A comparison of the haemodynamic effects of epidurally administered medetomidine and xylazine in dogs
Alpha2 agonists have a significant role in epidural anaesthetic techniques. However, there are few reports regarding epidural administration of these drugs especially in small animals (Greene et al. 1995; Keegan et al. 1995; Vesal et al. 1996). This study compared the haemodynamic effects of xylazine and medetomidine after epidural injection in dogs. Six dogs (four females and two males) weighing 27.5 ± 3.39 kg, aged 5.6 ± 1.42 years were studied on two separate occasions one month apart. Dogs were sedated with 0.5 mg kg−1 diazepam IM and 0.1 mg kg−1 acepromazine IM. After 20 minutes, a lumbosacral epidural injection of 0.25 mg kg−1 xylazine was administered (group X). One month later, following the same sedation, 15 µg kg−1 medetomidine was administered epidurally (group M). Haemodynamic variables (ECG and indirect blood pressure (Doppler)), respiratory rate and rectal temperature were recorded before (baseline) and then every 5 minutes after the epidural injection, up to 60 minutes. Differences between groups were compared by a paired t-test. Within group changes were compared to basal values by anova. A p-value of < 0.05 was considered statistically significant. Both groups showed significant reductions in heart rate (106.3 ± 7.7 beats minute−1 baseline versus 67.7 ± 7.6 (group M); 91 ± 3.8 baseline versus 52.3 ± 9 (group X)) and mean arterial blood pressure (113.1 ± 12.3 mm Hg baseline versus 87 ± 11 (group M); 118 ± 7 baseline versus 91 ± 14 (group X)). There were no differences between groups in these variables. After epidural injection, first degree atrioventricular block was recorded significantly more often in group X (50% against 33%) but second degree block was significantly more frequent in group M (66% against 33%). Also 50% of dogs in group X and 66% in group M showed sinus arrest. Respiratory rate decreased significantly in both groups following the epidural injection (20.66 ± 0.66 minute−1 baseline versus 16.33 ± 4.77 (group M); 37.66 ± 0.56 baseline versus 16.33 ± 1.81 group X), but no differences between groups were observed. Rectal temperature decreased significantly in group X (38.16 ± 0.21) with respect to the basal measurement (39.30 ± 0.14 °C). In group M, there was no significant reduction in temperature, however, no statistical difference in rectal temperature was found between groups. This study shows that 0.25 mg kg−1 xylazine and 15 µg kg−1 medetomidine produce similar, significant cardiovascular and respiratory changes following lumbosacral epidural administration in dogs.
Mohammad R. Sedighi. "A comparison of the haemodynamic effects of epidurally administered medetomidine and xylazine in dogs" Veterinary Anaesthesia and Analgesia 30.2 (2003): 87-98.
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