Neck Position and Ultrasound Landmark of Cricothyroid Membrane
Condition: Cricothyroid Membrane; Ultrasound; Airway; Cricothyroidotomy
Study type: Observational

Summary: 
      Cricothyroid membrane (CTM) localization is a critical step prior to emergent surgical airway
      access. Ultrasound-guided localization of the CTM on the skin of the neck had been suggested
      prior to induction of general anesthesia so that a marked entry point can be used to quickly
      establish emergent front of neck access if required. In this prospective observational study,
      the investigators aim to determine the potential for migration of the CTM markings in the
      sagittal plane during neck repositioning.
    

Detailed description: 
      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.
    

Intervention name(s): Movement
Intervention type(s): Other
Intervention description(s): Re-positioning of neck
Observational model: Cohort
Time perspective: Prospective
Sampling method: Probability Sample
Study population: 
        Adult volunteers over age 19