EVALUATION OF ACUTE PHYSIOLOGY AND CHRONIC HEALTH EVALUATION-III PREDICTIONS OF HOSPITAL MORTALITY IN AN INDEPENDENT DATABASE

Objective: To assess the accuracy and validity of Acute Physiology and Chronic Health Evaluation (APACHE) III hospital mortality predictions in an independent sample of U.S. intensive care unit (ICU) admissions . Design: Nonrandomized, observational, cohort study. Setting: Two hun dred eighty-five ICUs in 161 U.S. hospitals, including 65 members of t he Council of Teaching Hospitals and 64 nonteaching hospitals. Patient s: A consecutive sample of 37,668 ICU admissions during 1993 to 1996; including 25,448 admissions at hospitals with greater than or equal to 400 beds and 1,074 admissions at hospitals with <200 beds. Interventi ons: None. Measurements and Main Results: We used demographic, clinica l, and physiologic information recorded during ICU day 1 and the APACH E III equation to predict the probability of hospital mortality for ea ch patient. We compared observed and predicted mortality for all admis sions and across patient subgroups and assessed predictive accuracy us ing tests of discrimination and calibration. Aggregate hospital death rate was 12.35% and predicted hospital death rate was 12.27% (p = .541 ), The model discriminated between survivors and nonsurvivors well (ar ea under receiver operating curve = 0.89). A calibration curve showed that the observed number of hospital deaths was close to the number of deaths predicted by the model, but when tested across deciles of risk , goodness-of-fit (Hosmer-Lemeshow statistic, chi square = 48.71, 8 de grees of freedom, p< .0001) was not perfect. Observed and predicted ho spital mortality rates were not significantly (p < .01) different for 55 (84.6%) of APACHE Ill's 65 specific ICU admission diagnoses and for 11 (84.6%) of the 13 residual organ system-related categories. The mo st frequent diagnoses with significant (p<.01) differences between obs erved and predicted hospital mortality rates included acute myocardial infarction, drug overdose, nonoperative head trauma, and nonoperative multiple trauma. Conclusions: APACHE III accurately predicted aggrega te hospital mortality in an independent sample of U.S, ICU admissions. Further improvements in calibration can be achieved by more precise d isease labeling, improved acquisition and weighting of neurologic abno rmalities, adjustments that reflect changes in treatment outcomes over time, and a larger national database.