Endotracheal Intubation & LMA

Securing the airway is the single most important skill in anaesthesia and emergency medicine. This note covers orotracheal and nasotracheal intubation, supraglottic airway devices (chiefly the laryngeal mask airway), the equipment behind each, and — most tested of all — how you confirm the tube is in the trachea and not the oesophagus.

Airway anatomy you must own

The larynx sits at C3–C6 in adults, higher (C2–C3) in infants, which is why paediatric airways behave differently. Key sensory supply:

• Above the cords → internal branch of superior laryngeal nerve (a branch of vagus).
• Below the cords → recurrent laryngeal nerve.
• Anterior tongue and oropharynx sensation matters for awake techniques.

The narrowest part of the adult airway is the glottis (vocal cords); in children under ~8 years it is classically the cricoid cartilage (a complete ring) — though MRI data show it is more dynamic than the old "funnel" teaching. The cricoid is the only complete cartilaginous ring, which is why cricoid pressure (Sellick's manoeuvre) is applied there.

High-yield: The epiglottis is the landmark for a straight (Miller) blade, which lifts it directly. The curved (Macintosh) blade tip sits in the vallecula and lifts the epiglottis indirectly by tensioning the hyo-epiglottic ligament.

Indications for intubation

Remember the mnemonic "PROTECT" style logic — broadly: failure to maintain/protect the airway, failure to oxygenate/ventilate, and anticipated clinical course.

1. Apnoea or inadequate ventilation (e.g., GCS ≤ 8 → intubate).
2. Airway protection from aspiration (loss of gag, bleeding, vomiting).
3. Need for positive-pressure ventilation / high oxygen requirement (ARDS).
4. Anticipated deterioration (burns with inhalation injury, expanding neck haematoma).
5. General anaesthesia requiring muscle relaxation and controlled ventilation.

Equipment essentials

Equipment	Key exam point
Laryngoscope (Macintosh curved / Miller straight)	Macintosh #3 adult, Miller preferred in neonates/infants
ET tube (cuffed)	Adult male 8.0–8.5 mm ID; adult female 7.0–7.5 mm ID
Paediatric tube size	Uncuffed = age/4 + 4; Cuffed = age/4 + 3.5
ET tube depth (oral)	~21 cm (female), 23 cm (male) at the lips; child = age/2 + 12
Stylet / bougie	Bougie gives "tracheal clicks" + "hold-up" sign
Magill forceps	For nasotracheal intubation to guide tube into glottis
Capnograph (EtCO₂)	The confirmation gold standard

High-yield: Cuff pressure should be kept 20–30 cmH₂O (below mucosal capillary perfusion pressure ~32 cmH₂O) to prevent tracheal ischaemia and later stenosis.

Pre-intubation airway assessment

Predicting the difficult airway is examined repeatedly. Use "LEMON":

• L — Look externally (beard, buck teeth, facial trauma, obesity).
• E — Evaluate 3-3-2 rule (3 fingers mouth opening, 3 fingers hyoid–chin, 2 fingers thyroid–floor of mouth).
• M — Mallampati class.
• O — Obstruction / Obesity.
• N — Neck mobility.

Mallampati classification (seated, mouth open, tongue out, no phonation)

Class	Visible structures	Implication
I	Soft palate, uvula, pillars (fauces)	Easy
II	Soft palate, uvula	Usually easy
III	Soft palate, base of uvula	Difficult predicted
IV	Hard palate only	Difficult

Other red flags: inter-incisor distance < 3 cm, thyromental distance < 6 cm (Patil's test), sternomental distance < 12.5 cm, upper-lip-bite test grade III, and limited atlanto-occipital extension.

High-yield: Mallampati III–IV, thyromental < 6 cm, and reduced neck extension together strongly predict difficult laryngoscopy. No single test is sensitive enough alone.

Cormack–Lehane grading (what you see at laryngoscopy)

This grades the laryngoscopic view, not the pre-op prediction — a frequent NEET PG distractor.

Grade	View
I	Full glottis (most of cords) visible
II	Only posterior cords / arytenoids visible (IIa = partial cords, IIb = arytenoids only)
III	Only epiglottis visible (IIIa liftable, IIIb adherent)
IV	Neither glottis nor epiglottis visible

Grades III and IV define a difficult laryngoscopy. The BURP manoeuvre (Backward–Upward–Rightward Pressure on the thyroid/cricoid cartilage) often improves the view by one grade.

Stepwise approach to orotracheal intubation

Preparation → Positioning → Preoxygenation → Pretreatment/Induction → Paralysis → Placement → Proof → Post-intubation (the "7 Ps" of RSI).

