Effect of Butorphanol on Anaesthesia Induction by Isoflurane in the Green Iguana (Iguana iguana)

A total of 10 clinically healthy green iguanas (5 males and 5 females, body weight ranging from 1 350 to 2 770 g) were given butorphanol by intramuscular injection following 24 h fasting. Inhalation anaesthesia was administered by mask (5% isoflurane with oxygen, 1.0 l/min), once reactions to external stimuli had decreased (15.45 ± 1.54 min later). Tracheal intubation was performed as soon as the iguanas exhibited complete tolerance to mechanical stimuli. A second study was performed 4 weeks later using the same green iguanas with no pre-medication. Marked individual reactions to masking were observed during both experiments. Some iguanas exhibited breath holding which prolonged anaesthetic induction. Physical stimulation was used in these cases in order to stimulate spontaneous breathing. The mean anaesthetic induction time was similar in both groups of green iguanas (4.34 ± 0.47 and 4.93 ± 0.88 min). There was also a comparable interval from masking to safe tracheal intubation in both experimental groups (15.21 ± 4.26 and 14.31 ± 1.39 min). In view of the results, pre-medication with butorphanol cannot be considered an effective method of anaesthetic induction in green iguanas