A comparison of epidural anaesthesia with lignocaine, bupivacaine and a lignocaine-bupivacaine mixture in cats

A mixture of 2% lignocaine (LIG) and 0.5% bupivacaine (BUP), at respective dose rates of 2 mg/kg and 0.5 mg/kg (LIG-BUP), was compared to LIG (4 mg/kg) and BUP (1 mg/kg) for lumbosacral epidural anaesthesia in 5 sedated cats. Each cat received all 3 treatment regimens at 1-week intervals. The cats were premedicated with an intramuscular injection of atropine sulphate (0.04 mg/kg) and ketamine hydrochloride (10 mg/kg). Onset and duration of analgesia, and time to walking were determined. Associated changes in heart rate (HR), respiratory frequency (fR) and rectal temperature (RT) were recorded. Onset of analgesia with epidurally administered LIG-BUP (4.5 +/- 0.7 min), LIG (3.9 +/- 1.0 min) and BUP (5.0 +/- 1.0 min) was similar. Duration of analgesia with LIG-BUP (49.4 +/- 4.5 min) was significantly (P<0.05) longer than with LIG (40.2 +/- 1.0 min) but shorter than with BUP (79.4 +/- 6.3 min). There were no significant differences in times to standing with LIG-BUP (26.3 +/- 6.4 min), LIG (20.4 +/- 4.7 min) and BUP (22.6 +/- 10.3 min). Minimal changes were observed in HR, fR and RT. In conclusion, duration of analgesia produced by LIG-BUP was shorter compared with BUP but longer compared with LIG. Neither LIG nor LIG-BUP has any advantage over epidural BUP in terms of onset of analgesia, time to standing and physiological responses. Therefore, lumbosacral epidural administration of BUP appears to be the best choice for a long surgical procedure lasting more than 1 hour when compared with either LIG or LIG-BUP.