Why should we not use APACHE II for performance measurement and benchmarking?

The Acute Physiology and Chronic Health Evaluation (APACHE) is the most frequently used general severity-of-illness score in adult intensive care units (ICUs). APACHE scores use clinical, physiological and laboratory data observed at admission and during the first 24 hours after ICU admission. This is in order to estimate a given patient’s severity of illness by providing a severity score and a probability of hospital death. Although severity of illness scores including APACHE scores should not be used to guide decisions for individual patients, they are useful for characterizing patients in clinical studies, evaluating ICU performance and benchmarking, for which case mix correction is needed.(1) The first version of the APACHE score dates back to the early 80s.(2) However, the APACHE I was too complex and time-consuming for routine use in the ICU. The APACHE II score was released more than 35 years ago in 1985 using data from 5,815 patients admitted between 1979 and 1982 to 13 hospitals in the United States (US).(3) The number of variables was reduced from 34 to 12, and 50 admission disease groups were provided to improve the accuracy of outcome predictions. The APACHE II score was quickly adopted by ICUs worldwide and is the most used score in clinical studies to date. The APACHE III score was published in 1991 using data from 17,440 patients admitted to 40 US hospitals.(4) More sophisticated statistical modeling approaches were used, and both the number of admission disease groups and the physiological variables were expanded. Moreover, new equations to predict outcomes other than hospital mortality were provided. Updated versions of the APACHE III score were made available during the 90s. However, despite such updates, deteriorations in the model’s performance over time indicated that the modeling of new equations would be required.(5,6) Therefore, the APACHE IV, which represents the most recent version of APACHE scores, was introduced in 2006.(5) Investigators used data from more the 110,000 ICU admissions in 45 hospitals that were still restricted to the US. The number of admission disease groups was expanded to 116. Why are severity-of-illness scores regularly updated? It is not surprising that the performance of severity-of-illness scores deteriorates overtime. Such deterioration is invariably characterized by the worsening of discrimination (i.e., the ability to discriminate between survivors and non-survivors) and more Marcio Soares1, Dave A. Dongelmans2