“…The model contained nine candidate predictors: Physiological and Operative Severity Score for the enumeration of Mortality and morbidity (POSSUM) score, sex, history of coma (history of transitional conscious disturbance before admission, discovered when doctors were collecting the patient’s medical history), history of hypertension (systolic blood pressure ≥140 mm Hg, with or without diastolic pressure ≥90 mm Hg; or simple hypertension with systolic blood pressure ≥140 mm Hg only diagnosed previously before admission by clinicians and had recorded in the medical record), history of diabetes (diagnosed before admission by clinicians and recorded in the medical record), mechanical ventilation, history of alcohol dependence (based on International Statistical Classification of Diseases and Related Health problems (10th Revision) (ICD-10)22 and diagnosed by clinicians), acid–base imbalance (including metabolic acidosis, metabolic alkalosis, respiratory acidosis and respiratory alkalosis, identified by the first blood gas analysis) and length of operation. For each candidate predictor, at least 5–10 patients with delirium were required based on the sample size formula for modeling23; as the minimum incidence of ICU-POD is 27.6%,3 we used this value. With an anticipated delirium incidence of 27.6% and an expected attrition of 10%–20%, we aimed to enrol at least 1960 patients (9×5 × (1+0.2) / 0.276).…”