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Original Research: CRITICAL CARE MEDICINE |

Mortality Probability Model III and Simplified Acute Physiology Score II: Assessing Their Value in Predicting Length of Stay and Comparison to APACHE IV

Eduard E. Vasilevskis, MD; Michael W. Kuzniewicz, MD, MPH; Brian A. Cason, MD; Rondall K. Lane, MD, MPH; Mitzi L. Dean, MS, MHA; Ted Clay, MS; Deborah J. Rennie, BA; Eric Vittinghoff, PhD; R. Adams Dudley, MD, MBA
Author and Funding Information

From the Philip R. Lee Institute for Health Policy Studies (Drs. Vasilevskis, Kuzniewicz, Lane, and Dudley, Ms. Dean, Mr. Clay, and Ms. Rennie), the Divisions of General Internal Medicine (Dr. Vasilevskis), Hospital Medicine (Dr. Vasilevskis), Neonatology (Dr. Kuzniewicz), and Pulmonary and Critical Care Medicine (Dr. Dudley), and the Departments of Anesthesiology and Perioperative Medicine (Drs. Cason and Lane), and Epidemiology and Biostatistics (Dr. Vittinghoff), University of California at San Francisco, San Francisco, CA; Veterans Affairs Medical Center (Dr. Cason), San Francisco, CA; the Department of Medicine (General Internal Medicine and Public Health) [Dr. Vasilevskis], Vanderbilt University, Nashville, TN; and Geriatric Research Education and Clinical Care (Dr. Vasilevskis), and the Clinical Research Training Center of Excellence (Dr. Vasilevskis), Department of Veterans Affairs, Tennessee Valley Healthcare System, Nashville, TN.

Correspondence to: Eduard E. Vasilevskis, MD, Vanderbilt University Medical Center; 1215 Twenty-First Ave South, 6006 Medical Center East, NT, Nashville, TN 37232-8300; e-mail: eduard.vasilevskis@vanderbilt.edu


Dr. Vasilevskis had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Responsibility for areas of the study were as follows: study concept and design: Drs. Vasilevskis, Kuzniewicz, and Dudley; acquisition of data: Drs. Kuzniewicz, Cason, Lane, and Dudley, and Ms. Dean; analysis and interpretation of data: Drs. Vasilevskis, Kuzniewicz, Cason, Lane, Vittinghoff, and Dudley, Ms. Dean, Mr. Clay, and Ms. Rennie; drafting of the manuscript: Drs. Vasilevskis and Dudley; critical revision of the manuscript for important intellectual content: Drs. Vasilevskis, Kuzniewicz, Cason, Lane, Vittinghoff, and Dudley, Ms. Dean, Mr. Clay, and Ms. Rennie; statistical analysis: Drs. Vasilevskis and Vittinghoff, and Mr. Clay; obtained funding: Dr. Dudley; administrative, technical, or material support: Drs. Cason and Lane, Ms. Dean, and Ms. Rennie; and study supervision: Ms. Dean and Dr. Dudley.

The views expressed in this article are those of the authors and do not necessarily represent the views of the US Department of Veterans Affairs.

This work was supported by the California Office of Statewide Health Planning and Development and the Agency for Healthcare Research and Quality (R01 HS13919-01). Dr. Dudley's work was also supported by an Investigator Award in Health Policy from the Robert Wood Johnson Foundation. Dr. Vasilevskis was supported by a Ruth L. Kirschstein National Research Service Award institutional research training grant T32, the Veterans Affairs Clinical Research Center of Excellence, and the Geriatric Research Education and Clinical Center, Veterans Affairs, Tennessee Valley Healthcare, Nashville, TN.

The authors have reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/site/misc/reprints.xhtml).


© 2009 American College of Chest Physicians


Chest. 2009;136(1):89-101. doi:10.1378/chest.08-2591
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Background:  To develop and compare ICU length-of-stay (LOS) risk-adjustment models using three commonly used mortality or LOS prediction models.

Methods:  Between 2001 and 2004, we performed a retrospective, observational study of 11,295 ICU patients from 35 hospitals in the California Intensive Care Outcomes Project. We compared the accuracy of the following three LOS models: a recalibrated acute physiology and chronic health evaluation (APACHE) IV-LOS model; and models developed using risk factors in the mortality probability model III at zero hours (MPM0) and the simplified acute physiology score (SAPS) II mortality prediction model. We evaluated models by calculating the following: (1) grouped coefficients of determination; (2) differences between observed and predicted LOS across subgroups; and (3) intraclass correlations of observed/expected LOS ratios between models.

Results:  The grouped coefficients of determination were APACHE IV with coefficients recalibrated to the LOS values of the study cohort (APACHE IVrecal) [R2 = 0.422], mortality probability model III at zero hours (MPM0 III) [R2 = 0.279], and simplified acute physiology score (SAPS II) [R2 = 0.008]. For each decile of predicted ICU LOS, the mean predicted LOS vs the observed LOS was significantly different (p ≤ 0.05) for three, two, and six deciles using APACHE IVrecal, MPM0 III, and SAPS II, respectively. Plots of the predicted vs the observed LOS ratios of the hospitals revealed a threefold variation in LOS among hospitals with high model correlations.

Conclusions:  APACHE IV and MPM0 III were more accurate than SAPS II for the prediction of ICU LOS. APACHE IV is the most accurate and best calibrated model. Although it is less accurate, MPM0 III may be a reasonable option if the data collection burden or the treatment effect bias is a consideration.

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