27 AIRWAYS

👩‍⚕️ The airway is the first letter of ATLS for a reason — hypoxic brain injury starts within minutes. Learn the landmarks cold: the cricothyroid membrane (between thyroid and cricoid cartilages) is your emergency front-of-neck access, and the cricoid is the only complete cartilage ring — the anchor for almost every airway question.

Anatomy of the airway

The conducting airway is a single tube that changes name and structure as it descends:

➡ Oral and nasal cavities → warm, filter and humidify air; nasal cavity is the larger conduit at rest.

➡ Pharynx → nasopharynx, oropharynx and laryngopharynx (hypopharynx). The laryngopharynx ends at C6, where it becomes the oesophagus posteriorly and the larynx anteriorly.

➡ Larynx → C3 to C6. Houses the vocal cords at approximately C5/C6. Composed of nine cartilages: three unpaired (thyroid, cricoid, epiglottis) and three paired (arytenoid, corniculate, cuneiform).

➡ Trachea → C6 to T4/T5. About 10–12 cm long with 15–20 incomplete C-shaped cartilage rings open posteriorly (the trachealis muscle closes the C).

➡ Carina → bifurcation at the sternal angle (T4/T5). The right main bronchus is shorter, wider and more vertical — aspirated foreign bodies and migrated ET tubes preferentially enter the right lung.

Key surface landmarks (memorise these)

Landmark	Vertebral level
Hyoid	C3
Thyroid cartilage (Adam's apple, upper border)	C4
Vocal cords	C5/C6
Cricoid cartilage	C6
Suprasternal notch	T2/T3
Carina	T4/T5

👩‍⚕️ The cricoid is the only complete cartilage ring in the airway. Every other ring (tracheal rings included) is C-shaped. This is why cricoid pressure (Sellick's manoeuvre) works — pressing it transmits force circumferentially and compresses the underlying oesophagus.

Innervation of the larynx — a high-yield SBA topic

The larynx is split by the vocal cords:

- Above the cords: sensory supply from the internal branch of the superior laryngeal nerve (a branch of CN X, but mediating the same reflex arc as IX in the pharynx — exam stems sometimes muddle this with the pharyngeal CN IX supply).

- Below the cords: sensory supply from the recurrent laryngeal nerve (CN X).

- Motor supply to all intrinsic laryngeal muscles: recurrent laryngeal nerve, EXCEPT the cricothyroid, which is supplied by the external branch of the superior laryngeal nerve.

Nerve injury	Effect
Unilateral RLN	Hoarseness; ipsilateral cord in paramedian position; weak cough
Bilateral RLN	Both cords adducted → stridor and airway obstruction (emergency)
External branch of SLN	Loss of pitch control (cricothyroid paralysis) — classic post-thyroidectomy "monotone voice"
Internal branch of SLN	Loss of supraglottic sensation → risk of aspiration

👩‍⚕️ Mnemonic: "PCA opens" — the posterior cricoarytenoid is the only abductor of the vocal cords. Every other intrinsic muscle adducts or tenses.

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Basic airway management

The airway algorithm escalates from simple to invasive. Master the order.

Manoeuvres (no equipment)

- Head-tilt–chin-lift — first-line in unconscious patients with no suspicion of cervical spine injury. Lifts the tongue off the posterior pharyngeal wall.

- Jaw thrust — preferred when C-spine injury is suspected (trauma, fall, RTA). Maintains in-line stabilisation while opening the airway.

Simple adjuncts

- Oropharyngeal airway (OPA / Guedel) — sized from the incisors to the angle of the mandible (or tragus to the corner of the mouth). Tolerated only in patients without a gag reflex.

- Nasopharyngeal airway (NPA) — sized from the nostril to the tragus. Better tolerated in semi-conscious patients. Contraindicated in suspected basal skull fracture (panda eyes, Battle's sign, CSF rhinorrhoea) — the tube can traverse the cribriform plate into the cranial cavity.

Supraglottic airway devices

- Laryngeal mask airway (LMA) — classic LMA or i-gel. Sits in the hypopharynx with the cuff (or gel) sealing around the laryngeal inlet. Quick to insert, does not require laryngoscopy, but does not protect against aspiration. Plan B in the difficult airway algorithm.

Definitive airway — endotracheal intubation

A definitive airway = cuffed tube below the cords, secured, connected to oxygen.

- Sizing (internal diameter, mm): adult male 8.0–9.0, adult female 7.0–8.0, paediatric (age/4) + 4.

- Depth: roughly 3 × tube size in cm at the lips (e.g. a size 8 sits at ~22–24 cm).