1. Position — "sniffing the morning air": neck flexed on chest + head extended at atlanto-occipital joint, aligning oral–pharyngeal–laryngeal axes. In obesity, ramped position (ear-to-sternal-notch) is superior.
2. Preoxygenate — 100% O₂ for 3 minutes (or 8 vital-capacity breaths) to fill the FRC and extend safe apnoea time.
3. Induce + paralyse — e.g., propofol + suxamethonium 1–1.5 mg/kg (fastest onset, ~45 s) or rocuronium 1.2 mg/kg for rapid sequence.
4. Laryngoscopy — hold in left hand, insert from the right, sweep tongue to the left, advance blade tip into the vallecula, lift along the handle axis (45°) — do NOT lever on the teeth.
5. Pass the tube through the cords under vision; cuff just below the cords.
6. Inflate cuff, confirm placement, secure, set ventilator.

High-yield: Rapid Sequence Induction (RSI) = preoxygenation + cricoid pressure + induction agent + fast-acting relaxant with no bag-mask ventilation in between, to minimise aspiration risk in the full-stomach patient. Suxamethonium remains the classic relaxant; rocuronium (reversible with sugammadex) is the modern alternative.

Confirming correct placement

This is the highest-yield testable area. Methods are split into definitive vs supportive.

Gold standard = sustained EtCO₂ waveform (capnography) over ≥ 6 breaths. A persistent, square-shaped capnograph trace confirms tracheal placement. Oesophageal placement shows an absent or rapidly diminishing trace.

Method	Reliability
Continuous capnography (EtCO₂)	Best / gold standard
Direct visualisation of tube passing cords	Highly reliable
Bilateral chest auscultation + absent epigastric sounds	Supportive
Bilateral chest rise, fogging in tube	Supportive, not definitive
Oesophageal detector device (self-inflating bulb)	Useful, esp. in cardiac arrest (low EtCO₂)
Fibreoptic visualisation of tracheal rings/carina	Reliable
Chest X-ray	Confirms depth, not tracheal vs oesophageal placement

High-yield: In cardiac arrest, EtCO₂ may be falsely low/absent due to poor pulmonary blood flow — here the oesophageal detector device or direct visualisation is more useful. A rising EtCO₂ during CPR also signals return of spontaneous circulation (ROSC).

Check for endobronchial (usually right main bronchus) intubation: unilateral chest rise, absent left-sided breath sounds — withdraw the tube. Right main-stem is favoured because it branches at a less acute angle.

Nasotracheal intubation

Used when oral access is limited (oral surgery, trismus, dental procedures, mandibular fixation).

• Tube passed through the more patent nostril, along the floor of the nose, then directed into the glottis — often with Magill forceps under direct laryngoscopy, or blindly/fibreoptically in awake technique.
• Contraindications: suspected base-of-skull fracture (raccoon eyes, Battle's sign, CSF rhinorrhoea — risk of intracranial tube passage), severe coagulopathy, nasal polyps, basilar fracture.
• Complications: epistaxis, turbinate trauma, bacteraemia, smaller tube size needed.

Laryngeal Mask Airway (LMA) and supraglottic devices

The LMA (invented by Archie Brain, 1981) is a supraglottic device — it sits over the glottis, sealing around the laryngeal inlet, without passing the cords. It is the device of choice for short elective procedures in fasted patients with low aspiration risk, and a key rescue device in the difficult airway.

LMA sizing (by body weight)

LMA size	Weight	Max cuff volume (air)
1	< 5 kg (neonate)	4 mL
1.5	5–10 kg	7 mL
2	10–20 kg	10 mL
2.5	20–30 kg	14 mL
3	30–50 kg (small adult)	20 mL
4	50–70 kg (adult)	30 mL
5	70–100 kg (large adult)	40 mL

Insertion flow: deflate and lubricate cuff → patient in sniffing position → press the LMA against the hard palate with the index finger → advance along the palatopharyngeal curve until resistance is felt (tip seats in the hypopharynx at the upper oesophageal sphincter) → inflate cuff → confirm ventilation by EtCO₂ and chest rise.

High-yield: The LMA tip rests in the hypopharynx against the upper oesophageal sphincter; the cuff seals the laryngeal inlet. It does not protect against aspiration as well as a cuffed ET tube — hence avoid in full-stomach/non-fasted patients.

Types of supraglottic airways

Device	Distinguishing feature / use
Classic LMA	Reusable, basic supraglottic seal
LMA ProSeal	Extra drain (gastric) tube → higher seal, allows gastric decompression
LMA Fastrach (Intubating LMA)	Conduit for blind intubation; rescue in difficult airway
LMA Supreme	Single-use, gastric channel, improved insertion
i-gel	Non-inflatable thermoplastic gel cuff, gastric channel, very fast insertion
Combitube / King LT	Dual-lumen oesophageal–tracheal, blind insertion, emergency use

High-yield: The intubating LMA (Fastrach) and the i-gel are favoured rescue conduits in the "can't intubate, can ventilate" scenario and feature prominently in difficult airway algorithms.

Video laryngoscopy

Devices such as GlideScope, C-MAC, McGrath, Airtraq project an indirect, magnified glottic view, improving the Cormack–Lehane grade and first-pass success — especially in anticipated difficult airways and restricted neck movement. They are now first-line in many difficult-airway and trauma protocols. A stylet/hyperangulated blade is often required to direct the tube to the cords.

