Magnetic resonance imaging study of the in vivo position of the extraglottic airway devices i-gel™ and LMA-Supreme™ in anaesthetized human volunteers.

BACKGROUND

Exact information on the anatomical in situ position of extraglottic airway (EGA) devices is lacking. We used magnetic resonance imaging (MRI) to visualize the positions of the i-gel™ and the LMA-Supreme™ (LMA-S) relative to skeletal and soft-tissue structures.

METHODS

Twelve volunteers participated in this randomized, prospective, cross-over study. Native MRI scans were performed before induction of anaesthesia. Anaesthesia was induced, and the two EGAs were inserted in a randomized sequence. Their positions were assessed functionally, optically by fibrescope, and with MRI scans of the head and neck.

RESULTS

The LMA-S protruded deeper into the upper oesophageal sphincter than the i-gel™ (P<0.001). Both devices reduced the area of the glottic aperture (P<0.001), and the LMA-S had the largest effect (P=0.049). The i-gel™ significantly compressed the tongue (P<0.001). Both devices displaced the hyoid bone ventrally (P<0.001); the i-gel™ to a greater degree (P=0.029). The fibreoptically determined position of the bowl of the devices was identical.

CONCLUSIONS

The LMA-S and i-gel™ differ significantly with regard to in situ position and spatial relationship with adjacent structures assessed by MRI, despite similar clinical and fibreoptical findings. This could be relevant with regard to risk of aspiration, glottic narrowing, and airway resistance and soft-tissue morbidity.