Selection of appropriate endotracheal tube size using thoracic radiography in Beagle dogs

To determine the optimal endotracheal tube size in Beagle dogs using thoracic radiography.

Prospective, randomized, crossover experimental study.

A total of eight healthy adult Beagle dogs.

Lateral thoracic radiographs were used to measure the internal tracheal diameter at the thoracic inlet. This measurement was multiplied by 60, 70 and 80% to determine the outer diameter of the endotracheal tube for each dog. In each treatment, medetomidine (5 μg kg^-1) was administered intravenously (IV) for premedication. Anesthesia was induced with alfaxalone (2 mg kg^-1) IV and maintained with isoflurane. After induction of anesthesia, the resistance to passage of the endotracheal tube through the trachea was scored by a single anesthesiologist. Air leak pressures (P_leak) were measured at intracuff pressures (P_cuff) of 20 and 25 mmHg (27 and 34 cmH₂O). The results were analyzed using Friedman tests and repeated measures anova.

There were statistically significant increases in resistance as the endotracheal tube size increased (p = 0.003). When P_cuff was 20 mmHg, mean P_leak for the 60, 70 and 80% treatments were 9.7 ± 6.7, 16.2 ± 4.2 and 17.4 ± 3.9 cmH₂O, respectively, but no significant differences were found. When P_cuff was 25 mmHg, mean P_leak for the 60, 70 and 80% treatments were 10.6 ± 8.5, 19.7 ± 4.9 and 20.8 ± 3.6 cmH₂O, respectively, and statistically significant increases were found between treatments 60 and 70% (p = 0.011) and between treatments 60 and 80% (p = 0.020). Three dogs in the 80% treatment had bloody mucus on the endotracheal tube cuff after extubation.

Results based on resistance to insertion of the endotracheal tube and the ability to achieve an air-tight seal suggest that an appropriately sized endotracheal tube for Beagle dogs is 70% of the internal tracheal diameter measured on thoracic radiography.