Paracetamol and Mannitol Injection and Postoperative Delirium

Inclusion Criteria: * Age ≥ 60 years; * Admitted to ICU after a noncardiac surgical procedure * Moderate to severe acute pain, with a postoperative pain score ≥ 5 based on the 11-point Numerical Pain Rating Scale (NPRS) * Signed informed consent form Exclusion Criteria: * Preoperative medical history: schizophrenia, epilepsy, Parkinson's disease, or severe myasthenia gravis * History of psychiatric disease or significant neurocognitive disorder such as dementia or retardation, making POD assessment impossible * Language or communication barrier making POD assessment impossible * Intracranial surgery * Severe hepatic dysfunction prohibiting the use of acetaminophen per the standard of care * Participation in a competing study within 30d * Patients experienced intraoperative or postoperative complications, and the investigator determined the subject was unsuitable to continue participation in the study * Intolerant to paracetamol or opioid drugs