Today’s post on Resus.me by @cliffreid was yet another reminder of how challenging (if not impossible) it is to predict a difficult airway.
The study he quotes (1) looked at ~188000 intubations by anesthetists in Denmark. For each case, the anesthetists recorded pre-intubation if they expected a difficult intubation and if they expected the patient to be difficult to ventilate via bag-valve mask. Provider were left to their own devices as to how to determining what would predict a difficult airway. After the case, the anesthetist recorded whether or not the intubation and ventilation was actually difficult. Difficult airways were defined as 3 or more attempts.
Of the ~3100 difficult airways, 93% were unanticipated.
In cases in which the provider anticipated difficult airway, only about 25% actually ended up being difficult.
The numbers for predicting difficult bag-value mask ventilation were similar.
As many pointed out on Foam-o-sphere, the lesson here is not that we should stop assessing for difficult airway. Doing this evaluation forces us to think and plan the airway. This data implies that we should be ready for a difficult airway during even the most routine intubation.
So let’s review:
How does one assess for difficult airway?
The easiest approach is to use the LEMON mnemonic, which stands for Look, Evaluate 3-3-2 rule, Malempati, Obstruction of the airway, Neck Mobility. It has been well rehashed here and here (video). Some (2), however, have suggested it might be challenging to apply to ED patients.
A mnemonic for identifying a patient likely to be difficult to bag mask ventilate is BONES: Beard, Obese, Neck, Elderly, Snores. (3)
There are other mnemonics, so just pick a couple you like and get familiar with them.
What does it mean to be ready for a difficult airway?
This is the subject of many blog posts, papers, tweets and debate. There are two generally accepted concepts:
- If the airway goes south, something needs to change on the subsequent attempts. This can be any number of things, including the method of cord visualization, incorporating specialized equipment (eg. boujie), changing the operator, etc.
- If you cannot get the airway after several attempts or if the SpO2 gets unacceptably low in a can’t ventilate situation, be ready to pull the trigger on cricothyrotomy.
There are several mental models to archive the above two goals. Here are a couple to start off with:
- Strayer Airway Algorithm
- The Vortex Approach
- Shock Trauma Failed Airway Approach
- Cricon2 Approach (for surgical airway)
(1) Nørskov, A. K., et al. “Diagnostic accuracy of anaesthesiologists’ prediction of difficult airway management in daily clinical practice: a cohort study of 188 064 patients registered in the Danish Anaesthesia Database.” Anaesthesia (2014).
(2) Reed, Matthew J., et al. “Is the ‘LEMON’method an easily applied emergency airway assessment tool?.” European Journal of Emergency Medicine 11.3 (2004): 154-157.
(3) Kheterpal, Sachin, et al. “Incidence and predictors of difficult and impossible mask ventilation.” Anesthesiology 105.5 (2006): 885-891.