Author: Flora Liu, MD
The Daily Dose
Electroencephalography allows anesthesiologists to monitor the brain directly during anesthesia. However, commercially available monitors often reduce complex EEG activity to a single processed index. Relying exclusively on that number can conceal important information contained in raw EEG waveforms, density spectral arrays, and spectral edge frequency.
At the 2026 IARS and SOCCA Annual Meeting, experts discussed how EEG patterns vary dramatically among neonates, infants, adults, older patients, and critically ill patients. Understanding these age-specific differences may allow anesthesiologists to personalize drug dosing and reduce excessive anesthetic exposure.
EEG changes across the lifespan
Matthias Kreuzer, PhD, explained that EEG reflects functional brain age rather than chronological age alone. Functional age is influenced by brain structure, neural connectivity, neurochemistry, cognition, and the effects of anesthetic medications.
EEG patterns change rapidly during the first two years of life. Infants younger than six months generally lack the prominent alpha oscillations commonly observed in anesthetized adults. In infants younger than three months, EEG activity is dominated by slow delta oscillations, and commonly used measurements such as the burst suppression ratio may be unreliable.
Aging produces a different set of changes. Older patients generally have lower EEG amplitudes and higher baseline frequencies, which can result in higher processed EEG index values despite an adequate depth of anesthesia.
Because many commercial algorithms do not adequately account for these age-related differences, a single target number cannot be applied safely to every patient. EEG-guided anesthetic titration that avoids burst suppression may reduce emergence delirium in children and postoperative delirium in older adults.
EEG monitoring in older and critically ill patients
Carolina Frederico, MD, EDAIC, emphasized that older and critically ill patients are especially vulnerable to anesthetic overdose. Baseline processed EEG values tend to increase with age, creating a risk that clinicians will administer additional anesthetic while attempting to reach a predetermined numerical target.
Age-related reductions in alpha power may reflect weakened communication between the thalamus and cerebral cortex. These changes make the older brain more susceptible to burst suppression during general anesthesia.
Intraoperative burst suppression has been identified as an important independent risk factor for postoperative delirium. Gentle, carefully titrated induction may help reduce this risk.
EEG may also reveal signs of inadequate analgesia or surgical stimulation. Potential nociceptive patterns include beta arousal, loss of alpha activity, and paradoxical delta arousal.
Dr. Frederico recommended reviewing EEG information in the following order: examine the raw waveform first, review the density spectral array next, and consider the processed index last.
EEG in neonates and infants
Mauricio Ibacache, MD, PhD, reviewed the unique EEG patterns of neonates and infants. Young patients are particularly sensitive to anesthetic drugs, increasing the risk of hemodynamic instability and potentially excessive anesthetic exposure.
In neonates, immature corticothalamic and thalamocortical pathways produce predominantly slow-delta EEG activity. Between approximately three and nine months of age, these pathways remain incompletely developed, producing weak and poorly organized alpha activity.
By about nine months of age, maturation of the corpus callosum and other neural pathways allows more adult-like alpha activity to appear. Classic adult alpha-delta anesthesia patterns generally do not become established until after the first year of life.
EEG discontinuity is common in premature infants but is considered pathologic in full-term neonates. It is also frequently observed during anesthesia in infants and may indicate excessive anesthetic exposure, although its complete clinical significance remains uncertain.
Using spectral edge frequency in infants
Combining the density spectral array with spectral edge frequency may help guide anesthetic administration in infants younger than six months.
For infants between three and six months:
• A spectral edge frequency below 10 Hz may suggest deep anesthesia.
• A value between 10 and 15 Hz may indicate an appropriate anesthetic level.
• A value above 15 Hz may suggest light anesthesia or emergence.
In neonates younger than one month, isoelectric periods seen on the density spectral array may indicate excessive anesthetic exposure. Spectral edge frequency alone does not reliably correlate with anesthetic concentration in this age group.
Clinical significance
EEG patterns associated with adequate anesthesia differ significantly across the lifespan. A processed index that appears appropriate for a healthy adult may be misleading in an infant, an older patient, or a critically ill patient.
Anesthesiologists should avoid treating processed EEG indices as universal measurements of anesthetic depth. Raw EEG waveforms, density spectral arrays, spectral edge frequency, the patient’s age, neurologic condition, medication exposure, and clinical response should all be considered together.
Age-specific EEG interpretation may help clinicians personalize anesthetic dosing, avoid burst suppression, reduce unnecessary drug exposure, and potentially lower the risk of emergence delirium and postoperative delirium.
Thank you to The Daily Dose and IARS for allowing us to summarize this important discussion of EEG-guided anesthesia across the lifespan.