Anesthetic Challenges for Intraoperative Neurophysiological Monitoring under General Anesthesia

Keywords

electrocorticography - evoked potentials - general anesthesia - depth of anesthesia

Introduction: Intraoperative-neurophysiological monitoring (IONM) is important to delineate the epileptogenic lesions from the eloquent cortex. Many anesthetic agents have significant interference in monitoring of electrocorti-cography (ECoG), somatosensory evoked potentials (SSEPs), and motor evoked potentials (MEPs). Complete relaxation with moderate depth is needed for ECoG, while muscle relaxation will not elicit MEP. Hence, a narrow balance is required to conduct recording of ECoG, SSEP, and MEP simultaneously. Here, we present successful management of two such cases under general anesthesia where judicious use of anesthetic agents provided least interference to IONM.

Methodology/Description: A 7-year-old child presented with premotor cortical dysplasia posted for right frontotemporal craniotomy. Aim was to develop anesthetic technique to elicit adequate ECoG and MEP/SSEP waveforms. The patient was maintained on desflurane (MAC 0.4–0.5) with oxygen-nitrous oxide (N₂O), dexmedetomidine (0.05–0.07 µg/kg/min), and intermittent fentanyl at 1 µg/kg. Depth of anesthesia was lightened for ECoG recording by shutting off N₂O 10 minutes prior and intermittent succinylcholine was given to avoid motor movement. This provided short duration relaxation and did not interfere with ongoing MEP and SSEP recordings. Similar case was performed in a 28–year-old young adult where depth of anesthesia was maintained with propofol infusion (50–75 µg/kg/min) and dexmedetomidine and fentanyl boluses. Total intravenous anesthesia was sufficient to provide adequate plane for ECoG, MEP, and SSEP recordings continuously. No form of muscle relaxation was used in this case. Depth of anesthesia was monitored by bispectral index (BIS) and supplemented with scalp block in both cases.

Conclusion: Hence, IONM can be used conducted under general anesthesia successfully.

• References

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• 2 Bithal PK. Anaesthetic considerations for evoked potentials monitoring.. J Neuroanaesth Crit Care 2014; 1: 2-12