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
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