Trial to compare two airway ultrasonography techniques for speed and accuracy

INTERVENTION: Volunteers will be exposed to both a new and a known airway ultrasound technique to locate the cricothyroid membrane. The known airway ultrasound technique is called the "3‐Level Technique" and is from Kristensen MS, Teoh WH, Rudolph SS, Hesselfeldt R, Borglum J, Tvede MF. A randomised cross‐over comparison of the transverse and longitudinal techniques for ultrasound‐guided identification of the cricothyroid membrane in morbidly obese subjects. Anaesthesia. 2016; 71: 675‐83). It involves performing transverse airway ultrasonography at the midline of the anterior neck as follows: Aim to start scan at the thyroid cartilage, once the thyroid cartilage is identified then scan caudally over the cricothyroid membrane (CTM), hopefully identifying it on the first pass, but continue scanning caudally until identify the cricoid cartilage, then scan cephaladly until confident over the CTM, then finish. This is expected to take less than 1 minute, in Kristensen's paper it took a mean time of just 24 seconds to identify the CTM. This will be the control for the study to compare the new technique to. The new technique, called the "2‐Level Technique" is a modification of the 3‐level technique, which is hoped will be identify the CTM quicker, while being just as accurate. It is a transverse midline ultrasounography technique, performed as follow:: Aim to start at the thyroid cartilage, once the thyroid cartilage is identified then carefully scan caudally until confident over the CTM, then finish. This technique is also expected to take less than 1 minute, likely less than 24 seconds. Student participants will have the scans performed on them up to 3 times each during the training period (total scan time of up to 6 minutes ultrasonography). Mock patient participants will have the scans performed on them up to 6 times each (total scan time of up to 12 minutes). These total scan times are much less than an obstetric ultrasound in clinical practice, which includes scanning the fetus and can take up to 40 minutes. On the training day, initially an specialist anaesthetist with much experience in airway ultrasonography with perform some scans on the 5th year medical students to demonstrate the two techniques, then they will practice on each other to gain experience and learn the techniques, which are relatively easy to learn and perform. Then, on the research day, these trained 5th year medical students participants (who will be assessed for accuracy and timing to locate the CTM) will perform the scans on the mock patient participants. On the research day, each student participant will have perform both techniques once each on a single mock patient participant, with at least 10 minute break between scans. During the 10 minute break though, another student or students may perform their first or second scan. CONDITION: Difficult intubation requiring front of neck (infraglottic) airway access PRIMARY OUTCOME: Time taken (speed) to locate the cricothyroid membrane will be assessed for watch scan by a blinded timing observer. This observer will not watch the scan, but will face the other way. This observer will measure with a stop watch from when the scanning participant says “start” (when the ultrasound transducer contacts the ultrasound transmission gel on skin of the neck) to when they say “done” (when they believe they have located the CTM on the image). SECONDARY OUTCOME: Accuracy will be assessed in two ways. A blinded accuracy observer will not watch the scan, but face the other way until it is completed, then will assess accuracy by: ; 2. Assessing if the student participant's saved CTM localisation images actually show the CTM or not. ; INCLUSION CRITERIA: Medical student participants: 5th year medical students at University of Tasmania's Launceston Clinical School, must be aged over 18 years of age. ; 1. Assessing the transducer location at CTM localisation agrees with the location of the premarked invisible ink. (Note: Invisible ink on the skin will mark the ultrasound located CTM site, this will be performed by a specialist anaesthetist before then covered with a transparent dressing before any student participant scans are performed on the research day) & Mock patient participants: must be over 18 years of age and BMI>30