Evaluation of Endotracheal Tube Size Determination Using Thoracic Radiography in Dogs

Abstract

The present study was conducted 1) to develop a method to select the optimal endotracheal tube size in dogs using thoracic radiography, 2) to determine how time affects intracuff pressure and air leak pressures after intubation with an appropriately sized endotracheal tube, and 3) to evaluate the reliability and usefulness of this novel method in clinical practice.<br/> In chapter I, the internal tracheal diameter of a lateral thoracic radiographic image was measured at the thoracic inlet in Beagle dogs and was multiplied by 60, 70 and 80% to determine the endotracheal tube size. Considering the resistance felt during endotracheal tube insertion through the trachea and the ability to prevent aspiration by attaining a proper seal between the cuff and tracheal mucosa, it was determined that 70% of the internal tracheal diameter was suitable for choosing the appropriate endotracheal tube size in Beagle dogs. <br/> In chapter II, changes in endotracheal tube intracuff pressures and air leak pressures over time were evaluated in anesthetized Beagle dogs. In part I, intracuff pressure measurements were recorded for 1 hour in eight endotracheal tubes studied in an in vitro setting under four treatments: room temperature without lubricant (RTWOL), room temperature with lubricant (RTWL), body temperature without lubricant (BTWOL), and body temperature with lubricant (BTWL). In part II, nine Beagle dogs were endotracheally intubated with an appropriately sized endotracheal tube and changes in intracuff pressures and air leak pressures were evaluated. In part I, intracuff pressure differed significantly between the RTWOL and RTWL treatments, and between the BTWOL and BTWL treatments. In part II, intracuff pressures significantly decreased over time in all dogs while air leak pressures significantly changed according to the individual. The decrease in intracuff pressures was attributed to the elastic properties of the cuff, the use of a lubricant, and muscle relaxation due to anesthesia.<br/> In chapter III, the reliability and usefulness of using thoracic radiography to determine the appropriate endotracheal tube size was assessed in 51 client-owned dogs. When the correlation between individual tracheal diameters and endotracheal tube sizes was examined, significantly high correlations were found between tracheal diameter and endotracheal tube size, and between tracheal diameter and cuff diameter.<br/> Based on the results of the present studies, measuring the internal tracheal diameter of a thoracic radiographic image was a useful and reliable method to predict the optimal endotracheal tube size in dogs. It is expected that this method will allow for more accurate endotracheal tube size selection in small animal clinical practice. Furthermore, this method could be used for future studies to develop more objective recommendations and criteria for sizing endotracheal tubes in various situations. <br/>