Anaesthetic, analgesic and cardiorespiratory effects of three intramuscular anaesthetic protocols in cats

Abstract

Objectives To compare the anaesthetic, analgesic and cardiorespiratory effects of intramuscular 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 healthy cats. Materials and methods Cats received a combination of medetomidine (60 μg kg-1) and ketamine (10 mg kg-1) alone (MedK) or combined with morphine (0.2 mg kg-1) (MedKM) or tramadol (2 mg kg-1) (MedKT) intramuscularly. Time of different events and physiological parameters were recorded by a blinded researcher. Pre-surgery arterial and venous blood gases were measured. Heart rate (HR), respiration rate (fR), systolic arterial blood pressure (SABP), peripheral haemoglobin saturation (SpO2) and end-tidal carbon dioxide tension (PETCO2) were recorded every 5 minutes of general anaesthesia and at each surgical stage. Post-operative analgesia was evaluated with a visual analogue scale, a multidimensional composite scoring system and a rigid tip von Frey mechanical threshold device every hour from 3 to 8 hours post-injection of the initial combination of drugs. Data were analysed 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 (5.8, 14.9) for induction and 128 (95, 143), 166 (123, 210) and 143 (123, 180) for recovery, with MedK, MedKT and MedKM, respectively. All three combinations caused similar low partial pressure of arterial oxygen (PaO2) values (mean ± SD: 66.2 ± 1.7 mmHg). Surgery had a significant effect on SABP (p < 0.001), SpO2 (p < 0.001), fR (p = 0.003) and HR (p = 0.002), which increased; and PETCO2 (p = 0.003), which decreased, with all combinations. Non-significant differences were found in pain scores and von Frey results among treatments; however, the von Frey changes over time did vary by treatment (p < 0.001) with 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 should be supplemented.