- Difficult intubation is described as an intubation in which an anaesthetist with at least 2 years' training, using a traditional laryngoscope blade:
- Achieves only a poor view at direct laryngoscopy (Cormack and Lehane grade 3 or 4), or
- Requires >3 attempts at direct laryngoscopy, or
- Requires >10mins to intubate, or
- Requires additional equipment in order to secure the airway
- How this definition holds up in modern times, where video laryngoscopy ± bougie is becoming de riguer, is not clear
- A broader definition may be: 'a difficult airway is one where a healthcare provider who is skilled at airway management experiences difficulty with one or more recognised techniques'
Difficult Intubation
Difficult Intubation
This much-feared complication of airway intervention is a frequent exam question, particularly the Primary FRCA.
The keen-eyed will notice a lack of a 'management' section; this is because management of the (unanticipated) difficult airway follows the below-linked DAS guidelines, so I haven't replicated them here.
Resources
- NAP4 (RCoA & DAS, 2011)
- Predicting the difficult airway (BJA Education, 2014)
- Difficult Airway Society guidelines for management of unanticipated difficult intubation in adults (DAS, 2015)
- Airway Assessment (ANZCA, 2016)
- Postoperative management of the difficult airway (BJA Education, 2017)
- Emergency front of neck access in airway management (BJA Education, 2019)
- Difficult intubation occurs in approximately 1 in 65 patients, although this depends greatly on the studied population and the definitions used
- Serious adverse airway events occur in 1 in 22,000 general anaesthetics, with an incidence of death or brain damage in 1 in 180,000
Patient factors
- Anterior column i.e. face and oropharynx
- Obesity ± large breasts
- Beard
- Acromegaly
- Retro- or micro-gnathia
- Congenital syndromes e.g. Pierre-Robin, Treacher-Collins, Klippel-Feil, Goldenhaar's
- Dental abscess, Ludwig's angina
- Facial fractures or burns
- Previous neck surgery and/or radiotherapy
- Middle column i.e. laryngeal structures
- Peri-laryngeal infections e.g. epiglottitis, supraglottitis, croup
- Cancers of the larynx, base of tongue, thyroid
- Previous prolonged intubation i.e. risk of tracheal stenosis
- Posterior column i.e. cervical spine
- C-spine immobilisation (e.g. trauma) or fixation (e.g. previous surgery)
- Down's syndrome
- Rheumatoid arthritis
- Ankylosing spondylitis
- Other
- Previous difficult intubation
- Paediatric patients
- Obstetric patients
Non-patient factors
- Junior anaesthetist
- Emergency intubation
- Intubation outside of theatre environment e.g. ICU, ED
- Poor airway assessment and/or planning
- Improper positioning
- Inadequate paralysis
- Inadequate equipment e.g. blade size/curvature
Airway history
- Review previous anaesthetic charts for grade of airway (see below)
- Review available imaging inc. CT, MRI and nasendoscopy
- History from patient looking for features known to increase risk of difficult airway (see above)
Airway inspection
- Anterior and side of head and neck e.g. masses, beards, swellings, fat pads, aberrant anatomy
- Oropharynx e.g. teeth, Mallampati grading
- Inter-incisal gap (ideally >3 of patients own finger widths)
- Thyromental distance (ideally >6.5cm)
- Sternomental distance (ideally >12cm)
Airway movements
- TMJ subluxation (A, B or C)
- C-spine movements
- Nostril patency (especially if nasal intubation planned)
- No single test the can predict difficult intubation
- Composite scores such as the Wilson, Arne
- 20% of all difficult intubations are unpredicted
| Test | Sensitivity | Specificity | Positive predictive value |
| Mallampati | 42-60% | 81-89% | 4-21% |
| Modified Mallampati | 65-81% | 66-82% | 8-9% |
| Thyromental distance | 65-91% | 81-82% | 8-15% |
| Sternomental distance | 82% | 89% | 27% |
| Wilson | 42-55% | 86-92% | 6-9% |
| Arne | 80-98% | 91-94% | 25-42% |
| Mouth opening | 26-47% | 94-95% | 7-25% |
| Jaw protrusion | 17-26% | 95-96% | 5-21% |
Mallampati score
- The archetypal airway asssessment, which involves visual inspection of the oropharynx with the patient sitting upright, head in neutral position, mouth wide open and tongue protruding
- Graded as:
- Soft and hard palate, tonsillar pillars and entirety of uvula visible
- Soft palate and pillars visible but only part of the uvula
- Only hard palate and base of uvula visible
- No hard palate visible
- Is reasonable sensitive and specific, but with poor positive predictive value
Wilson risk score
