Difficulty: Intermediate | Prerequisites: Basic airway anatomy, general anaesthesia principles (ASA monitoring standards, intubation basics).
This is the first of three sets of notes covering Chapter 43 on anaesthesia for ear, nose, throat (ENT) and maxillofacial surgery. The defining challenge of the entire chapter is the shared airway: you and the surgeon are working in the same space, the operating table is often turned away from you, and the patient's anatomy is frequently abnormal (that is why they need the surgery in the first place). Everything else in the chapter flows from that single constraint.
Part 1 covers the 11 goals of ENT anaesthesia, functional anatomy of the head and neck (nose, pharynx, larynx, cranial nerves), and practical preparation including positioning, table turning, line placement, and specialised endotracheal tubes. Parts 2 and 3 cover pharmacology, techniques, and procedure-specific management.
ENT anaesthesia revolves around sharing the airway with the surgeon while managing distorted anatomy, fire risk, nerve preservation, bleeding, and PONV. A solid grasp of laryngeal innervation and the anatomy of the nose, pharynx, and larynx is essential before you touch any of the clinical material that follows.
Shared airway
The fundamental concept in ENT anaesthesia: the surgeon and anaesthetist both need access to the patient's airway simultaneously. The endotracheal tube (ETT) may need to be smaller, repositioned to the opposite side of the surgical field, or replaced by alternative ventilation strategies.
In simple terms, you and the surgeon are both trying to work in the same narrow space at the same time.
Waldeyer tonsillar ring
A ring of lymphoid tissue in the oropharynx formed by the palatine tonsils, adenoids (pharyngeal tonsil), lingual tonsil, and tubal tonsils. The tonsils within it are the most sensitive structures in the oropharynx.
Think of it as the immune system's ring of guards around the entrance to the throat.
Rima glottidis
The opening between the vocal cords. In adults, this is the narrowest point of the airway.
In simple terms, it is the bottleneck of the adult airway, right at the vocal cords.
Cricoid ring
The only complete cartilaginous ring of the airway. In children (traditionally up to about age 10), the cricoid ring, not the vocal cords, is the narrowest point.
Think of it as a rigid signet ring sitting below the vocal cords. In a child, it is the tightest spot the tube has to pass through.
Recurrent laryngeal nerve (RLN)
A branch of the vagus (X) that runs between the trachea and oesophagus. Supplies motor innervation to all intrinsic laryngeal muscles except the cricothyroid. Also carries sensory fibres from the laryngeal mucosa below the vocal cords.
In simple terms, if this nerve is damaged, the vocal cords cannot move properly, and the patient may be hoarse or, if both sides are injured, unable to breathe.
Superior laryngeal nerve (SLN)
A vagus (X) branch with two divisions: an internal (sensory) branch supplying the mucosa above the vocal cords, and an external (motor) branch supplying the cricothyroid muscle (which tenses and elongates the cords).
Think of it as the nerve that handles sensation above the cords and pitch control of the voice.
RAE tube
A preformed right-angle endotracheal tube (named after inventors Ring, Adair, Elwyn). Available as oral or nasal, cuffed or uncuffed. The right-angle bend routes the tube and circuit away from the surgical field.
In simple terms, a tube with a built-in bend so the breathing circuit sits out of the surgeon's way.
THRIVE (transnasal humidified rapid-insufflation ventilatory exchange)
A noninvasive technique using a high-flow (10 to 12 L/min) humidified, warmed nasal cannula for passive apnoeic oxygenation. Extends safe apnoea time without the barotrauma risks of jet ventilation.
Think of it as a gentler alternative to jet ventilation: high-flow oxygen through the nose that buys extra time before desaturation.
PONV (postoperative nausea and vomiting)
Nausea and vomiting after surgery. ENT procedures, especially middle-ear surgery, carry a particularly high incidence. A multimodal antiemetic approach is standard.
In simple terms, the patient feels sick and vomits after the operation, and ENT patients are especially prone to it.
These goals frame every clinical decision in the chapter. They are worth memorising as a checklist.
Airway knowledge – thorough understanding of airway anatomy and function before induction.
Technique selection – choose and prepare the right airway-management approach for the specific procedure.
Complication management – anticipate and manage airway complications (obstruction, fire, bleeding).
Selective relaxation – provide profound muscle relaxation for extreme stimulation (e.g. suspension laryngoscopy) while allowing rapid recovery.
