In-depth tube assessment by ultrasound: double twist sign to evaluate endotracheal tube depth—results of a cadaver diagnostic accuracy study

PURPOSE: An adequate endotracheal tube depth is crucial for airway management and effective mechanical ventilation, as both too deep and superficial tube placement can be harmful to the patient. The aim of this study was to evaluate endotracheal tube depth using the ultrasound double twist sign as a new diagnostic tool using a cadaver model. METHODS: In this diagnostic accuracy study, ultrasounds were performed by 12 sonographers (2 expert and 10 novice users, consisting of residents and specialists) on 3 cadavers. Novice users learned the technique in 15 min. Tubes were randomized to be placed in adequate, deep (tube tip touching main carina) or superficial (cranial edge of cuff touching vocal cords) position. RESULTS: The double twist sign showed an overall success rate of 90.6% to identify tube depth. It was particular reliable in identifying and ruling out deep placement, with a sensitivity of 99.2%, a specificity of 98.5%. The mean time to identify deep placement was 6.4 s; with an overall mean assessment time of 18.4 s. Test performance was not significantly impacted by cadaver (BMI, neck circumference) or sonographer characteristics ( sonographer experience); however, the study was not powered to exclude clinically meaningful effects of anatomy. CONCLUSION: In an embalmed cadaver model, the double twist sign enabled rapid and accurate assessment of endotracheal tube depth using POCUS( Point of care ultrasound)with an air-filled cuff. These findings support feasibility and diagnostic potential, but clinical performance in ventilated patients and comparison against radiography require prospective validation.