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A clinical study of the effects of rocuronium in isoflurane-anaesthetized cats

Auer, Ulrike, Mosing, Martina
Veterinary anaesthesia and analgesia 2006 v.33 no.4 pp. 224-228
cats, castration, ovariectomy, anesthesia, muscle relaxants, rapid methods, veterinary drugs, general anesthetics, isoflurane, drug evaluation, combination drug therapy, drug interactions, dosage, intravenous injection, physiological response, neurophysiology, muscle physiology, respiratory physiology, circulatory system physiology
To evaluate the neuromuscular blocking and chronotropic effects of rocuronium bromide in cats anaesthetized for surgery. Prospective clinical trial. Twenty-two healthy cats of mixed breed presented for ovariectomy (n = 13) or castration (n = 9). Mean body mass (±SD) was 3.6 ± 0.65 kg and mean age was 10.25 ± 2.63 months. Anaesthesia was induced with intravenous (IV) midazolam (0.3 mg kg⁻¹), ketamine (3 mg kg⁻¹) and butorphanol (0.4 mg kg⁻¹). Tracheal intubation was performed and anaesthesia was maintained with isoflurane delivered in 100% oxygen. Neuromuscular function was monitored using acceleromyography applied at the ulnar nerve. This was stimulated by using the train-of-four (TOF) stimulus pattern (2 Hz) delivered every 15 seconds. The first train was made to establish baseline values for the first twitch (T1) and the TOF-ratio (T4:T1). Rocuronium (0.6 mg kg⁻¹ IV) was given and the following periods were recorded beginning at the end of injection: (1) lag time (LT) - to the first signs of T1 depression; (2) onset time (OT) - to the total ablation of T1; (3) duration of action (T1₂₅) - to 25% recovery of the baseline value for T1; (4) T1₅₀- to 50% baseline T1 restoration; (5) to TOF-ratios of 0.7 and 0.9. The time taken for T1 to recover from 75% to 25% depression (T1₂₅₋₇₅) was also recorded. Heart rate (HR) was taken every minute for 15 minutes, beginning 5 minutes before rocuronium was injected. Rocuronium (0.6 mg kg⁻¹) had a mean LT of 15.0 ± 0 seconds, OT of 46 ± 11 seconds and T1₂₅ of 13.2 ± 2.7 minutes. The mean time for TOF 0.7 and 0.9 was 17.3 ± 5.4 and 20.7 ± 5.4 minutes respectively. The mean T1₂₅₋₇₅ was 4.8 ± 2.4 minutes. No significant changes in HR were observed at any of the time intervals recorded. Rocuronium is an effective nondepolarizing muscle relaxant in the cat under the clinical conditions of this study. It has a rapid onset, a short duration of action and did not cause significant changes in HR.