Applications of airway Ultrasound in RICUMaiada Kamal El-Din HashemChest dept - Assiut university

Objectives What is airway ultrasound? What and how to see? Clinical applications How to learn airway US?

What and How to see?

Position: • Supine position with a pillow under the occiput to

achieve optimum head extension Orientation: • Sagittal• Parasagittal• transverse

What and How to see? (cont.)

What and How to see? (cont.)

Hyoid bone: On the transverse view the hyoid bone is visible as a

hyperechoic, inverted U–shaped structure with posterior acoustic shadowing.

On the sagittal and parasagittal views, the hyoid bone is visible in cross section as a narrow, hyperechoic, curved structure that casts an acoustic shadow.

What and How to see? (cont.)

Thyroid cartilage: Thyroid cartilage is visible on sagittal and parasagittal

views as a linear hypoechoic structure highlighted by the bright A-M interface at its posterior surface.

On the transverse view, it had an inverted V shape, within which the true and false vocal cords were visible.

What and How to see? (cont.)

Vocal cords: Thyroid cartilage provides the best window to view the vocal

cords. Vocal cords are seen forming a triangle with a central tracheal

shadow. Vocal cords are delineated medially by the hyperechoic vocal

ligaments. During phonation, the true cords oscillate and move towards the

midline.

What and How to see? (cont.)

Cricoid Cartilage and Cricothyroid Membrane: In the parasagittal view the cricoid cartilage has an oval

hypoechoic appearance. In the transverse view seen as a hump. The posterior surface is delineated by a bright A–M

interface and reverberation artefacts. The cricothyroid membrane is seen as a hyperechoic

band linking the hypoechoic thyroid and cricoid cartilages.

What and How to see? (cont.)

Thyroid gland: At the level of the suprasternal notch in the transverse

view, the two lobes and isthmus of the thyroid gland can be visualized anterolateral to the trachea.

What and How to see? (cont.)

Trachea: In the midline of the neck with the cricoid cartilage

marks the superior limit of the trachea. In the parasagittal and sagittal view the tracheal rings

are hypoechoic, and they resemble a “string of beads” . In the transverse view, they resemble an inverted U

highlighted by a hyperechoic air-mucosa interface and by reverberation artifact posteriorly.

What and How to see? (cont.)

Esophagus: The cervical esophagus is visible posterolateral to the

trachea on the left side at the level of the suprasternal notch.

The concentric layers of esophagus result in a characteristic “bull’s-eye” appearance.

The esophagus can be seen to compress and expand with swallowing, and this feature can be used for accurate identification.

Clinical applications:

Identification of endotracheal tube placement:• Easy , fast and useful• How ?

Linear arrayLateral esophagus

Clinical applications: (cont.)

Prediction of difficult intubation:An abundance of pretracheal soft tissue at the level of the vocal cords by ultrasound is a good predictor of difficult laryngoscopy.

Clinical applications: (cont.)

Prediction of the appropriate diameter of endotracheal, endobronchial or tracheostomy tube:• Ultrasound measurements of the outer diameter of the

trachea just above the sternoclavicular joint in the transverse section

• The ratio between left main-stem bronchus diameter on and outer tracheal diameter measured with US is 0.68

Clinical applications: (cont.)

Guidance of percutaneous tracheostomy and cricothyroidotomy:• By localization of the cricothyroid membrane.• Identification the anterior tracheal wall, thyroid and

cricoid cartilages, tracheal rings, and pretracheal tissues, including the relationship of the thyroid gland and the vascular structures of the neck to the trachea.

Clinical applications: (cont.)

Guidance of retrograde intubation:

Clinical applications: (cont.)

Prediction of post-extubation stridor:• AC shape• ACW ratio• ACW difference

Clinical applications: (cont.)

Prediction of subglottic and tracheal stenosis:• Diameter and air column• Mucosal lining• filling

How to learn airway US

After 8.5 h of focused training comprising a didactic course, which included essential views of normal and pathologic conditions and three hands-on sessions of 2 h, physicians without previous knowledge of US can competently perform basic general ultrasonic examinations.*

*Chalumeau-Lemoine L, Baudel JL, Das V, Arrivé L, Noblinski B, Guidet B, Offenstadt G, Maury E. Results of short-term training of naïve physicians in focused general ultrasonography in an intensive-care unit.

Intensive Care Med 2009;35: 1767–71.

Take home message US has many advantages for imaging the airway: It is safe, quick,

repeatable, portable, widely available, and gives real-time dynamic images relevant for several aspects of management of the airway.

US must be used dynamically for maximum benefit in airway management and in direct conjunction with the airway management: Immediately before, during, and after, airway interventions.

US can be used for direct observation of whether the tube enters the trachea or the esophagus by placing the ultrasound probe transversely on the neck at the level of the suprasternal notch during intubation, thus confirming intubation without the need for ventilation or circulation.

US can be used for detection of post-extubation stridor and decrease rate of reintubation by evaluating air column width.