Contents:

1. What are supraglottic airways and how do they work?
2. Types of SGAs

What are supraglottic airways and how do they work?

Supraglottic airways are airway devices that allow hands-free airway maintenance

without the need for tracheal intubation.

Advantages

Disadvantages

1. Can be placed without direct visualisation of the larynx 2. Fast and easy to place compared to tracheal intubation 3. Increased CVS stability on insertion and emergence 4. Improved O2 saturation and lower frequency of coughing 5. Minimal rise in intraocular pressure on insertion 6. Can be used as a conduit for oral tracheal intubation due to the anatomical alignment of its aperture with the glottic opening 7. Useful back up in the ‘can’t intubate, can’t ventilate’ scenario 8. Cheap and easy to train people to use, no other equipment required to insert

1. Little or no protection against aspiration of refluxed gastric contents 2. Will trigger the gag reflex 3. Higher risk of leak than tracheal intubation 4. Sizing can be an issue if patients are between sizes 5. Downfolding of the epiglottis can occur which obstructs the airway, and laryngospasm may occur 6. Flexi and standard LMAs can shift position during the procedure.

I would caution the use of SGAs in patients whom you are not sure if they are fasted, or if they are at the extremes of weight that do not fit the sizing guidance for the devices.

SGAs can move intraoperatively or when you are moving the patient from the anaesthetic room onto the theatre table, or theatre table positioning. If you are doing a procedure that does not allow you to keep checking its position e.g. shoulder surgery, it is your responsibility to ensure that your airway device is in place and fastened appropriately.

If the device does not ‘sit’ appropriately and you are getting a leak or having to use copious amounts of tape or manually hold it in place, consider switching device eg. LMA to iGel, or size, or if very concerned, have a low threshold for considering a switch to endotracheal intubation. Trying to switch after the procedure is under way and you have to go under the drapes on a positioned patient with a massive leak or desaturation or regurgitation is incredibly difficult!

Types of supraglottic airway:

LMA (laryngeal mask airway)

Clear plastic cuff that needs a syringe for inflation, and a 15mm connector. The cuff has some slits in it that allows gas exchange.

This is the classic insertion technique:

This is what it looks like in position – as you can see the tip of the cuff should block air from entering the oesophagus, but if the position isn’t exactly perfect (which in reality is hard to achieve because there are quite set sizes), you can see how some air may enter the oesophagus, or some stomach content come back out into the larynx. You can also see that the vocal cords need to be open for air to enter the trachea – hence you have to ensure the patient does not go into laryngospasm when they have a supraglottic airway in place.

iGel airway:

This airway is also supraglottic but has a silicone type plastic that moulds to the patient’s larynx when warmed without the need for an inflatable cuff.

It also has a side port that an NG tube or suction catheter can fit down in case a patient starts to regurgitate. (Or the stomach contents may flow out of the port as your first indication that regurgitation is happening!)

The wide cross section body is meant to function as a bite block.

Because it does not require a syringe to inflate and can be easily inserted, it is the preferred supraglottic airway for emergency scenarios.

Flexible-LMA (Flexi-LMA):

A stainless steel wire is embedded in the wall of this LMA, making them kink and crush resistant. The tubes are very flexible and can be moved without moving the cuff from the larynx. A throat pack can be used with them and this is the preferred choice for procedures such as dental extraction and some ENT procedures.

However, they have smaller internal diameters because of the thicker wall, and longer lengths than the standard LMA, causing an increase in flow resistance (Aha, Hagen-Poiseuille!). This makes their use with spontaneous ventilation for prolonged periods less suitable.

LMA supreme:

LMA supreme incorporates a second seal designed to reduce the risk of stomach insufflation during ventilation and has a drain tube orifice much like the iGel. The body of the supreme is fixed in hard plastic so it will sit at an almost 90 degree angle from the glottis. It also requires a syringe to inflate the cuff, and has a bite block. This is great if it fits the patient’s larynx exactly but provides very little flexibility if the fit isn’t entirely perfect.

Intubating LMA:

The Intubating LMA was designed to allow endotracheal intubation via the LMA itself either blindly or with a fibrescope. The LMA is inserted first, then the ETT is insertion follows. Note that the ETT used has to be the standard ETT that comes with the iLMA kit – you can’t use other standard sizes.

Here is a video of iLMA insertion:

References:

1. Baha al-Shaikh and Simon Stacey’s Essentials of Anaesthetic Equipment Fourth Edition
2. Intersurgical website