In light of the COVID-19 pandemic, the authors highlight their protocol of transcutaneous laryngeal ultrasonography as an alternative to flexible fibreoptic laryngoscopy when appropriate. This is to reduce the risk of aerosolisation posed by laryngoscopy. Ultrasonography is a rapid, non-invasive way of assessing vocal cord function. It can be used in evaluating patients pre and post thyroid or laryngeal surgery, postcardiac or thoracic surgery, with recent intubation, cerebrovascular event, or suspicion based on clinical signs of aspiration and voice change. Previous studies have reported a sensitivity and specificity in detecting motion abnormalities ranging from 53.8% to 93.3% and 50.5% to 97.8%, respectively. Concordance with laryngoscopy findings ranges from 70% to upward of 95%. Their technique uses a high-frequency ‘small parts’ transducer of 7.5 to 15MHz with frequency adjusted to the lowest end and gain increased as needed. Patients are usually supine (but can be seated) with neck in extension. The transducer is applied to the skin with gel in the midline anterior to the vertical midpoint of the thyroid cartilage or inferior to it, angling the transducer slightly superiorly. Vocal fold abduction and adduction are visualised during respiration and breath-holding. When the patient is asked to stop breathing momentarily, the vocal folds adduct and when asked to resume respiration, vocal fold abduction is noted, confirming bilateral vocal fold mobility. The true vocal folds are typically hypoechoic but may be distinguished by a fine hyperechoic line at their medial edges. The false vocal folds and arytenoids are hyperechoic.
Vocal fold mobility during passive breathing can be assessed in the unconscious patient.
If vocal folds are not visible from the midline, due to calcification or poor transducer contact, then each vocal fold can be assessed independently from a more lateral perspective, although symmetry cannot be directly compared.