Anaesthetic, analgesic and cardiorespiratory effects of intramuscular medetomidine-ketamine combination alone or with morphine or tramadol for orchiectomy in cats.

OBJECTIVES To compare the anaesthetic, analgesic and cardiorespiratory effects of intramuscular (IM) medetomidine and ketamine administered alone or combined with morphine or tramadol, for orchiectomy in cats. STUDY DESIGN Randomised, blinded, prospective clinical study. ANIMALS Thirty client-owned cats. MATERIALS AND METHODS Cats (n = 10 in each group) received a combination of medetomidine (60 μgkg(-1) ) and ketamine (10 mg kg(-1) ) alone (MedK); combined with morphine (0.2 mg kg(-1) ) (MedKM), or combined with tramadol (2 mg kg(-1) ) (MedKT) IM. Time of induction, surgical and recovery events were recorded, and physiological parameters measured and recorded. Analgesia was evaluated with a visual analogue scale, a composite scoring system and the von Frey mechanical threshold device, every hour from three to eight hours post-drug administration injection. Data were analyzed with a linear mixed model, Kruskal-Wallis or Chi-square tests (p < 0.05). RESULTS Median (IQR) induction and recovery times (minutes) were not significantly (p = 0.125) different between groups: 5.6 (2.7-8.0), 7.4 (5.1-9.6) and 8.0 (5.8-14.9) for induction and 128.5 (95.1-142.8), 166.4 (123.1-210.0) and 142.9 (123.4-180.2) for recovery, with MedK, MedKT and MedKM, respectively. Two cats (MedKM) required alfaxalone for endotracheal intubation. In all groups, three or four cats required additional isoflurane for surgery. Arterial oxygen tension overall (mean ± SD: 66 ± 2 mmHg) was low. Surgery resulted in increased systolic arterial blood pressure (p < 0.001), haemoglobin saturation (p < 0.001), respiratory (p = 0.003) and heart rates (p = 0.002). Pain scores did not differ significantly between groups. Von Frey responses decreased over time; changes over time varied by treatment (p < 0.001), MedK returning to baseline values more rapidly than MedKM and MedKT. No cat required rescue analgesics. CONCLUSION AND CLINICAL RELEVANCE All three protocols can provide adequate anaesthesia and analgesia for orchiectomy in cats. However, rescue intervention to maintain surgical anaesthesia may be required in some cats. Oxygen supplementation is advised.