I’m an anaesthetic registrar in North East London (@andrewwilko1986). On a daily basis I perform airway assessments. Although not a classic medical school patient examination, it’s an extremely important process. Fortunately it’s very simple, and in this blog I’d like to highlight why it’s important, and some concepts to think about when dealing with a patient that might require a definitive airway in the ED.
One main reason is NAP41. If you’re scratching your head and wondering what NAP4 is then you’re in luck and have the delight of reading it for the very first time after this blog. And PLEASE do, you won’t regret it. It’s a phenomenal audit project investigating the nature of airway management complications across the UK, both in and out of theatre. One of their major conclusions was that ‘poor airway assessment contributes to poor airway outcomes’ and ‘failure to assess the airway is a failure in professional duty’.
The familiar adage ‘failure to prepare is preparing to fail’ couldn’t be more poignant than with the acutely unwell patient that requires intubation.
Now I know that emergency medicine (EM) rapid sequence intubation (RSI) is a hot topic for debate but I want to focus on the step before this that I believe is more important than the person wielding the laryngoscope blade. After all, you can teach a monkey to put a correctly shaped block through a hole.. and presumably put an endotracheal tube into the trachea. Point being: it’s not a difficult psychomotor skill to master.
We know that the incidence of difficult intubation (grade 3 or 4 view) in the ED is up to 7 fold greater than for elective surgical cases, with the percentage of difficult intubations quoted at 8.5% in a large multi-centre prospective study of urban EDs in Scotland2. I’m fully aware that there are significant confounding factors with these figures this but it reinforces the importance of a quality airway assessment allowing us to prepare appropriately.
In ED, when you have a patient requiring an RSI, before you get caught up with the type and dose of induction agent, size of endotracheal tube and laryngoscope blade, DON’T forget the airway assessment!
To assess a patient’s airway we need to have an organised, structured approach and be aware of features that worry us.
Like any patient assessment it can be neatly divided into history, examination and investigations. In the ED, I can appreciate that history and investigations are not always available, but that’s OK because the crucial component of an airway assessment is the physical examination. Virtually all of the information is gained visually.
It is made up of multiple single assessments:
- Mallampati score (I,II,III,IV)
- Mouth opening (>3cm is good)
- Thyromental distance (>6.5cm is good)
- Mandibular protrusion/upper lip bite test
- Neck movements
A well described assessment is the Mallampati score (see appendix below) which is simple to perform. However, a large meta-analysis demonstrated ‘only 35% of patients with a difficult intubation were identified as Mallampati III or IV’4. Similarly poor sensitivity/specificity is seen in all single assessments if performed in isolation. So what we must do is utilise an amalgamation of these single tests.
Grouped assessments (see appendix):
- WILSON’s score (5 parameters – weight, neck movement, jaw movement, receding mandible, buck teeth)
- LEMON (Look, Evaluate, Mallampati, Obstruction, Neck movements)
I personally like to break the airway assessment down into what will be difficult for the given patient;
- Difficult BVM = ‘BONES’ – Beard, Obese, No teeth, Elderly, Sleep apnoea
- Difficult larngoscopy = Mouth opening < 3cm or unable to put 3 fingers between inscisors.
- Difficult larnygeal view = Inability to align the 3 axis of the airway, see below.
- Difficult surgical airway = ‘SHORT’ – Surgery, Haematoma, Obese, Radiation, Tumour
Predicting difficult laryngeal view
I’m going to concentrate on the issue of a predicted difficult laryngeal view in more detail, because if we identify a problem here then it’s vital we make a contingency plan prior to pushing the drugs (having said that, one should always make a contingency plan even if the airway is predicted to be easy, particularly in the ED).
The reasons for difficult laryngeal views are due to an inability to line up the three axes of the airway (laryngeal axis, pharyngeal axis and oral axis) with the line of our vision.
Predictors for difficult laryngeal view includes:
- Mallampati grade III or IV
- Buck teeth/awkward dentitian
- Limited mandibular protrusion/Retrognathia
- Short/fat neck = Thyromental distance < 6.5cm
- Reduced neck movements (particularly extension) or C-spine immobility.
If you highlight any of these then I recommend that you alert the anaesthetic team, and insist on senior airway supervision for the RSI. I also highly recommend that the primary intubator’s first line laryngoscope blade should be a video laryngoscope. DAS guidelines for RSI suggest that you should have NO more than 3 laryngoscope attempts; therefore, make your first attempt your best attempt!
A landmark paper on ED RSI from Fogg et al in 2012, found that the significant majority (65.4%) are carried out due to patients having low conscious states (GCS <8)3.
Levitan et al (2004) published a retrospective study looking at airway assessments in ED RSI’s, which found that ‘Mallampati scoring, neck mobility testing, and measurement of thyromental distance could have been done in only one third of non-cardiac arrest ED intubations and in none of the rapid sequence intubation failures’5.
This is often the reason given for not formally carrying out an assessment (i.e. patient unable to comply with assessment); however, this is an unacceptable excuse as the majority of airway assessment tests can be performed without patient co-operation. All that’s required, is a modified approach.
To do so, put a pair of gloves on and simply look and feel your way through the assessments; short, fat neck, receding mandible, open mouth and inspect dentition, mobilise the neck (provided no risk of C-spine injury). In my opinion the only one that you definitely can’t do is the Mallampati assessment and I have already explained that it’s fairly poor at identifying the difficult intubation if used as the only method of airway assessment.
Ultimately, if you feel you are unable to perform an adequate airway assessment then the patient should be classed as a predicted difficult airway, and the airway plan should reflect that.
Final thoughts and recommendations
Airway assessment is the cornerstone to preparing for your ED RSI. There is NO excuse for its omission. ‘Failure to assess the airway is a failure in professional duty’.
There is always time to perform an airway assessment.
If a potential difficult airway is identified, ensure you have senior airway support.
Obtain immediate feedback from your own airway assessment even if you aren’t the primary intubator. Guess the suspected Cormack and Lehane grade and see if you were correct in suspecting an easy or difficult view.
Have a low threshold for use of a video laryngoscope with the proviso that you are familiar with the device available in your hospital. If you aren’t, then go and practice. Introduce yourself to a friendly anaesthetic colleague and ask to practice in the calm environment of elective theatre. We will always be eager to teach, as we know that airway management transcends specialty boundaries.
Total score <5 easy intubation, 5-7moderate intubation, >7 difficult intubation
Look externally – facial trauma, deformity, beard, poor dentition, large tongue etc
Evaluate – 3-3-2 rule of finger breaths. 3 (mouth opening) – 3 (hyoid to chin) – 2 (thyroid to floor of mouth)
Mallampati – (I-IV)
Obstruction – soft tissue swelling, trauma to the face or neck, foreign bodies, obesity etc.
Neck movements – restricted
- NAP4 – http://www.rcoa.ac.uk/nap4
- Graham C et al. Rapid sequence intubation in Scottish urban emergency departments. EMJ 2003;20:3–5.
- Fogg T et al. Prospective observational study of the practice of endotracheal intubation in the emergency department of a tertiary hospital in Sydney, Australia. EMA 2012, 24: 617-624.
- Lundstrom L et al. Poor prognostic value of the modified Mallampati score: a meta-analysis involving 177 088 patients. BJA. 107 (5)
- Levitan R et al. Limitations of difficult airway prediction in patients intubated in the emergency department. Ann Emerg Med. 2004;44:307-13.