Identification of the cricothyroid membrane to facilitate surgical cricothyrotomy
In the context of surgical airways, POCUS can also be used to identify the cricothyroid membrane in children [21]. Ultrasound outperforms digital palpation of the cricothyroid membrane in children [22]. Furthermore, it’s application has been linked to improved success rates in correct cricothyroid tube placement in adult patients [23]. However, it is important to note that using ultrasound in this context can be more time consuming. Ultrasound use will typically take 17s, compared to traditional palpation which takes about 8s [25]. This time cost may be worthwhile in patients with higher BMI where palpation may be more difficult or in the anticipated difficult airway when there is sufficient time prior to intubation.
Airway POCUS has also been proposed as a risk prediction tool for difficult laryngoscopy in adults. Pediatric literature on prediction of airway difficulty is scant and beyond the scope of this module.
The cricothyroid membrane can be visualized by ultrasound using the linear probe placed in the longitudinal plane (Figure 3B). Figure 2 C-D demonstrates the sonoanatomy. The probe should first be placed at the suprasternal notch where the tracheal rings (the string of pearls) may be identified. The probe is moved cephalad until a larger pearl is seen: the cricoid with its posterior acoustic shadowing. Above it, the other hyperechoic structure with hypoechoic shadow is the thyroid cartilage. In between lies the cricothyroid membrane. Following its identification, the clinician can mark the skin and use this information as a static landmark for surgical airway.
In general, you will see the same overall landmarks—cricoid and thyroid cartilages with the cricothyroid membrane in between—throughout the lifespan. However, the echogenic appearance and degree of posterior acoustic shadowing can vary with patient age. This is largely because pediatric laryngeal cartilages are more pliable and less calcified than those of older adolescents or adults. As patients get older and the cartilage begins to calcify, you will see a more prominent hyperechoic line with a stronger acoustic shadow.
In younger children, the cartilage tends to appear less bright (less calcified) on ultrasound, and the shadows they cast are often more subtle. Nevertheless, the positional relationships—thyroid cartilage, cricothyroid membrane, cricoid cartilage—remain the same, so you can still use the same “string of pearls” approach and carefully identify the membrane for procedural marking. The “pearls” may be a smaller and dimmer in younger pediatric scans compared to older patients.
Cricothyrotomy is an advanced skill that is rarely performed by physicians. Use of ultrasound should never delay definitive airway establishment. Expert surgical consultation should be sought early.