Twenty adult dogs weighing between 1·4 and 53·5 kg and aged between six months and nine years were anaesthetised and the brachial plexus was localised with the aid of a nerve stimulator. In 10 of the dogs a brachial plexus block was induced with a mixture of lidocaine and bupivacaine and the other 10 each received 0·25 ml/kg saline as a control. The end-tidal isoflurane concentration was maintained between 1·3 and 1·4 per cent during surgery for carpal arthrodesis or a fracture of the radius or ulna. Acute heart rate or blood pressure increases of 20 per cent or more were treated with 1 µg/kg fentanyl intravenously. Postoperatively, signs of pain were scored by a single blinded observer at hourly intervals until eight hours after the block had been induced, on a scale from 0 to 18. Dogs with pain scores above 5 received 0·1 to 0·2 mg/kg methadone intravenously, repeated as necessary. During surgery the control dogs received significantly more fentanyl (median 0·05 µg/kg/minute, range 0·02 to 0·20 µg/kg/minute) than the group given local anaesthetic (median 0 µg/kg/minute, range 0 to 0·02 µg/kg/minute). Postoperatively, the control group required significantly more methadone (median 0·2 mg/kg, range 0·1 to 1 mg/kg) than the treated group (median 0 mg/kg, range 0 to 0·13 mg/kg).
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