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Simple New Test for Difficult Airway

March 28, 2019

But first, after reading yesterday’s post, Dr. Hahn from Mt. Sinai told me about a rap he did on how to detect tamponade using POCUS. Oh my gosh…it is incredible! I’m serious, you must watch this video! I will never, ever, ever be that cool. And I have microphone envy. Watch it.

Now, on to an evidence-based approach to predicting a difficult airway.

Written by Nicole McCoin

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An abnormal upper lip bite test, in which the patient’s lower incisors cannot extend to reach the upper lip, increases the probability of a difficult intubation from 10% to >60%.

Why does this matter?
Any physical examination finding that is easy to identify as a potential predictor of a difficult airway is helpful, so the clinician can prepare appropriately with airway adjuncts and extra backup.

Don’t listen to the orthodontist… underbites are good…at least in this situation…
The authors of this article reviewed 62 studies that involved over 33,000 patients primarily in the OR setting. 10% of these patients were deemed difficult to intubate (primarily by either the Cormack-Lehane grading scale or Intubation Difficulty Scale). They looked at factors that best predicted difficult intubation. Here are some of their findings with associated likelihood ratios of difficult intubation. This list was not surprising to me:

  • History of difficult intubation (+LR 16-19)

  • Snoring (+LR 3.4)

  • Overweight or obese (+LR 2.2)

  • Short hyomental distance [range of <3-5.5 cm] (+LR 6.4)

  • Retrognathia [mandible measuring <9 cm from angle of jaw to tip of chin] (+LR 6.0)

  • Wilson score which includes parameters of weight; neck and jaw mobility; mandible length; and characteristics of dentition/bite [range of >2-3] (+LR 9.1)

  • Modified Mallampati score of 3 or more (+LR 4.1) 

However, here is a new parameter to add to your armamentarium of difficult airway predicting tools. The upper lip bite test:

From cited article, Figure 1. Not sure if that’s the vermillion border or a milk mustache…

From cited article, Figure 1. Not sure if that’s the vermillion border or a milk mustache…

A class 3 upper lip bite test means that the lower incisors cannot extend to reach the upper lip. When that finding is present, the probability of a difficult intubation increases from 10% to >60% (+LR 14). We all know that we often aren’t able to perform long airway assessment scoring systems or measurements in the ED given the acuity of our patients and the emergent nature of our intubations. There will be some acutely decompensating patients or those with altered mental status such that this upper lip bite test may not be feasible. However, it could come in handy for many of our patients, and I will take any new pearl I can find to help me identify a potentially hard airway. So, add this one to your fanny packs of information and combine it with the difficult airway predictors you already knew! An underbite never looked so good!

Will This Patient Be Difficult to Intubate?: The Rational Clinical Examination Systematic Review. JAMA. 2019 Feb 5;321(5):493-503. doi: 10.1001/jama.2018.21413.

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Reviewed by Thomas Davis