The effect of intramuscular dexmedetomidine and medetomidine on cardiorespiratory variables during isoflurane anaesthesia in sheep

The hypoxaemic effects of intravenous alpha2-agonists in sheep are well documented. Based on preliminary trials we hypothesized that intramuscular (IM) administration of medetomidine and dexmedetomidine would lead to less severe side effects than IV administration. Nineteen healthy nonpregnant ewes of various breeds undergoing different orthopaedic procedures were studied. Pre-anaesthetic medication was 15 µg kg−1 dexmedetomidine IM [group A, n = 9] or 30 µg kg−1 medetomidine IM [group B, n = 10] 30 minutes prior to induction of anaesthesia with ketamine (2 mg kg−1) IV. Anaesthesia was maintained with isoflurane in 100% oxygen. End expired anaesthetic concentration (F eiso) and respiratory frequency (fR) were determined with a methane insensitive infrared gas analyser (Anaesthetic Gas Monitor Type 1304, Bruel & Kjaer, Naerum, Denmark). Direct mean arterial blood pressure (MAP) and a lead II ECG were monitored continuously. Arterial blood samples were taken 10 minutes after induction of anaesthesia and then at 30 minute intervals. Data were averaged over time and tested for differences between groups by independent t-tests or anova for repeated measures followed by Bonferroni corrected t-tests. The results are presented as mean ± SD. There were no significant (p