Effects of different doses of dexmedetomidine on anaesthetic induction with alfaxalone--a clinical trial.

OBJECTIVE: To document the effects of two doses of dexmedetomidine on the induction characteristics and dose requirements of alfaxalone. STUDY DESIGN: Randomized controlled clinical trial. ANIMALS: Sixty one client owned dogs, status ASA I-II. METHODS: Dogs were allocated randomly into three groups, receiving as pre-anaesthetic medication, no dexmedetomidine (D0), 1 µg kg(-1) dexmedetomidine (D1 ) intramuscularly (IM) or 3 µg kg(-1) dexmedetomidine IM (D3). All dogs also received 0.2 mg kg(-1) methadone IM. Level of sedation was assessed prior to induction of anaesthesia. Induction of general anaesthesia was performed with alfaxalone administered intravenously to effect at a rate of 1 mg kg(-1) minute(-1) ; the required dose to achieve tracheal intubation was recorded. Anaesthesia was maintained with isoflurane in oxygen. Cardiopulmonary parameters were recorded throughout the anaesthetic period. Quality of intubation, induction and recovery of anaesthesia were recorded. Quantitative data were compared with one-way anova or Kruskal-Wallis test. Repeated measures were log-transformed and analysed with repeated measures anova (p < 0.05). RESULTS: Treatment groups were similar for categorical data, with exception of sedation level (p < 0.001). The doses (mean ± SD) of alfaxalone required for intubation were D0 1.68 ± 0.24, D1 1.60 ± 0.36 and D3 1.41 ± 0.43, the difference between D0 and D3 being statistically significant (p = 0.036). Heart and respiratory rates during the anaesthetic period were significantly different over time and between groups (p < 0.001); systolic arterial blood pressure was significantly different over time (p < 0.001) but not between groups (p = 0.833). Induction quality and recovery scores were similar between groups (p = 1.000 and p = 0.414, respectively). CONCLUSIONS AND CLINICAL RELEVANCE: The administration of alfaxalone resulted in a good quality anaesthetic induction which was not affected by the dose of dexmedetomidine. Dexmedetomidine at 3 µg kg(-1) IM combined with methadone provides good sedation and enables a reduction of alfaxalone requirements.

Clinical efficacy and cardiorespiratory effects of alfaxalone, or diazepam/fentanyl for induction of anaesthesia in dogs that are a poor anaesthetic risk.

OBJECTIVE: To evaluate the clinical efficacy and cardiorespiratory effects of alfaxalone as an anaesthetic induction agent in dogs with moderate to severe systemic disease. STUDY DESIGN: Randomized prospective clinical study. ANIMALS: Forty dogs of physical status ASA III-V referred for various surgical procedures. METHODS: Dogs were pre-medicated with intramuscular methadone (0.2 mg kg(-1) ) and allocated randomly to one of two treatment groups for induction of anaesthesia: alfaxalone (ALF) 1-2 mg kg(-1) administered intravenously (IV) over 60 seconds or fentanyl 5 µg kg(-1) with diazepam 0.2 mg kg(-1) ± propofol 1-2 mg kg(-1) (FDP) IV to allow endotracheal intubation. Anaesthesia was maintained with isoflurane in oxygen and fentanyl infusion following both treatments. All dogs were mechanically ventilated to maintain normocapnia. Systolic blood pressure (SAP) was measured by Doppler ultrasound before and immediately after anaesthetic induction, but before isoflurane administration. Parameters recorded every 5 minutes throughout subsequent anaesthesia were heart and respiratory rates, end-tidal partial pressure of carbon dioxide and isoflurane, oxygen saturation of haemoglobin and invasive systolic, diastolic and mean arterial blood pressure. Quality of anaesthetic induction and recovery were recorded. Continuous variables were assessed for normality and analyzed with the Mann Whitney U test. Repeated measures were log transformed and analyzed with repeated measures anova (p<0.05). RESULTS: Treatment groups were similar for continuous and categorical data. Anaesthetic induction quality was good following both treatments. Pre-induction and post-induction systolic blood pressure did not differ between treatments and there was no significant change after induction. The parameters measured throughout the subsequent anaesthetic procedures did not differ between treatments. Quality of recovery was very, quite or moderately smooth. CONCLUSIONS AND CLINICAL RELEVANCE: Induction of anaesthesia with alfaxalone resulted in similar cardiorespiratory effects when compared to the fentanyl-diazepam-propofol combination and is a clinically acceptable induction agent in sick dogs.