Revisiting the validity of APACHE II in the trauma ICU: Improved risk stratification in critically injured adults
Introduction
A growing focus on health quality and benchmarking has highlighted the need for accurate severity scoring systems for stratified risk adjustment.11 Accurate severity scoring allows for comparison of clinical outcomes across centres and countries, and provides a means for the comparison of interventions and outcomes in a research setting. As the number and complexity of demographic and clinical characteristics impacting clinical outcomes has grown, so too has the number and complexity of severity scoring systems.1, 10, 14, 15, 17, 18, 19, 21, 23, 24
The risk stratification of trauma patients has traditionally focused on anatomic or physiologic scores specific to trauma populations. This stems from the belief that the trauma patient population is inherently different from the general patient population. Trauma patients are considered younger, healthier and plagued with unique “disease” patterns; all factors which many believe limit the usefulness of scores addressing broader categories of patients and diseases. Several systems have been developed for stratification of trauma patients and these scores have been previously reviewed.7 Among the most commonly used are the injury severity score (ISS) and the Trauma and Injury Severity Score (TRISS). ISS is a strictly anatomic scoring system developed in 1974 for the purpose of describing the multiple trauma patient.3 The lack of physiologic data led rapidly to revisions of the ISS, as it was shown to be inferior to severity scores which incorporate these parameters.9 TRISS is one such revision which takes into account the ISS, but also incorporates the Revised Trauma Score (RTS), the patient's age and the mechanism of injury to determine a patient's predicted survival.4 For many years, TRISS has been the premier quantitative measure of injury treatment quality, but a number of recent studies have identified the limitations to this scoring system, particularly among the critically injured.
Despite the known and inherent limitations in trauma specific scores, they continue to dominate trauma registries and the literature since scores used in general critical care populations, such as APACHE II,12 are considered invalid in the trauma patient. Criticisms of the use of APACHE II in the trauma population have been based primarily on the poor correlation between APACHE II and ISS or TRISS, and the inability of APACHE II to accurately predict hospital or intensive care unit length of stay.16 Importantly, the criticism has not been based on an inability to predict death. In fact, when APACHE II has been evaluated as a predictor of clinical outcomes in trauma patients it has proven to be a useful predictor, particularly those who are critically injured.2, 22
Our goal was to evaluate the ability of commonly used severity scores and their subcomponents to predict death in a large prospective cohort of critically ill trauma patients. We hypothesized that in the trauma ICU, the injury and illness severity scores incorporating physiological data would be superior to anatomic only systems, and that APACHE II would be a useful predictor of death in this select group of trauma patients.
Section snippets
Study design and participating centres
This study represents a secondary analysis of a multi-institutional prospective cohort study of critically ill or injured surgical patients. The primary purpose of the study was to determine the role of gender and sex hormones on outcomes in critically ill patients. All patients 18 years of age or older, admitted to the Surgical or Trauma Intensive Care Units (ICUs) of Vanderbilt University Medical Center and the University of Virginia Health Sciences Center were eligible for enrolment. In
Patient demographic and clinical characteristics
1019 patients met entry criteria and were available for analysis. There were 138 deaths for an overall mortality rate of 14%. The demographic and clinical characteristics of patients by outcome are summarized in Table 1. Non-survivors were older and had higher APACHE II scores (23 ± 5.5) compared to survivors (16 ± 5.5, p < 0.001). Other components of APACHE II which were statistically different between the groups included temperature and serum creatinine, but these variables were not impressively
Discussion
National benchmarking initiatives such as the National Surgical Quality Improvement Program (NSQIP) have highlighted the need for accurate risk stratification in both the surgical and trauma patient.11 Historically, the usefulness of severity scores has been in their ability to stratify patients for research and prognostic applications, but they now have implications for stratifying outcomes for both reimbursement and credentialing purposes. In short, the stakes for accurate stratification have
Conflict of interest
The authors have no conflicts of interest to disclose.
Acknowledgements
This work was supported by a National Institutes of Health Grant—RO1 AI49989-01 (Clinical Trials.gov identifier NCT00170560) and an Agency for Healthcare Research and Quality grant—T32 HS 013833. Portions of this data will be presented in poster form at the 2008 Eastern Association for the Surgery of Trauma meeting Amelia Island, FL.
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