The 3:3:2 Rule for predicting The Difficult Airway from resustv.com on Vimeo.

www.resustv.com is coming in late APRIL 2010- videos of lectures on all of acute medicine

The L.E.M.O.N. approach is just that, an approach to predicting the potentially difficult airway. It is a way of adding some measurable parameters to what should become a ‘gestault’ approach, where you know, or have a ‘vibe’, a feeling, call it what you will, about the relative ease or difficulty of any airway.

This gestault is usually gained following years of experience. BUT it can be taught.

The LEMON rule  allows us to remember to look externally and to look at those parameters that will make the intubation simple or difficult.

LEMON stands for:

L - Look externally - Is the patient obese, do they have a high arched palate, a short neck, facial or neck trauma?

E - Evaluate the 3:3:2 rule - 3cm mouth opening, 3 cm thyromental distance, 2cm between hyoid bone and thyroid notch. If unsure as to how much a cm is, just use the 3 fingers or 2 fingers approach.

M - Mallampati Score - remember a Mallampati 4 is associated with a >10% chance of difficult airway

O - Obstruction - Is there a tumour, epiglottitis, recent neck surgery?

N - Neck mobility - Is the patient in a cervical collar, are they elderly?

OK, so let’s look at what the LEMON Rule really tells us. The most important aspects of it are: Can you open your mouth wide enough, can you move your neck to allow better positioning and is there adequate space in the floor of the mouth into which to displace the tongue.

Remember in airway, the tongue is the enemy, the patient’s enemy and yours. The tongue falls backwards into the hypopharynx and is responsible for obstructing the airway in most cases. The goal is to clear the tongue out of the way, or at least to lift it, so that we can ventilate. This is what procedures like chin lift and jaw thrust do. Movement of the mandible, to which the tongue is attached, moves the tongue.

When intubating, we need to have adequate room, to get the laryngoscope blade in, as well as the endotracheal tube and be able to see. We then need to displace the tongue with the laryngoscope blade. The only real place to displace it into is the floor of the mouth. There has to be adequate volume at the base of the mouth to push the tongue into. This is why patients with micrognathia can be so difficult to intubate, they have an inadequately sized lower jaw, and so almost no place to displace the tongue into.

How useful is predicting really? The reality is that it doesn’t change the fact that you need to secure the airway stat. These patients are not elective patients, but come in in a decompensated state and need immediate assistance.

The ability to predict the potentially difficult airway is useful in that it puts you in the right frame of mind, you start thinking about alternatives, should you not be able to intubate.

One of the greatest dangers in any life saving procedure is to get fixated. “I’ve got to get the tube, I’ve got to get the tube, I’ve got to get the tube” You try again and again and the patient starts to desaturate and now you are playing catch-up. With the ability to predict a potentially difficult airway, you may say to yourself, I’ll try a tube and it should be in, if I use all those techniques that I’ve learnt, like using an introducer in the endotracheal tube and bending the end at 35-40 degrees, getting correct positioning and even getting an assistant to open the mouth further for me by pulling the cheek further open. If I can’t tube, I may try again, or go straight to a bougie…. It’s this thought process that allows you to see the big picture and not fixate.

Which is better? BURP or Bimanual. Is Cricoid Pressure of any use?

Sellick described cricoid pressure in 1961. How useful is it? Well its purpose is to minimise the passive movement of gastric contents into the oropharynx and the potential aspiration of those contents, during rapid sequence intubation. How good is it? I was recently asked this at an Airway Workshop and I had to say for what we have, it’s pretty good. BUT the evidence is not that great!

In fact some of the newer evidence now says, it may be detrimental and can affect intubation. It can further affect ventilation of the patient!
Initially the recommended pressure was 44Newtons which is equivalent to 4.5kg(10 pounds). At this pressure it was found that there was occlusion of the glottis in 50% of patients in one study(Anaesthesia 2000 march 263-268). To be fair, the conditions in this study, which was a small one(n=30) were somewhat artificial and not really reflecting the real scenarios.

In other studies where the effect of cricoid pressure on actually passing a tube through the cords was looked at. It was found that in a small number of cases, the cricoid pressure affected the ability to pass the tube(Anaesthesia 2007 May;62; 456-9). In those cases where the tube was getting stuck at the level of the glottis ie., at the posterior cartilages, where usually a 90 degree rotation of the tube would relieve the issue, cricoid pressure made this more difficult.

In an MRI study looking at cricoid pressure, there was direct visualisation of the hypo-pharynx being occluded when cricoid pressure was applied (Anesth Analg 2009. Nov; 109;1546).

The correct use of cricoid pressure is of utmost importance, and the ability to use it to minimise the chance of aspiration remains to be tested. There is certainly evidence that it can make intubation far more difficult than no cricoid pressure being applied(J Emerg Med 2001 Jan 20;29-31) and if there is a difficulty in intubating then cricoid should be relaxed of even released.

