Modeling the severity of illness of ICU patients. A systems update

To review recent revisions of systems for estimating the probability of hospital mortality of adult intensive care unit (ICU) patients. Emphasis on comparison of components of systems and potential uses.

Published articles in which the systems were presented.

Acute Physiology and Chronic Health Evaluation (APACHE III), Simplified Acute Physiology Score (SAPS II), and Mortality Probability Models (MPM II) are the major severity systems for ICU patients.

Information on variables collected in the systems, characteristics of databases from which they were developed, and reported performance of models were evaluated from published articles.

APACHE III and SAPS II produce a score and probability of hospital mortality based on worst values of several variables during the first 24 hours in ICU. The MPM II system has four models, one at ICU admission and one at 24, 48, and 72 hours into the ICU stay. The SAPS II and MPM II models can be implemented from published information. The APACHE III score can be calculated from published information; weights to convert score to probability are proprietary. All reported good areas under receiver operating characteristic curve. Goodness of fit was good for SAPS II and MPM II models and was not reported for APACHE III models.

All models were based on rigorous research and reported performance is good. All can be used to assist in assessing prognosis, to compare ICU performance, and to stratify patients for clinical trials. Direct comparison on a common cohort is needed.