The aim of this multi-center RCT is to investigate the effect of intravenous acetaminophen (paracetamol and mannitol injection) on postoperative delirium, comparing with intravenous sufentanil, in elderly noncardiac surgical patients admitted to ICU.

Delirium is a common complication after surgery. It is associated with increased morbidity and mortality, longer intensive care unit (ICU) and hospital stay, prolonged mechanical ventilation, higher risk of institutionalization, and higher healthcare cost. Depending on patient population and screening method, the incidence of delirium in elderly patients admitted to ICU can be as high as 58-76%. The choice of analgesics and the adequacy of pain control are among the modifiable precipitating factors for postoperative delirium (POD). Whether the use of intravenous acetaminophen decreases the occurrence of POD in elderly noncardiac surgical patients admitted to ICU remains inadequately studied.

Objectives: To investigate the effect of intravenous acetaminophen (paracetamol and mannitol injection) on postoperative delirium, comparing with intravenous sufentanil, in elderly noncardiac surgical patients admitted to ICU.

Study design: A randomized controlled trial. Setting: 34 ICUs from different regions across China. Patients: 1092 elderly patients (≥ 60 years), having noncardiac surgery and admitted to ICU after surgery, are eligible.

Intervention: Patients are randomly assigned to intravenous acetaminophen or sufentanil groups. Intravenous acetaminophen is the analgesic of choice for patients in the acetaminophen group. Intravenous sufentanil is the analgesic of choice for patients in the sufentanil group (control).

Outcomes: The primary endpoint is the incidence of delirium within the first 5 days after surgery. Delirium is assessed using the confusion assessment method for the intensive care unit (CAM-ICU). The secondary endpoints include the level of pain assessed using the Numeric Rating Scale (NRS) on postoperative day 1 to 5 and day 30, 30-day mortality, length of ICU and hospital stay, quality of life assessed on postoperative day 30, cognitive function assessed on postoperative day 30, and biomarkers and neurofunctional testing for delirium.

Predicted duration of the study: 24 months.

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