EEG-Guided Anesthesia: No Effect on Post-Op Delirium Risk

Nicola M. Parry, DVM

February 05, 2019

Among older adult patients, electroencephalography (EEG)-guided anesthesia during surgery did not reduce the risk for postoperative delirium, shows a study published online February 5 in JAMA.

However, 30-day mortality, a secondary trial endpoint, was lower in patients who underwent EEG-guided anesthesia.

"Older adults often become delirious after major surgery," write Troy S. Wildes, MD, Washington University School of Medicine, St Louis, Missouri, and colleagues.

"A mechanism for delirium reduction might be the avoidance of burst suppression, an electroencephalographic pattern suggesting excessively deep anesthesia," they add.

With this in mind, the researchers conducted the single-center, randomized Electroencephalography Guidance of Anesthesia to Alleviate Geriatric Syndromes (ENGAGES) trial. They aimed to determine whether reducing anesthetic administration and minimizing electroencephalogram suppression during surgery decreased the incidence of postoperative delirium.

They randomly assigned 1232 adults (aged 60 years and older) who were undergoing major surgery to receive EEG-guided anesthesia or usual anesthesia care.

Overall, 157 of 604 patients (26.0%) in the EEG-guided group still experienced delirium in the first 5 days after surgery, compared with 140 of 609 (23.0%) in the usual care group. The difference was not statistically significant (difference, 3.0%; 95% CI, −2.0% to 8.0%; P = .22).

However, the delivered dose of anesthetic agent was significantly lower in the EEG-guided group than in the usual care group (0.69 vs 0.80 minimum alveolar concentration; difference, −0.11; 95% CI, −0.13 to −0.10).

In addition, 30-day mortality was significantly lower in the EEG-guided group (4 of 614 patients; 0.7%) versus the usual care group (19 of 618 patients; 3.1%) (difference, −2.42%; 95% CI, −4.3% to −0.8%; P = .004).

Although recent meta-analyses have reported that EEG-guided anesthesia reduces postoperative delirium incidence by up to one half, Wildes and colleagues conclude that findings from the ENGAGES trial do not support use of this technique for preventing postoperative delirium among older adults undergoing major surgery.

"On the other hand, the lower 30-day mortality in the guided group warrants further investigation," they say.

In an accompanying editorial, Thomas E.F. Abbott, PhD, MRCP, and Rupert M. Pearse, MD, FRCA, both from Queen Mary University, London, United Kingdom, note that evidence supporting use of EEG-guided anesthesia remains controversial.

"Even though the trial did not demonstrate an effect on delirium, the lower 30-day mortality rate observed among the EEG-guided group is intriguing and appears consistent with the findings of the secondary analysis of a 2010 randomized trial," they write.

This difference in mortality may be a chance finding, they explain. Alternatively, it could be linked to a greater risk of cardiovascular instability in patients in the usual care group as a result of higher anesthetic doses.

According to the editorialists, even though both groups in ENGAGES experienced similar durations of intraoperative hypotension, patients in the usual care group received more phenylephrine (1.37 mg vs 2.02 mg; difference, −0.63 mg; 95% CI, −1.22 to −0.03). This suggests that anesthesiologists had to manage more episodes of arterial hypotension in these patients.

"There is robust evidence to suggest that more episodes of hypotension would lead to an increased incidence of perioperative myocardial injury that might explain the higher mortality rate," Abbott and Pearse write.

The implications of the ENGAGES trial could be wide-ranging, they say, especially if other ongoing studies corroborate its findings.

Replication of these results would fail to support use of EEG-guided anesthesia for preventing unintentional awareness under anesthesia and maybe for preventing postoperative delirium. However, in contrast, the editorialists emphasize that reducing hypotension-related myocardial injury could save many lives.

"The choice of anesthetic dose remains critically important in the context of an aging surgical patient population, and the role of good-quality, safe anesthesia is as important as ever," Abbott and Pearse conclude.

The study was funded by grants from the National Institutes of Health and Dr Seymour and Rose T. Brown Endowed Chair at Washington University. Several authors have reported receiving personal fees from Takeda, Aptinyx, Alkermes, Barnes Jewish Foundation, Taylor Family Institute for Innovative Psychiatric Research, Lundbeck, and McKnight Brain Research Foundation. Several authors have also reported receiving nonfinancial support from Alkermes and Janssen outside the submitted work. One editorialist has reported holding research grants and having given lectures and/or performed consultancy work for GlaxoSmithKline, B. Braun, Intersurgical, and Edwards Lifesciences.

JAMA. Published online February 5, 2019. Abstract, Editorial

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