- Confirmation: end-tidal CO₂ trace (gold standard), equal bilateral chest rise, auscultation in both axillae and the epigastrium, CXR shows tip 2–3 cm above the carina.

👩‍⚕️ Right main bronchus intubation is the most common malposition — if breath sounds are louder on the right and absent on the left, withdraw the tube 2 cm and re-auscultate.

Rapid sequence induction (RSI)

Used when the patient is at high risk of aspiration (full stomach, trauma, pregnancy, bowel obstruction).

1. Preoxygenate with 100% O₂ for 3 minutes (denitrogenation).

2. Induction agent: propofol or thiopentone (ketamine if haemodynamically unstable).

3. Paralysis: suxamethonium (fast on, fast off) or rocuronium (longer-acting; reversed by sugammadex).

4. Cricoid pressure (Sellick's manoeuvre) — applied at loss of consciousness, released after cuff inflation and tube position confirmed.

5. Intubate without bag-mask ventilation in between (minimises gastric insufflation).

Surgical airway

When intubation fails and oxygenation cannot be maintained — "Can't Intubate, Can't Oxygenate" (CICO) — proceed to emergency front-of-neck access (eFONA).

Cricothyroidotomy — the emergency airway

- Site: cricothyroid membrane, between thyroid and cricoid cartilages.

- Technique: stabilise the larynx, transverse 2 cm incision through skin and membrane, dilate with forceps or bougie, insert a size 6.0 cuffed tube.

- Faster than tracheostomy because the membrane is subcutaneous with minimal overlying structures.

Tracheostomy — the elective/definitive airway

- Site: midway between the cricoid and suprasternal notch, through the 2nd to 4th tracheal rings.

- The thyroid isthmus overlies rings 2–4 and is either retracted superiorly or divided.

- Indications: prolonged ventilation (>7–10 days, to avoid subglottic stenosis), upper airway obstruction, airway protection in bulbar palsy, secretion clearance.

	Cricothyroidotomy	Tracheostomy
Setting	Emergency (CICO)	Elective / definitive
Site	Cricothyroid membrane	2nd–4th tracheal rings
Time	Seconds–minutes	20–30 minutes
Long-term use	No — convert to tracheostomy within 24–72 h	Yes
Main risk	Subglottic stenosis if left in situ	Haemorrhage, tracheo-innominate fistula

👩‍⚕️ Mnemonic for structures at risk during tracheostomy — TAGIR: Thyroid isthmus, Anterior jugular veins, Great vessels, Inferior thyroid veins, Recurrent laryngeal nerve.

The difficult airway

Predict difficulty before you induce. Bedside assessment uses LEMON (ATLS) or the individual predictors:

- Mallampati score — view of the oropharynx with the patient sitting, mouth wide open, tongue out. Class I (full view of tonsillar pillars and uvula) is easy; Class IV (only hard palate visible) predicts difficulty.

- Mouth opening — < 3 finger-breadths (≈ 4 cm) is concerning.

- Thyromental distance — chin to thyroid notch with neck extended; < 6 cm predicts difficulty.

- Neck extension — limited in ankylosing spondylitis, rheumatoid arthritis, C-spine collar.

- Other red flags: obesity, beard, short neck, buck teeth, previous neck radiotherapy or surgery.

CICO algorithm (DAS, simplified)

- Plan A: face mask ventilation + tracheal intubation (max 3 attempts).

- Plan B: supraglottic airway (LMA / i-gel).

- Plan C: return to face mask ventilation, wake the patient.

- Plan D: emergency front-of-neck access — cricothyroidotomy.

👩‍⚕️ "Can't Intubate, Can't Oxygenate" is defined by oxygenation, not intubation. If sats are maintained on an LMA, you have time. If they are falling on every device, move to eFONA without further delay.

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Test yourself

What is the optimal site for a surgical tracheostomy?

• ((1 cm above the suprasternal notch::Too low — risks the brachiocephalic vein and pleural dome.))
• ((Midway between suprasternal notch and cricoid::☑️ Targets the 2nd–4th tracheal rings, the optimal tracheostomy site.))
• ((Between thyroid and cricoid cartilage::That is the cricothyroid membrane — used for emergency cricothyroidotomy.))
• ((At the level of the 1st tracheal ring::Too high — risks cricoid damage and subglottic stenosis.))

The surface landmark for tracheostomy is midway between the suprasternal notch and which structure?

• ((Cricoid::☑️ Cricoid is palpable just below the larynx; midpoint targets rings 2–4.))
• ((Hyoid::Too superior — sits at C3, well above the trachea.))
• ((Thyroid cartilage::Close but imprecise; cricoid is the standard inferior landmark.))
• ((Sternal angle::At T4/5 — level of the carina, far too inferior.))

