Today, I link to and excerpt from Ultrasound-guided Cricothyrotomy and a Novel 3-D Printed Training Model, Emergency Ultrasound Newsroom*, January 31, 2022.
*Be sure to visit Emergency Ultrasound Newsroom. It is an outstanding resource for all POCUS clinicians, not just emergency medicine physicians.
Thomas Lawyer, MD, Ultrasound Fellow at Osceola Regional Medical Center / University of Central Florida in Kissimmee, FL
Javier Rosario, MD, FACEP, Co-Chair of Emergency Ultrasound Section Simulation Subcommittee, Ultrasound Division Director at Osceola Regional Medical Center / University of Central Florida in Kissimmee, FL
All that follows is from the above resource.
Background
Cricothyrotomy is a high acuity, low occurrence procedure that is reserved for scenarios in which the provider cannot intubate or oxygenate the patient. This procedure is classically performed by identifying the cricothyroid membrane (CTM) by palpation. Many patient factors including obesity make localization of the CTM by palpation difficult.1Ultrasound has been shown to improve localization of the CTM, and both increase success rate and decrease complications of cricothyrotomy several fold.2,3Procedural training for ultrasound-guided cric has been described using cadavers, animal, and combination plastic/meat models.4,5,6Here we review the advantages of US guided cric and describe a novel 3-D printed ultrasound-guided cric training model.
Cricothyrotomy by Ultrasound Guidance vs Palpation Alone
EM physicians are familiar with the technique of performing cricothyrotomy after identifying the CTM by palpation. In 2012, Keith Curtis and colleagues described a novel technique of ultrasound-guided, bougie assisted cricothyrotomy in cadavers.7In this study, operators viewed the laryngeal cartilaginous structures including the CTM with the linear ultrasound transducer in long axis, the CTM was cut with a scalpel under active ultrasound guidance, then the bougie and endotracheal tube (ETT) were passed. This study reported a success rate of 20/21 attempts and an average time to completion of 26.2 seconds. Others have described ultrasound guidance for percutaneous tracheostomy with the probe in a transverse orientation on the neck.8Ultrasound has been shown to improve localization of the CTM, increase success rate and decrease complications of cricothyrotomy.2,3,9
A Novel 3-D Printed Model for Ultrasound-guided Cricothyrotomy Training
Procedural training for ultrasound-guided cric has been described on cadavers, animal-derived and combination plastic/meat models, each model with its own advantages and drawbacks for use as a training model.4,5,6Cadavers are realistic, but expensive, difficult to transport, and not re-usable. Animal derived and meat models also provide realistic anatomy but can be difficult to obtain and to store.
Here we describe a novel model for US-guided cric training that uses 3-D printed structures to provide the realism of cadavers, and the re-usability and durability of synthetic models.
3-D printable designs for cricothyrotomy using the palpation method have been available for free for educational purposes online. Using a free download computer design program, a 3-D model of the neck was redesigned to allow for greater pre-tracheal soft tissue, to create a model where palpation of the landmarks for performing cric is difficult or impossible. This model was converted into a format to be printed on a 3-D printer. The 3-D printable components of this model can be found for free download for educational use on Thingiverse.com by searching for ultrasound guided cric trainer.
The model can be re-created by downloading the model for 3-D printing, and following the following steps:
- Print the neck model and riser blocks (used to vary the depth of pre-tracheal soft tissue, if desired) on the 3-D printer out of hard plastic polylactic acid (PLA) or similar material.
- Print the larynx on a 3-D printer out of more flexible thermoplastic polyurethane (TPU) or similar material. This allows for a more realistic feel of passing the tube through the larynx, without rigid plastic to for the tube to get caught on.
- Ballistic gel is available commercially with various firmness. Gel that mimics fat tissue works well for this application. Melt the gel in a pot to create slabs of gel of the desired thickness of pre-tracheal soft tissue. This model allows up to approximately 2.5 cm of pre-tracheal soft tissue. Once cool, cut the gel into slabs that fit the model.
- Create an artificial cricothyroid membrane on the model by covering the space for the CTM with a layer of tape.
- For a simulated difficult cricothyrotomy, consider placing the model larynx directly into the neck model without riser blocks behind it. This allows for the largest amount of space in front of the larynx to be filled with ballistic gel acting as pre-tracheal soft tissue.
- Apply generous amounts of ultrasound gel on top of the model larynx, and on top of the ballistic gel to optimize ultrasound images.
