This article was initially published as a twitter thread covering the anaesthetic airway assessment for novices.
It includes links to online resources that I've found useful and some seminal papers that I think are important for trainees to know of as they underpin much of our anaesthetic learning and practice.
Introduction
The first resource that I recommend you look at is the 4th National Audit Project (NAP4). This huge study addressed major complications of airway management. It really contextualises why an airway assessment is important and has greatly influenced anaesthetic practice since. Read the executive summary for the key findings. The salient points for this brief article are that airway complications are associated with:
Poor anaesthetic assessment
Poor planning for the anticipated difficult airway
Poor planning for the unanticipated difficult airway
Poor judgement and training
and 1/3 of adverse airway events occurred during emergence.
I recommend that you are familiar with all the National Audit Projects given the impact they have on our practice (they are also popular exam topics).
Focus of an airway assessment
At this point, I want to stress that the airway assessment is really a risk assessment for any subsequent airway management we may be required to provide.
Airway management is not just about intubation.
Assessment is important to identify potential problems with:
Self ventilation
BMV ventilation
SGA insertion
Laryngoscopy and intubation
FONA
Extubation
The broader context of the airway assessment is covered in this BMJ article. Part of this assessment involves a focused airway examination which takes less than 2 minutes to complete (see our video below)
There are many individual airway tests that can be incorporated into the anaesthetic airway examination. You’ll go mad trying to learn them all! The Australia and New Zealand College of Anaesthetists has an excellent document here that brings the whole airway assessment together, including multiple specific airway tests (analysing their sensitivity and specificity).
As mentioned before, the airway assessment is a risk stratification tool. It therefore doesn't matter if you think an airway will be difficult and turns out to be straightforward to manage (surely a relief). This doesn't represent a "failure" of the tests. From an epidemiological point of view we demand our screening tests should have high sensitivity even at the cost of specificity!
Mask Ventilation
Mask ventilation is the first airway management we are likely to perform on our patients. We can grade the difficulty from 0-4. A detailed discussion of the topic can be found here.
25% of patients will be grade ≥2 and require some form of airway adjunct to facilitate good quality mask ventilation (BMV).
Take BMV seriously as it is a rescue technique in difficult airway management
Laryngoscopy and Intubation
We put lots of worth on intubation and is considered an anaesthetists signature manoeuvre. There are 2 main theories on optimising our technique
3-axis alignment nicely explained here by AirwayJedi.com
2 curves theory described in this BJA article
Neither theory gives the whole story, but they both offer important insights into how we position our patients (sniffing the morning air) and optimise them for direct laryngoscopy. Also if we are having difficulty, then it provides us with a framework of manoeuvres to employ that can make our task much easier.
Extubation
Extubation and emergence are dangerous times for airway management as mentioned above. Respiratory complications are the most common major problem in the immediate postoperative period.
The Difficult Airway Society (DAS) has created guidelines for planning extubation of patients with difficult airways
Planning extubation should begin as early on as during our airway assessment but we won't know the patient has a difficult airway until we actually try to manage it, which may allow us to change our approach to extubation accordingly.
Predicting difficulty
Hopefully you can appreciate the importance of an airway assessment. But it is dependent on the tests employed. The ability of the tests to predict difficulty with airway management has been analysed in this Cochrane review. Importantly, we can't just rely on a sole Mallampati score.
50% of patients with difficult laryngoscopy will be missed using Mallampati alone.
However, Mallampati with thyromental distance and mandible protrusion significantly increase your positive predictive value, sensitivity and specificity.
Ultimately, the tests employed depend on the airway management technique envisioned. Given the problems we are trying to avert, we should adopt a pragmatic and risk-averse approach. Chose tests that are timely, sensitive and evidence based.
If some of the anticipated difficult airways turn out to be straightforward, then that's a relief. If they do in fact turn out to be problematic...you will be glad to have anticipated the problems and taken steps to prepare yourself, equipment and team into mitigating harm to the patient
Managing the difficult airway
In stressful situations where you are struggling with your approach to manage the patient's airway you need a structured and calm approach. Part of the IAC involves simulated management of the unanticipated difficult airway and a CICO scenario to prepare for this.
For the UK exams, this is covered by the DAS guidelines and their algorithm should be followed. However, there is another interesting concept to be aware of, that most novices will not have heard of... the Vortex Approach by @NicholasChrimes.
It provides another way of thinking about factors that make airway management difficult and an approach in an emergency. Well worth a look.
We've made a lecture covering all the above and more – hopefully it's useful. It is a bit long as there is so much to cover.
Good luck!
