Anaesthesia. 2018 Jul;73(7):856-862

# Changes in hardness and resilience of i-gel™ cuffs with temperature: a benchtop study.

Dingley J, Stephenson J, Allender V, Dawson S, Williams D

The i-gelTM is a supraglottic airway with a gel-like thermoplastic cuff. It has been suggested that the seal around the larynx improves following insertion. Perhaps the most intuitive hypothesis proposed for this is that cuff softening occurs during warming from ambient to body temperature. We investigated this using a food industry texture analyser over a wide temperature range. Size 2 and 3 i-gels were secured to a platform within a temperature-controlled water bath, which was in turn mounted on a texture analyser test stand. Both water and i-gel cuff temperatures were recorded. A spherical probe was advanced 4 mm into the surface of each i-gel at a rate of 1 mm.s-1 , then retracted at the same rate while the upward pressure on the probe was recorded. Three runs made at each of the 11 temperatures (10 °C to 60 °C, 5 °C increments) gave 105,864 data points, from which values for hardness (the peak force on the probe at maximum indentation), and resilience (the rate at which the material recovers its original shape) were calculated. Over 10 to 60 °C, the smallest hardness value expressed as a proportion of the largest was 88.2% and 89.8% for size 2 and 3 i-gels, respectively, and for resilience these were 92.8% and 86.2%, respectively. Over room temperature to body temperature range (21-37.4 °C), hardness decreased by 3.15% and increased by 0.47% for i-gel sizes 2 and 3, respectively, whereas resilience values decreased by 1.85% and 2.68%, respectively. Cuff hardness and resilience did generally reduce with warming, but the effect was minimal over temperature ranges that may be encountered during clinical use.