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Airway Dogmalysis #4: For HEAVEN’s Sake

Airway Dogmalysis #4: For HEAVEN’s Sake

I love attending airway training courses. No matter how basic it seems; no matter how routine the information appears to be; I always get something out of it. I either get a new idea or conceptualization of something, or reinforcement of something I had neglected to keep in the forefront of my thinking. One thing I do not really see a ton of focus on is the assessment. Roughly 98% of the time there is some mention of an assessment (usually HEAVEN or LEMON), but the discussion usually stops there. But the concept is so much deeper and so much more important.

I find that too often, some instructors jog through the important elements of airway management to get to the “sexy,” highly visible skills like cric and intubation. Leaving the students (be it novice or advanced level) with a massive hole in their airway management game.

Bottom Line:

Reinforcing and performing the physical skills of airway assessment should be dominating as much of the training time as performing the physical skills of intubation or placing another type of airway. No it is not as sexy as intubation or other skills, but it is just as important. To the degree that it is not something that an educator can just gloss over with “LEMON” and ignore the operational realities of selecting this as the foundational assessment for predicting airway difficulty.

Importance of an Airway Assessment

How important is it? In one analysis of claims outcomes in anesthesia legal cases, three main themes were found to be causal in the loss of the case:1

  • No assessment was performed.
  • Inadequate assessment was performed.
  • Clinician did not act on the findings of the assessment that was performed.

Why are these specific themes important? Because the airway assessment exists to identify and qualify the likelihood that any airway management procedure will fail or require some sort of “thinking on your feet” modification to successfully secure the airway. It ensures that the clinician has assessed for, acknowledges, and works to mitigate the risk to the patient by “predicting” difficulty through the assessment. Having guidelines and pre-planned procedures is a great starting point, but these do not negate the truth of the age- old boxing wisdom of Mike Tyson:

“Everyone has a plan until they get punched in the mouth…”

The “standard approach” prescribed by an agency or medical director can be thwarted by any number of anatomical, physiologic, or contextual issues present in a given clinical scenario. Operators find out they need to adjust that approach early (before they initiate the procedure) or later (after they needed to know they needed to change something).

Things get dangerous when the operator finds themselves in a difficult situation they were not prepared for and did not see coming. This leads to potentially deleterious behaviors like flailing and perseverating. To flail is a form a panic in which the operator is grasping at anything and everything to get them out of a bad situation. Sometimes they guess right and land on a maneuver that can get them out of a jam, and sometimes they do not.

Perseveration is worse. To perseverate is to continually and repetitively execute an approach/technique that has failed. Perseveration is noted as a causal factor of losing the case in 25% of the cases cited in a review of anesthesia airway management cases.1 The mindset surrounding this being “it will work this time.”  To defeat this, most great instructors and courses I have been to will always advise students to “change something” after a first pass miss. Change a blade, change the device, or change the patient’s position etc. Be careful not to flail. Make a disciplined and intentional choice in what to change, hopefully to directly address a specific problem encountered in the attempt.

 Suck a LEMON…

To be clear, this is not a criticism of the utility of the LEMON assessment. It is, however, a criticism of relying on and teaching LEMON as the sole assessment tool in the face of the operational realities of the prehospital environment. Moreover, I am criticizing the shortcut instructors take by just regurgitating something that does not stand up to operational scrutiny in an environment in which it was never designed to be used… like LEMON. 

“Airway management in EMS is apples and oranges to anything else.”  – Jim Ducanto MD

Dr. Ducanto’s thoughts highlight the fact that EMS is truly a different clinical animal and not everything can be easily extrapolated to be used in that setting. Useful in some cases? Perhaps. But not everything done inside the hospital has a place in the prehospital world. The contexts are night and day different in some cases.

Yet, the EMS/HEMS community routinely adopts and repurposes tools designed for use in an environment that does not match the environment in which it will be employed. Case and point is LEMON. One of the glaring holes in this is that the M in LEMON stands for Mallampati. This is a test that requires that the patient sit up and stick their tongue out as far as possible.2 Not all of our patients are stable, elective intubations (which is what LEMON is designed for), and the majority of our patients lack the mental status required to sit up or follow such commands. There must be a tool better suited for the prehospital environment…

Enter the HEAVEN assessment. This assessment was derived from a retrospective review of a little over 500 airway cases in which 63 of them required more than 1 attempt. All 63 of those cases had one or more elements of the HEAVEN criteria.3 In the author’s opinion it casts a wider net to find physical or physiologic difficulties and does a fantastic job at predicting difficulty…

… with VL and DL approaches to intubation. VL and DL are but two options in the overall system of airway management, and herein lies the flaw in thinking about predicted difficulty in airway management in the prehospital environment… one size fits all.

