Predictors of difficult intubation

Why this matters (new starter focus)

• Difficult intubation is usually manageable if anticipated: the risk comes from being surprised.
• Prediction is imperfect: use multiple features + overall impression, not one test.
• Your aim is to identify: (1) difficult mask ventilation, (2) difficult laryngoscopy/intubation, (3) difficult rescue (supraglottic airway/front-of-neck access).
• If you suspect difficulty: optimise positioning, pre-oxygenate well, have a clear plan (A/B/C), and involve senior help early.

Key definitions (simple and exam-friendly)

• Difficult laryngoscopy: poor view of the vocal cords at laryngoscopy (often described using Cormack–Lehane grading).
• Difficult intubation: needing multiple attempts, alternative devices, or another operator to place a tracheal tube.
• Difficult mask ventilation: hard to maintain oxygenation/ventilation with a face mask (often due to poor seal or obstruction).
• Difficult airway: difficulty with face mask, supraglottic airway, tracheal intubation, or front-of-neck access.

History clues (often the strongest predictors)

• Previous difficult intubation or difficult mask ventilation (ask what worked: videolaryngoscope, bougie, awake technique).
• Known airway pathology: tumours, radiotherapy changes, airway stenosis, tracheostomy history.
• Symptoms suggesting obstruction: stridor, voice change, dysphagia, positional breathing difficulty.
• Obstructive sleep apnoea (OSA): loud snoring, witnessed apnoeas, daytime somnolence; often linked with difficult mask ventilation and rapid desaturation.
• Rheumatoid arthritis/ankylosing spondylitis: limited neck movement; consider cervical spine instability in RA.
• Burns/scarring, previous head and neck surgery, or facial trauma.

Look–Feel–Move: quick bedside assessment

• LOOK: facial hair (seal issues), obesity/large neck, small jaw (receding chin), prominent upper incisors, facial trauma, swelling, limited mouth opening.
• FEEL: assess jaw size and space under the chin (submandibular space); a “full” or small space can make laryngoscopy harder.
• MOVE: mouth opening (inter-incisor distance), neck flexion/extension, and ability to adopt the sniffing position.

Common bedside predictors of difficult laryngoscopy/intubation

• Mallampati score (I–IV): higher grades can suggest difficulty, especially when combined with other features (check sitting, mouth open, tongue out, no phonation).
• Reduced mouth opening: inter-incisor distance <3 finger breadths (or <3 cm) suggests difficulty inserting laryngoscope/videolaryngoscope and using adjuncts.
• Thyromental distance: short distance (often <6–6.5 cm) suggests reduced space to displace the tongue and align the view.
• Limited neck extension: makes it harder to align airway axes and obtain a good view.
• Large neck circumference (often >40 cm) and obesity: associated with difficult laryngoscopy and rapid desaturation.
• Upper airway obstruction or distorted anatomy: infection, tumour, swelling, trauma.

Predictors of difficult mask ventilation (don’t forget this)

• Poor mask seal: beard, facial deformity, missing teeth/edentulous face (can worsen seal), nasogastric tubes.
• Upper airway obstruction: OSA, large tonsils, reduced jaw thrust, sedation-related collapse.
• Obesity and large neck: increased airway collapsibility and reduced functional residual capacity (desaturates quickly).
• Limited jaw protrusion or restricted mouth opening: harder to perform effective jaw thrust and adjunct placement.
• High risk of regurgitation/aspiration: may limit ability to use positive pressure ventilation safely (plan accordingly).

LEMON approach (simple structure for new starters)

• L – Look externally: face/neck features, trauma, beard, obesity, large tongue.
• E – Evaluate 3-3-2: mouth opening (~3 fingers), hyoid–mentum (~3 fingers), thyroid notch–mouth floor (~2 fingers) as a rough screen.
• M – Mallampati: higher grade increases risk when combined with other findings.
• O – Obstruction: stridor, swelling, infection, tumour, foreign body.
• N – Neck mobility: reduced extension/flexion increases difficulty.

Practical tips when predictors are present (safe first-time actions)

• Call for senior help early if you see multiple predictors or any red flag (don’t wait for failed attempts).
• Optimise positioning: “sniffing” position; in obesity use head-elevated laryngoscopy position (ramped) so external auditory meatus aligns with sternal notch.
• Pre-oxygenate thoroughly; consider nasal oxygen during attempts (apnoeic oxygenation) if available locally.
• Have a clear Plan A/B/C: e.g., videolaryngoscope early, bougie ready, supraglottic airway as rescue, and know local emergency front-of-neck access pathway.
• Limit attempts: change something each attempt (operator, device, position) and avoid repeated trauma.
• Prepare adjuncts: suction, oral/nasal airway, bougie/stylet, different blade sizes, supraglottic airway, and difficult airway trolley.

Common “first on-call” scenarios

• Obese patient for emergency laparotomy: anticipate rapid desaturation; ramp, pre-oxygenate, consider videolaryngoscope first-line, have suction and rescue plan ready.
• Trauma with cervical spine precautions: limited neck movement; use manual in-line stabilisation as required, consider videolaryngoscope, minimise attempts.
• ENT infection/swelling (e.g., deep neck space infection): obstruction risk; involve seniors/ENT early; consider awake technique depending on severity and local practice.
• OSA patient for urgent surgery: difficult mask ventilation risk; ensure good mask seal, two-person technique early, airway adjuncts ready.