Effects of ketamine and alfaxalone on application of a feline pain assessment scale

Abstract

Objectives The objective of this study was to compare the effects of ketamine and alfaxalone on the application of a validated feline-specific multidimensional composite pain scale (UNESP-Botucatu MCPS). Methods In a prospective, randomized, blinded, crossover trial, 11 adult cats (weight 4.4 ± 0.6 kg) were given dexmedetomidine (15 μg/kg) and hydromorphone (0.05 mg/kg) with either alfaxalone (2 mg/kg) or ketamine (5 mg/kg) as a single intramuscular injection for the induction of general anesthesia. After orotracheal intubation, general anesthesia (without surgery) was maintained for 32 mins with isoflurane, followed by atipamezole. The following parameters were recorded at baseline, 1–8 h and 24 h post-extubation: pain (pain expression and psychomotor subscales) and sedation scale scores. Alfaxalone treatment injection sites were examined for inflammation at baseline, postinjection, and 8 h and 24 h post-extubation. Results Psychomotor scores were higher with ketamine at hours 1 (3.5 [0–5.0], P <0.0001), 2 (2.5 [0–4.0], P <0.0001) and 3 (0.5 [0–4.0], P = 0.009) post-extubation compared with alfaxalone (hour 1, 0 [0–2]; hour 2, 0 [0–0]; hour 3, 0 [0–0]). Six cats in the ketamine group crossed the analgesic intervention threshold. In contrast, pain expression scores did not differ significantly between treatments at any time ( P >0.05); one cat from each group crossed the analgesic intervention threshold. Sedation was greater with ketamine (1 [0–3], P = 0.02) than alfaxalone (0 [0–1]) 1 h post-extubation. No cats had visible inflammation at the injection sites at any time. Conclusions and relevance Ketamine has a confounding effect on the psychomotor subscale of the pain scale studied, which may lead to erroneous administration of rescue analgesia. In contrast, alfaxalone was not associated with significant increases in either pain subscale. These effects of ketamine should be considered when evaluating acute postoperative pain in cats.