Comparison of two transverse airway ultrasonography techniques for speed and accuracy to localise the cricothyroid membrane in obese female volunteers

The cricothyroid membrane (CTM) is the site of emergency front of neck airway access (cricothyroidotomy) during anaesthesia. Cricothyroidotomy is required when a patient cannot be oxygenated using facemask, laryngeal mask or endotracheal intubation, a rare emergency. Locating the CTM in obese females by palpation can be impossible, whereas ultrasonography is more accurate but slower. We found that a new 2-Level transverse ultrasonography technique is significantly faster than the previously fastest known technique (the “thyroid-airline-cricoid-airline”, TACA, technique) to locate the CTM. We also found that the 2-Level technique is significantly more accurate within 27s (a window of time to perform the scan that is considered to still allow cricothyroidotomy to be performed before morbidity could occur in obese female patients due to low oxygen in the body). Overall accuracy though, not considering time, was not significantly different between the two techniques. So, overall, the 2-Level technique was found to be superior in speed, and in accuracy at 27s. This result was found despite simple randomisation, and one scanning participant’s error (unintentionally performing scans in reverse order to allocation), resulting in a skewed distribution with the 2-Level technique performed initially (before crossover) more (62%) than the TACA (38%), that could possibly favour the TACA technique due to recall bias in this study. Concluding, the 2-Level technique may reduce morbidity in obese female patients during anaesthesia by reducing the time taken from the declaration of an airway emergency until the successful performance of cricothyroidotomy.