Both the extended neck position and insertion of a supraglottic airway device increases the height of the cricothyroid membrane in females. A prospective observational study

Background: Emergency Front of Neck access (eFONA) via cricothyroidotomy using a size 6 internal diameter tracheal tube is recommended by the Difficult Airway Society in the event of a 'can't intubate, can't oxygenate' (CICO) scenario in adults. There is a lack of clear guidance on whether to retain or remove a previously inserted supraglottic airway device (SAD) before eFONA. We aimed to study the effect of both neck extension and insertion of an SAD on sagittal cricothyroid membrane (CTM) height.

Methods: We recruited 40 adult female patients attending for minor gynaecological surgery under general anaesthesia and suitable for an SAD. Sagittal ultrasound images of the CTM were obtained in the neutral and extended neck position, both before and after insertion of the i-gel® (160 images). The CTM height was measured from the images by a blinded assessor and the data analysed to determine the magnitude of change in CTM height and its relevance for cricothyroidotomy.

Results: There was a significant difference in the height of the CTM between the groups (P<0.001). The extended neck position accounted for 10% increase over the neutral position. Inserting an i-gel® and extending the neck increased the CTM height by 26% over neutral position, thereby lengthening it sufficiently to accommodate a size 6.0 tracheal tube in 100% of the patients.

Conclusions: Both neck extension and the insertion of an i-gel® increased the sagittal height of the CTM. This suggests there may be benefit to retaining or re-inserting an SAD during eFONA.