Difficult Airway
A difficult airway is defined as a clinical situation where a trained anaesthetist experiences difficulty with facemask ventilation, laryngoscopy, intubation, or SGA placement, requiring structured algorithm-based management.
Key Facts
Difficult intubation occurs in approximately 1-4% of all anaesthetics; unanticipated in ~1-2% LEMON assessment: Look externally, Evaluate 3-3-2, Mallampati, Obstruction, Neck mobility DAS 2015 guidelines provide a 4-plan algorithm: Plan A (intubation) → Plan B (SGA) → Plan C (facemask) → Plan D (eFONA) Maximum 3+1 intubation attempts — repeated attempts cause airway trauma and oedema, worsening the situation Awake fibreoptic intubation (AFOI) is the gold standard for anticipated difficult intubation Sugammadex 16mg/kg provides immediate reversal of rocuronium — a rescue option in failed intubation Videolaryngoscopy should be available for all intubations and significantly improves success in difficult airways NAP4 highlighted that failure to plan for known difficult airways was the most common contributing factor in airway-related deaths
Overview
Key Facts
The difficult airway represents one of the most challenging scenarios in anaesthetic practice. Unanticipated difficulty accounts for significant morbidity and mortality. Structured pre-operative assessment and adherence to algorithms are the cornerstones of safe management.
Epidemiology
Difficult intubation occurs in 1-4% of anaesthetics. Failed intubation in 1 in 2,000 routine cases, rising to 1 in 400 in obstetrics. CICO events occur in approximately 1 in 50,000. NAP4 found that human factors (poor planning, failure to use algorithms) contributed to the majority of airway disasters.
Aetiology
Predictors of difficult intubation:
- Mallampati III-IV, short thyromental distance (<6.5cm), limited mouth opening (<3cm)
- Obesity (BMI >30), short thick neck, large tongue
- Previous difficult intubation (documented in notes/alert card)
- Head and neck pathology: tumours, radiotherapy, burns, infection
- Cervical spine immobility: trauma, rheumatoid arthritis, ankylosing spondylitis
- Pregnancy: Airway oedema, large breasts, weight gain
Pathophysiology
Difficult airway situations create a physiological crisis of progressive hypoxaemia. Each failed attempt at laryngoscopy worsens airway oedema and bleeding, further reducing the chances of subsequent attempts. The safe apnoea time (time to critical desaturation) varies: healthy adult ~8 minutes (after pre-oxygenation), obese patient ~3 minutes, pregnant patient ~2-3 minutes, child ~2 minutes.
Clinical Presentation
Pre-Operative Assessment Findings Suggesting Difficulty
- Previous difficult intubation documented
- Mallampati III/IV
- Reduced mouth opening (<3 finger-breadths)
- Short thyromental distance (<6.5cm)
- Receding mandible, prominent upper incisors
- Limited neck extension
- Obesity, short neck, high BMI
- Head/neck pathology (radiation, tumour, abscess)
Intra-Operative Difficult Airway
- Poor laryngoscopic view (Cormack-Lehane 3 or 4)
- Multiple failed intubation attempts
- Failed SGA placement
- Inability to ventilate via facemask
- Progressive desaturation
Red Flags
- SpO2 falling below 90% — declare emergency, escalate to next plan in DAS algorithm
- Cannot ventilate despite SGA and facemask — declare CICO
- Stridor or voice change pre-operatively — suggests supraglottic pathology
- History of previous failed intubation/tracheostomy — awake technique essential
Differential Diagnosis
| Scenario | Key Features | Primary Approach |
|---|---|---|
| Anticipated difficult intubation | Known risk factors, previous documentation | Awake fibreoptic intubation |
| Unanticipated difficult intubation | Poor view at laryngoscopy after induction | DAS algorithm — Plan A to D |
