Authors: Dragovic SZ et al.
Anesthesia & Analgesia, 142(2):249–260, February 2026
Summary
Processed EEG indices (e.g., BIS and other frontal EEG–derived metrics) are routinely used to titrate anesthetic depth. However, many studies — and much of clinical practice — assume that equivalent processed values reflect equivalent brain states, regardless of whether the patient is receiving propofol or a volatile anesthetic. This “one-size-fits-all” assumption may oversimplify important neurophysiologic differences between agents.
In this retrospective study of 108 surgical patients, the authors compared steady-state frontal EEG under propofol versus fluranes (sevoflurane and desflurane). They analyzed conventional spectral measures and two newer analytic approaches:
• Fitting oscillations & one-over-f (separates periodic oscillations from broadband background activity)
• Variational mode decomposition (a signal processing technique that isolates intrinsic oscillatory modes)
Both advanced methods detected clear spectral differences between propofol and fluranes, even when patients were clinically titrated to similar anesthetic levels.
Key findings:
• Propofol produced higher central alpha frequency (approximately 1.5–2 Hz higher) compared with fluranes.
• The “one-over-f” exponent — reflecting background spectral slope — was lower with propofol, suggesting differences in broadband cortical activity.
• These differences were consistent across lower (8–15 Hz) and higher (15–21 Hz) spectral edge frequency ranges.
• Receiver operating characteristic (ROC) analysis showed strong discrimination between agents (AUC up to 0.88).
Importantly, conventional methods were less sensitive in differentiating the anesthetic states compared with the newer analytic techniques.
The authors conclude that propofol and flurane anesthetics produce distinct EEG spectral signatures and that advanced analytic approaches may allow development of agent-specific EEG indices rather than relying on a universal processed number.
Key Points
• Equivalent processed EEG values do not necessarily reflect equivalent brain states across anesthetic agents.
• Propofol shifts alpha frequency higher compared with sevoflurane/desflurane.
• Background broadband activity (1/f slope) differs between agents.
• Advanced signal decomposition methods better capture agent-specific neurophysiology.
• These findings raise the possibility of developing agent-specific anesthetic depth indices.
What You Should Know
For practicing anesthesiologists — especially those leading anesthesia care teams or evaluating depth monitoring standards — this paper challenges the assumption that a BIS of 45 under propofol is neurophysiologically equivalent to a BIS of 45 under sevoflurane.
From a clinical operations perspective, this has implications for:
• Research design (avoid grouping volatile and propofol data without stratification)
• Device development (future monitors may need drug-specific algorithms)
• Precision anesthesia approaches
• Interpretation of intraoperative EEG in cognitively vulnerable patients
As your practice continues to emphasize evidence-based monitoring and potential neurologic protection strategies, agent-specific EEG interpretation may become increasingly relevant.
Thank you to Anesthesia & Analgesia for allowing us to summarize and share this important article.