Mortality prediction using acute physiology and chronic health evaluation II and acute physiology and chronic health evaluation IV scoring systems: Is there a difference?

The outcomes of patients admitted to the Intensive Care Units (ICUs) depend on numerous factors including the age, sex, type, and severity of underlying illness and various clinical and laboratory parameters. Several scoring systems have been developed over the years to assess and describe the severity of the illness and predict the mortality rate of patients admitted to the ICU. One of the earliest valid mortality prediction tools is the Acute Physiology and Chronic Health Evaluation (APACHE) II system which was described in 1981. The tool is administered on a patient admitted to the ICU within 24 h of admission wherein various parameters including the patient demographics, clinical features, and laboratory features are entered, and an APACHE score ranging between 0 and 71 is computed. Although APACHE scores may not be useful to determine outcomes of individual patients, it can work as a good guide to prognosticate in the cohort of patients admitted to ICU. Moreover, comparison of the actual mortality rates in an ICU with the predicted mortality rate (PMR) can be used to indicate the performance of an ICU and to compare outcomes across different ICUs. In 1991, APACHE II was modified to the APACHE III score which was more elaborate with 20 variables and used several additional parameters with better predictive ability. ckground: Mortality prediction in the Intensive Care Unit (ICU) setting is complex, and there are several scoring systems utilized for this process. The Acute Physiology and Chronic Health Evaluation (APACHE) II has been the most widely used scoring system; although, the more recent APACHE IV is considered an updated and advanced prediction model. However, these two systems may not give similar mortality predictions. Objectives: The aim of this study is to compare the mortality prediction ability of APACHE II and APACHE IV scoring systems among patients admitted to a tertiary care ICU. Methods: In this prospective longitudinal observational study, APACHE II and APACHE IV scores of ICU patients were computed using an online calculator. The outcome of the ICU admissions for all the patients was collected as discharged or deceased. The data were analyzed to compare the discrimination and calibration of the mortality prediction ability of the two scores. Results: Out of the 1670 patients' data analyzed, the area under the receiver operating characteristic of APACHE II score was 0.906 (95% confidence interval CI -0.890-0.992), and APACHE IV score was 0.881 (95% CI -0.862-0.890). The mean predicted mortality rate of the study population as given by the APACHE II scoring system was 44.8 26.7 and as given by APACHE IV scoring system was 29.1 28.5. The observed mortality rate was 22.4%. Conclusions: The APACHE II and IV scoring systems have comparable discrimination ability, but the calibration of APACHE IV seems to be better than that of APACHE II. There is a need to recalibrate the scales with weights derived from the Indian population.