Impact of Acetaminophen on Postoperative Delirium Elderly Patients After Non-cardiac Surgery

Inclusion Criteria: 1. Scheduled to ICU after non-cardiac surgery for any reasons； 2. Report having moderate to severe acute pain as determined by a pain score ≥ 5 from the 11-point Numeric Pain Rating Scale (NPRS) scale after postsurgery； 3. Able to take oral medication or by stomach tube； 4. Provide written informed consent. Exclusion Criteria: * Patients who meet any of the following criteria will be excluded. 1. Preoperative history of schizophrenia, epilepsy, Parkinsonism, or myasthenia gravis; 2. Inability to communicate in the preoperative period because of coma, profound dementia or language barrier; 3. Brain injury or neurosurgery; 4. Severe hepatic dysfunction (eg, aspartate aminotransferase, alanine aminotransferase, or bilirubin greater than or equal to 3.0 times the upper limit of normal), active hepatic disease, evidence of clinically significant liver disease, or other condition (eg, alcoholism, cirrhosis, or hepatitis) that suggests the potential for an increased susceptibility to hepatic toxicity with study drug exposure. 5. Subject has a positive test result for drugs of abuse (amphetamines, barbiturates, benzodiazepines, cannabinoids, cocaine, methamphetamine, methadone, or methylenedioxy-methamphetamine) at Screening. 6. Subject has participated in another clinical study within 30 days prior to day-of-surgery or plans to participate in another clinical study while concurrently enrolled in this study. 7. Subject has a history of any drug allergy, hypersensitivity, or intolerance to acetaminophen or morphine or to any of the excipients in the IV or oral formulations used. 8. Subject has intra- or postoperative complications, which in the view of the investigator, makes the subject unsuitable for the participation of the study. 9. Subject has a history of any drug allergy, hypersensitivity, or intolerance to acetaminophen or opioid or to any of the excipients in the IV or oral formulations used. 10. Unable to take medications orally or by stomach tube