Seen and Ignored: Are We Undermining Studies of Brain Health Interventions Before We Start?

Abstract

See Article, p e52 Intraoperative electroencephalography (EEG) provides a direct measurement of the effects of anesthetics and sedatives on the brain, and the development of processed EEG monitors has promised the practicing anesthesiologist a more simplified interpretation in the perioperative setting, where attentional resources are divided among competing needs. Particularly in light of the ongoing concerns for anesthetic contributions to perioperative neurocognitive disorders (PNDs), EEG measures are increasingly posited to provide value, not just as a tool to monitor the risk of anesthetic awareness with recall, but as a warning signal about patients with brains vulnerable to PND. Several studies have examined whether anesthetic titration in response to processed EEG monitoring could improve patient outcomes.1 While there are clearly challenges in the use of current processed EEG monitors, the recommendations for best practices for postoperative brain health2 suggest that “there is strong support for the general principle of EEG-based anesthetic titration to reduce PND rates in older adults.” In this edition, Gross et al3 offer us a glimpse into the real-world behavior of clinicians currently incorporating processed EEG in their anesthetic management. Specific intraoperative patterns of EEG, most significantly burst suppression, are associated with poor outcomes.4,5 While burst suppression does not seem to predict poor cognitive recovery in healthy volunteers,6 in surgical populations, using EEG monitors to titrate anesthetic delivery to avoid specific EEG patterns might be beneficial.1 The recent Electroencephalography Guidance of Anesthesia to Alleviate Geriatric Syndromes (ENGAGES) trial did not support the use of EEG-guided anesthetic administration for the prevention of postoperative delirium, but did find a lower 30-day mortality on patients with EEG-guided anesthetic.7 Despite multiple studies that have clearly demonstrated the potential benefit of using EEG during anesthesia care, the failure of intraoperative EEG use to reduce the incidence of postoperative delirium in ENGAGES risks the elision of previous studies altogether rather than prompting a more rigorous and nuanced debate over the practical implications of each. Thankfully, some discussion of the nuances of processed EEG measures, aging, and the vulnerable brain is developing in the literature.8,9 And yet there may be important behavioral issues beyond the limitations of the monitors themselves; for example, a recent retrospective analysis indicated that the use of bispectral index (BIS) was associated with worse outcomes, without ever articulating how the BIS values were managed.10 As with all monitors, clinical judgment is crucial to interpreting EEG physiologic data within the context of an anesthetic; any changes in outcomes from using a monitor will depend on clinician response to monitors. For there to be a change in outcome, the clinicians must incorporate information from all available monitors to optimize care for the individual patient. Patient assessment should include evaluation and correlation of EEG data with hemodynamic and other monitoring data, within the greater clinical context. That is, EEG information is additive to the patient assessment, providing clinicians with valuable signals for their practice, observation, and care. Gross et al3 performed a retrospective analysis of 138 patients undergoing a target-controlled infusion of propofol and remifentanil for robotic surgery at the Foch University Hospital in Suresnes, France, between July and December of 2017, and looked into the frequency of BIS values outside the manufacturer-recommended range during the intraoperative period. They found that, despite using the BIS monitors to guide the anesthetic, over 35% of patients had values under 40, indicating excessive anesthetic delivery. Also, burst suppression was still present in 17.8% of patients. As expected, this was more frequent in