The Effect of a Head Elevated Positioning Device on Position, Height and Depth of the Cricothyroid Membrane in Morbidly Obese Pregnant Women in the Third Trimester.

The cricothyroid membrane (CTM) is situated in the anterior neck and may be readily palpated in most people. In the event of difficulties securing the airway during a general anesthetic the CTM can facilitate emergency access to the upper airway to allow rescue oxygenation and ventilation. Caesarean sections are today carried out using either a spinal or epidural anaesthesia and for good reason. Due to physiological effects of pregnancy a patient's airway is known to be more challenging when pregnant than outside of pregnancy. The pregnant airway can even change over the course of labor. Airway ultrasound has become increasingly popular and allows accurate identification of airway structures including the cricothyroid membrane. It has already shown to be more accurate than palpation alone in identifying the cricothyroid membrane in obese pregnant women. The incidence of obesity in pregnancy continues to increase. Although regional anesthesia is preferred when these women require Caesarean section this is not always possible or successful. Use of a device to optimise patient position for airway management is the standard of practice for obese pregnant patients. These devices are known as head elevating laryngoscopy position pillows, the TROOP elevation pillow ® is one such device. However, the investigators do not know if and how positioning the obese pregnant patient on a TROOP elevation pillow ® affects position, depth and height of the cricothyroid membrane. The investigators want to know if the TROOP elevation pillow ® will hinder or facilitate the performance of a surgical airway in the event of failed airway management in the pregnant obese patient.

The investigators hypothesize that in pregnant obese patients in the third trimester use of the TROOP elevation pillow ® will change the position, height and depth of the CTM compared to the neutral position. Based on previous evidence the investigators believe the position of the membrane will move superiorly in relation to the sternal notch, will increase in height and the depth from the skin to the membrane will be reduced. The investigators also hypothesize that CTM identification and marking prior to final patient positioning may be misleading.