LAUSR

Cricothyroidotomy is considered the preferred emergency front-of-neck airway access technique, as it has shown a significantly reduced incidence of late complications compared to emergency tracheostomy. Even so, when attempting cricothyroidotomy during the acute phase of a ‘Can’t oxygenate’ crisis, failure to achieve an airway in adequate time is still possible, and more likely in patients with difficult necks where the cricothyroid membrane (CTM) is poorly palpable. Difficult necks may occur in obese patients and in conditions associated with neck oedema or altered airway anatomy. When the CTM is impalpable, current Difficult Airway Society (DAS) guidelines recommend performing an 8–10 cm incision to aid in locating it (plan D). Such length incisions could act as a psychological barrier in the transition to cricothyroidotomy. Also, anaesthetists performing plan D in difficult neck simulations achieved only low cricothyroidotomy success (<46%) despite long skin incisions (up to 14 cm). Although most achieved ventilation (>96%), this appears not infrequently to have been via airways placed through the laryngeal cartilages or trachea, and times to ventilation were relatively long (median 105 seconds). Cannula cricothyroidotomy remains a possible clinical option even in difficult necks (with support from United States and Australian guidelines) and it can avoid long incisions, but it has shown low success (40%) in difficult neck simulations. Furthermore, when a cannula is used for infraglottic access in the difficult neck, it may kink or migrate out of the infraglottic airway more easily than an endotracheal tube. We hypothesised that point-of-care ultrasound guidance may facilitate minimally invasive (single-stab) scalpel cricothyroidotomy during ‘Can’t oxygenate’ emergencies in patients with difficult necks. Ultrasound-guided (US) single-stab scalpel-bougie cricothyroidotomy has shown high success (95%) in cadavers with body mass index (BMI) ranging from 12.2 to 44.9 kg/m. However, many may not have had difficult necks (mean BMI only 21.9 kg/m), and there was no control group. We performed a simulation experiment to assess the accuracy and speed of US single-stab scalpel-bougie cricothyroidotomy in simulated difficult neck models compared to non-US cannula cricothyroidotomy. After ethics committee approval (UTas H0018256), this experiment was conducted at the Launceston General Hospital on 16 December 2019 and 10 June 2020. The sole participant was the first author (KG, the proceduralist, an anaesthetist experienced in airway ultrasonography). Sixty-two bespoke phantom models were pre-produced to simulate difficult adult human necks, with invisible and poorly palpable airway landmarks, see Figure 1. We have named these DiffNeckModels. The airway of each model used Microfoam (3M, North Ryde, NSW) to simulate the CTM, and this was covered with enough opaque, thickened jelly to produce CTM depths similar to that found in patients with a BMI of 45 kg/m or greater. The