Ram Parekh MD, performs a life-saving cricothyrotomy on a post-arrest patient:
introduction
surgical cricothyroidotomy is an emergency procedure to create a patent airway by creating a hole in the cricothyroid membrane and passing a tube such as an endotracheal tube to allow ventilation of a compromised airway.
anatomic considerations
the position and size of the cricothyroid membrane is quite variable depending on age, height, habitus and racial characteristics
the position of the cricothyroid membrane is:
just inferior to the lower border of the thyroid cartilage
in southern Indian study:
the lower border stab site distance from sternal notch is 7.9cm in the extended neck and 5.0c on the neutral neck position
ie. half-way between sternal notch and chin when neutral and a 1/3rd of the way to the chin if extended.
the aim is to create a transverse incision into the lower aspect of the cricothyroid membrane to avoid hitting the transverse cricothyroid artery which runs close to the lower border of the thyroid cartilage.
it is important that the stab wound is not too deep that it penetrates the posterior wall of the trachea which may lead to a tracheo-oesophageal fistula - the depth at this level in adults varies from 13-25mm, with a mean of ~20mm in men and ~15mm in women.
the height of the cricothyroid membrane is 5-7mm in the southern Indian study, while the Caucasian study by Dover et al, the mean height was 10.0mm for men and 9.5mm for women, while width dimensions were similar in both studies.
in the field, operator can use their little finger to dilate the wound, ensure trachea has been penetrated and is of sufficient size for the ETT 1)
in theory, the largest possible ETT should be used to ensure the least airway resistance but the larger the ETT, the more difficult it is to insert, and there are limits due to anatomic size with recommendations2):