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ARTICLE

Variations in Mortality and Length of Stay in Intensive Care Units

William A. Knaus; Douglas P. Wagner; Jack E. Zimmerman; and Elizabeth A. Draper

15 May 1993 | Volume 118 Issue 10 | Pages 753-761

Objective: To evaluate the amount of variation in in-hospital mortality and length of intensive care unit (ICU) stay that can be accounted for by clinical data available at ICU admission.

Design: Inception cohort study.

Setting: Forty-two ICUs in 40 hospitals, including 26 hospitals that were randomly selected and 14 large tertiary care hospitals that volunteered for the study.

Participants: A consecutive sample of 16 622 patients and 17 440 ICU admissions.

Measurements and Main Outcomes: Data on selected demographic characteristics, comorbidity, and specific physiologic variables were recorded during the first ICU day for an average of 415 admissions at each ICU; hospital discharge status (dead or alive) and length of ICU stay were recorded for individual patients; and the ratio of actual to predicted in-hospital mortality, standardized mortality ratios, and the ratio of actual to predicted length of ICU stay were recorded for individual ICUs.

Results: Unadjusted in-hospital mortality rates for the 42 units varied from 6.4% to 40%, and 90% (R² = 0.90) of this variation was attributable to patient characteristics at admission. The standard mortality ratio varied from 0.67 to 1.25. The mean unadjusted length of ICU stay varied from 3.3 to 7.3 days, and 78% of the variation (R² = 0.78) was attributed to patient and selected institutional characteristics. The best performing unit had a length of stay ratio of 0.88, whereas the poorest performing unit had a ratio of 1.21.

Conclusions: Clinicians can use readily available admission data to adjust for considerable variations in patient severity and type in different ICUs. Such data should permit precise evaluation and comparison of ICU effectiveness and efficiency, which varied substantially in this study, and result in improved methods of risk prediction and evaluation of new medical practices.

Author and Article Information

From George Washington University Medical Center and APACHE Medical Systems, Inc., Washington, DC.
Requests for Reprints: William A. Knaus, MD, ICU Research Unit, 2300 K Street, NW, George Washington University Medical Center, Washington, DC 20037.
Disclosure: Drs. Knaus, Zimmerman, and Wagner are founders of and shareholders in APACHE Medical Systems, Inc. (AMS) and are prohibited by University policy from receiving any payment, royalties, or other fees from AMS. Elizabeth Draper is an employee of and shareholder in AMS. APACHE Medical Systems produces a management information system for critical care units and holds the commercial copyright on the equations for in-hospital mortality and length of ICU stay. APACHE and APACHE III are trademarks of AMS. Although both equations and the APACHE III database are protected by commercial copyright, they are available to researchers for independent verification and further analysis by contacting the authors or AMS.
Acknowledgments: The authors thank participating hospitals for their data collection efforts and leadership; Theodore Lotring for research assistance; and Vea Thomas for clerical support.
Grant Support: In part by the Agency for Health Care Policy and Research (grant HS 5787), the John A. Hartford Foundation (grant 87267), the Department of Anesthesiology, George Washington University Medical Center, and APACHE Medical Systems, Inc.

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