Beyond EEG Indices: What Is Really Happening in the Brain Across the Lifespan?

Flora Liu, MD

Electroencephalography (EEG) allows anesthesiologists to directly monitor the brain—the true target organ of anesthesia. While commercially available EEG monitors rely on proprietary indices to estimate anesthetic depth, valuable physiologic information can be overlooked when anesthesiologists fail to incorporate further information such as the raw waveforms, density spectral arrays (DSA), and spectral edge frequency (SEF). Moderated by Gerhard Schneider, MD, professor and director of the Department of Anesthesiology and Intensive Care at the Technical University of Munich in Germany, this session, “EEG‑Based Anesthesia Monitoring Across the Lifespan: From the Very Young to the Old and Sick,” held on Friday, May 1, for the 2026 Annual Meeting, presented by IARS and SOCCA, explored how EEG patterns change across the lifespan, from neonates to elderly and critically ill patients, and how understanding these differences can help personalize anesthetic care.

Matthias Kreuzer, PhD, who leads the Neuromonitoring Laboratory at the Klinikum rechts der Isar, Technical University of Munich in Germany, opened the session with “Analyzing the EEG Across the Age Span: What Is the Same, What Is Different?” Dr. Kreuzer emphasized that EEG reflects a patient’s functional age, encompassing brain structure, network connectivity, and neurochemistry, and anesthetic interactions. Chronologic age does not correlate with cognitive or functional brain age.

During early neurodevelopment, EEG characteristics evolve rapidly. In the first two years of life, marked changes occur, with alpha oscillations, commonly seen in adults, are absent in infants younger than six months. In infants younger than three months, EEG activity is dominated by slow delta oscillations, and commonly used markers such as burst suppression ratio may be unreliable. At the other end of the spectrum, aging is associated with decreased EEG amplitude and higher baseline frequencies, which can translate into higher processed EEG indices. Because commercial EEG algorithms do not account for these age‑related changes, a “one‑size‑fits‑all” approach to brain monitoring is inadequate. Evidence suggests that EEG‑guided titration to avoid burst suppression may reduce emergence delirium in pediatric patients and postoperative delirium in older adults.

Carolina Frederico, MD, EDAIC, an anesthesiologist at Hospital Quirón Barcelona with expertise in total intravenous anesthesia, neuroanesthesia, and intraoperative EEG monitoring, followed with “EEG Monitoring in the Elderly and the Critically Ill: Challenges and Opportunities.” As the population ages and surgical complexity increases, Dr. Frederico highlighted the need for anesthetic titration in patients who are both vulnerable and physiologically heterogeneous. Baseline EEG indices tend to increase with age, making it dangerous to “chase the number” without contextual interpretation, as this may lead to anesthetic overdose.

Age‑related decreases in alpha power reflect thalamocortical disconnection and cortical hyperexcitability, rendering the elderly brain more susceptible to burst suppression under general anesthesia. Importantly, intraoperative burst suppression has been identified as a major independent risk factor for postoperative delirium. Dr. Frederico advocated for gentle inductions to minimize this risk of burse suppression. She also demonstrated how EEG can reveal nociceptive signatures intraoperatively, including beta arousal, alpha dropout, and paradoxical delta arousal, reinforcing the importance of examining raw waveforms and DSA before relying on processed indices. Dr. Frederico emphasized the importance of looking at the waveform first, then the DSA, and leaving the indices last.

The final presentation, “Interpreting EEG in Neonates and Infants: A Different Brain, A Different Signal,” was delivered by Mauricio Ibacache, MD, PhD, associate professor at the Pontifical Catholic University of Chile. Dr. Ibacache emphasized that infants exhibit heightened sensitivity to anesthetics, raising concerns for both hemodynamic instability and potential neurotoxicity. In neonates, limited development of corticothalamic and thalamocortical tracts results in predominant coherent slow‑delta activity. Between three and nine months of age, these pathways are only weakly established, producing a poorly coherent alpha activity, while by approximately nine months, corpus callosum maturation allows for adult‑like alpha activity. EEG discontinuity is common in premature infants, always pathologic in full‑term neonates, and frequently observed during infant anesthesia.

Although the full clinical significance remains uncertain, such patterns may indicate excessive anesthetic exposure. In practice, combining DSA with SEF can guide anesthetic dosing in infants younger than six months. In infants aged three to six months, slow and delta activity dominate; an SEF less than 10 Hz suggests deep anesthesia, 10–15 Hz indicates adequate anesthesia, and values greater than 15 Hz may reflect light anesthesia or emergence. In neonates younger than one month, isoelectric periods on DSA may suggest excessive anesthesia, while SEF does not reliably track anesthetic concentration.

Across the lifespan, EEG signatures of adequate anesthesia vary significantly, with classic alpha–delta patterns emerging only after the first year of life. Understanding age‑specific EEG patterns and their modulation by anesthetics enables more individualized monitoring and drug titration.