Difficulty: Intermediate | Prerequisites: Basic cranial nerve anatomy, general anesthesia pharmacology
Tags: nerve preservation, intraoperative neuromonitoring, EMG, facial nerve, cranial nerves, ear surgery anesthesia, head and neck surgery, CRNA, nurse anesthesia, electromyography, acoustic neuroma, glomus tumour
Surgical procedures of the ear, face, head and neck place cranial nerves at direct risk of injury. The anaesthetist's role is not just to keep the patient asleep: the anaesthetic technique must be tailored so that intraoperative nerve monitoring can function reliably. Damage to these nerves produces visible, lasting morbidity (think unilateral facial droop), and prevention is far better than any attempt at surgical repair afterwards. If you are revising ENT anaesthesia, this is the foundation topic, because nerve-monitoring constraints shape every drug choice that follows.
During ear and head/neck surgery, cranial nerves (especially CN VII) are monitored in real time using EMG. To keep that monitoring accurate, muscle relaxants must be limited to induction/intubation only, and local anaesthetics are avoided entirely. The anaesthetic technique (typically remifentanil plus a short-acting volatile agent) is built around preserving the EMG signal.
Intraoperative neuromonitoring (IONM)
The use of electrophysiological techniques during surgery to identify and assess the function of vulnerable nerves in real time. In simple terms, the surgical team watches a live readout of nerve activity so they can avoid cutting or stretching something they shouldn't.
Electromyography (EMG)
A method of recording electrical activity produced by skeletal muscles. In ENT surgery, EMG electrodes are placed near the muscles supplied by at-risk nerves, and the surgeon uses a stimulating probe on or near the nerve to confirm it is intact and functioning. Think of it as a "nerve finder" that lights up when the nerve works.
Facial nerve (CN VII)
The most commonly monitored nerve in otologic and facial surgery. It traverses the middle ear cavity and exits the skull via the stylomastoid foramen, supplying the muscles of facial expression. Injury produces unilateral facial paresis, which is cosmetically and functionally devastating.
Recurrent (inferior) laryngeal nerve
A branch of the vagus nerve (CN X) monitored during thyroid and neck surgery. Damage causes vocal cord paralysis and hoarseness.
Brainstem auditory-evoked potential (BAEP)
An electrophysiological test that measures the brain's response to auditory stimuli. Used alongside electrocochleography to isolate and verify nerve function during procedures near the auditory pathway.
Electrocochleogram (ECoG)
A recording of electrical potentials generated in the inner ear and auditory nerve in response to sound. Used with BAEP for nerve isolation during skull base and ear surgery.
Acoustic neuroma
A benign tumour (schwannoma) arising from the vestibular portion of CN VIII. Resection carries a significant risk of facial nerve injury, making neuromonitoring essential.
Glomus tumour
A vascular tumour of the head and neck (often at the jugular bulb or middle ear) whose resection requires careful identification of multiple cranial nerves.
Deep extubation
Removing the endotracheal tube while the patient is still under a plane of anaesthesia deep enough to suppress coughing and straining. Used selectively in ear surgery to prevent postoperative bleeding and graft displacement.
Every ear surgery case centres on four issues. Exam questions frequently ask you to list all four:
Nerve preservation (protecting the facial and other cranial nerves)
The effect of N₂O on the middle ear (pressure changes in a closed air space)
Control of bleeding (a bloodless field is mandatory for microsurgery)
PONV (postoperative nausea and vomiting, which is common and must be minimised)
Nerve preservation is covered in this document. N₂O, bleeding control and PONV are covered in the companion notes.
Motor branch of the facial nerve (CN VII) – the most commonly monitored nerve in otologic/facial surgery.
Recurrent (inferior) laryngeal nerve (CN X) – a branch of the vagus, monitored in thyroid and neck surgery.
Vagus nerve (CN X) – monitored during neck dissection.
Spinal accessory nerve (CN XI) – and other lower cranial nerves, monitored less frequently.
The surgeon isolates the nerve and applies electrical stimulation directly. The EMG electrodes detect the resulting muscle response. Two additional modalities used for nerve isolation in the auditory pathway are brainstem auditory-evoked potentials (BAEP) and electrocochleogram (ECoG) monitoring.
This is the high-yield material. The drugs you give (or withhold) determine whether the monitoring works.
Patient movement must be prevented. This is especially critical when a positioning device is used for craniotomy.
Muscle relaxants: induction and intubation only. After that, they are withheld for the remainder of the case. Residual neuromuscular blockade suppresses the EMG signal and can make a functioning nerve appear damaged.
Local anaesthetics are contraindicated during monitoring. They suppress muscle action potential amplitudes and muscle movement, degrading the very signal the team relies on.
Volatile agents and N₂O are acceptable, but N₂O must be discontinued well before closing any cavity (covered in companion notes on N₂O).