Flawed Mindsets and Logic

The typical mindset/ logic reads something like this:

“We need to know if the VL/DL attempt(s) will be complicated by using the HEAVEN criteria, and if we do encounter an issue that foils our attempts at intubation, we need to have a well developed system of contingencies. Those contingencies include, SGA, BVM, or the final common pathway of airway management: eFONA.”

Here is the hole in that logic:

The same things that make VL/DL difficult, can also defeat our contingency responses. To put it a little more plainly: the contingency responses are not guaranteed to work.

  • The thought process of “well I can just bag them” is flawed. The instructor should be attentive to this mindset and be prepared to redirect the student with the knowledge that the BVM can be defeated by a myriad of anatomical difficulties.
  • The thought of “we can just go to an SGA” is equally as flawed. This too can be defeated by a myriad of anatomical issues.
  • Surely the cric is undefeated. It is the final emergency airway after all. Sadly, it is easily defeated as well. The inherent weakness in eFONA is that it too relies on the ability to locate anatomical landmarks in order to be successful. Instructors who teach with the assumption that every cricothyroid membrane (CTM) can be palpated further contribute to flawed logic and bad mental models. The reality is, even the best operator cannot palpate everyone’s CTM. For more on some new thoughts and proclivities on eFONA check out this piece on emsairway.com: https://emsairway.com/2024/09/04/simple-but-not-easy-efona-2024-part-1/

Kill the Flaw

Teaching better airway assessments starts with knowing the baked in weaknesses of each tool available in the system. How can VL fail? How does DL fail? Why would a surgical airway fail?

ALiEM has a great resource for the difficult airway predictors, so good in fact that you need to click and check it out: https://www.aliem.com/mnemonics-for-difficult-airway/. MOANS, ROMAN, RODS, SMART, are great ways to quickly run down the list of ways that the device can fail. Students should be just as well acquainted with these assessment pneumonics as they are SAMPLE and OPQRST. These make great hand-outs or one-pagers for airway courses as well.

Circling back to the HEAVEN criteria for a moment. There is a hole or contradiction in my argument for this not being a great, sole source assessment for difficult airways. If you did not pick up on it already, I will reiterate it here:

If it is a predictor of VL/DL difficulty, it is likely a good predictor for SGA, BVM, and eFONA difficulty as well. While each of these approaches has their own pneumonic for assessment, HEAVEN does cast a wide net to catch predictable difficulties. The clinician just has to think a little deeper than the word the pneumonic uses. For example, if the patient has a small mouth that makes for some difficult with VL/DL, then the operator must assume that the same difficulty will be present with SGA or anything else inserted into the mouth.

To that point, instructors must not allow students to merely gloss over what the letter stands for in the HEAVEN pneumonic. They have to make the student dig a little deeper than just “anatomical difficulty” and be able to describe exactly what anatomical difficulty they are assessing and what it looks like. Add some slides to your presentations of various faces (AI is a great tool to use here as well) and have the students run through each of those acronyms from ALiEM and see how many difficulties they can identify.

But do not stop there…

As Dr. Levitan says, “Predicting difficulty is much less important than knowing what to do when it is encountered.”

Along with the assessment, the student must demonstrate the ability to select the appropriate mitigation strategies for the encountered/predicted difficulty. Teach them to stack the contingencies (some subtle foreshadowing there) and escalate or de-escalate as necessary.

Close Out

It is not just about assessing for the ability to oxygenate and ventilate. It is about assessing the patient’s physical ability to support a chosen approach, in the current anatomical context. We have to know if the patient can physiologically tolerate the procedure as well. We have to know how the chosen approaches can fail and have planned contingencies ready to respond to predicted or encountered difficulty. These are the lessons that have to be passed on in airway management training. There is so much more depth to these training events than merely intubation and surgical airways.

References:

  1. Joffe AM, Aziz MF, Posner KL, Duggan LV, Mincer SL, Domino KB. Management of Difficult Tracheal Intubation: A Closed Claims Analysis. Anesthesiology. 2019 Oct;131(4):818-829. doi: 10.1097/ALN.0000000000002815. PMID: 31584884; PMCID: PMC6779339.
  2. Roth D, Pace NL, Lee A, Hovhannisyan K, Warenits AM, Arrich J, Herkner H. Airway physical examination tests for detection of difficult airway management in apparently normal adult patients. Cochrane Database Syst Rev. 2018 May 15;5(5):CD008874. doi: 10.1002/14651858.CD008874.pub2. PMID: 29761867; PMCID: PMC6404686.
  3. Davis DP, Olvera DJ. HEAVEN Criteria: Derivation of a New Difficult Airway Prediction Tool. Air Med J. 2017 Jul-Aug;36(4):195-197. doi: 10.1016/j.amj.2017.04.001. Epub 2017 Apr 26. PMID: 28739243

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