Effects of chemical and mechanical stimulation on laryngeal motion during alfaxalone, thiopentone or propofol anaesthesia in healthy dogs

Abstract

OBJECTIVE : To compare the effect of chemical and mechanical stimulation on arytenoid cartilage motion during anaesthetic induction with alfaxalone, thiopentone or propofol. STUDY DESIGN : Masked, randomized, crossover study. ANIMALS : A group of eight adult Beagle dogs. METHODS : Anaesthesia was induced with thiopentone (7.5 mg kg–1), propofol (3 mg kg–1) or alfaxalone (1.5 mg kg–1) intravenously (IV), which were concurrently paired with either chemical (doxapram at 2.5 mg kg–1 IV) or mechanical (gentle pressure to the corniculate process of the right arytenoid cartilage using a cotton bud) stimulation for enhanced assessment of laryngeal motion, in random order, with a 1 week wash-out period between treatments. If deemed inadequately anaesthetized, supplemental boli of thiopentone (1.8 mg kg–1), propofol (0.75 mg kg–1) or alfaxalone (0.4 mg kg–1) were administered. Assessment of number of arytenoid motions and vital breaths, among others, was initiated immediately after induction. Chemical (doxapram) and mechanical stimulation were begun 2 minutes after anaesthetic induction. Data were collected at 2, 3 and 5 minutes after anaesthetic induction and the Friedman rank-sum or repeated-measures analysis of variance tests were used when applicable for statistical analysis. RESULTS : The duration of examination time was shorter among treatments combined with chemical stimulation (p=0.001). Examination time during induction was longer for alfaxalone-chemical (8.9 minutes) and -mechanical (10.9 minutes) compared to both induction with thiopentone-chemical (3.8 minutes) and propofol-chemical (4.0 minutes). The median number of arytenoid motions for both thiopentone (67) and propofol (59) induction combined with chemical stimulation was significantly higher in comparison to that of alfaxalone (1), thiopentone (2) and propofol (2), when combined with mechanical stimulation at 3 minutes after induction. CONCLUSION AND CLINICAL RELEVANCE : Among the regimens for assessing laryngeal motion assessed in the present study, combinations of thiopentone or propofol with doxapram are the most effective means of stimulating arytenoid motion and could improve the accuracy of diagnosis of laryngeal paralysis in dogs.