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Clinical Investigations in Critical Care |

Hospital Volume-Outcome Relationships Among Medical Admissions to ICUs*

Lakshmi Durairaj, MD; James C. Torner, PhD; Elizabeth A. Chrischilles, PhD; Mary S. Vaughan Sarrazin, PhD; Jon Yankey, MS; Gary E. Rosenthal, MD
Author and Funding Information

*From the Divisions of Pulmonary and Critical Care Medicine (Dr. Durairaj), Department of Internal Medicine, Roy J. and Lucille A. Carver College of Medicine and Department of Epidemiology, College of Public Health (Drs. Torner and Chrischilles), University of Iowa; and Center for Research in the Implementation of Innovative Strategies in Practice (Drs. Rosenthal, Vaughan Sarrazin, and Mr. Yankey), Iowa City VA Medical Center. Iowa City, IA.

Correspondence to: Gary E. Rosenthal, MD, Professor of Internal Medicine, Division of General Internal Medicine, SE618 GH, 200 Hawkins Dr, Iowa City, IA 52242; e-mail: gary-rosenthal@uiowa.edu



Chest. 2005;128(3):1682-1689. doi:10.1378/chest.128.3.1682
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Background: Positive relationships between hospital volume and outcomes have been demonstrated for several surgeries and medical conditions. However, little is known about the volume-outcome relationship in patients admitted to medical ICUs.

Objective: To determine the relationship between hospital volume and risk-adjusted in-hospital mortality for patients admitted to ICUs with respiratory, neurologic, and GI disorders.

Design: Retrospective cohort study.

Setting: Twenty-nine hospitals in a single metropolitan area.

Patients: Adult ICU admissions from 1991 through 1997.

Methods: Using Cox proportional hazards models, we compared in-hospital mortality between tertiles of hospital volume (high, medium, and low) for respiratory (n = 16,949), neurologic (n = 13,805), and GI (n = 12,881) diseases after adjusting for age, gender, admission severity of illness, admitting diagnosis, and source. Severity of illness was measured using the APACHE (acute physiology and chronic health evaluation) III methodology.

Results: Among respiratory and neurologic ICU admissions, hazard ratios were similar (p ≥ 0.05) in patients in low-, medium-, and high-volume hospitals. However, among GI diagnoses, risk of mortality was lower in high-volume hospitals, relative to low-volume hospitals (hazard ratio, 0.68; 95% confidence interval [CI], 0.54 to 0.85; p < 0.001), and was somewhat lower in medium-volume hospitals (hazard ratio, 0.83; 95% CI, 0.68 to 1.01; p = 0.06). Among subgroups based on severity of illness, high-volume hospitals had lower mortality, relative to low-volume hospitals, among sicker patients (APACHE III score > 57) in the respiratory cohort (hazard ratio, 0.77; 95% CI, 0.59 to 0.99) and the GI cohort (hazard ratio, 0.67; 95% CI, 0.53 to 0.85).

Conclusions: Associations between ICU volume and risk-adjusted mortality were significant for patients with GI diagnoses and for sicker patients with respiratory diagnoses. However, associations were not significant for patients with neurologic diagnoses. The lack of a consistent volume-outcome relationship may reflect unmeasured patient complexity in higher-volume hospitals, relative standardization of care across ICUs, or lack of efficacy of some accepted ICU processes of care.

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