Anesthesia Maintenance With Target-controlled Infusion of Propofol and Remifentanil at Fixed Ratio

Early postoperative neurocognitive complications are associated with worse perioperative and long-term outcomes, substantially affecting patients' prognosis and recovery and imposing a significant healthcare and economic burden. Bispectral index (BIS) is an objective and quantitative monitoring parameter used to assess patients' depth of anesthesia. Maintenance of general anesthesia under the guidance of BIS monitoring has been shown to reduce the incidence of early postoperative neurocognitive complications following inhalational anesthesia or combined intravenous-inhalational anesthesia.

However, the impact of different depths of anesthesia maintenance on early postoperative neurocognitive complications after total intravenous anesthesia (TIVA) remains controversial. In some studies investigating TIVA, anesthesiologists mainly achieve the target BIS by adjusting the dosage of propofol, whereas the dosage of opioids remains comparable between different anesthetic depth groups. Based on previous studies, the investigators supposed that target-controlled infusion of propofol to remifentanil at a fixed ratio might ensure adequate intraoperative sedation and analgesia and reduce postoperative neurocognitive complications.

This study is aimed to investigate the impact of different anesthesia depths by target-controlled infusion of propofol and remifentanil at a fixed effect-site concentration ratio on the incidence of early postoperative neurocognitive complications in older patients undergoing noncardiac surgery.

Inclusion criteria

• Aged ≥ 65 years.
• Scheduled to undergo noncardiac surgery expected to last ≥ 1 hour under general anesthesia.
• Require patient-controlled intravenous analgesia after surgery.
• Provide written informed consent.

Exclusion criteria

• Inability to communicate in the preoperative period because of coma, profound dementia, language barrier, or other reasons.
• Previous history of schizophrenia, epilepsy, Parkinson's disease, or myasthenia gravis.
• Traumatic brain injury or neurosurgery.
• Severe hepatic dysfunction (Child-Pugh class C), severe renal dysfunction (eGFR <30 ml/min/1.73 m2), or critical illness (preoperative American Society of Anesthesiologists physical status classification ≥IV).
• Planned ICU admission with endotracheal intubation after surgery.
• Enrolled in the other studies.
• Other reasons that are considered unsuitable for study participation by the responsible surgeons or investigators.