There needs to be some idea of how much pressure needs to be used. There is no formal teaching in this area. The original 4.5kg of pressure is now not used and 2kg or 20N of pressure is recommended, but how do you guarantee this? How do you know how much pressure is being applied at any one time? When I’m tubing I ask for cricoid. How do I know if that cricoid is appropriate and if it’s affecting the intubation?

We often talk about being able to predict the difficult airway. How useful is this really? In the scheme of things the Emergency Airway is just that, an emergency. Working out if the airway is potentially difficult or not, does not change the fact that the airway will need to be controlled in some way. The Emergency Airway is unlike the elective procedure-related anaesthetics airway. In those cases in theatre, the patient has usually attended a pre-op anaesthetics clinic and been reviewed. In theatre if there is an issue with the airway,  the patient, who in most cases is fasted, can be allowed to wake up and the procedure may be put off until another day.

In the emergency department this cannot be done, as the reason that that patient needed to have the airway secured in the first place, is still there! Also, most of our patients have a belly full of pizza and beer!

Having some way to predict, if an airway may be challenging, is still worthwhile however, as it puts us in a frame of mind, that we may encounter difficulty. The best way to be in any airway situation is to assume that every airway scenario is a potentially difficult one.

In the Airway Workshop we talk about the ‘LEMON’ approach and cover the main aspects of it:

L - Look externally, is the patient obese, is there a beard etc.,

E- Evaluate the 3-3-2 Rule

M-Mallampati

O-Any chance of an obstruction- infection, tumour etc.

N-Neck mobility

The ability to assess a difficult airway in my view comes down to two or three things:

1  Is there good neck mobility to allow you to move the head so as to align you oral, pharyngeal and laryngeal axes?

A trauma patient in a collar, is automatically classed as a potentially difficult airway.

2  Is there adequate distance(3 fingers) from tip of the chin to the hyoid bone?

This tells you if there is adequate space for you to displace the tongue into. Remember that the tongue is your foe.

It is the thing that drops back and blocks the airway. You must move it out of the way to get access to the chords.

3  What is the patients mouth opening like? Is there enough room to get in there?

In most cases you will still be able to intubate with a normal curved #3 blade and a 7.5 endotracheal tube with and introducer, the end bent at about 40 degrees. These are the cases however when I have a bougie at the ready.

You will hear me speaking about forgetting about your difficult intubation box!

I have serious concerns about difficult intubation boxes. We have them in our emergency departments and somehow everyone believes that these will have something magical in them to save us at the time of a difficult intubation. The things we don’t remember as educators, is that most people don’t practice difficult intubation, don’t use what is in those boxes frequently enough to be confident with them. If they do, it may be once per year, which is not enough. If you are a registrar, you may rotate through many departments and I can assure you that each will have a different set of contents in the difficult intubation box.

At that point of crisis, there is no time for you to work out what is in the box and certainly this is not the time to use something for the first time. It is the time to have your basic technique right.

I will always teach the use of :

-The curved #3 blade

-7.5mm ETT

-Introducer

-Bougie

-Know one or two other techniques such as the ‘ILMA’ or the ‘Airtraq’ as many departments will have one or other.

-Know your needle cric and surgical cric techniques.

Remember, assume every airway will be a difficult one, know the basics well and you will be able to intubate just about every patient and have one or two rescue techniques up your sleeve.

Good luck with those airways.

Here’s a glimpse of some nice comments made by people who have attended the workshop. Their kind words are really appreciated.

Just finished a great weekend with all the guys in Adelaide. We looked at Basic and Advanced Airway. The physiology, anatomy and the theory behind airway. There were practical sessions that covered, bag valve mask use, the laryngeal mask, intubation, the use of an introducer, the bougie, the intubating laryngeal mask(ILMA) and the ‘airtraq’.

A great weekend. We had people there from Royal Adelaide and Flinders, including doctors, nurses and paramedics. Everyone played all out! Well done!

Hello Everyone Greetings and Welcome

This is a call for everyone who has asked about improving their airway skills and resus skills. The airway workshop on 25th April in Melbourne still has a few places. Have a look and let’s see you there. This time I want you to have more and so am including the Airway DVD. For all those who have already purchased the airway DVD I will be sending you all out a bonus DVD. Yes that’s for everyone who has purchased the Airway DVD since we produced it. Wait for it in the post. For all of you who have not done the workshop and experienced the surgical airway on a pig’s trachea, the use of the ‘airtraq’, the intubation in a baby model, the ILMA and more more more, let’s get you along there to do it. If you need financial assistance, we can work something out. Get these skills, have them in your armament and have the confidence to know what to do when it counts.

Peter