Seven pharmacists were part of a team concluding that “the APACHE II score may be a valid tool to control for confounding or for the prediction of death among ICU and non-ICU patients with MRSA bacteremia.”1
The acute physiology and chronic health evaluation (APACHE) II score was developed and validated for use among intensive care unit (ICU) patients, but its utility among non-ICU patients is unknown. Retrospective data from about 200 patients were abstracted, including illness severity (APACHE II score); in-hospital vital status at 48 hours, 7 days, 14 days, and 30 days following the start of methicillin-resistant Staphylococcus aureus
(MRSA)-targeted therapy; and notation of an ICU admission at the time of MRSA bacteremia onset. In-hospital mortality and overall mortality were modeled using logistic regression at each time point using APACHE II scores for ICU and non-ICU patients. A model that included APACHE II scores was compared with an age-adjustment-alone model among all patients. APACHE II was a significantly better predictor of death at all time points in both ICU and non-ICU patients compared with random prediction and significantly improved the prediction of overall and 48-hour mortality compared with age adjustment alone.
Implications. Differences in disease severity in acute treatment episodes for seriously ill patients can be a vexing confounding factor in comparative effectiveness studies. This work provides a validated measure that can be used to control for confounding based on sound physiologic principles. Development and validation of other measures for this purpose (i.e., confounding) that can have widespread acceptance for incorporation into comparative effectiveness studies are needed.