For most of you, end-tidal anesthetic gas monitoring is a given, just like pulse oximetry and capnography. Indeed in 2023, it would be hard to even comprehend how to provide anesthesia without it. However, when anesthetic end-tidal gas analysis first became widely commercially available in the late 1980s, many practitioners wondered why it was necessary and wondered if it would diminish clinical acumen. As regular readers of the PAAD know, I think routine EEG monitoring intraoperatively will become indispensable and like pulse oximetry and capnography become equally ubiquitous in all ORs in the near future. Admittedly, I am no expert in this and when I read today’s article I knew I needed expert guidance to help me and our readers understand the article and its implications, so I asked Dr. Jerry Chao the lead author of the paper and frequent PAAD contributor to assist. Myron Yaster MD
Original article
Chao JY, Gutiérrez R, Legatt AD, Yozawitz EG, Lo Y, Adams DC, Delphin ES, Shinnar S, Purdon PL. Decreased Electroencephalographic Alpha Power During Anesthesia Induction Is Associated With EEG Discontinuity in Human Infants. Anesth Analg. 2022 Dec 1;135(6):1207-1216. PMID: 35041633
Electroencephalogram (EEG) voltage suppression or discontinuity can occur at high concentrations of anesthetic drugs reflecting a pattern of suppression or transient attenuation of electrocortical activity. This EEG pattern occurs frequently during general anesthesia in adults as well as in children and is defined by the presence of EEG amplitudes <25 microvolts that persist for >2 seconds.1, 2 Electroencephalogram (EEG) discontinuity reflects a state of low voltage electrical activity in the brain, which can occur at high concentrations of anesthetic drugs and as we’ve discussed in previous PAADs may be an indicator of unnecessarily deep anesthesia. While EEG discontinuities can be present in normal preterm infants during sleep-wake cycling, a pattern-labeled tracé alternant,3 in full-term infants suppression to <15 microvolts for >2 seconds (tracé discontinu), is nonphysiologic and abnormal.1, 3 A recent study found that increased duration of isoelectric events on the EEG, a more extreme degree of suppression to <2 microvolts, is associated with worse long-term neurologic outcomes in neonates undergoing cardiac surgery,4 but the clinical significance of EEG discontinuities during pediatric anesthesia for noncardiac surgery is not yet known.1
In today’s PAAD, Dr. Jerry Chao and colleagues examined EEG discontinuity during anesthesia induction in a cohort of infants, and the factors associated with its development.1 Building on prior work,2, 5 Dr. Chao and colleagues hypothesized that EEG discontinuity might be associated with younger age, increased dosing of anesthesia, and biomarkers of brain development on the EEG.
One important EEG biomarker is alpha power, which reflects the amount of energy in the 8-12 Hz frequency bandwidth that can be calculated using quantitative methods (i.e., power spectral analysis). Alpha power has been shown to first appear at around 6 months of age and is thought to reflect formation and connectivity of circuits between prefrontal cortical and thalamic areas of the brain.6, 7
The study investigators found that EEG discontinuity was common and observed in 37% of infant subjects during the period of anesthesia induction and was associated with alpha power and propofol dosing. This suggests that neurophysiologic markers like alpha power may be useful in anesthetic titration and identifying patients who may have a greater chance of developing discontinuity.
The study findings suggest that the degree of alpha power (or brain connectivity) seems to be protective against the development of low voltage EEG during anesthesia induction, even after taking into account chronological age and propofol administration. An important limitation of this study is that it was done in a relatively small sample size. In addition, the clinical meaning of low voltage EEG during routine clinical conduct of anesthesia during noncardiac surgery is not known.
In conclusion, neurophysiological biomarkers could be useful in identifying patients who may have a greater chance of developing low voltage EEG, and future research will further assess this and other questions.
Finally, please let us know if you are using EEG in your daily anesthetic practice and how it has changed your practice. Send your response to Myron who will post in a future reader response.
References
1. Chao JY, Gutiérrez R, Legatt AD, et al. Decreased Electroencephalographic Alpha Power During Anesthesia Induction Is Associated With EEG Discontinuity in Human Infants. Anesthesia and analgesia. Dec 1 2022;135(6):1207-1216. doi:10.1213/ane.0000000000005864
2. Yuan I, Xu T, Kurth CD. Using Electroencephalography (EEG) to Guide Propofol and Sevoflurane Dosing in Pediatric Anesthesia. Anesthesiology clinics. Sep 2020;38(3):709-725. doi:10.1016/j.anclin.2020.06.007
3. Tsuchida TN, Wusthoff CJ, Shellhaas RA, et al. American clinical neurophysiology society standardized EEG terminology and categorization for the description of continuous EEG monitoring in neonates: report of the American Clinical Neurophysiology Society critical care monitoring committee. J Clin Neurophysiol. Apr 2013;30(2):161-73. doi:10.1097/WNP.0b013e3182872b24
4. Seltzer L, Swartz MF, Kwon J, et al. Neurodevelopmental outcomes after neonatal cardiac surgery: Role of cortical isoelectric activity. The Journal of thoracic and cardiovascular surgery. Apr 2016;151(4):1137-42. doi:10.1016/j.jtcvs.2015.10.065
5. Cornelissen L, Bergin AM, Lobo K, Donado C, Soul JS, Berde CB. Electroencephalographic discontinuity during sevoflurane anesthesia in infants and children. Paediatric anaesthesia. Mar 2017;27(3):251-262. doi:10.1111/pan.13061
6. Flores FJ, Hartnack KE, Fath AB, et al. Thalamocortical synchronization during induction and emergence from propofol-induced unconsciousness. Proc Natl Acad Sci U S A. Aug 8 2017;114(32):E6660-e6668. doi:10.1073/pnas.1700148114
7. Akeju O, Pavone KJ, Thum JA, et al. Age-dependency of sevoflurane-induced electroencephalogram dynamics in children. British journal of anaesthesia. Jul 2015;115 Suppl 1(Suppl 1):i66-i76. doi:10.1093/bja/aev114