Impact of Change of Head and Neck Position on Cricothyroid Membrane Localization and Membrane Height in Parturient Patients

The cricothyroid membrane acts a route through which the upper airway can be accessed in order to provide oxygen and ventilation to patients. The need to provide oxygen and ventilation to patients is essential particularly under general anesthesia, where patients may lose the ability to breathe 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 that due to the physiological changes of pregnancy, the upper airway of the body undergoes changes that can make accessing the airway through traditional means more difficult. Ultrasound is becoming increasingly popular due to its ability to identify the cricothyroid membrane, to improve success in accessing the airway through the cricothyroid membrane. Studies to date in non pregnant adults have shown that alterations in the head and neck position can alter the position and size of the cricothyroid membrane. No study to date however has looked at how changing the position of the head and neck effects the position and size of the cricothyroid membrane in pregnant patients. It is important to study these changes in the pregnant population, given the physiological changes of pregnancy that make accessing the airway through traditional methods more difficult in non pregnant patients. The investigators hypothesize that in pregnant patients in the third trimester, that changing the head from the neutral to maximally extended neck position will alter the position of the cricothyroid membrane in relation to anatomical skin markings between positions. The investigators also hypothesize that in pregnant patients in the third trimester that changing the head from the neutral to maximally extended neck position will increase the size of the cricothyroid membrane. The investigatorsalso aim to determine at wha