Comparison of outcome from intensive care admission after adjustment for case mix by the APACHE III prognostic system

Abstract

Study objectives: To evaluate the acute physiology, age, chronic health evaluation III (APACHE III) scoring system in the context of general adult ICUs in the United Kingdom.

Design: Prospective, noninterventional, cohort study.

Setting: Seventeen general adult ICUs in a discrete area of southwest England.

Patients: 12,793 patients admitted between April 1, 1993 and December 31, 1995.

Measurements: Sociodemographic and severity-of-illness data were collected for all patients admitted to the study units. Formal goodness-of-fit tests were applied and observed mortality was compared with that predicted by using the APACHE III system.

Results: For the group of ICUs as a whole, the risk-adjusted standardized mortality ratio (SMR) was 1.23 (95% confidence intervals, 1.12-1.25). For 11 out of 17 ICUs, the SMR was significantly greater than unity (p < 0.05). Calibration, as tested by Hosmer-Lemeshow statistics, was poor (H2 = 312.54; C2 = 332.85; df = 8; p < 0.01); however, model discrimination was good with a total correct classification rate of 82.9% and an area under the receiver operating characteristic curve of 0.89.

Conclusions: The excess mortality observed after case-mix adjustment using the APACHE III system in this study may be the result of either poor intensive care performance as compared with the United States or a failure of the APACHE III equation to fit the UK data.