The multivariate logistic regression analysis showed that the risk factors for postoperative delirium were smoking (OR 4.51, 95% CI 1.56–13.02, p < 0.01), orthostatic hypotension (OR 3.42, 95% CI 0.90–13.06, p=0.07), preoperative MRI with silent brain ischemia or infarction (OR 2.36, 95% CI 0.90–6.14, p=0.08), MAOBIs (OR 3.07, 95% CI 1.17–8.04, p=0.02), HAMA score (OR 2.12, 95% CI 1.28–3.50, p < 0.01), and APOE level in plasma (OR 1.48, 95% CI 0.95–2.29, p=0.08). The gene discussed is APOE; the disease is orthostatic hypotension.