Cardiovascular stability – maintain haemodynamic control during intense surgical stimulation.
Omit relaxation when needed – withhold muscle relaxants when nerve monitoring (e.g. facial nerve EMG) requires it.
Fire prevention – prevent or contain airway fires (laser, electrosurgery, oxygen-enriched field).
Blood loss control – minimise intraoperative and postoperative bleeding.
Carotid reflex management – prevent adverse cardiac or respiratory responses from carotid sinus/body manipulation.
Postoperative measures – prevent PONV and manage postsurgical airway obstruction.
Nitrous oxide limit – avoid or limit N₂O during tympanoplasty and other closed-space grafting procedures.
Increased risk of unanticipated difficult airways, including cannot-intubate-cannot-ventilate scenarios.
Specialised ventilation techniques: insufflation, intermittent apnoea, apnoeic oxygenation.
ETT fire prevention in an oxygen-enriched, shared-airway field.
Restricted use of nitrous oxide and muscle relaxants.
Specialised equipment: laser tubes, high-frequency jet ventilation, THRIVE.
Potentially undiagnosed obstructive sleep apnoea and risk of significant bleeding.
The nose warms, filters, and humidifies inspired air. Structures include the external nose, nasal cavity, and four sets of paranasal sinuses (frontal, maxillary, ethmoid, sphenoid), all separated by the septum.
Turbinates (conchae) – superior, middle, and inferior shelves of highly vascular bone that massively increase surface area. Their rich blood supply is clinically important.
Clinical rule: always insert a nasal airway or tube along the superior margin of the hard palate (the floor of the nose). Straying upward into the turbinates risks severe bleeding. Inadvertent submucosal insertion into the palate causes bleeding and infection. The sinus bones are thin and can fracture, potentially causing a cerebrospinal fluid leak.
Three regions: nasopharynx, oropharynx, and laryngopharynx (hypopharynx), extending down to the level of C6.
The oropharynx contains the tongue base, soft palate, uvula, palatine tonsils, and adenoids, which together form the Waldeyer tonsillar ring. The tonsils are the most sensitive area.
Tonsil blood supply comes from branches of the external carotid, maxillary, and facial arteries, which is why even a "routine" tonsillectomy carries real bleeding risk.
Hypertrophy of the palatine or adenoid tonsils, soft palate, or uvula can cause serious airway compromise, particularly in young children.
During swallowing, the larynx is pulled superiorly so the epiglottis covers the laryngeal opening. The epiglottis does not passively flop shut like a lid. Glottic closure is coordinated by the superior laryngeal, recurrent laryngeal, and glossopharyngeal nerves.
The larynx is a rigid organ of cartilages supported by the hyoid bone.
Paired cartilages: arytenoid, corniculate, cuneiform.
Unpaired cartilages: thyroid, cricoid, epiglottis.
Narrowest point: adult = vocal cords (rima glottidis); child = cricoid ring (traditionally until about age 10). Studies now show no difference in postintubation croup between cuffed and uncuffed tubes in children, and newer low-pressure cuffed tubes (Microcuff) are well supported.
Facial nerve (VII) – six branches: four anterior (temporal, zygomatic, buccal, mandibular), one inferior (cervical), one posterior (posterior auricular). Motor to facial expression. The chorda tympani carries taste from the anterior two-thirds of the tongue.
Trigeminal nerve (V) – from the gasserian ganglion into ophthalmic (V1), maxillary (V2), and mandibular (V3) divisions. Sensory and motor to the nose, sinuses, palate, tongue; controls mastication.
Glossopharyngeal nerve (IX) – motor and sensory to the tongue base, nasopharynx, and oropharynx. Responsible for the gag reflex.
Vagus nerve (X) – gives off the superior laryngeal nerve (internal sensory branch through the thyrohyoid membrane; external motor branch over the thyroid cartilage to the cricothyroid) and the recurrent laryngeal nerve (between trachea and oesophagus, motor to all other intrinsic muscles). Laryngoscope or ETT contact with the epiglottis can trigger a vagal response.
SLN internal branch (sensory): laryngeal mucosa above the vocal cords and the inferior surface of the epiglottis.
RLN (sensory): laryngeal mucosa below the vocal cords.
Glossopharyngeal (sensory): superior surface of the epiglottis and tongue base.
RLN (motor): all intrinsic muscles except the cricothyroid.
SLN external branch (motor): cricothyroid only.
Cricothyroid – innervated by the SLN external branch – tenses and elongates the cords.
