Background: Intraoperative hypotension (IOH) is hypothesized to contribute to postoperative delirium (POD) in the elderly, but quantitative evidence linking its depth and duration to POD was limited in 2007. Methods: A prospective observational study of 486 patients aged ≥65 undergoing major non-cardiac surgery in 2007. Intraoperative mean arterial pressure (MAP) was recorded minute-by-minute. The primary exposure was the area under the threshold (AUT, mmHg*min) for MAP<65 mmHg. POD was assessed twice daily up to day 7 using the Confusion Assessment Method. Multivariable logistic regression adjusted for age, baseline cognition, comorbidity, and surgery type. Results: The incidence of POD was 22.6% (110/486). Patients with POD had significantly greater AUT for MAP<65 mmHg (median 85 vs. 25 mmHg*min, p<0.001). After adjustment, AUT for MAP<65 mmHg was independently associated with POD (adjusted odds ratio [aOR] per 60 mmHg*min increase: 1.28, 95% CI 1.12-1.47, p<0.001). Cumulative duration of MAP<65 mmHg (aOR per 30-min increase: 1.35, 95% CI 1.15-1.58) and AUT for lower thresholds (MAP<60, <55) were also significant predictors. Conclusion: The depth and duration of intraoperative hypotension, quantified as AUT below MAP thresholds of 65-55 mmHg, were independently associated with increased odds of postoperative delirium in elderly patients. These results suggest that minimizing both the magnitude and duration of intraoperative blood pressure decreases may be important for delirium prevention.

Postoperative Delirium; Intraoperative Hypotension; Aged; Anesthesia; Mean Arterial Pressure.