Difficult & failed airway — the algorithm

The "can't intubate, can't oxygenate" (CICO) scenario is the feared emergency.

Failed intubation → maintain oxygenation with bag-mask / supraglottic device → call for help → if CICO develops → emergency front-of-neck access (eFONA): cricothyroidotomy.

• Surgical cricothyroidotomy through the cricothyroid membrane is the emergency airway of choice in adults (faster, fewer complications than tracheostomy).
• Tracheostomy is the planned/long-term airway.
• The DAS (Difficult Airway Society) plan: A (laryngoscopy) → B (SAD/supraglottic) → C (face-mask) → D (eFONA).

High-yield: Cricothyroidotomy is the emergency surgical airway (through the cricothyroid membrane between thyroid and cricoid cartilage); tracheostomy is for elective/long-term airways and below the cricoid.

Complications

Immediate (during intubation):

• Trauma — dental damage, lip/tongue laceration, pharyngeal/laryngeal injury.
• Oesophageal intubation (catastrophic if unrecognised — capnography prevents this).
• Endobronchial intubation → atelectasis/hypoxia.
• Reflex responses: laryngospasm, bronchospasm, hypertension, tachycardia, arrhythmias, raised ICP/IOP.
• Aspiration of gastric contents.

Delayed / prolonged intubation:

• Sore throat (commonest minor complication), hoarseness.
• Tracheal stenosis, tracheomalacia (from high cuff pressure).
• Vocal cord granuloma, glottic/subglottic oedema.
• Sinusitis (nasal tube), nasal necrosis.
• Ventilator-associated pneumonia.

Extubation: laryngospasm, negative-pressure pulmonary oedema (forced inspiration against closed glottis), post-extubation stridor.

Key differentials / decision points

• ETT vs LMA: Cuffed ET tube → definitive airway, aspiration protection, prolonged ventilation, prone/laparoscopic surgery. LMA → short fasted cases, no relaxation needed, difficult-airway rescue.
• Macintosh vs Miller blade: Curved (vallecula, adults) vs straight (lifts epiglottis, neonates/infants where the epiglottis is long and floppy).
• Tube in trachea vs oesophagus: capnography is the discriminator — never rely on auscultation alone.
• Difficult laryngoscopy vs difficult mask ventilation: predicted by different factors; mask difficulty mnemonic "MOANS" (Mask seal, Obese, Age >55, No teeth, Stiff lungs).

Recently asked / exam angle

• Best/most reliable confirmation of ET tube placement → continuous capnography (EtCO₂ waveform). Recurringly tested over auscultation and CXR.
• Paediatric uncuffed tube size = age/4 + 4; oral depth = age/2 + 12.
• Cormack–Lehane grading vs Mallampati — examiners swap the definitions to trip you (Mallampati = pre-op prediction; C-L = actual laryngoscopic view).
• Narrowest part of airway: glottis in adults, cricoid in children < 8 yrs.
• LMA sizing by weight (size 3 = 30–50 kg, size 4 = 50–70 kg) and LMA tip location (upper oesophageal sphincter).
• Sellick's manoeuvre = cricoid pressure in RSI; BURP = improves laryngoscopic view.
• Cricothyroidotomy through the cricothyroid membrane as the CICO rescue.
• Sniffing position aligns the three airway axes; ramped position in the obese.
• Suxamethonium 1–1.5 mg/kg = fastest onset relaxant for RSI; rocuronium + sugammadex the modern alternative.
• Cuff pressure 20–30 cmH₂O to prevent tracheal mucosal ischaemia.

Rapid revision

1. Capnography (sustained EtCO₂ waveform) = gold standard for confirming tracheal intubation.
2. Adult ET tube: male 8.0–8.5, female 7.0–7.5 mm ID; depth ~23 cm (male)/21 cm (female).
3. Paediatric uncuffed tube = age/4 + 4, cuffed = age/4 + 3.5; depth = age/2 + 12.
4. Macintosh tip → vallecula; Miller lifts the epiglottis directly (use in infants).
5. Mallampati predicts difficulty pre-op; Cormack–Lehane grades the actual view (III–IV = difficult).
6. Sniffing position aligns oral–pharyngeal–laryngeal axes; ramped for the obese.
7. RSI = preoxygenation + cricoid pressure + induction + sux/roc, no bag-mask ventilation.
8. LMA size 3 = 30–50 kg, size 4 = 50–70 kg; tip sits at the upper oesophageal sphincter — no true aspiration protection.
9. i-gel = non-inflatable gel cuff; Fastrach = intubating LMA conduit for blind/rescue intubation.
10. Cricothyroidotomy (through cricothyroid membrane) = emergency airway in CICO; tracheostomy = elective/long-term.
11. Cuff pressure 20–30 cmH₂O; high pressure → tracheal stenosis/tracheomalacia.
12. Right main bronchus is the usual site of endobronchial intubation (less acute angle).