Impact of Labor and Delivery on Ultrasound Measured Cricothyroid Membrane Depth and Height

Overview

The cricothyroid membrane acts as a route through which the upper airway can be accessed to provide oxygen and ventilation to patients. Anesthesiologists need to deliver oxygen and ventilation to patients under general anesthesia, where patients may lose the ability to breath for themselves. Access through this membrane to provide oxygen and ventilation is critical in emergency situations where other traditional means to access the airway (e.g. through endotracheal ventilation, supraglottic airway devices or face mask ventilation) have failed. It is known, from previous studies, that due to the physiological changes that occur in labour, the upper airway of the body undergoes changes that can make accessing the airway through traditional means more difficult, specifically during the period of labor, delivery, and just after delivery. Ultrasound is becoming increasingly popular due to its ability both to identify the cricothyroid membrane and to improve success in accessing the airway through the cricothyroid membrane. What is not known, and has not been studied to date, is specifically how the anatomy (i.e. its height and its depth) specifically changes during the period of labour, delivery and just after delivery. The aim of this study would be to scan (using ultrasound) pregnant women's necks once at the very start of their labour, and once within 4 hours of delivery of their baby, to identify how the size and depth of the cricothyroid membrane changes. This information would improve the understanding of how to best approach accessing this membrane in laboring pregnant women. The investigators hypothesize that in labouring third trimester patient, that the depth to the cricothyroid membrane will increase, and there will be no change in the cricothyroid membrane height.