Effects of thiopental, propofol and alfaxalone on laryngeal motion during oral laryngoscopy in healthy dogs

Abstract

Objective: To compare the effects of thiopental, propofol and alfaxalone on arytenoid cartilage motion and establish dose rates to achieve a consistent oral laryngoscopy examination. Study design: Prospective, randomised, blinded crossover study. Animals: Six healthy adult beagle dogs. Methods: Each dog was administered three induction agents in a random order with a one week washout period between treatments. No premedication was used prior to induction of anaesthesia. Thiopental, propofol or alfaxalone were administered at 7.5 mg/kg, 3 mg/kg and 1.5 mg/kg, over 1 minute to effect, for induction of anaesthesia, respectively. If the dog was deemed inadequately anaesthetised then top-up boluses of 1.8 mg/kg, 0.75 mg/kg and 0.4 mg/kg, respectively, were administered over 10 seconds, repeated every 20 seconds, until an adequate anaesthetic plane had been reached. Continual examination of the larynx, using a laryngoscope, commenced once an adequate anaesthetic depth had been reached until recovery from anaesthesia. The number of arytenoid motions and deep inspiratory efforts (vital breaths) were counted within three time periods and compared over time among treatments. Data were analysed using Friedman test, Mann-Whitney U test, Spearman's rho, linear mixed model with post-hoc pairwise comparison with Tukey correction. Results interpreted at a 5% level of significance. Results: The median (range) induction time was 2.8 (2.0, 3.0), 2.7 (2.0, 3.3) and 2.5 (1.7, 3.3) minutes for thiopental, propofol and alfaxalone, respectively (p = 0.727). The median (range) dose rate required to achieve an adequate depth of anaesthesia was 6.3 (6.0, 6.6), 2.4 (2.4, 2.4) and 1.2 (1.2, 1.2) mg/kg/minute for thiopental, propofol and alfaxalone, respectively. Therefore, the median (range) total dose administered over the induction time was 17.8 (13.2, 18.8), 6.8 (5.3, 8.3) and 3.2 (2.3, 4.1) mg/kg for thiopental, propofol and alfaxalone, respectively. There was no significant difference for the total number of arytenoid motions (p =0.662) or vital breaths (p = 0.789) among induction agents. The median (range) examination times were 14.1 (8.0, 41.8), 5.4 (3.3, 14.8) and 8.5 (3.8, 31.6) minutes for thiopental, propofol and alfaxalone, respectively (p=0.016). Conclusion and clinical relevance: There was no significant difference in the total number of arytenoid motions among the induction agents. However, at the dose rates used in this study, propofol provided adequate conditions for evaluation of the larynx within a shorter examination time which may be advantageous during laryngoscopy in dogs.