Which structure is typically divided during a tracheostomy?

• ((Anterior jugular vein::Usually retracted laterally, not formally divided.))
• ((Thyroid isthmus::☑️ Overlies tracheal rings 2–4 and is divided or retracted superiorly.))
• ((Recurrent laryngeal nerve::Must be preserved — injury causes vocal cord paralysis.))
• ((Sternohyoid::Strap muscle — retracted laterally, not divided.))
• ((Platysma::Incised on entry but not the key structure at the tracheal level.))

Which structure is NOT at risk during a standard tracheostomy?

• ((Ascending pharyngeal artery::☑️ Branch of the external carotid; lies deep and posterior, away from the field.))
• ((Recurrent laryngeal nerve::Runs in the tracheo-oesophageal groove — at risk with lateral dissection.))
• ((Anterior jugular vein::Superficial midline vein commonly encountered.))
• ((Thyroid isthmus::Directly overlies rings 2–4.))
• ((Inferior thyroid veins::Variable midline veins — troublesome bleeding.))

👩‍⚕️ Remember TAGIR: Thyroid isthmus, Anterior jugulars, Great vessels, Inferior thyroid veins, Recurrent laryngeal nerve.

Which intrinsic laryngeal muscle abducts the vocal cords?

• ((Posterior cricoarytenoid::☑️ The only abductor — opens the cords; supplied by RLN.))
• ((Lateral cricoarytenoid::Primary adductor of the cords.))
• ((Cricothyroid::Tenses cords for pitch; supplied by external branch of SLN.))
• ((Thyroarytenoid::Shortens and relaxes the cords — an adductor.))
• ((Transverse arytenoid::Adducts by approximating the arytenoids.))

A cervical injury at which site is LEAST likely to compromise breathing?

• ((Hyoid::Fracture can obstruct the airway via tongue-base attachments.))
• ((Mandible::Loss of tongue support compromises airway patency.))
• ((Odontoid::Cord injury at C1/C2 paralyses the diaphragm — phrenic arises C3–5.))
• ((Thyroid cartilage::Laryngeal skeleton fracture causes airway obstruction.))
• ((Cricoid::☑️ Isolated cricoid injury is rare and less immediately catastrophic than the others listed.))

Where is the best site for an emergency surgical airway?

• ((Cricothyroid membrane::☑️ Between thyroid and cricoid — most rapid access with minimal dissection.))
• ((2nd–4th tracheal rings::Formal tracheostomy site — too slow for an emergency.))
• ((Thyrohyoid membrane::Too superior — enters the pharynx, not the airway.))
• ((Below the 4th tracheal ring::Too low — risks great vessels and pleural dome.))

👩‍⚕️ Cricothyroidotomy is the EMERGENCY airway; tracheostomy is the DEFINITIVE airway. Exam stems use urgency to discriminate.

A man with a Le Fort III fracture, pharyngeal haemorrhage and falling saturations. Next step?

• ((Surgical cricothyroidotomy::☑️ CICO scenario — oral/nasal access is unsafe with craniofacial disjunction.))
• ((Needle cricothyroidotomy::Temporising only — does not deliver adequate ventilation in adults.))
• ((Tracheostomy::Definitive but too slow for an acute emergency.))
• ((Orotracheal intubation::Often impossible with disrupted midface and active bleeding.))
• ((Nasotracheal intubation::Contraindicated — risks intracranial passage via cribriform plate.))

A 13-year-old asthmatic, unresponsive to bronchodilators, becomes hypercapnic with altered mental status. Next step?

• ((Intermittent positive-pressure ventilation::Needed AFTER airway is secured, not before.))
• ((CPAP::Inappropriate with altered consciousness — risks aspiration.))
• ((Endotracheal intubation::☑️ Life-threatening asthma with fatigue, hypercapnia and reduced GCS requires a definitive airway.))
• ((Systemic steroids::Already indicated but will not address ventilatory failure.))
• ((Increase nebulised salbutamol::Medical therapy has already failed.))

👩‍⚕️ A rising or "normal" pCO₂ in an acute asthmatic = exhaustion. Normo is not normal here.

A ventilated trauma patient suddenly desaturates during a log roll. Most likely cause?

• ((Kinked endotracheal tube::Possible but usually causes high airway pressures, not abrupt desaturation.))
• ((Neurogenic shock::Causes hypotension and bradycardia, not isolated hypoxia.))
• ((Displaced endotracheal tube::☑️ Movement commonly migrates the ETT into the right main bronchus or out of the trachea.))
• ((Tension pneumothorax::Possible but expect tracheal deviation, absent breath sounds, hypotension.))
• ((Bronchospasm::Causes wheeze and raised inflation pressures, not sudden desaturation.))

