Sathya K. Chinnadurai1,2, DVM, MS; Stephen J. Hernandez-Divers3, BVetMed, CBiol, MIBiol, DZooMed, DACZM, MRCVS; Ryan S. DeVoe2, DVM, DACZM, DABVP (Avian); Nadia Gadsen3; Amie Koenig3, DVM, DACVIM, DACVECC
Green iguanas (n=4) were instrumented with DSI Physiotel PA-C20 implantable pressure transducers to measure direct blood pressure. Medetomidine (50 µg/kg), followed 30 min later by atipamezole (350 µg/kg), was administered intravenously (IV) to awake iguanas to assess the effect on systemic blood pressure. In a separate experiment, hypotension was induced with isoflurane at 2.5–3%; direct blood pressure was monitored during sequential infusions of dopamine (0–40 µg/kg/min), phenylephrine (0–5 µg/kg/min) and norepinephrine (0–0.8 µg/kg/min).
No sedative or hypertensive effects were observed with medetomidine. Preanesthetic mean arterial pressure (MAP) was measured for all animals (MAP range: 65–85 mm Hg). Isoflurane delivered at 2.5–3% (1.25–1.5 times the minimum alveolar concentration in green iguanas)1 resulted in sustained depression of blood pressure, with MAP<40 mm Hg in all animals. An increase in systemic blood pressure was only observed with norepinephrine, which increased systemic blood pressure to preanesthetic levels or greater.
Of the adrenergic agonists commonly used in domestic mammal anesthesia,2 only norepinephrine at 0.3–0.5 µg/kg/min resulted in a significant increase in blood pressure when used in hypotensive green iguanas. In addition to the clinical applications of pressor agents, understanding the effects of certain pressor agents also allows better understanding of the physiologic regulation in the iguana.3,4
1. Mosely, C.A., D. Dyson, and D. Smith. 2003. Minimum alveolar concentration of isoflurane in green iguanas and the effect of butorphanol on minimum alveolar concentration. J. Am.Vet. Med. Assoc. 222:1559–1564.
2. Mazzaferro, E., and A.E. Wagner. 2001. Hypotension during anesthesia in dogs and cats: recognition, causes, and treatment. Compend. Cont. Ed. Pract. Vet. 23: 728–738.
3. Hohnke, L.A. 1975. Regulation of arterial blood pressure in the common green iguana. Am. J. Physiol. 228:386–391.
4. Read, M.R. 2004. Evaluation of the use of anesthesia and analgesia in reptiles. J. Am. Vet. Med. Assoc. 224:547–552.