Clinical effects of isoflurane and sevoflurane in lambs

Objective To compare isoflurane and sevoflurane in lambs undergoing prolonged anaesthesia for spinal surgery. Study design Prospective randomised clinical study. Animals Eighteen Scottish blackface lambs 3–6 weeks of age and weighing 10–17 kg. Methods After intramuscular medetomidine, anaesthesia was induced and maintained with either isoflurane (group I) or sevoflurane (group S) delivered in oxygen. Meloxicam, morphine, a constant rate infusion of ketamine and atracurium were given intravenously (IV) during surgery. Lungs were ventilated to maintain normocapnia. with peak inspiratory pressures of 20–25 cmH₂O. Ephedrine or dextran 40% was administered when mean arterial pressure (MAP) was <55 mmHg. Intrathecal morphine, and IV meloxicam and edrophonium were injected before recovery. Time to loss of palpebral reflex (TLPR) upon induction, cardiorespiratory variables, time at first swallowing and other movement, tracheal extubation, vocalisation, spontaneous head lifting (>1 minute), reunion with the ewe, and the number of MAP treatments were recorded. Statistical analysis utilised anova , Mann–Whitney, t‐test or Pearson’s correlation test as relevant. p < 0.05 was considered significant. Results End‐tidal carbon dioxide (mean ± SD) was significantly lower in group S (5.5 ± 0.6 kPa) than in group I (5.8 ± 0.5 kPa) while MAP (70 ± 11 mmHg) and diastolic arterial blood pressure (60 ± 11 mmHg) were higher in group S than in group I (65 ± 12 and 54 ± 11 mmHg, respectively). No differences were found with TLPR and MAP treatments. Time (median, range) from end of anaesthesia to ewe‐lamb reunion was briefer (p = 0.018) in group S (48, 20–63 minutes). Conclusion Isoflurane and sevoflurane are both suitable for maintaining general anaesthesia in lambs although sevoflurane, as used in this study, allows a more rapid reunion with the ewe. Clinical relevance The principal advantage of sevoflurane over isoflurane during prolonged anaesthesia in lambs is a more rapid recovery.