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Validity and Reliability of the Confusion Assessment Method for the Intensive Care Unit (CAM-ICU)

E. Wesley Ely, MD,MPH; Sharon K. Inouye, MD,MPH; Gordon R. Bernard, MD; Sharon Gordon, PsyD; Joseph Francis, MD,MPH; Lisa May, RN,BSN; Brenda Truman, RN,MSN; Theodore Speroff, PhD; Shiva Gautam, PhD; Richard Margolin, MD; Robert P. Hart, PhD; Robert Dittus, MD,MPH

JAMA. 2001;286:2703-2710.

Context  Delirium is a common problem in the intensive care unit (ICU). Accurate diagnosis is limited by the difficulty of communicating with mechanically ventilated patients and by lack of a validated delirium instrument for use in the ICU.

Objectives  To validate a delirium assessment instrument that uses standardized nonverbal assessments for mechanically ventilated patients and to determine the occurrence rate of delirium in such patients.

Design and Setting  Prospective cohort study testing the Confusion Assessment Method for ICU Patients (CAM-ICU) in the adult medical and coronary ICUs of a US university-based medical center.

Participants  A total of 111 consecutive patients who were mechanically ventilated were enrolled from February 1, 2000, to July 15, 2000, of whom 96 (86.5%) were evaluable for the development of delirium and 15 (13.5%) were excluded because they remained comatose throughout the investigation.

Main Outcome Measures  Occurrence rate of delirium and sensitivity, specificity, and interrater reliability of delirium assessments using the CAM-ICU, made daily by 2 critical care study nurses, compared with assessments by delirium experts using Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, criteria.

Results  A total of 471 daily paired evaluations were completed. Compared with the reference standard for diagnosing delirium, 2 study nurses using the CAM-ICU had sensitivities of 100% and 93%, specificities of 98% and 100%, and high interrater reliability ( = 0.96; 95% confidence interval, 0.92-0.99). Interrater reliability measures across subgroup comparisons showed values of 0.92 for those aged 65 years or older, 0.99 for those with suspected dementia, or 0.94 for those with Acute Physiology and Chronic Health Evaluation II scores at or above the median value of 23 (all P<.001). Comparing sensitivity and specificity between patient subgroups according to age, suspected dementia, or severity of illness showed no significant differences. The mean (SD) CAM-ICU administration time was 2 (1) minutes. Reference standard diagnoses of delirium, stupor, and coma occurred in 25.2%, 21.3%, and 28.5% of all observations, respectively. Delirium occurred in 80 (83.3%) patients during their ICU stay for a mean (SD) of 2.4 (1.6) days. Delirium was even present in 39.5% of alert or easily aroused patient observations by the reference standard and persisted in 10.4% of patients at hospital discharge.

Conclusions  Delirium, a complication not currently monitored in the ICU setting, is extremely common in mechanically ventilated patients. The CAM-ICU appears to be rapid, valid, and reliable for diagnosing delirium in the ICU setting and may be a useful instrument for both clinical and research purposes.

Author Affiliations: Department of Internal Medicine, Divisions of General Internal Medicine and Center for Health Services Research and the Veterans Affairs Tennessee Valley Health Care System Geriatric Research, Education and Clinical Center (Drs Ely, Gordon, Speroff, Gautam, and Dittus and Mss May and Truman), and Division of Allergy/Pulmonary/Critical Care Medicine (Drs Ely and Bernard), Department of Geriatric Psychiatry and Neuroscience (Drs Gordon and Margolin), Vanderbilt University School of Medicine, Nashville, Tenn; Department of Internal Medicine, Yale University School of Medicine, New Haven, Conn (Dr Inouye); Division of Quality and Data Management, St Vincent Hospital Health System, Indianapolis, Ind (Dr Francis); and the Department of Psychiatry, Virginia Commonwealth University Health Systems, Richmond (Dr Hart).

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