Comparison of Isoflurane and Sevoflurane Anesthesia Following Premedication with Butorphanol in the Green Iguana (Iguana iguana)
Sonia M. Hernandez-Divers1, DVM, DACZM; Juergen Schumacher1, Dr.med.vet., DACZM; Matt R. Read3, DVM, MVSc, DACVA; Scott Stahl4, DVM, ABVP (Avian); Stephen Hernandez-Divers1, BVetMed, DZooMed, MRCVS
1Exotic Animal, Wildlife and Zoological Medicine, Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia, Athens, GA, USA; 2Department of Small Animal Clinical Sciences, College of Veterinary Medicine, The University of Tennessee, Knoxville, TN, USA; 3Anesthesiology, Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia, Athens, GA, USA; 4Eastern Exotics Center, Fairfax, VA, USA
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.