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

Abstract

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 μg kg-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 (range) induction and recovery times (minutes) were not significantly (P=0.125) different among the three combinations: 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 in group MedKM required alfaxalone for intubation. In all groups, 3 or 4 cats required additional isoflurane for surgery, arterial oxygen tension (mean ± SD: 66 ± 2 mmHg) was low, and, surgery increased systolic arterial blood pressure (p<0.001), haemoglobin saturation (p<0.001), respiratory (p=0.003) and heart rates (p=0.002), and decreased end-tidal carbon dioxide (p=0.003). Pain scores did not differ significantly between groups. Von Frey responses decreased over time, changes over time varied by treatment (p<0.001), the MedK group returning to baseline values more rapidly than MedKM and MedKT. None of the cats required rescue analgesics.CONCLUSION AND CLINICAL RELEVANCE All three protocols provide adequate anaesthesia and analgesia for orchiectomy in cats. However, rescue intervention to maintain surgical anaesthesia such as isoflurane may be required in some cats. Oxygen supplementation is advised. Keywords feline, medetomidine, ketamine, morphine, tramadol, anaesthesia, orchiectomy