Abstract

Twenty-three, male captive-bred green iguanas (Iguana iguana) weighing 0.51–0.67 kg were anesthetized to determine the effectiveness and the cardiopulmonary effects of butorphanol­ sevoflurane and butorphanol-isoflurane. Baseline heart and respiratory rates were recorded on all animals prior to administration of intramuscular butorphanol (2 mg/kg). Thirty minutes after premedication, the heart rate and respiratory rate of each iguana was recorded and 12 animals were induced with isoflurane (5% in 100% oxygen), and 11 were induced with sevoflurane (8% in 100% oxygen), via face mask. Following the loss of the righting reflex, each iguana was intubated and intermittent positive pressure ventilation (IPPV) was provided at 10–12 breaths/min with a small animal ventilator. Mean maintenance isoflurane and sevoflurane concentrations were 2% and 4%, respectively. Heart rate, functional oxygen hemoglobin saturation (SpO₂) , and end-tidal CO₂ concentrations were measured every 5 min. The presence or absence of the righting, palpebral, and foot withdrawal reflexes were recorded to judge anesthetic depth. Arterial blood gases (pH, PO₂, PCO₂) were determined at 10 and 30 min following induction. In both groups, anesthesia was maintained for an average of 45 min. Inductions with butorphanol-sevoflurane (6.0±3.0 min; mean±SD) were smoother and significantly shorter than with butorphanol-isoflurane (9.0±4.0 min). During maintenance of anesthesia, cardiopulmonary parameters were well maintained in both groups. In both groups pulse oximeter readings (SpO₂) were <90% during the first 5 min of anesthesia, indicating potential hypoxemia. For the remainder of the anesthetic period SpO₂ values were >90%. End-tidal CO₂ concentrations were between 20–40 mm Hg during the first 5 min of anesthesia and decreased to a range between 15–20 mm Hg for the remainder of the anesthetic event. No significant differences in heart rate, oxygen hemoglobin saturation, and end-tidal CO₂ concentrations were noted between the two groups. Mean recovery time was significantly longer (35.0±27.0 min) in the butorphanol-isoflurane group than in the butorphanol-sevoflurane group (7.0±4.0 min). In conclusion, the cardiopulmonary effects of butorphanol-isoflurane and butorphanol-sevoflurane were similar, however quality and speed of induction and recovery was significantly shorter with sevoflurane when compared to isoflurane.