Posterior cricoarytenoid – innervated by the RLN – the only abductor of the vocal cords. High-yield: if asked "which is the only muscle that opens the cords?" the answer is the posterior cricoarytenoid.
All remaining intrinsic muscles (thyroarytenoid, vocalis, lateral cricoarytenoid, transverse arytenoid, aryepiglottic, oblique arytenoid) are innervated by the RLN and either relax, adduct, or close the cords/glottis.
Sternohyoid and sternothyroid: cervical plexus C1 to C3.
Thyrohyoid: hypoglossal nerve, C1 to C2.
Thyroepiglottic: recurrent laryngeal nerve.
Stylopharyngeus: glossopharyngeal nerve.
Inferior pharyngeal constrictor: pharyngeal plexus (vagus).
Plan with the surgical team before induction. The ETT may need to be a smaller diameter and positioned on the side opposite the operative field.
The table is often rotated 90 to 180 degrees away from the anaesthetist.
Constant assessment: monitor chest movement, auscultation, pulse oximetry, end-tidal CO₂, and blood gases. Sudden loss of breath sounds, rising inspiratory pressure, or falling end-tidal CO₂ signals cuff deflation, ETT obstruction, dislodgement, circuit disconnect, or an ETT severed during dissection.
Air-leak signs may be more sensitive than electronic monitors: bubbling sounds, escaping-air noise, or the smell of anaesthetic agent. Precordial and oesophageal stethoscopes remain useful.
The surgeon should announce field changes (laryngoscope repositioning, dark blood, carotid-body manipulation, head-position changes).
Secure the ETT with tape (transparent occlusive dressing) or suture.
Add extension length to IV lines, invasive lines, monitors, and the breathing circuit. Pad pressure points.
Before turning: ventilate with 100% O₂ for 3 to 5 minutes to denitrogenate the functional residual capacity and build an oxygen reservoir. Add IV anaesthesia if volatile is the sole agent. Target 100% saturation. Briefly disconnect the circuit during the turn to prevent traumatic extubation.
After turning: reconnect immediately and reassess tube placement, breath sounds, chest expansion, saturation, anaesthetic depth, lines, and end-tidal CO₂. Use a heat-moisture exchanger (HME) or humidifier for long cases.
Place a large-bore IV (plus arterial or central venous pressure lines) on the non-operative side nearest the anaesthetist. The calf can be used for non-invasive blood pressure. Neuromuscular monitoring can go at the tibial nerve (big-toe flexion) if the arm is inaccessible. Place a Foley catheter for cases longer than 3 hours.
At the side of the table with a standard circle circuit, or at the foot of the bed with a coaxial (Bain) circuit.
Alternatively, the surgeon may perform a tracheostomy and suture a flexible ETT in place.
Some cases also require access to the chest, abdomen, or extremities for grafts.
General principle: tube diameter and length affect ventilation and seal. A tube that is too small for a large airway creates more resistance and poor cuff contact. Specialty small-diameter tubes distribute cuff pressure more evenly.
RAE tubes: preformed right-angle, oral or nasal, cuffed or uncuffed. Oral RAE is used for cleft palate, tonsillectomy, UPPP, and eye or upper-face procedures. Nasal RAE is used for maxillofacial, oral cavity, mandible, and malocclusion procedures. The preformed bend can sit too distally or proximally, so always check breath sounds and inspiratory pressures after placement. Avoid nasal tubes in facial trauma (risk of brain penetration through a fractured cribriform plate); review head CT beforehand.
Armoured/reinforced tubes: contain an embedded wire or plastic coil for flexibility and kink resistance. Used for acute neck flexion, skull-base surgery, and posterior-neck surgery. Even an edentulous patient can occasionally bite one shut.
Laser tubes: metal-impregnated to resist airway fire. The cuff is filled with saline (ideally dyed with methylene blue to reveal perforation). Wrapping a standard tube with reflective tape is not adequate: the tape dries out and becomes more flammable.
Laryngeal mask airway (LMA) / intubating LMA: controls the airway without tracheal stimulation, leading to less coughing on emergence. Can be placed without relaxants. Useful as a conduit to the glottis or trachea, for neurological monitoring without relaxants, and for isolating the glottis from pharyngeal bleeding. Contraindicated in some laryngeal pathology.
"The epiglottis works like a passive trap door." It does not. The larynx is actively pulled upward during swallowing so the epiglottis covers the opening; glottic closure is a coordinated neuromuscular event.
