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Abstract

Objective:

To evaluate the relation between annual pediatric intensive care unit (PICU) admission volume and mortality.

Design:

Nonconcurrent cohort design.

Setting:

Pediatric patients included in the most currently available research database from the Pediatric Intensive Care Unit Evaluations (PICUEs).

Patients:

A total of 34,880 consecutive pediatric admissions to a contemporary volunteer sample of 15 U.S. PICUs.

Measurements and Main Results:

We conducted an instrumental variable analysis and adjusted for similarities between patients admitted to different PICUs using mixed-effects, hierarchical techniques. Case mix and severity of illness was adjusted for using patient-level data and the Pediatric Risk of Mortality, version III (PRISM III). On average, admission to higher-volume PICUs was associated with lower severity-adjusted mortality (odds ratio = 0.68 per 100 patient increase in volume; 95% confidence interval: 0.52–0.89) when volume was analyzed as a linear term; however, when PICU volume was analyzed as a quadratic term, we found the lowest severity-adjusted mortality rates among PICUs with annual admission volumes between 992 and 1,491. Furthermore, lower severity-adjusted mortality rates were primarily found among patients with less than a 10% PRISM III predicted risk of mortality.

Conclusions:

Although there is an association between lower severity-adjusted mortality among higher volume PICUs, our data suggest that best outcomes are among mid- to large-sized PICUs. These data support minimum annual admission criteria for PICUs but raise the concern that PICUs with very high annual admission volumes may operate beyond an ideal capacity.

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