Management Of Hypnosis And Analgesia By Electro-Encephalographic Monitoring During Propofol And Fentanyl Anesthesia

Satoshi Hagihira, MD, PhD *, Masaki Takashina, MD #, Takahiko Mori, MD§, Osamu Nagata, MD, PhD ¶, Makoto Ozaki, MD, PhD ¶ and Takashi Mashimo, MD, PhD †

* Department of Anesthesiology, Osaka Prefectural Habikino Hospital, # Surgical Center Osaka University Hospital, § Department of Anesthesiology, Osaka Prefectural General Hospital, † Department of Anesthesiology, Osaka University Graduate School of Medicine, Osaka Japan; ¶ Department of Anesthesiology, Tokyo Women’s Medical University, Tokyo, Japan.

Background: Anesthesiologists usually try to keep the adequate level of anesthesia by controlling the concentration of hypnotic agents. But according to the concept of “balanced anesthesia” it would not always be adequate, because hypnotic agents can not properly prevent the surgical stimuli. In this point of view, we should rather control the analgesic agents during surgery. EEG during surgery is determined by the balance of the following three factors: effects of hypnotic agents; surgical stimuli; and effect of analgesic agents. When the effect site concentration of hypnotic agent was kept constant, the changes of EEG would reflect the changes of the balance between the effects of analgesic agents and surgical stimuli. With this concept we tried to manage the hypnosis and analgesia during surgery with EEG monitoring.

Materials and Methods: After gaining institutional approval and written informed consent from the participants, we enrolled 16 elective abdominal surgery patients (24-76 yrs, ASA-PS I-III). Each patient, 30 min before the admission to the operating room, intramuscularly received premedication with 0.5 mg of atropine. We continuously recorded the output from a single EEG lead (FP₁-A₁) using a 514X-2 EEG telemetry system (GE Marquette, Tokyo, Japan), and used our original software BSA¹⁾ to analyze the data in real time. Anesthesia was induced with propofol (initial target blood concentration was set at 3.5μg/ml) using our original software ConGrase TCI system²⁾ followed by 3 μg/kg of fentanyl. After endotracheal intubation, target concentration of propofol was adjusted by referencing EEG derived parameters including SEF90 (spectral edge frequency 90%), RBR (relative β ratio) and bicoherence before incision, and once it was determined we maintained it throughout the operation. 2-3 μg/kg of fentanyl was also added before incision. Vecuronium was given as required. We added every 1 μg/kg of fentanyl by referencing EEG parameters. After finished the operation, infusion of propofol was stopped and muscle relaxation was reversed. We recorded the interval to response to call name and extubation. On the first postoperative day, we interviewed the participants when they were aware.

Results: Adjusted target concentrations of propofol were 3.3±0.6 μg/ml (Mean±SD). Intervals to extubation were 12.4±3.6 minutes. Anesthesia time was 142±29 minutes. One case, whose respiratory rate was 7/min when he responded to call his name, required 0.08 mg of naloxone before extubation. None of the participants complained of wound pain just after extubation. None of them could recall intra-operative events. Only three of them could recall when they were transferred to the ward.

Conclusion: We could successfully manage hypnosis and analgesia in all cases without changing the target concentration of propofol, except one case of opioid overdose.

References:

1. Hagihira S, et al. Anesth Analg, 93(4), p966-70, 2001.

2. Nagata O, et al. Masui, 47(10), p1246-52, 1998.