| Cannot intubate, can oxygenate | Failed ETT but SGA effective | Maintain oxygenation, wake patient or proceed via SGA |
| CICO | Cannot intubate AND cannot oxygenate | eFONA — scalpel cricothyroidotomy |
| Supraglottic obstruction | Tumour, abscess, anaphylaxis | ENT standby, awake technique, consider tracheostomy |
| Subglottic stenosis | Previous intubation, stridor | CT neck, ENT assessment, careful planning |
Diagnosis / Investigation
Bedside
- Structured airway assessment: LEMON, Mallampati, thyromental distance, mouth opening, neck extension, dentition
- Review previous anaesthetic records: Essential — check for documented difficulty
- Alert card/bracelet: Patient may carry difficult airway information
Bloods
- Not specifically required for airway assessment
Imaging
- CT/MRI neck: If tumour, abscess, tracheal deviation, or subglottic stenosis suspected
- Lateral cervical spine X-ray: Assess atlantoaxial subluxation (rheumatoid arthritis, Down syndrome)
- Nasendoscopy: ENT assessment of supraglottic and glottic anatomy
Special Tests
- Ultrasound of neck: Identify cricothyroid membrane (especially in obese patients or those with abnormal anatomy)
- Point-of-care airway ultrasound: Increasingly used for pre-operative planning
Management
Non-pharmacological
- Pre-operative planning: Discuss with patient, document plan, brief theatre team
- Equipment preparation: Full difficult airway trolley available; videolaryngoscope, fibreoptic scope, cricothyroidotomy kit
- Positioning: Optimal head position (ramped in obese patients)
- Pre-oxygenation: 3 minutes tidal breathing or 8 vital capacity breaths with 100% O2
Pharmacological
- Awake fibreoptic intubation: Topical 4% lidocaine (nebulised + spray-as-you-go), sedation with remifentanil TCI 1-3ng/mL
- Neuromuscular blockade: Rocuronium (allows sugammadex reversal) preferred over suxamethonium in many anticipated difficult scenarios
- Sugammadex 16mg/kg: Immediate reversal of rocuronium — use in failed intubation before Plan D if applicable
- Dexamethasone 8mg IV: May reduce airway oedema from repeated instrumentation
Surgical/Interventional
- Emergency front-of-neck access (eFONA): Scalpel-bougie-tube technique (DAS 2015)
- Surgical tracheostomy: Under local anaesthesia for anticipated impossible intubation
- Retrograde intubation: Wire-guided technique (rarely used with availability of fibreoptic)
Referral Criteria
- Known difficult airway — senior/consultant anaesthetist involvement
- Anticipated surgical airway — ENT/maxillofacial surgery standby
- Post-CICO event — critical incident review, patient follow-up, difficult airway alert documentation
Prognosis
- AFOI success rate: >95% in experienced hands
- Videolaryngoscopy: Improves first-pass success rate to >95% even in difficult airways
- eFONA success rate: >90% when performed promptly using scalpel technique
- Morbidity from repeated laryngoscopy: Airway oedema, bleeding, dental damage — limits subsequent success
- Litigation: Airway management claims are among the most common in anaesthetic negligence cases
Other Relevant Information
DAS 2015 Unanticipated Difficult Intubation Algorithm
| Plan | Strategy | Key Actions |
|---|---|---|
| A | Facemask + intubation | Optimal positioning, videolaryngoscopy, bougie; max 3+1 attempts |
| B | Maintain oxygenation — SGA | Second-generation SGA (e.g., i-gel, ProSeal); max 3 attempts |
| C | Facemask ventilation | Two-person technique, oropharyngeal airway, consider waking patient |
| D | CICO — eFONA | Scalpel cricothyroidotomy (scalpel-bougie-tube technique) |
Risk Factors for Difficult Mask Ventilation (MOANS)
| Factor | Description |
|---|---|
| M | Mask seal (beard, facial trauma) |
| O | Obesity/obstruction |
| A | Age >55 |
| N | No teeth (edentulous) |
| S | Stiff lungs/snoring (OSA) |