Anaesthetic depth and delirium after major surgery: a randomised clinical trial

Br J Anaesth. 2021 Nov;127(5):704-712. doi: 10.1016/j.bja.2021.07.021. Epub 2021 Aug 28.


Background: Postoperative delirium is a serious complication of surgery associated with prolonged hospitalisation, long-term cognitive decline, and mortality. This study aimed to determine whether targeting bispectral index (BIS) readings of 50 (light anaesthesia) was associated with a lower incidence of POD than targeting BIS readings of 35 (deep anaesthesia).

Methods: This multicentre randomised clinical trial of 655 at-risk patients undergoing major surgery from eight centres in three countries assessed delirium for 5 days postoperatively using the 3 min confusion assessment method (3D-CAM) or CAM-ICU, and cognitive screening using the Mini-Mental State Examination at baseline and discharge and the Abbreviated Mental Test score (AMTS) at 30 days and 1 yr. Patients were assigned to light or deep anaesthesia. The primary outcome was the presence of postoperative delirium on any of the first 5 postoperative days. Secondary outcomes included mortality at 1 yr, cognitive decline at discharge, cognitive impairment at 30 days and 1 yr, unplanned ICU admission, length of stay, and time in electroencephalographic burst suppression.

Results: The incidence of postoperative delirium in the BIS 50 group was 19% and in the BIS 35 group was 28% (odds ratio 0.58 [95% confidence interval: 0.38-0.88]; P=0.010). At 1 yr, those in the BIS 50 group demonstrated significantly better cognitive function than those in the BIS 35 group (9% with AMTS ≤6 vs 20%; P<0.001).

Conclusions: Among patients undergoing major surgery, targeting light anaesthesia reduced the risk of postoperative delirium and cognitive impairment at 1 yr.

Clinical trial registration: ACTRN12612000632897.

Keywords: anaesthesia; bispectral index; cognitive dysfunction; delirium; electroencephalography; postoperative delirium.

Publication types

  • Multicenter Study
  • Randomized Controlled Trial

MeSH terms

  • Aged
  • Anesthesia, General / adverse effects*
  • Anesthesia, General / methods
  • Cognition
  • Cognitive Dysfunction / epidemiology*
  • Cognitive Dysfunction / etiology
  • Consciousness Monitors
  • Electroencephalography
  • Emergence Delirium / epidemiology*
  • Emergence Delirium / prevention & control
  • Female
  • Follow-Up Studies
  • Humans
  • Intensive Care Units / statistics & numerical data
  • Length of Stay
  • Male
  • Middle Aged
  • Postoperative Complications / epidemiology*
  • Postoperative Complications / prevention & control
  • Time Factors