The distance between the glottis and the cuff of a tracheal tube placed through three supraglottic airway devices in children: A randomised controlled trial.

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Study design

A two part RCT involving children < 7yrs of age utilising 3 versions of Supraglottic Airway devices (SAD): I-gel, Ambu AuraGain & air-Q laryngeal airway. A total of 89 children were enrolled (30, 29, 29 for each SAD).

Part 1(In vivo): Size 1, 1.5 &2 SAD’s placed after a standardised GA (including paralysis) in appropriately sized ASA1/2 children with “normal” airways.

In vivo measurement of:

1. Distance between glottis and ventilation outlet of the SAD using a previously reported Fibreoptic bronchoscope technique.
2. FOB view of glottis (FOB)
3. Oropharyngeal leak pressure (OLP)

In vitro measurement of:

1. Distance between SAD ventilation outlet (VO) and beginning of proximal cuff (PC) for the size appropriate ETT.
2. Repeat measurement of above using one and two-size smaller ETT.

A “Safety Margin” (defined as distance (SAD VO to PC) – (SAD VO to Glottis)) was then calculated for each SAD and all three ETT sizes.

Results Summary

OLP was significantly lower in airQ compared to the I-gel and AuraGain, immediately after insertion. This difference disappeared when remeasured 10 minutes later. FOB  score was worst in the I-gel group.

Safety Margins etc

With the largest size ETT the Safety margin was 1.9cm, 4.4cm & 7.9cm in the I-gel, AuraGain and air-Q respectively. With one size smaller ETT, the measurements were 0.7, 3.1 & 5.8cm respectively. With two sizes smaller the Safety Margins were -0.7, 1.2 & 4.4 cm respectively.

Using the largest appropriate ETT size, the cuff was predicted to rest below the VC’s in all SAD’s. With AuraGain and air-Q this was also true for one and two size smaller ETT. However with the I-gel the cuffs would be below the VC in 69% (one size smaller) and 29% (two size smaller) respectively. The ETT tip was predicted to pass the VC’s in all groups in the largest and one size-smaller tubes, but not in one child in the I-gel group.

Discussion / Commentary.

The use of a SAD for routine and/or emergency airway management has been widely acknowleged and now forms an important part of many emergency/difficult aiway guidelines. FOB guided intubation using a SAD as a conduit (either directly or via some form of exchange catheter) is also recognised as an effective technique. This paper illustrates that the airQ had the widest Safety Margin followed by the AuraGain then the I-gel. The I-gel also had the lowest FOB score. This may reflect both differences in length of the airway tube and degree of angle of orientation of the ventilation outlet relative to the anterior facing infant glottis. The authors advise caution in choosing the I-gel as an intubation conduit in this age group.

Take Home Message

This is a nice, well conducted study that looks at an important issue regarding a rare but potentially risky procedure. Although no patients were actually intubated in this study (which might strengthen the clinical relevance of the findings) anaesthetists that have been in this situation will be aware of the concerns and potential problems of a poorly positioned ETT within a SAD and the potential ensuing complications which  may occur when trying to remove the SAD. Perhaps all departments should formally investigate this issue using their chosen SAD (s) and ‘scope combinations?

Reviewed by: Dr H Hack