Failed Intubation

Failed intubation is failure to place a tracheal tube after a reasonable number of attempts (usually 3 by the first operator plus one more by a second experienced operator). Difficult laryngoscopy is a related but separate finding with a poor view (Cormack-Lehane grade 3 or 4).

Epidemiology. Difficult laryngoscopy occurs in 1.5% to 8% of intubations. Failed intubation affects about 1 in 2,000 general anaesthetics and about 1 in 250 to 1 in 300 in obstetric general anaesthesia.

Risk factors. Mallampati class 3 or 4, mouth opening under 3 cm, thyromental distance under 6 cm, limited neck extension or jaw protrusion, obesity, beard, prominent upper incisors, cervical spine disease, previous neck radiotherapy, neck mass, sleep apnoea and pregnancy.

Causes. Anatomical and pathological factors, poor positioning, inadequate muscle relaxation, bleeding or secretions, limited experience and unsuitable equipment.

Pathophysiology.

Anatomical features that prevent alignment of oral, pharyngeal and laryngeal axes limit the view of the glottis, and repeated attempts cause oedema, bleeding and trauma that convert a difficult airway into an emergency.

Poor view of glottis, inability to pass the tube, bougie or tube arrest at a fixed point, oesophageal placement with no capnography trace, desaturation, trauma to teeth and mucosa, bleeding and secretions.

Red flags.

• Desaturation under 92% with failed ventilation (CICO).
• Third unsuccessful attempt.
• Bleeding or oedema worsening the view.
• Stridor or known airway mass.

Confirm tracheal placement only by sustained waveform capnography over at least 4 to 6 breaths. Review airway assessment, tools used and view obtained.

Differential diagnosis.

• Oesophageal intubation.
• Laryngospasm.
• Opioid induced chest wall rigidity.
• Inadequate relaxation.
• Equipment failure.

Prepare for a difficult airway: use ramped position, preoxygenation to end tidal oxygen 85% or more, apnoeic oxygenation (nasal oxygen 15 L/min or high flow 30 to 70 L/min), a video laryngoscope and a bougie.

Plan A (tracheal intubation). Optimise position, external laryngeal manipulation, bougie and video laryngoscope; no more than 3 attempts, plus one more by a second operator. Maintain oxygenation and anaesthesia between attempts.

Plan B (supraglottic airway). Insert a second generation supraglottic airway, check ventilation by capnography, and limit attempts to 3.

Plan C (wake up). If ventilation is adequate, stop and wake the patient (use sugammadex after rocuronium if needed), then re-plan with awake intubation or a regional technique.

Plan D (front-of-neck access). If oxygenation fails, proceed to scalpel cricothyroidotomy at once, since delay causes hypoxic injury.

• Rocuronium: 1.2 mg/kg IV once; maximum 1.2 mg/kg; monitor train-of-four; dose on ideal body weight in obesity.
• Sugammadex: 16 mg/kg IV once for rapid wake up; maximum 16 mg/kg; avoid if creatinine clearance is under 30 mL/min.

Awake intubation for a planned difficult airway.

• Lidocaine (topical, 4% by spray, nebulisation or gargle): total dose up to 9 mg/kg of lidocaine during the procedure; maximum 9 mg/kg; monitor for perioral numbness, tinnitus, seizures and arrhythmia; reduce by 25% to 50% in hepatic impairment, heart failure and older adults.
• Dexmedetomidine sedation: 1 microgram/kg IV over 10 minutes, then 0.2 to 0.7 microgram/kg/h; maximum 1.4 microgram/kg/h; monitor heart rate, blood pressure and airway; reduce in older adults and hepatic impairment; avoid in heart block.

Obstetric failed intubation. Prioritise maternal oxygenation. Use a second generation supraglottic airway and continue the operation if urgent, or wake the mother if not. Front-of-neck access if oxygenation fails.

After the event. Record the findings, tell the patient, issue an alert letter and inform the general practitioner. Review for airway trauma, aspiration and desaturation.

Monitoring. Continuous capnography and saturation, and observation for swelling, bleeding and aspiration.

Referral and escalation. Senior anaesthetic help after the first failure. ENT review for airway pathology. Airway clinic after the event.

Special groups. Obese, pregnant and paediatric patients desaturate quickly. Use video laryngoscopy early.