Interruption of bispectral index monitoring by nerve integrity monitoring during tympanoplasty -A case report-
A 45 year-old male patient came to the hospital to receive tympanoplasty for chronic otitis media. There were no past history or family history before the surgery. The patient was 66.6 kg and 164 cm tall, and all physical and general examination results were normal other than the ventricular bradycardia of 58 beats per minute in the ECG. Glycopyrrate (0.2 mg) was IM injected as a pre-anesthetic medication, while vital signs before anesthesia were normal other than the ventricular bradycardia of 45 beats per minute.\nIntravenous anesthesia was planned, rather than anesthesia using a volatile agent, in order to perform nerve integrity monitoring during surgery. Before inducing anesthesia, the BIS sensor was attached while the patient was conscious, and the BIS values registered 95. Medication was started with Fresofol® MCT 2% (Fresenius Kabi, Bad Homburg, German), with a target site concentration of 6 µg/ml and Remifentanil target site concentration of 4 ng/ml using Orchestra base primea (Fresenius Kabi, Bad Homburg, German). After confirming loss of consciousness, rocuronium (50 mg) was IV injected and manual ventilation was maintained with oxygen at 6 L/min. After confirming that there was sufficient muscle relaxation and with BIS values decreased to 44, oral intubation was performed with an endotracheal tube, with a diameter of 7.5 mm (Safety-Flex™, Mallinckrodt), using a curved laryngoscope. Ventilation was maintained with O2 of 1.5 L/min and air of 2 L/min, and with a target site concentration of 3.5 µg/ml and Remifentanil target site concentration of 3.0 ng/ml being continuously IV injected, the BIS values were maintained between 41 to 60.\nSubsequently, the NIM-2 was attached, and when electricity was applied to measure the resistance in the facial nerve monitoring mode, a severe artifact in the EEG was observed intermittently for 15 seconds on the BIS monitor. A message then appeared on the BIS monitor indicating that the data unavailable due to poor signal quality, so further BIS monitoring was impossible (). Hence, when NIM-2 monitoring was discontinued, the EEG was monitored normally again and it was observed that the BIS monitor was able to read the values.\nIt was impossible to monitor NIM-2 and BIS simultaneously, but the BIS values had been stable during continuous IV injection of the medication before starting NIM-2 monitoring, while the surgery itself was a stable surgery, so it was decided not to observe BIS values during NIM-2 monitoring, and instead, a continuous IV injection speed with target site concentration of Fresofol at 3.5 µg/ml and Remifentanil at 3.0 ng/ml was maintained. The surgery continued without BIS monitoring, but when NIM-2 monitoring was suspended, before the suturing of the operated area at the completion of tympanoplasty, EEG waves were detected on the BIS monitor again. After completing the suture and dressing of the operated area, all administered anesthetics were suspended. When spontaneous respiration was observed, following the increase in BIS values, pyridostigmine (10 mg) and glycopyrrolate (0.4 mg) were administered in order to reverse muscle relaxation. When spontaneous respiration was sufficiently recovered, BIS monitor showed a value of 91 and the patient was able to open his eyes and obey oral commands. At this point, extubation was performed and the patient was moved to the recovery room. The total surgery time was 3 hours, with the anesthesia time at 3 hours and 45 minutes.\nThe patient was moved to the ward from the recovery room with no special problems, and was discharged after undergoing a recovery period of 5 days in the hospital ward.