While historically anesthesiologists rely on pharmacokinetics to track the loss of consciousness, new research in anesthesiology has identified the salient features of the electroencephalogram (EEG) that correlate to states of sedation and unconsciousness induced by different anesthetic drugs. While the EEG features of many sedative-hypnotic anesthetics have been well- characterized, the opioid analgesic drugs have not been analyzed in detail in this way. A characterization of the EEG signatures of opioid analgesic drugs could be useful in monitoring and titrating the effects of these drugs.

Fentanyl is one of the most commonly used opioid analgesic drugs. Prior to induction of general anesthesia, fentanyl is frequently administered to blunt the nociceptive response to intubation. A typical scenario is to administer 2 to 4 mcg/kg of fentanyl first, followed by a sedative hypnotic drug such as propofol to induce general anesthesia. In this study, we propose to administer a total of 4 mcg/kg of fentanyl, administered in 2 boluses, before administering a sedative hypnotic drug. At this dose, fentanyl will serve to blunt nociception during intubation, but will also contribute to intraoperative pain management. During this time, we will record the EEG using standard EEG-based anesthetic monitors that are routinely used in the operating room. We will assess the patient's level of responsiveness using an auditory task and ulnar nerve stimulation. These measurements will allow us to identify the EEG signatures of fentanyl for future use in EEG-based anesthetic monitoring. During this study we will measure EEG and responses to auditory and ulnar nerve stimuli during induction of general anesthesia in surgical patients. The anesthetic will be administered according to a typical sequence in which fentanyl is first administered, followed by a sedative hypnotic drug for induction of general anesthesia. The primary difference is that, in this study, we will record the EEG and response data for a short period of time after initial administration of fentanyl and prior to administration of a sedative hypnotic drug to induce general anesthesia.

Inclusion Criteria:

-Undergoing surgery anticipated to take 2 hours or longer

Exclusion Criteria:

• Craniofacial abnormalities
• Allergies to fentanyl, bisulfite, eggs or egg products, latex, soybeans, soybean oil BMI ≤ 30 (kg/m2)
• Known or suspected difficult intubation
• Known or suspected need for rapid sequence induction and intubation
• History of obstructive sleep apnea requiring CPAP
• History of uncontrolled gastroesophageal reflux disease (GERD)
• Opiate use within 24 hours
• History of opiate abuse within 3 years

Only those patients capable of giving their own consent will be considered for this study. All study subjects will be American Society of Anesthesiologists (ASA) physical status classification P1 to P3. That is, all study subjects will have at most mild to moderate systemic disease.

31 subjects were enrolled. 25 subjects finished the protocol.

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Adverse events are "any untoward or unfavorable medical occurrence including any abnormal sign, symptom or disease,...whether or not associated with the subject's participation in the research". Internal adverse events that are unexpected and related/possibly related to the research and external adverse events that are serious, unexpected and related/possibly related must be reported to the IRB within 5 working days/7 calendar days of the date the investigator first become aware of them.

We report these findings from a moderate-sized sample of subjects undergoing a structured protocol prior to general anesthesia. The sample size however is comparable and exceeds previous studies of fentanyl EEG effects. The EEG is commonly regarded as being noisy and prone to artifact, but in this clinical setting and with appropriate analyses methods we observed clear EEG signatures that correlated with predicted fentanyl effect site concentrations and with physiological and behavioral changes.