Thomas Drew1, Waqas Khan2, Conan McCaul3. 1. Department of Anaesthesia, The Rotunda Hospital, Dublin, Ireland. Electronic address: drtomdrew@gmail.com. 2. Department of Anaesthesia, The Rotunda Hospital, Dublin, Ireland. 3. Department of Anaesthesia, The Rotunda Hospital, Dublin, Ireland; Department of Anaesthesia, Mater Misericordiae Hospital, Dublin, Ireland; School of Medicine and Medical Science, University College Dublin, Dublin, Ireland.
Abstract
BACKGROUND: Identification of the cricothyroid membrane is frequently inaccurate in females because of less distinct anatomy compared with males. Supraglottic airway devices cause ventral displacement of the laryngeal structures. We investigated if this would impact on the accuracy of cricothyroid membrane identification using palpation. METHODS: We recruited 64 adult females who underwent assessment by volunteer participants with and without a sited i-gel® supraglottic airway device. The primary outcome was accuracy in identifying the cricothyroid membrane. Secondary outcomes included distance from participant estimate to actual cricothyroid membrane location and perceived difficulty using a visual analogue scale. Ultrasound images were analysed to determine the effect of the i-gel® on the anatomical structures relevant to cricothyroidotomy. RESULTS: The cricothyroid membrane was identified correctly in 42/64 subjects with the i-gel® in place (66%) vs 23/64 of controls (36%; P<0.001, mean difference 30%; 95% confidence interval, 12-47%). VAS (P<0.001) and distance to the cricothyroid membrane (P<0.001) decreased in the intervention group. Analysis of the ultrasound image series showed a reduction in the mean angle between the cricothyroid membrane and anterior wall of the trachea in the i-gel® group, because of the more ventral position of the cricoid cartilage compared with control images (166° vs 151°, P<0.001). CONCLUSIONS: The presence of the i-gel® improved accuracy of identifying the cricothyroid membrane using palpation in females. The cricoid cartilage was pushed ventrally by the i-gel® in the hypopharynx, creating a more palpable prominence. It may therefore be advantageous to retain a sited supraglottic airway, rather than remove it, before performing emergency cricothyroidotomy.
BACKGROUND: Identification of the cricothyroid membrane is frequently inaccurate in females because of less distinct anatomy compared with males. Supraglottic airway devices cause ventral displacement of the laryngeal structures. We investigated if this would impact on the accuracy of cricothyroid membrane identification using palpation. METHODS: We recruited 64 adult females who underwent assessment by volunteer participants with and without a sited i-gel® supraglottic airway device. The primary outcome was accuracy in identifying the cricothyroid membrane. Secondary outcomes included distance from participant estimate to actual cricothyroid membrane location and perceived difficulty using a visual analogue scale. Ultrasound images were analysed to determine the effect of the i-gel® on the anatomical structures relevant to cricothyroidotomy. RESULTS: The cricothyroid membrane was identified correctly in 42/64 subjects with the i-gel® in place (66%) vs 23/64 of controls (36%; P<0.001, mean difference 30%; 95% confidence interval, 12-47%). VAS (P<0.001) and distance to the cricothyroid membrane (P<0.001) decreased in the intervention group. Analysis of the ultrasound image series showed a reduction in the mean angle between the cricothyroid membrane and anterior wall of the trachea in the i-gel® group, because of the more ventral position of the cricoid cartilage compared with control images (166° vs 151°, P<0.001). CONCLUSIONS: The presence of the i-gel® improved accuracy of identifying the cricothyroid membrane using palpation in females. The cricoid cartilage was pushed ventrally by the i-gel® in the hypopharynx, creating a more palpable prominence. It may therefore be advantageous to retain a sited supraglottic airway, rather than remove it, before performing emergency cricothyroidotomy.