Changes in Ultrasound-guided Skin Markings of the Cricothyroid Membrane in Three Different Neck Positions: a Prospective Observational Pilot Study

As defined in recent difficult airway guidelines, successful and rapid cricothyroidotomy depends on identification of the cricothyroid membrane (CTM), coupled with skillful and efficient technique. Unfortunately, identification of the CTM is often inaccurate and complicated by patient factors such as female gender and obesity. Further studies go on to demonstrate the rates for correct identification of the CTM using palpation methods are low and range between 11% and 42%, with even lower success of identifying the midline of the CTM. This traditional palpation method was demonstrated to be fraught with error by different users including: 2 finger palpation, 4 finger palpation, and neck crease successfully identified the CTM 62%, 46%, and 50% of the time at time intervals between 11-14 seconds in non emergency settings.

As a result of previously mentioned patient factors and multiple technical factors, including poor landmarking, cricothyrotomy has a failure rate as high as 60%, exposing patients to high risks of mortality and morbidity. Therefore, more accurate methods of CTM identification are greatly needed at present.

Suggestions of implementing ultrasound in airway management have been brought forth, with applications such as predicting airway difficulty prior to instrumentation, confirming endotracheal tube position, or marking the CTM prior to induction of anesthesia. There have been multiple studies addressing questions such as mean time to identification of CTM in obese subjects using ultrasound and comparison of transverse versus longitudinal scanning technique. One group assessed translational movement of the CTM in neutral neck position versus extended in 23 healthy volunteers, and found a difference in transverse and longitudinal markings of 0.91mm and 1.04mm respectively, with CTM length ranging from 10.6mm to 17mm.

Of interest to the investigators is using ultrasound to predict CTM position accurately and ensuring ability to gain emergency airway access, as the accuracy of ultrasound identification of the CTM in different neck positions is unknown. What is specifically unknown is the translational movement of the cricoid between neck positions.

Therefore, the investigators propose an observational prospective trial looking at cricoid cartilage translation with three different neck positions: neck neutral, neck extension, and neck sniffing. The investigators will use GE Venue 50 (GE HealthcareTM) ultrasound machine, and a linear transducer probe with a frequency of 8-13MHz (GE LOGIQ 12L-SC) for measurements. The measurements will originate at the sternal notch to the superior border of the cricoid cartilage where the cricoid membrane inserts. These will also be referenced to exterior skin markings. The outcomes will address if the airway significantly moves during manipulation by the degree of cricoid cartilage translation between neutral, sniffing and extended neck positions. Secondarily, The investigators will also aim to address the directionality of a pre-marked neck and cricoid migration with neck manipulation.