"Cuffed ETTs should never be used in children under 8." Current evidence shows no difference in postintubation croup between cuffed and uncuffed tubes in children. Newer low-pressure cuffed tubes (Microcuff) are well supported.
"Wrapping a standard ETT with reflective tape is a safe substitute for a laser tube." It is not. The tape dries and becomes more flammable, increasing fire risk.
"The posterior cricoarytenoid adducts the cords." It is the only abductor. All other RLN-innervated intrinsic muscles either adduct, relax, or close the cords.
The shared-airway concept is not abstract: in every ENT case, the anaesthetist physically loses direct line-of-sight and hands-on access to the tube. The protocols for turning the table (preoxygenation, circuit disconnection, immediate reassessment) are built from incidents where patients desaturated or tubes dislodged during repositioning. The anatomy of turbinate vascularity and the nasal floor rule directly prevent epistaxis during nasal intubation, one of the most common avoidable complications in ENT anaesthesia.
⚠️ The narrowest airway point differs by age: adult = vocal cords (rima glottidis), child = cricoid ring. This is a classic exam question.
⚠️ The recurrent laryngeal nerve innervates all intrinsic laryngeal muscles except the cricothyroid (which is innervated by the external branch of the superior laryngeal nerve). Know this cold.
⚠️ The posterior cricoarytenoid is the only abductor of the vocal cords. Every other intrinsic muscle closes or relaxes them.
⚠️ Nasal tubes and nasogastric tubes are contraindicated in facial trauma with suspected cribriform plate disruption (Le Fort II/III). Always review head CT first.
⚠️ Before turning the table: preoxygenate with 100% O₂ for 3 to 5 minutes, briefly disconnect the circuit during the turn to prevent traumatic extubation, then reconnect and reassess immediately.
True or false: In an adult, the narrowest point of the airway is the cricoid ring.
Fill in the blank: The only intrinsic laryngeal muscle innervated by the superior laryngeal nerve (external branch) is the __________.
True or false: Wrapping a standard ETT in reflective tape is an acceptable substitute for a laser-specific tube.
Fill in the blank: The __________ is the only muscle that abducts the vocal cords.
True or false: You should maintain positive-pressure ventilation continuously while turning the table 180 degrees.
Answers: 1. False (it is the vocal cords/rima glottidis). 2. Cricothyroid. 3. False. 4. Posterior cricoarytenoid. 5. False (briefly disconnect the circuit during the turn to prevent traumatic extubation).
Q: Name the three unpaired cartilages of the larynx.
A: Thyroid, cricoid, and epiglottis.
Q: Which cranial nerve is responsible for the gag reflex?
A: The glossopharyngeal nerve (CN IX).
Q: A nasal ETT should be directed along which anatomical landmark to avoid epistaxis?
A: Along the superior margin (floor) of the hard palate.
Q: What are the two branches of the superior laryngeal nerve and what does each supply?
A: The internal branch is sensory to the laryngeal mucosa above the vocal cords. The external branch is motor to the cricothyroid muscle.
Q: During a shared-airway case, which clinical signs may indicate ETT compromise before electronic monitors alarm?
A: Bubbling, escaping-air sounds, and the smell of anaesthetic agent (air-leak signs detected by the anaesthetist's senses, often before monitors respond).
Q: What is the "rule" for inserting a nasal airway or tube to minimise bleeding?
A: Direct the tube along the floor of the nose (superior margin of the hard palate), avoiding the highly vascular turbinates above.
The cranial nerve anatomy here connects directly to neuroanatomy and cranial nerve examination in general physiology and neurology courses.
Airway assessment and management principles link to the difficult-airway algorithm (ASA Difficult Airway Guidelines).
The shared-airway concept reappears in paediatric anaesthesia, where small airways and limited reserve make the challenges even more acute.
ENT anaesthesia, shared airway, airway anatomy, laryngeal cartilages, recurrent laryngeal nerve, superior laryngeal nerve, cricothyroid muscle, posterior cricoarytenoid, rima glottidis, vocal cords, cricoid ring, paediatric airway, turbinates, conchae, nasal intubation, epistaxis, pharynx, Waldeyer ring, RAE tube, armoured tube, reinforced tube, laser tube, LMA, intubating LMA, THRIVE, apnoeic oxygenation, table turning, shared endoscopic space, Chapter 43, ENT surgery, maxillofacial anaesthesia