Background: The purpose of this study was to evaluate a new, physiologically inspired method for the analysis of the electroencephalogram during propofol-remifentanil anesthesia. Based on fixed-order autoregressive moving-average modeling, this method was hypothesized to be capable of dissociating the effects that hypnotic and analgesic agents have on brain electrical activity.
Methods: Raw electroencephalographic waves from a previously published study were reanalyzed. In this study, 45 American Society of Anesthesiologists status I patients were randomly allocated to one of three groups according to a specific target effect-site remifentanil concentration (0, 2, and 4 ng/ml). All patients received stepwise-increased targeted effect-site concentrations of propofol (CePROP). At each step change in target CePROP, the Observer's Assessment of Alertness/Sedation score was evaluated. Raw electroencephalograph was continuously acquired from frontal electrodes. Electroencephalography traces were analyzed using a fixed-order autoregressive moving average model to give derived measures of Cortical State and Cortical Input. Response surfaces were visualized and modeled using Hierarchical Linear Modeling.
Results: Cortical State (a measure of cortical responsiveness) and Cortical Input (a measure of the magnitude of cortical input) were shown to respond differently to CePROP and effect-site remifentanil concentration. Cortical Input decreased significantly with increasing effect-site remifentanil concentration, whereas Cortical State remained unchanged with increasing effect-site remifentanil concentration but decreased with increasing CePROP.
Conclusion: Because Cortical State responds principally to variations in CePROP, it is a potential measure of hypnosis, whereas the dependence of Cortical Input on effect-site remifentanil concentration suggests that it may be useful as a measure of analgesic efficacy and the nociceptive-antinociceptive balance.
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Article Synopsis
- The study investigates how different processed EEG indices, specifically qCON (hypnotic level) and qNOX (nociception), interact during propofol anesthesia in patients.
- It finds strong linear relationships among qCON, qNOX, EMG activity, and burst suppression, indicating that these indices can help differentiate the hypnotic and pain-relief aspects of anesthesia.
- A key conclusion is that high qCON levels depend on EMG activity, highlighting potential challenges in detecting wakefulness without EMG, and noting that high opioid doses may affect the relationship between qCON and qNOX.
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