Sensitivity and specificity of the animal fluency test for predicting postoperative delirium

Preoperative cognitive impairment is a major risk factor for postoperative delirium. We therefore investigated the prognostic significance and feasibility of administering a brief cognitive screen before surgery.

Patients > 65 yr of age undergoing hip, knee, or spine surgery were enrolled. A 60-sec cognitive screen, the animal fluency test (AFT), was administered preoperatively. Postoperative delirium was measured using a chart-based tool previously validated using criteria from the Confusion Assessment Method.

Of the 362 patients satisfying the inclusion/exclusion criteria, 199 (55%) underwent the AFT. Among them, 57 patients (29%) had an AFT score < 15, and 38 patients (19%, 95% confidence interval [CI]: 14 to 25%) developed postoperative delirium as measured by chart review. Patients with scores of < 15 were more likely to develop postoperative delirium than those who scored ≥ 15 (54% vs 5%, P < 0.01). A multiple logistic regression, with postoperative delirium as the dependent variable, identified an AFT score of < 15 (odds ratio 20.1, 95% CI: 7.9 to 51.4) and high American Society of Anesthesiologists classification (odds ratio 3.5, 95% CI: 1.3 to 9.2) as independent predictors.

The AFT is a potentially useful brief cognitive screen for identifying patients at risk of developing postoperative delirium. Limited participation by eligible participants in this study, however, raises questions about how useful and feasible systematic administration of the test is. Large studies using prospective measurement of postoperative delirium are indicated to validate our results.