Abstract
- The cartilaginous and bony structures of the larynx include the hyoid bone as well as the thyroid and cricoid cartilages. The trachea begins below the cricoid cartilage.
- The hyoid bone, thyroid cartilage, and tracheal cartilages are incomplete rings, with posterior membranous walls. In contrast, the cricoid cartilage is a complete ring, forming an important structural attachment for muscles and ligaments of the larynx. The cricoid cartilage ensures airway patency by stenting the larynx open.
- The cricothyroid membrane is situated between the thyroid and cricoid cartilages in the midline anteriorly. It is located directly beneath the skin, providing direct and easy access to the airway. This membrane is bordered superiorly by the thyroid cartilage, inferiorly by the cricoid cartilage, and laterally by the paired cricothyroid muscles. In adults, it is approximately 1 cm tall and 2–3 cm wide.
- The vocal cords are enclosed within the thyroid cartilage, approximately 1 cm from the upper border of the cricothyroid membrane.
- The cricothyroid membrane is about four fingerbreadths from the suprasternal notch.
Surgical Anatomy
The cartilaginous and bony structures of the larynx include the hyoid bone as well as the thyroid and cricoid cartilages. The trachea begins below the cricoid cartilage.
The hyoid bone, thyroid cartilage, and tracheal cartilages are incomplete rings, with posterior membranous walls. In contrast, the cricoid cartilage is a complete ring, forming an important structural attachment for muscles and ligaments of the larynx. The cricoid cartilage ensures airway patency by stenting the larynx open.
The cricothyroid membrane is situated between the thyroid and cricoid cartilages in the midline anteriorly. It is located directly beneath the skin, providing direct and easy access to the airway. This membrane is bordered superiorly by the thyroid cartilage, inferiorly by the cricoid cartilage, and laterally by the paired cricothyroid muscles. In adults, it is approximately 1 cm tall and 2–3 cm wide.
The vocal cords are enclosed within the thyroid cartilage, approximately 1 cm from the upper border of the cricothyroid membrane.
The cricothyroid membrane is about four fingerbreadths from the suprasternal notch.
Figure 2.1 Anatomy of the larynx. (a, b) Anatomy of the cricothyroid space: The cricothyroid space is formed by the inferior border of the thyroid cartilage and the superior border of the cricoid cartilage. It is partially covered laterally by the cricothyroid muscles. In adults, the cricothyroid membrane is about 1 cm in height and 2–3 cm wide.
General Principles
A cricothyroidotomy is the emergency surgical airway of choice when attempts at orotracheal intubation or airway rescue techniques, such as the laryngeal mask airway (LMA), have failed.
The choice of open versus percutaneous technique is determined by personal preference and experience.
The rapid identification of surface landmarks is critical. In most patients, the thyroid notch is easily visualized or at least palpated in the anterior midline. Palpation immediately caudal to the thyroid cartilage reveals a soft depression, the cricothyroid membrane, which is the target for cricothyroidotomy.
In some patients, this anatomy can be obscured. This may occur in obese patients and those with neck trauma, especially in the presence of a large hematoma. In these patients, the four-finger technique provides a rapid and easy way of estimating the location of the cricothyroid membrane. With the operator’s four fingers extended side by side, the small finger of the hand is placed against the patient’s sternal notch. The surgeon’s index finger is then pointing at incision site, at the cricothyroid membrane.
(a) Surface anatomy of the cricothyroid space. The cricothyroid space includes the inferior border of the thyroid cartilage and the superior rim of the cricoid arch. In adults, the cricothyroid membrane is about 1 cm in height and 2–3 cm wide.
Cricothyroidotomy is relatively contraindicated in pediatric patients (less than 12 years of age), in whom the rates of long-term complications after cricothyroidotomy, particularly stenosis, are high. In these patients, transtracheal needle jet ventilation is preferred.
Care should be taken when considering a cricothyroidotomy for patients with airway injuries. Suspected tracheal transection distal to the cricothyroid membrane is a contraindication to cricothyroidotomy.
Routine conversion of cricothyroidotomy to tracheostomy is unnecessary.
(a) Open cricothyroidotomy equipment. A, endotracheal tube; B, tracheostomy tube; C, tracheal hook; D, scalpel; E, forceps; F, Metzenbaum scissors; G, Senn retractors; H, Kelly clamp; I, 4 × 4 gauze.
