Comparison of isoflurane and sevoflurane anesthesia after premedication with butorphanol in the green iguana (Iguana iguana).

The anesthetic and cardiopulmonary effects of butorphanol followed by sevoflurane or isoflurane were compared in 23 male green iguanas (Iguana iguana). Heart and respiratory rates were recorded before administration of butorphanol (2 mg/kg i.m.) and at 30 min after premedication. Anesthesia was induced in 12 iguanas (group 1) with isoflurane (5%) and in 11 iguanas (group 2) with sevoflurane (7%). Heart rate, relative arterial oxygen hemoglobin saturation (SpO2), and end-tidal CO2 concentrations (EtCO2) were measured every minute for the first 5 min and every 5 min thereafter. Arterial blood gas parameters were determined at 10 and 40 min after induction. Thirty minutes after butorphanol administration, no significant changes in heart and respiratory rate were seen as compared with baseline values. Quality and time to induction were superior with butorphanol-sevoflurane (6 +/- 3 min) than with butorphanol-isoflurane (9 +/- 4 min). Vaporizer settings during maintenance ranged between 1-3% and 2-4%, respectively. No significant differences in heart rate were noted between groups. In the sevoflurane group, SpO2 values were > 90% throughout. Although SpO2, values were < 90% at 20, 25, and 30 min in the isoflurane group, no significant differences in SpO2 values were seen over time and between groups. A significant decrease in EtCO2 with time was present in both groups, with no significant differences between the groups. At 10 and 40 min, arterial blood oxygen saturation values were > 90% in both groups and no significant differences were noted with time and between groups. Recovery time was significantly longer in the butorphanol-isoflurane group (35 +/- 27 min) than in the butorphanol-sevoflurane group (7 +/- 4 min). The cardiopulmonary effects of butorphanol-isoflurane and butorphanol-sevoflurane assessed in this study are similar, and both inhalants appear to be safe and effective for induction and maintenance in the green iguana.