Posted by Matthew Mac Partlin on Wednesday, January 16, 2013

Back when I started up the ASMMR and put out a newsletter, I wrote a piece on the range of airway devices available, from simple oropharyngeal airways to endotracheal intubation (You can read it here: ASMMR Vol 1, Issue 3, July 2009). Recently I came across a review article in Anaesthesia & Analgesia devoted just to extraglottic airways (also known as supraglottic airways, though there is some semantics involved) and it makes a good read.

Evolution of the Extraglottic Airway: A Review of Its History, Applications, and Practical Tips for Success. Michael R. Hernandez, MD, P. Allan Klock Jr., MD and Adranik Ovassapian, MD. Anaesthesia & Analgesia February 2012 vol. 114 no. 2 349-368.

The authors go through the evolution of EGA devices, argue the difference between the terms extraglottic airway (EGA) and supraglottic airway (SGA), outline the various EGA designs and types and describe the different EGA uses, including special populations and difficult airway management options. They also include the original Dr. Archie Brain description of classic LMA (cLMA) insertion technique, with diagrams.

Two of the 3 authors declare financial links with EGA companies, though one of them is unfortunately now deceased.

Some of the useful general points made include:

1) LMA use beyond the traditional spontaneously ventilating patients is acceptable as long as the pericuff leak is not excessive and there are no clear indications for proceeding directly to a formal ETT (Note: Arguably competitors are likely to have a stomach full of hydration fluid and
so may be at risk of aspiration if consciousness is impaired)

2) There is evidence supporting successful airway management of patients in non-supine positions, including prone (Proseal LMA and LMA supreme).

3) Applying cricoid pressure may prevent the LMA tip from reaching its final proper position. One study mentioned  demonstrated a decrease in successful EGA placement from 92% to 56% following application of Sellick's manouvre. (More reasons not to apply cricoid pressure)

4) Easy ventilation does not guarantee good position. This gives us some comfort because it suggests there is a wide margin of error for rescuing a patient. It's also bad because there may be an unrecognised increased risk of aspiration with an ill-placed EGA.

5) The estimated frequency of aspiration for anaesthetised patients in general is 0.01 - 0.06%. For a Classic LMA it is 0.02% ... pretty encouraging, but remember that anaesthetised patients are generally fasted and prepared for their procedure.

6) For LMA type devices,swallowing movements by the patient can dislodge a well positioned LMA. So either a relatively deep level of sedation or use of a NMB agent may be required.

7) Factors that contribute to failed EGA placement:

  • Operator experience
  • Poor technique
  • Inadequate sedation

The EGAs that are reviewed in this article are:

  • LMA: Classic, Flexible, Proseal, FastTrach, Supreme
  • Air-Q/Intubating laryngeal airway
  • Ambu: AuraOnce, AuraFlex, Aura Straight, Aura40, Aura-i
  • Intersurgical i-Gel
  • King Systems Laryngeal Tube: LT, LT-D, LTS-D, LTS-II and G-LT
  • Oesophageal-tracheal combitube
  • Pulmodyne Cobra perilaryngeal airway
  • Teleflex Medical EasyTube

The authors include some helpful tables, such as:

  • Table 1: Classes of EGAs (Not a standard categorisation)
  • Table 2: Features of currently available EGAs at a glance

Design variations generally involve airway stem angle and flexibility, presence or absence of aperture bars, gastric drainage port, integrated bite block or separate pharyngeal cuff and the ability or not to pass an endotracheal tube via the EGA with or without fibreoptic assistance. Most companies produce both single use and reuseable EGAs. Some EGAs also have integrated monitors such as for temperature or EtCO2 (e.g. Pulmodyne CobraPLA).

In general, head to head comparisons vary in population number and rarely show a significant difference between devices with respect to ease of insertion, successful ventilation, need for readjustments or complications.

Special population uses of EGAs reviewed include:

  • Pre-hospital - Difficult environment with unprepared patient.
  • Resuscitation - Why facemask ventilate poorly or waste time and oxygen intubating when you could justt sink an EGA? Though they hint at it, the authors don't specifically go into the details of the controversial animal trial that demonstrated carotid artery flow impairment during resuscitation of pigs that were being ventilated with an adult EGA device - Impairment of carotid artery blood flow by supraglottic airway use in a swine model of cardiac arrest. Segal N, Yannopoulos D, Mahoney BD, Frascone RJ, Matsuura T, Cowles CG, McKnite SH, Chase DG. Resuscitation. 2012 Aug;83(8):1025-30. doi: 10.1016/j.resuscitation.2012.03.025. Epub 2012 Mar 28. (Here are two discussions on this paper from EM Crit and Emergency Medicine Ireland.)
  • Obstetrics - I'll leave this one to the experts.
  • Paediatrics - (Don't laugh. There are young kids karting and competing on dirt bikes.) Epiglottic down-folding is relatively common, particuarly with younger children, but does not usually interfere with ventilation. It may interfere with blind, per-EGA intubation however. The authors also make note of an interesting issue with cuff pressure where 1 in 5 children had recorded cuff pressures greater than the recommended maximum of 60mmHg, even though no additional air had been put into the cuff beyond what existed from the packaging. And the younger the child the greater the discrepancy, with potential for local injury.

Finally, the authors go through the use of EGAs for difficult airway management and describe:

  • Primary ventilation management
  • Blind tracheal intubation via the EGA
  • 2-step bougie-aided blind intubation
  • Fibreoptic-aided intubation

The paper is a pretty easy read and gives a good overview of the range and scope of currently popular EGAs. It's useful to consider how an EGA might impact on trackside airway management of an injured driver and how they might rescue an airway where intubating skills may be underdeveloped.

I carry an i-Gel in my personal pack for several reasons, including the gastric channel, the thermoplastic cuff and the minimal mouth opening required to place it. I'd be interested in hearing what others use, so leave any comments below or on the Rollcage Medic Twitter or Facebook page.