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TDK conference 2019

Determination of the optimal endotracheal tube size in dogs
Steiner Flóra - year 5
University of Veterinary Medicine Budapest, Department of Surgery
Supervisor: Dr. Miklós Pál Dunay


The aim of our study was to examine tracheal diameters and establish optimal endotracheal tube sizes in dogs.

In the first, retrospective period, we evaluated radiographs of breeds common in Hungary and breed groups known to have tracheal disorders (n=17) in the digital radiography archives (2013 to 2019) of the University of Veterinary Medicine Budapest. In the appointed study groups standard laterolateral radiographs of dogs older than one year of age (n=590) were viewed. Thoracic inlet and tracheal luminal diamaters were taken at three different reference points. Patient data (signalment and values measured) were summarised in a data base.

In all patient groups studied, thoracic inlet tracheal diameters were the smallest thus being the limiting factor in enothacheal tube selection (p<0.05). TD/TI indexes (considered the most commonly used formula to differentiate normal and hypoplastic tracheae) of all study groups were taken and described, thereby contributing to the literature available on the topic.

An optimal choice of the endotracheal tube used is a factor reducing anaesthetic risk. However, no objective recommendations for tube size exist in the literature. In the present work, no significant correlation was found between body weight and tracheal sizes. Therefore we have developed a method to assist correct tube size selection. Limiting tracheal diameters (as based on the reference points) were modified to neutralise radiographic magnification. A corrective coefficient of 1.1 was used in small breed patients, but a coefficient of 1.2 was found to be more precise for medium and large breeds. According to literature sources, optimal tube size in situ is described as the tube and the cuff accounting for 70% and 30% of the tracheal lumen diameter, respectively. Optimal tube sizes were calculated as the magnification corrected limiting luminal diameter of the trachea minus the optimal space occupied by the cuff and the tube wall diameter. The result was rounded up or down to fit actual available tube sizes (in increments of 0.5mm).

An optimal tube size may be selected for any patient in the study group, even without the knowledge of the limiting tracheal diameter by applying descriptive statistic data (mean, mean ±SD, mean ±2SD or minimum-maximum values) presented in the study. The prospective period of the study (long term evaluation of tube sizes adjusted to specific breeds) at the Clinic of University of Veterinary Medicine Budapest has begun in september 2019. Results are planned to be published in the Hungarian Veterinary Journal after the conclusion of the study.

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