SUPRAGLOTTIC AIRWAY DEVICES IN THE CRITICALLY ILL

The last five or so years there has been a shift in airway management in cardiac arrest. Endotracheal intubation in CPR used to be the gold standard, but recently supraglottic airway devices (SAD) have been gaining ground. SADs can be placed blindly, rapidly and without pausing CPR compressions. A small animal study in Resuscitation challenges that practice.

Background
The country I work in has taken it even further by removing all ETI equipment from the ambulances, in favor of equipping our paramedics and EMTs with laryngeal tubes. All our patients in cardiac arrest, or with a reduced enough LOC, is likely to get a laryngeal tube in the field before transport and ED arrival.

I have noticed I change in the EDs too. Docs are happy leaving the prehospital laryngeal tube in during resuscitation or CPR.  Other docs I met have given up intubating altogether. They say using a SAD avoids the pauses in compressions we often get when intubating, or avoids intubating a moving target which can result in tissue damage.

Then recently, there has been more and more noise on blogs and in forums about how this practice may not be ideal after all. Specifically there are fears that retropharyngeal pressure from the SGA can compress the carotid arteries, thereby impairing an already crappy blood flow to the brain.

The study in Resuscitation by Segal & co should be read with that buzz as a background. It is not the first study of it’s kind, the concerns have been around for quite some time but, at this moment, the timing is perfect.

The study
It is a small animal study. Nine pigs were anaesthetised with propofol, ET-intubated and had their carotid arteries surgically exposed and cerebral blood flow was measured using a Doppler. Other measurements where aortic pressure,CVP and intracranial pressure.

Then VF was induced with a direct current into a right ventricular pacing wire. At the same time ventilation and the propofol infusion was stopped. After four minutes of untreated VF, standard CPR was performed with chest compresssions 100 bpm and continuous ventilations through the various airway devices.

After removing the ET-tube the three SGA were inserted, in a randomised sequence, and inflated as per the manufacturers instructions. The physiologic effects of three airway devices were registered and compared to an open airway and compared to an endotracheal tube.

Results
The physiologic effects of three airway devices were compared with  that of an ET-tube, the Combitube, the King tube and an LMA flexible.

The results are striking.

In the diagram on the right, carotid blood flow during CPR with the different SADs is compared to blood flow with an endotracheal tube.

The combitube stand out as the worst but in this study all SADs impair carotid blood flow to a significant degree.

Below is the real-time tracings from one of the subjects. It nicely illustrates what is going on.

Take-home message
This is a tiny animal study and one needs to be very careful with jumping to any conclusions. It could, however, correctly illustrate the physiologic effects SADs have in patients in cardiac arrest. If that is the case, it is a big deal.

If other studies confirm this, it could have significant implications for the prehospital systems that jumped on the SAD bandwagon.

As for me, until this is settled, I will keep intubating moving targets. I will keep replacing the supraglottic airways with endotracheal tubes as soon as the patient arrives in the ED.

Find the study here. I would say it is essential reading.

Impairment of carotid artery blood flow by supraglottic airway use in a swine model of cardiac arrest, Resusitation, 2012.

You should also listen to this podcast on EMCrit. There is an interesting discussion in the comments section. Some very talented people are having a go. That too, is essential reading as it gives you an idea of where CPR, including airway management, could be going.

 

This entry was posted in Cardiology, CPR, Emergency Medicine, Prehospital Medicine. Bookmark the permalink.

10 Responses to SUPRAGLOTTIC AIRWAY DEVICES IN THE CRITICALLY ILL

  1. Andy Neill says:

    This idea that LMA might be causing anoxic brain injury doesn’t seem to hold face value for me. In the operating room setting these are used all the time for procedures and there’s no concerns there about people stroking out or waking up having lost a decade or two of memories.

    Of course, cerebral blood flow is more than a little bit compromised in cardiac arrest but i’m not sure i buy it.

    Great find though!

    • K says:

      Hi Andy,
      Fair points and you might be right. It is an incredibly small study. The LMA has been a revolution in anaesthesiology and I have placed hundreds and hundreds of them. Still I am a bit concerned about the patients with compromised blood flow. Like I said, here all cardiac arrests get a King LT tube prehospitally instead of an ETT since five or so years. I am just hoping we won’t regret that.

      But then again, it is not as simple as that. The ETT and kit was removed for a reason. Our paramedics, especially the ones working outside the bigger cities, didn’t get enough intubations to become proficient. That resulted in a few oesophageal intubations and more importantly resulted in the younger or rural paramedics hesitating to make the decision to intubate. (equals no airway).

      So it’s complicated.
      /K

  2. Sing Tan says:

    Interedting. I do wonder if sga devices like the i gel, that don’t have an inflatable cuff cause the same issue.

    • Thomas D says:

      The i-gel would probably give you the same problem, as the silicone “cuff” is already inflated and is most likely pressing on the carotids as well. The upside is that the i-gel is a little bit smaller, and you can’t over-inflate it. Still, a tube would be better – as far as carotid blood flow goes.

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  4. Thomas D says:

    Dr. Weingart at EMcrit.org has picked up on the original article and made a short and informative interview with the lead author of this controversial paper, Dr. Nicolas Segal. Hear the interview here.

    Dr. Nicolas Segal is ass. prof. of emergency medicine at Lariboisière Hospital in Paris and has written several papers on resuscitation. It also seems he and his team are conducting research to get see if their findings with SGA in swine are transferrable to humans. Now, that will be a study to look out for.

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