👩‍⚕️ Run DOPES for sudden desaturation: Displacement, Obstruction, Pneumothorax, Equipment failure, Stacking (auto-PEEP).

A post-RTA patient develops perioral swelling with SpO₂ 72%. Immediate next step?

• ((Adrenaline IM::Treats anaphylaxis — primary issue here is airway loss from trauma.))
• ((Hydrocortisone IV::Too slow for an acute airway emergency.))
• ((Endotracheal intubation::☑️ ATLS — A before B before C; secure the airway first.))
• ((Salbutamol::Treats bronchospasm, not upper-airway obstruction.))
• ((Emergency cricothyroidotomy::Only if intubation fails — first-line is ETT.))

A patient intubated in ICU for 8 days develops new respiratory distress after extubation. Most likely cause?

• ((Subglottic stenosis::☑️ Prolonged intubation causes mucosal ischaemia at the subglottis — the narrowest adult airway segment.))
• ((Tracheomalacia::Usually congenital or post-tracheostomy.))
• ((Laryngomalacia::Congenital, infants only.))
• ((Supraglottic stenosis::Much rarer than subglottic post-intubation.))
• ((Tracheo-oesophageal fistula::Presents with aspiration on swallowing, not isolated respiratory distress.))

👩‍⚕️ This is why tracheostomy is considered if ventilation is likely to exceed 7–10 days.

A lateral neck radiograph shows a U-shaped bone at C3. Which structure?

• ((Hyoid::☑️ U-shaped, at C3 — the only bone with no articulation to another bone.))
• ((Cricoid::Complete ring at C6 — lower.))
• ((Thyroid cartilage::Shield-shaped, at C4/5.))
• ((Epiglottis::Leaf-shaped elastic cartilage, not bony on X-ray.))

A fire victim from a smoke-filled house — which finding mandates early intubation?

• ((Respiratory rate 35/min::Tachypnoea alone is not an absolute indication.))
• ((pH 7.2::Acidosis needs treatment but does not alone mandate intubation.))
• ((Sweating, confusion and anxiety::☑️ Altered mental status = imminent airway loss and aspiration risk.))
• ((pCO₂ 5.7 kPa::Normal range.))
• ((Singed nasal hairs alone::Suggests inhalation injury but not enough alone.))

Which is an indication for intubation in a burns patient?

• ((Hypoxia::Often managed initially with supplemental O₂.))
• ((Dyspnoea::Non-specific.))
• ((Decreased conscious level::☑️ Risk of airway loss and aspiration mandates intubation.))
• ((Facial burns::Risk factor but not absolute alone.))
• ((Hoarse voice::Warning sign — escalate monitoring, but progression triggers intubation.))

👩‍⚕️ Mnemonic SHADES for burn intubation: Stridor, High TBSA (>40%), Altered mental status, Deep facial burns, Edema/carbonaceous sputum, Saturations falling.

Revision summary

- Airway anatomy: oral/nasal cavity → pharynx → larynx (cords at C5/6) → trachea (C6 to T4/5) → carina at sternal angle T4/5 → right main bronchus shorter, wider, more vertical.

- Cricoid = only complete cartilage ring, at C6 — basis for Sellick's manoeuvre.

- Innervation: above cords sensory = internal SLN; below cords sensory = RLN. Motor = RLN to all intrinsic muscles EXCEPT cricothyroid (external SLN). PCA is the only abductor.

- Adjuncts: head-tilt–chin-lift (no C-spine concern), jaw thrust (trauma). OPA sized incisors-to-angle of mandible. NPA sized nostril-to-tragus — contraindicated in basal skull #.

- Supraglottic: LMA / i-gel — Plan B; no aspiration protection.

- Definitive: cuffed ETT. Sizes: male 8.0–9.0, female 7.0–8.0, paeds (age/4)+4.

- RSI: preoxygenate → propofol/thiopentone + sux/rocuronium → cricoid pressure → intubate without bagging.

- Surgical airway: cricothyroidotomy (cricothyroid membrane, emergency) vs tracheostomy (rings 2–4, definitive; through thyroid isthmus).

- Difficult airway predictors: Mallampati, mouth opening, thyromental distance, neck extension.

- CICO algorithm: Plan A intubate → B supraglottic → C mask → D front-of-neck access (cricothyroidotomy).

- DOPES for sudden desaturation in a ventilated patient.

- TAGIR for tracheostomy danger structures.