- This is included as it is beloved by the RCoA for examination purposes
| Risk Factor | Score 0 | Score 1 | Score 2 |
| Weight (kg) | <90 | 90-110 | >110 |
| Head and neck movement | >90° | ~90° | <90° |
| Jaw movement | Inter-incisor gap >5cm TMJ A |
Inter-incisor gap <5cm TMJ B |
Inter-incisor gap <5cm TMJ C |
| Receding mandible | Normal | Moderate | Severe |
| Protruding teeth | Normal | Moderate | Severe |
- A total score of >2 predicts 75% of difficult intubations
Cormack & Lehane
- The Yentis & Lee (1998) modification to the original Cormack & Lehane (1984) grading is probably the most widely used
- The view at direct larygnoscope is described as being grade:
- Grade 1 - most of the glottic opening seen
- Grade 2
- 2a - partial view of glottis
- 2b - only arytenoids or posterior part of cords seen
- Grade 3 - epiglottis but no glottis seen
- Grade 4 - epiglottis not seen
Modifications for videolaryngoscopy
- With the growing use of videolarngoscopy (BJA, 2022), alternate grading systems have been proposed
- The Fremantle score describes both the view at VL and the ease of intubation
- Fremantle grading may be more accurate, and with a greater inter-user reliability, than the Cormack & Lehane score when assessing VL (Anaesthesia, 2017)
- There's some suggestion a simplification of laryngoscopic view into 'easy', 'restricted' or 'difficult' may be better than improperly used and imperfect scoring systems (Anaesthesia, 2002)
| View at laryngoscopy | Ease of intubation |
| Full | Easy 1st attempt |
| Partial | Modified >1 technique ± adjunct |
| None | Unachievable Technique abandoned |
- This was a prospective audit of major airway complications
- Its results imply 2.9 million general anaesthetics/year in the UK, of which 56% are done with a supraglottic device in situ, 5% use a face mask only and 38% are intubated
- Key findings include:
- Poor airway assessment (incomplete, omissions) ± failure to alter plan to findings contributed to poor airway outcomes
- Poor airway planning contributed to poor airway outcomes
- Aspiration was the single commonest cause of death in anaesthesia-related events and often arose due to poor judgement
- SAD often used when ETT ± RSI should have been used
- There was an under-use of awake tracheal intubation
- Obese patients featured twice as prominently in NAP4 cases but it was under-recognised as a cause of difficult airway
- 1/3rd of events occur during emergence, with obstruction being the commonest event (leading to pulmonary oedema in 10%)
- 25% of NAP4 events occurred in ICU/ED and had a higher risk of morbidity/mortality
- Most ED events were complications of RSI
- Failure to use capnography was a factor in 70% of ICU-related airway deaths
- Displaced tracheostomies were a major cause of morbidity on ICU
- eFONA had an incidence of 1 in 12,500–50,000 general anaesthetics during NAP4
Optimal technique
- There is debate about the optimal technique: scalpel or needle cricothyroidotomy
- NAP4 demonstrated a 63% failure rate of cannula cricothyroidotomy but near universal success of a scalpel technique
- This is reflected in the pre-hospital world, where a scalpel technique was significantly more likely to succeed than a needle technique (BJA, 2023)
- In light of this, the recommendation from DAS/RCoA/AAGBI/FICM/ICS is the scalpel-bougie-tube technique
- Other nations have different approaches:
- ANZCA - either scalpel or needle cricothyroidotomy, depending on preference
- Canada - percutaneous needle-guided wide-bore cannula, or open surgical approach
- USA - percutaneous or surgical technique
Complications
- Failure
- Device misplacement and failure to adequately oxygenate/ventilate
- Bleeding
- Damage to laryngotracheal structures, including posterior tracheal wall
- Specific to trans-tracheal jet ventilation; barotrauma, pneumothorax, pneumomediastinum, subcutaneous emphysema
- Subglottic stenosis
- Neck scarring
- Formulate immediate airway management plan
- May involve surgical review to transition eFONA to definitive airway
- Monitor for complications
- If eFONA has occurred, need to monitor for pharyngeal or oesophageal injury, and mediastinitis
- Proceed or abandon surgery as indicated
- Anticipate difficult extubation, especially if surgical intervention is likely to have exacerbated issues, particularly head and neck surgery
After the event
- Debriefing with team
- Complete airway alert form
- Provide information to:
- Patient; written and verbal
- GP in writing
- Local database