It is safe to say most anesthesiologists don’t monitor the effect of their anesthetic technique on the brain. Minimum alveolar concentration (MAC) is simply a population average measure of the likelihood of movement to a surgical stimulus. The value is not intended to be a surrogate of consciousness, although anesthesiologists use it as such. During total intravenous anesthesia (TIVA) (without target-controlled infusion, or TCI), shunning electroencephalography (EEG) means running an anesthetic based on vital signs, one’s clinical experience, and perception of anesthetic adequacy.

The intraoperative EEG story is one of many promises and dashed hopes. The massive uptake in EEG usage guided by the seductive simplicity of an index number met skepticism after the publication of several manuscripts (N Engl J Med 2008;358:1097-108; Anesth Analg 2003;97:488-91). These early studies represented the beginning of decades’ worth of research and trials that are still ongoing. Published studies assessing the value of limiting anesthetic dose in reducing delirium risk and POCD have been mixed (J Neurosurg Anesthesiol 2013;25:33-42; Br J Anaesth 2013;110:i98-105; Clin Ther 2015;37:2700-5; JAMA 2019;321:473-83). More recent focus targets limiting EEG suppression and optimizing alpha power with the goal of enhancing analgesia (Anesth Analg 2016;122:234-42; Front Syst Neurosci 2022;15:767489; Br J Anaesth 2019;122:635-42).

The differences in target populations, study methods, endpoints, and even delirium diagnostic criteria have led to an uninterpretable mess; disparate opinions from thought leaders have further muddied the field. With the advancement of technologies, current monitors display additional processed data, such as the color spectrogram (density spectral array, or DSA) and spectral edge frequency (“SEF”), which have been utilized in recent studies. The specialty awaits additional high-impact EEG trials in the coming years.

Neuroanesthesiologists are typically heavy users and proponents of the technology, but there has never been any inquiry about their usage patterns and perceptions of utility. The mission of the Committee on Neuroanesthesiology is to promulgate advances in neuroanesthesia care to the ASA membership. As most neuroanesthetics are carried out by generalists, timely summaries of novel techniques and management paradigms may enhance the quality and safety of routine patient care. Additionally, it is important for practitioners to be aware of controversies that surround emerging technologies and their application to the practice of neuroanesthesia.

In the hope that it might be helpful to the ASA membership, the committee commissioned a survey of its members and those of the Educational Track Subcommittee on Neuro Anesthesia, all of whom are neuroanesthesiologists, on their intraoperative usage and assessment of the utility of EEG technology. We surveyed specific details of EEG application, resources for education in EEG, and opinions on the existing evidence for and barriers to its broader use. The survey pertains to broad EEG use and is not specific to neuroanesthesiology. Herein we present the results of the survey (see Table).

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The survey was created by two committee members with input from a third. After accounting for dual membership, the committees totaled 50 members, of whom 34 (68%) participated in the survey. Mid-survey input led to the addition of two questions, which were answered by 20 late-responding participants.

The most important finding of the survey is that virtually all responding committee members use intraoperative EEG, even if infrequently (33/34 responders, or 97%). In their respective practices, colleagues use EEG almost as often (30/34, or 88% respondents’ perception). Surprisingly, only 56% of respondents utilize DSA EEG, despite its availability.

The following answers express the opinion/practice patterns of a super-majority of respondents (over 70%):

  • 79% of respondents monitor the raw EEG tracing
  • 79% use their device’s index value
  • 70% utilize EEG during carotid endarterectomy (CEA)
  • 82% of respondents use EEG during TIVA
  • 88% of respondents interpret or contribute to the interpretation of EEG by virtue of being the anesthesiologist on record, but often, in 76% of responses, there is intraoperative neuromonitoring technologist and neurologist involvement as well.
  • Many use EEG to limit anesthetic dosage: 74% to prevent delirium, 70% to facilitate hemodynamic management, and the same number to ensure rapid emergence. 76% confirm the integrity of TIVA delivery using EEG.

    What endpoints do they target?

  • 82% avoid burst suppression

    What indications do they teach their residents to use EEG for?

  • 44% for general titration and to assess depth of hypnosis, and another 44% to assess adequacy of their TIVA technique.

The respondents encounter oft-repeated arguments against intraoperative EEG monitoring. Those most commonly invoked are: lack of evidence of its utility or necessity (29%), high cost (26%), and a sense that the modality “does not work” and “cannot be relied upon” (20%).

The most commonly cited learning resources on EEG interpretation that are also recommended to trainees include:

  • EEGforAnesthesia.iars.org: 55%
  • SNACC.org: 50%
  • Icetap.org: 35%

Finally, when asked how the Committee on Neuroanesthesiology should devote its effort regarding EEG usage, there were many distinct suggestions. Grouping answers was challenging, but the committee’s general sentiment favored education and promotion. Interestingly, there was an almost universal (88% of respondents) agreement that the committee should devote effort to research.

Leaders in neuroanesthesiology are clearly comfortable using EEG intraoperatively. However, although EEG seems to have clearly defined indications (TIVA, CEA) and presumed benefits for its usage (decreased delirium incidence, decreased hypotension, faster emergence and confirmation of intravenous hypnotic delivery), this questionnaire did not reveal universal agreement on any of the topics addressed.

Interpretation of these results is difficult. The questionnaire was distributed to a very small sample size, which may not be representative of the opinions of the subspecialty. However, it is clear that these surveyed leaders are supporters of the technology, as well as of additional research. Without a question, neuroanesthesiologists will critically evaluate the results of new studies, which will guide the future utility of the technology and may impact the approach to anesthetizing our patients.