Evered LA, Chan MTV, Ha et al. (2021)
British Journal of Anaesthesia, 127(5), pp. 704–712.
Aim of Study
To determine whether light general anaesthesia (BIS target 50) was associated with a lower incidence of post operative delirium (POD) than deep general anaesthesia (BIS target 35.
Design and Location
Multicenter randomized clinical trial of 655 at-risk patients undergoing major surgery from eight centers in three countries, Australia, China (including Hong Kong Special Administrative Region), and the USA.
Methodology
Patients were enrolled from the BALANCED study and were subjected to light (BIS target 50 ) or deep anaesthesia (BIS target 35).
They were assessed for delirium for 5 days postoperatively using the 3 min confusion assessment method (3D-CAM) or CAM-ICU.
Cognitive screening using the Mini-Mental State Examination(MMSE) done at baseline and discharge and the Abbreviated Mental Test score (AMTS) at 30 days and 1 yr.
Primary Outcome
The presence of postoperative delirium on any of the first 5 postoperative days
Secondary Outcomes
Mortality at 1 yr, Cognitive decline at discharge, Cognitive impairment at 30 days and 1 yr, Unplanned ICU admission, length of stay in hospital and Time in electroencephalographic burst suppression.
Statistics
Mantel-Haenszel x2 test was used for comparison of primary and secondary outcomes between randomised groups. The pooled estimate of the odds ratio (OR) and 95% confidence interval (CI) was used to describe the statistical comparison.
Results
BIS-guided lighter anaesthesia decreased the risk of POD compared with BIS-guided deeper general anaesthesia. Targeting BIS 50 resulted in a 34% relative reduction in patients suffering an episode of POD, an absolute reduction of 9% when compared with targeting BIS 35
Patients with an episode of POD had more unplanned ICU admissions, stayed 2 days longer in hospital, had a higher incidence of myocardial infarction, were more likely to have impaired cognitive function on the MMSE at discharge and the AMTS score at 30 days and 1 yr.
Conclusions/Discussions
This study demonstrated targeting a BIS of 50 to reduce POD compared with a BIS of 35 prevented 1 in 10 cases of delirium. This is the first study to investigate POD with two specific BIS targets.
Patients randomized to light anaesthesia (BIS 50) have a lower incidence of poor cognitive screening scores at 1 yr compared with those randomized to deep anaesthesia (BIS 35).
Reduction in the risk of mortality at 1 yr in patients who did not suffer delirium.
Stated Limitations from the Study
The study design did not control for other factors that may influence POD outcomes, such as benzodiazepine exposure, anticholinergic drugs, or opioid use.
Although most baseline variables appeared well matched, a chance difference in cardiovascular disease may have confounded the relationship between depth of anaesthesia and POD, although this risk may have been balanced by a higher incidence of stroke in the BIS 50 group.
Because of time limitations, the cognitive assessments undertaken in this study were screening measures designed to identify at-risk patients who may require further investigation.
Discussion from Journal Club Meeting
There is a benefit of targeting a higher BIS during general anaesthesia in the elderly population to reduce POD as a significant number of elderly patients presents for elective and emergency surgery especially trauma.
The time in burst suppression can affect the incidence of POD (which was found to be higher in the lower BIS group in this study), therefore it would be beneficial to look into studies which compare these factors.
Summary by Dr T Dissanayake. Journal Club Meeting 25 May 2023.
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