The use of ultrasound to estimate tracheal diameter in unclipped brachycephalic dogs; a pilot study

Background A significant contributory factor to the brachycephalic obstructive airway syndrome index of bulldogs is the diameter of their tracheas. Bulldogs are predisposed to tracheal hypoplasia. A non-invasive, financially reasonable and widely accessible screening test for tracheal diameter would be useful for assessing the most appropriate dogs to breed from within bulldog populations and may help in predicting results following upper airway surgery. Method A prospective, method comparison study was conducted involving 10 client owned brachycephalic dogs. Each patient underwent tracheal ultrasonography using a handheld ultrasound device (Butterfly IQ+) followed by extubated computed tomography (CT) scanning of the head and neck. Ultrasonographic tracheal measurements were compared with CT tracheal measurements and analysed for agreement, accuracy, and inter-observer and intra-observer repeatability. Results Bland-Altman analysis showed there was good agreement between the ultrasound and CT tracheal measurements, however the 95% limits of agreement were wide (+0.43cm and -0.29cm), indicating that the ultrasound measurements lacked a high level of accuracy. Ultrasound in general overestimated the tracheal diameter by 0.07cm (P <0.05). Intra-observer repeatability (mean range 0.12cm, average coefficient of variation (COV) observer one; 7.36%, observer two; 5.53%, observer three; 6.10%) was more consistent than inter-observer repeatability (mean range 0.26cm, average COV; 8.47%). Conclusion The accuracy of tracheal diameter measurements using an affordable handheld ultrasound device on unclipped brachycephalic patients was relatively low. However, technique modifications may significantly improve results, and further investigation is warranted to explore this method’s utility as a screening tool for tracheal hypoplasia in bulldog populations.