[Locating the cricothyroid membrane in learning phase: value of ultrasonography?]

Emergency cricothyroidotomy is recommended as life-saving maneuver when mask ventilation and tracheal intubation are impossible. It requires the puncture of the cricothyroid membrane (CTM) whose clinical identification is difficult. The objective of this study is to evaluate if ultrasound can help locating the CTM by comparing palpation and ultrasonographic evaluation.

After ultrasound localization of CTM by a referent physician in two overweight volunteers, twelve residents without prior anatomy recall, defined by palpation an entry point for CTM. After a rapid training in CTM ultrasound localization, residents identified an ultrasound-guided puncture point. For each puncture site were registered: relevance, time and ease to localization. Six months later, residents renewed clinical and ultrasound identification of CTM on the same subjects.

The CTM was accurately identified by palpation and ultrasound by 46% and 100% of residents respectively (P<0.05). Six months later, residents remained more effective identifying CTM with ultrasound than with palpation (78% vs. 33%) (P<0.05). Time to localization of CTM by palpation in the 2 volunteers was 15 s [11-18] and 24 s [9-39] (average [CI 95%]) whereas it was 21 s [16-25 s] and 28 s [19-36] by ultrasound respectively (ns). The ultrasound identification of CTM was also considered easier than clinical identification.

Following a limited training phase, ultrasound allowed a more effective localization of CTM by residents when compared to clinical palpation in overweight patients. This benefit remained significant when assessment was repeated 6 months later.