Validation of the Confusion Assessment Method for the Intensive Care Unit in Older Emergency Department Patients

Abstract

In the emergency department (ED), health care providers miss delirium approximately 75% of the time, because they do not routinely screen for this syndrome. The Confusion Assessment Method for the Intensive Care Unit (CAM-ICU) is a brief (<1 minute) delirium assessment that may be feasible for use in the ED. The study objective was to determine its validity and reliability in older ED patients. In this prospective observational cohort study, patients aged 65years or older were enrolled at an academic, tertiary care ED from July 2009 to February 2012. An emergency physician (EP) and research assistants (RAs) performed the CAM-ICU. The reference standard for delirium was a comprehensive (~30 minutes) psychiatrist assessment using the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision criteria. All assessments were blinded to each other and were conducted within 3hours. Sensitivities, specificities, and likelihood ratios were calculated for both the EP and the RAs using the psychiatrist's assessment as the reference standard. Kappa values between the EP and RAs were also calculated to measure reliability. Of 406 patients enrolled, 50 (12.3%) had delirium. The median age was 73.5years old (interquartile range [IQR]= 69 to 80years), 202 (49.8%) were female, and 57 (14.0%) were nonwhite. The CAM-ICU's sensitivities were 72.0% (95% confidence interval [CI]=58.3% to 82.5%) and 68.0% (95% CI=54.2% to 79.2%) in the EP and RAs, respectively. The CAM-ICU's specificity was 98.6% (95% CI=96.8% to 99.4%) for both raters. The negative likelihood ratios (LR-) were 0.28 (95% CI=0.18 to 0.44) and 0.32 (95% CI=0.22 to 0.49) in the EP and RAs, respectively. The positive likelihood ratios (LR+) were 51.3 (95% CI=21.1 to 124.5) and 48.4 (95% CI=19.9 to 118.0), respectively. The kappa between the EP and RAs was 0.92 (95% CI=0.85 to 0.98), indicating excellent interobserver reliability. In older ED patients, the CAM-ICU is highly specific, and a positive test is nearly diagnostic for delirium when used by both the EP and RAs. However, the CAM-ICU's sensitivity was modest, and a negative test decreased the likelihood of delirium by a small amount. The consequences of a false-negative CAM-ICU are unknown and deserve further study.