Delirium and mortality risk prediction: a story in evolution

and colleagues, which proposed that delirium measured within 24 hours of admission did not improve the Acute Physiology and Chronic Health Evaluation (APACHE) II in-hospital mortality prediction [1]. Th eir data should be interpreted after considering the study design and statistical limitations. First, the Confusion Assessment Method for the Intensive Care Unit (CAM-ICU) measurements include assessing the level of con scious ness (using any valid sedation scale), which is highly correlated with the Glasgow Coma Score. Th erefore it is not surprising that addition of delirium to the APACHE score (which includes the Glasgow Coma Score) on the fi rst intensive care unit day does not alter predictions; however, earlier detection of delirium at the initial evalu at ion of Emergency Department patients is an important predictor of death [2]. We have found that the level of consciousness (via the Richmond Agitation-Sedation Scale) has been predictive of in-hospital mortality, but this relationship is not as strong as the independent value of delirium duration (via the CAM-ICU) for predicting long-term survival, even after adjusting for APACHE II score and sedatives [3,4]. Second, the authors base their conclusions upon comparisons of areas under the curve using the c statistic. Recent insights suggest that this analytic method is insensitive and open to type II error [5]. A more sensitive method to assess additive predictive ability applies likelihood ratio testing between models with and without additional risk factors. In addition, substantial improvements in risk reclassi fi cation may be apparent despite limited increases in the c statistic. In sum, it may be true (but confi rmation is required) that adding delirium to a measurement such as the APACHE score is not of value. Clinicians and hospital quality offi cers should continue to consider early detection of delirium and ongoing delirium detection as an important prognostic tool.