Endotracheal intubation is a common practice in veterinary medicine that provides a patent airway with the ability to deliver positive pressure ventilation, offers protection from airway aspiration, and prevents environmental contamination of waste anesthetic gasses in unconscious animals for procedures that require general inhalant anesthesia. However, orotracheal intubation may be challenging in rabbits due to the anatomic characteristics that limit direct visualization of the airway, including a relatively large tongue, long and narrow oropharyngeal cavity, and small glottis.1,2 Furthermore, sublaryngeal tracheal injury and ulceration have been described in rabbits after orotracheal intubation with uncuffed and cuffed endotracheal tubes (ETT), suggesting that rabbits may be predisposed to serious injury from routine intubation, including subglottic and tracheal stenosis, which can increase their morbidity and mortality rate.3–5 While multiple intubations, prolonged intubation time, and using cuffed ETT likely contribute to worse outcomes, there is a paucity of literature on rabbit tracheal measurements and ETT size selection.3,4,6
There is significant variation in the literature regarding the ETT size used in different rabbits.7–10 The authors acknowledge the importance of ETT size selection in rabbits with no elaboration of selection criteria.3,4,8,11 Some authors correlate ETT size with rabbit body weight, such as recommending uncuffed 1- to 2-mm internal diameter (ID) ETT for rabbits weighing less than 2 kg and uncuffed 2- to 3-mm ID ETT for rabbits weighing more than 3 kg,2 but no reported airway measurement supports this selection. Furthermore, some recommendations suggest direct or indirect visualization (such as radiography) instead of weight cut-offs as the best way to select ETT size.11
At the authors’ institution, many rabbits are sedated for computed tomography (CT) before intubation and general anesthesia for a procedure (dental, emergency abdominal procedure, mass removal, etc.). This retrospective study aimed to analyze laryngotracheal luminal height, width, and cross-sectional areas at different locations using CT scans of male and female adult domestic rabbits (Oryctolagus cuniculus) of varying body weights, body condition scores (BCS), and breeds; assess the relationship of these measurements with rabbit body weight and determine the anatomic location of the narrowest laryngotracheal measurement. As a secondary objective, the relationship between the most common narrowest laryngotracheal measurement, ETT size, and body weight were assessed. We hypothesize that a robust population of adult rabbits will reveal a positive correlation between body weight and laryngotracheal measurements.
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Statistical analysis was supported through the NIH Clinical and Translational Science Award (CTSA) program (grant UL1TR002373).
The authors declare no conflict of interest.
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