Identifying CN IX and X using endotracheal tube electrodes
Reviewed by Gauri Mankekar

This clinical study describes the possible usefulness of endotracheal tube electrodes in monitoring vocal cord function during cerebellopontine angle surgery in 20 patients. Lower cranial nerves, especially IX and X are at risk of injury during skull base surgery although the risk is low in vestibular schwannoma and trigeminal neuralgia surgery. For the study, the authors used intravenous non-depolarising cisatracurium to enable endotracheal intubation following total intravenous anaesthesia with propofol and remifentanil. Subsequently, no other neuromuscular blocking agent or volatile anaesthetic was administered. Modified endotracheal tubes with four electrodes placed above the cuff were used for endotracheal intubation. Needle electrodes were also placed in the masseter muscle, orbicularis oculi, oris, soft palate surrounding the uvula, the trapezius and the anterior aspect of the tongue. Bipolar motor stimulation of motor rootlets in the CPA led to simultaneous recording of compound motor action potential (CMAP) from both surface and soft palate electrodes. The authors found that there was high inter-individual but low intra-individual variability in the amplitude and latencies of vocal cord CMAPs. In two patients, vocal cord CMAPs were lost during surgery and were associated with postoperative hoarseness and dysphagia. With more data being published, endotracheal tube electrode monitoring may become de rigueur in identifying vocal cord motor rootlets in the CPA / skull base and functional impairment during skull base surgery.

Endotracheal tube electrodes to assess vocal cord motor function during surgery in the cerebellopontine angle.
Romagna A, Rachinger W, Schwartz C, et al.
NEUROSURGERY
2015;77:471-8.