Effect of dexmedetomidine constant rate infusion on the bispectral index during alfaxalone anaesthesia in dogs

ObjectiveTo assess the effect of two rates of infusion of dexmedetomidine on the bispectral index (BIS) in dogs anaesthetized with alfaxalone constant rate infusion (CRI). Study designProspective, randomized, blinded' experimental study. AnimalsSix healthy Beagles (three females and three males). MethodsDogs received as premedication saline (group D0), 1g kg(-1) (group D1) or 2g kg(-1) (group D2) dexmedetomidine, intravenously (IV). Anaesthesia was induced with alfaxalone (6mgkg(-1) to effect IV) and maintained with alfaxalone at 0.07mg kg(-1)minute(-1) and a CRI of saline (D0) or dexmedetomidine 0.5g kg(-1)hour(-1) (D1) or 1g kg(-1)hour(-1) (D2) for 90minutes. BIS, electromyography (EMG), signal quality index (SQI) and suppression ratio (SR) were measured at 10minute intervals and the median values were calculated. Nociceptive stimuli were applied every 30minutes and BIS and cardiorespiratory values were compared before and after stimuli. Cardiorespiratory parameters were recorded throughout the study. ResultsBIS and EMG values differed significantly among groups, being lower in D2 (718) than in D0 (85 +/- 10) and D1 (84 +/- 9). SQI was always over 90% and SR was zero throughout all the treatments. There were no significant differences between pre- and post-stimulus values of BIS, EMG and SQI for any treatment, although in D0 and D1, heart rate, respiratory rate and arterial pressuresincreased significantly after the nociceptive stimulus. Conclusions and clinical relevanceAdministration of dexmedetomidine (2gkg(-1)+CRI 1g kg(-1)hour(-1)) decreases the BIS values and avoids the autonomic responses of a nociceptive stimulus during alfaxalone anaesthesia at 0.07mg kg(-1)minute(-1) in dogs. However, further studies are needed to verify whether this combination produces an adequate degree of hypnosis under surgical situations.