Anesthesia Dose and Delirium—A Picture Coming Into Focus

Abstract

In this issue of JAMA, 1 Deschamps and colleagues report results of the Electroencephalographic Guidance of Anesthesia to Alleviate Geriatric Syndromes-Canada (ENGAGES-Canada) trial. ENGAGES-Canada compared rates of postoperative delirium among 1140 patients 60 years or older undergoing cardiac surgery who were randomly assigned to 1 of 2 strategies to prevent excessive dosing of inhaled general anesthetics: electroencephalogram (EEG)-guided dosing vs usual care, in which anesthesia dose was guided by expired anesthesia gas levels and hemodynamic measurements. Although some previous studies have found an association between deep general anesthesia and postoperative delirium, 2,3 it remains unknown whether using EEG guidance to minimize time with intraoperative EEG suppression-a marker of deep anesthesia-might reduce delirium compared with usual care.Conducted at 4 Canadian hospitals, ENGAGES-Canada achieved an 18% reduction in median inhaled anesthesia dose with an EEG-guided strategy, accompanied by a reduction of total time with EEG suppression from 12 to 4 minutes. However, the study found no difference in delirium incidence by group, with 18% of patients in each group experiencing this outcome; other outcomes-including awareness under anesthesia, length of hospital stay, ICU utilization, and mortalityalso did not differ by group.These findings add detail to a growing literature investigating the relationship between general anesthesia dose and postoperative delirium. The results of ENGAGES-CANADA mirror those of the earlier ENGAGES trial. 4 This prior study enrolled patients undergoing both cardiac and noncardiac surgical procedures and found that an EEG-guided strategy led to an approximately 14% reduction in anesthesia dose and a reduction in EEG suppression from 13 to 7 minutes, but no change in delirium incidence compared with usual care.In contrast, a substudy of the international Anesthetic Depth and Complications After Surgery (BALANCED) 2 trial compared 2 EEG-guided anesthesia dosing strategies among 655 older adults undergoing primarily noncardiac surgical procedures. Patients were assigned to receive either deep vs light general anesthesia, based on 2 different target values of the bispectral index, a numerical EEG parameter that can be used to guide anesthesia dosing. BALANCED successfully reduced the median anesthesia dose by 25% between the 2 study groups, along with a reduction in EEG suppression time from 5 minutes to 2 minutes. Yet, unlike in ENGAGES-Canada, these changes in the BALANCED trial were associated with a decrease in postoperative delirium, from 28% to 19% among patients assigned to deeper vs lighter anesthesia. Similarly, 2 randomized trials pub-