Comparison of methohexital and propofol as induction agents for evaluation of laryngeal function in healthy dogs

Abstract

Objective To determine the influence of propofol or methohexital, with and without doxapram, on the examination of laryngeal function in dogs. Study design Experimental study. Animals Forty healthy dogs randomly assigned to 4 groups: propofol with saline (n = 10), propofol with doxapram (n = 10), methohexital with saline (n = 10), or methohexital with doxapram (n = 10). Methods Propofol and methohexital were administered to effect. Investigators examined laryngeal function (initial) simultaneously with video laryngoscopy. Doxapram or saline was administered, and laryngeal function was reevaluated (second). Laryngeal motion, quality of laryngeal exposure, and the degree of swallowing, laryngospasm, and jaw tone were scored at each evaluation. Adverse events were recorded. Initial and second videos were evaluated by a masked observer, and still images obtained from both evaluations were evaluated for change in rima glottidis size by 2 masked observers. Results Administration of doxapram and saline was delayed with propofol (P = .001). Laryngeal function did not differ between dogs receiving propofol or methohexital, irrespective of doxapram administration. Doxapram improved breathing scores in both groups (P < .001). Jaw tone increased with propofol during the second evaluation (P = .049). Swallowing was more prevalent at initial examination (P = .020). Methohexital resulted in an increased heart rate (P < .001) compared with propofol. Twenty‐five percent of dogs receiving methohexital developed seizure‐like activity (n = 5/20). Conclusion Evaluation of laryngeal function did not differ between healthy dogs anesthetized with propofol or methohexital. Methohexital provided shorter examination times with less jaw tone but was associated with adverse events. Clinical significance This study provides evidence to recommend propofol over methohexital as an induction agent for laryngeal function examination.

The Influence of Anaesthetic Drugs on the Laryngeal Motion in Dogs: A Systematic Review

“…Only one of the studies included dogs with suspected laryngeal paralysis, in a non-blinded, non-randomised design [17]. Most studies (83%) provided a direct comparison between anaesthetic drugs, with two studies including a control group [10,13]. A total of 58% of studies evaluated laryngeal function objectively by measurement of the normalised glottal gap area (NGAA) or normalised rima glottides surface area (RGSA) via video laryngoscopy.…”

“…The agreement between assessors of laryngeal function was excellent in only one study [12]. Brown et al found disagreements in the assessment of laryngeal function, swallowing and the incidence of laryngospasm between direct and masked observers [10]. Also, disagreement between observers was reported by McKeirnan et al in 58% of the cases, with some dogs being classified by some observers as having laryngeal paralysis and healthy by others [16].…”

“…In a crossover, blinded level II study, doxapram improved laryngeal function when assessed objectively only in dogs receiving dexmedetomidine alone and not when combined with opioids or propofol [7]. In the only controlled study, doxapram resulted in no improved laryngeal motion in all non-premedicated dogs, however the agreement between assessors was inconsistent [10]. Doxapram was effective in stimulating laryngeal function in non-premedicated dogs [11].…”

“…Tachycardia, seizure-like activity, vomiting and regurgitation were reported in 25% of the dogs in a study evaluating methohexital for its effects on laryngeal motion [10]. No difference between methohexital and propofol was detected regarding laryngeal function.…”

“…Manuscripts were scored based on their level of evidence (LoE) following the 2011 Oxford Centre for Evidence-based Medicine approach, which includes high quality levels (I-LoE) with evidence obtained from a systematic review and lower quality (II-LoE) with evidence obtained from properly designed, randomised controlled trials or non-randomised trials (III-LoE) [10]. The methodological quality of the studies was assessed according to the modified SIGN Methodology Checklist 2 of randomised controlled trials (RCTs), in which a bias rating of low (++) moderate (+), or high (-) is Figure 1.…”