DAS Project Grants

Background
The cricothyroid membrane (CTM) is located at the front of the neck, between the thyroid cartilage and cricoid cartilage. It is a small area and is an alternative access to the lungs to provide oxygenation. During a 'can't intubate, can't oxygenate' (CICO) situation, the front of neck airway access, also known as cricothyroidotomy is advocated via the CTM. Cricothyroidotomy was shown to be associated with high failure rate if not performed correctly. The usual way of identifying the CTM is by digital palpation which is fairly inaccurate (24-72%) and even worse in obese subjects (0-46%). Recent studies have shown that ultrasound can increase the accuracy of identifying the CTM (62.5-100%). Using the ultrasound is not an invasive technique in identifying the CTM but cricothyroidotomy is an invasive procedure associated with morbidity and mortality. In identifying the CTM accurately, the complication rate of performing cricothyroidotomy could be decreased. We have recently developed the Guildford Cricothyroid membrane Ultrasound Technique (GCUT), which is an ultrasound technique in identifying the CTM in the transverse plane. This new technique is accurate in identifying the CTM and also relatively easy and quick to perform. Hence, we propose conducting a prospective controlled observational study of comparing the accuracy and time taken to identify the CTM using the landmark technique and ultrasound techniques, both in sagittal and transverse planes in two subjects with different neck pathologies.

Aims
Comparing the accuracy and time taken to identify the CTM with the ultrasound in the sagittal and transverse plane.

Methodology
We will perform a prospective controlled observational study. Anaesthetists who have never used the ultrasound in identifying the CTM will be recruited from the department. Training will be provided to the participants on using the ultrasound in identifying the CTM with both sagittal and transverse techniques. They will also be able to practice the ultrasound techniques on a human subject (normal BMI). We require two human subjects with neck pathology but otherwise medically stable for the study itself. Participants will be randomized to both subjects in identifying the CTM first by digital palpation followed by the ultrasound techniques. Participants will be further randomized to which ultrasound technique to be performed first. Primary outcomes to be measured are accuracy and time taken in identifying the CTM. Secondary outcomes include user confidence, learning and preference.

Expected outcomes
Ultrasound is accurate in identifying the CTM compared to digital palpation in both subjects. In comparing the ultrasound techniques, the transverse technique is equally accurate but quicker to perform compared to sagittal technique. Participants will prefer the transverse technique as it is easier to learn and perform.

Implications
Ultrasound should be used in identifying the CTM accurately. The transverse ultrasound technique is easy to learn and can be performed quickly. With the increased use of ultrasound in anaesthesia, anaesthetists should also equip themselves with an ultrasound technique to identify the CTM.

Once a patient has been given a general anaesthetic ('put to sleep') they rely on their anaesthetist to ensure that they continue to breathe for themselves or that specialised equipment is used to take over their breathing for them.

If an anaesthetised patient's lungs and hence brain, do not receive oxygen, irreversible brain damage or death may rapidly result. This is a rare and 'time critical' emergency that must be identified and treated promptly to avoid such devastating complications.

All anaesthetists must have a robust and well rehearsed plan to follow if they encounter difficulties delivering oxygen to their anaesthetised patients. To this end, in 2015, a group of specialist anaesthetists called the 'Difficult Airway Society' (DAS) updated their guidelines for all anaesthetists to read, memorise and follow in such an emergency.

These revised guidelines advise that if oxygen cannot be delivered to a patient's lungs through the mouth or nose because of a blockage therein, then, if all other methods fail, the anaesthetist should make a cut with a scalpel in the front of the neck (i.e. below any blockage) and introduce a breathing tube into the wind pipe allowing oxygen to get to the lungs. This operation is called a scalpel cricothyroidotomy and is something anaesthetists have not usually performed. Before these updated guidelines were published, anaesthetists had preferred to pass a needle through the front of the neck to administer oxygen: a so called needle cricothyroidotomy.

The reason DAS have advised that scalpel cricothyroidotomy supersede needle cricothyroidotomy, is that there is evidence to suggest that the scalpel method is both quicker and safer to perform. Unfortunately, most anaesthetists are not familiar with using a scalpel to perform a cricothyroidotomy.

Our hospital has a unique training program combining teaching on how to use a scalpel on a manikin as well as a patient having a tracheostomy as part of their elective operation (under the supervision of a consultant surgeon). A tracheostomy is the insertion of breathing tube into the wind pipe lower down in the neck than a cricothyroidotomy and is performed routinely for patients undergoing major head and neck surgery. Although a different procedure to a cricothyroidotomy, there are many similarities that make it invaluable training for anaesthetists such as: positioning the patient and identifying the relevant anatomy, learning how to hold and use a scalpel to cut through the skin down onto the windpipe plus experiencing the tactile and visual sensations the procedure entails.

We wish to investigate whether this training improves the confidence and ability of 10 trainee anaesthetists to perform a scalpel cricothyroidotomy, on their own, under emergency conditions. A practical assessment will be made by studying how the anaesthetists react to, and deal with, three identical life-like simulations of an emergency requiring a scalpel cricothyroidotomy. These simulations will be prior to and after completing the program as well as unexpectedly 6 months later. They will also undergo a structured interview at each stage to further assess whether the training made a difference.