Haemostasis during neck dissection is less critical than during otologic or skull base neurosurgery, but an opioid infusion (remifentanil or sufentanil) still helps control blood pressure and supports haemostasis.
Common techniques pair remifentanil (short-acting opioid infusion) with a short-acting volatile agent, with or without N₂O. Midazolam given preoperatively provides amnesia and supports rapid emergence. Deep extubation is considered selectively: straining at emergence increases postoperative bleeding and may force re-exploration.
In a real OR setting, the neuromonitoring technician will alert the anaesthetist if EMG signals are degraded. The first question asked is usually whether any muscle relaxant is still on board. Understanding this relationship between pharmacology and monitoring is not just exam knowledge, it directly changes how you run the case.
Students sometimes think muscle relaxants are avoided for the entire case including induction. They are permitted at induction/intubation; the restriction applies to maintenance and beyond.
Local anaesthetics are not just "less preferred" during neuromonitoring. They are contraindicated. The distinction matters on exams.
Students may confuse the roles of EMG (muscle response to nerve stimulation) and BAEP/ECoG (auditory pathway monitoring). EMG is for motor nerve integrity; BAEP and ECoG are for auditory/sensory pathways.
Deep extubation is not the default for all ear cases. It is selected when the benefits (no coughing/straining) outweigh the risks (loss of airway reflexes in a patient who may not be easily reintubated).
⚠️ "Name the four major anaesthetic concerns in ear surgery" is a classic list question. Know all four cold.
⚠️ The rule on muscle relaxants (induction only) and local anaesthetics (contraindicated) during neuromonitoring is tested frequently in both multiple-choice and clinical-scenario formats.
⚠️ Know which cranial nerves are monitored and during which procedures: CN VII for otologic/facial, recurrent laryngeal (CN X) for thyroid/neck, vagus (CN X) for neck dissection, CN XI less frequently.
⚠️ Deep extubation comes up in scenarios asking how to manage emergence after ear surgery. The reasoning (prevent straining, protect graft, reduce bleeding) is as important as the technique.
True or false: Muscle relaxants should be avoided entirely, including at induction, when intraoperative neuromonitoring is planned.
Fill in the blank: Nitrous oxide is _____ times more soluble than nitrogen in blood.
True or false: Local anaesthetics are acceptable during EMG-based neuromonitoring as long as the dose is low.
Fill in the blank: The most commonly monitored cranial nerve in otologic/facial surgery is CN _____.
True or false: Deep extubation is used to prevent coughing and straining at emergence.
Answers: 1. False (permitted at induction/intubation, then withheld). 2. 34. 3. False (contraindicated). 4. VII (facial nerve). 5. True.
Q: A patient is undergoing acoustic neuroma resection with intraoperative facial nerve EMG monitoring. The surgeon reports absent EMG signals. What anaesthetic-related cause should you rule out first?
A: Residual neuromuscular blockade. Muscle relaxants suppress the EMG signal and should only be given at induction/intubation. Check train-of-four and confirm full recovery of neuromuscular function.
Q: Why are local anaesthetics contraindicated during intraoperative neuromonitoring?
A: They suppress muscle action potential amplitudes and muscle movement. This degrades the EMG signal, making it impossible to distinguish a functioning nerve from an injured one.
Q: List the four cranial nerves (by name and number) most commonly monitored during head and neck surgery.
A: Motor branch of the facial nerve (CN VII), recurrent (inferior) laryngeal nerve (CN X), vagus nerve (CN X), and spinal accessory nerve (CN XI).
Q: What is the purpose of deep extubation in ear surgery, and when is it contraindicated?
A: Deep extubation prevents coughing and straining at emergence, which can increase postoperative bleeding and dislodge grafts or prostheses. It is contraindicated when there is concern about loss of airway reflexes or difficulty with reintubation.
Q: Describe a typical anaesthetic technique for a case requiring intraoperative neuromonitoring in ear surgery.
A: Remifentanil infusion paired with a short-acting volatile agent, with or without N₂O. Midazolam preoperatively for amnesia. Muscle relaxants given at induction/intubation only. Local anaesthetics avoided. Deep extubation considered if no contraindications.
This material connects directly to the companion notes on N₂O and middle ear pressure, since the decision to use or avoid N₂O is one of the four core concerns listed here. It also ties into pharmacology of neuromuscular blocking agents (understanding onset, duration, and reversal is essential for the "induction only" rule) and airway management (deep extubation technique and its risks).
nerve preservation, intraoperative neuromonitoring, IONM, EMG, electromyography, facial nerve monitoring, CN VII, recurrent laryngeal nerve, vagus nerve, spinal accessory nerve, acoustic neuroma, vestibular schwannoma, glomus tumour, brainstem auditory-evoked potential, BAEP, electrocochleogram, ECoG, deep extubation, remifentanil, muscle relaxants, neuromuscular blockade, ear surgery anaesthesia, head and neck anaesthesia, CRNA, nurse anesthetist, otologic surgery, skull base surgery