Screening for delirium after surgery: validation of the 4 A's test (4AT) in the post-anaesthesia care unit

Postoperative delirium is common and has multiple adverse consequences. Guidelines recommend routine screening for postoperative delirium beginning in the post-anaesthesia care unit. The 4 A's test (4AT) is a widely used assessment tool for delirium but there are no studies evaluating its use in the post-anaesthesia care unit. We evaluated the performance of the 4AT in the post-anaesthesia care unit in a tertiary German medical centre. Adults who were able to provide informed consent, were not scheduled for postoperative intensive care, and who did not have dementia or severe neuropsychiatric disorders underwent screening by trained research staff with the Nurse Delirium Screening Scale and a new German translation of the 4AT in a random order at the point of discharge from the post-anaesthesia care unit. Reference standard assessment of delirium was psychiatric evaluation by experienced clinicians. Five hundred and forty-three patients (mean age (SD) 52 (18) years) were analysed; 22 (4.1%) patients developed delirium. The sensitivity and specificity of the 4AT were 95.5% (95%CI 77.2-99.9) and 99.2% (95%CI 98.1-99.8), respectively. The area under the receiver operator characteristic curve was 0.998 (95%CI 0.995-1.000). The Nursing Delirium Screening Scale had a sensitivity of 27.3% (95%CI 10.7-50.2) and specificity of 99.4% (95%CI 98.3-99.9), with an area under the curve of 0.761 (95%CI 0.629-0.894). These findings suggest that the 4AT is an effective and robust instrument for delirium detection in the post-anaesthesia care unit.