Comparison between a Tail Clamp and Electrical Stimulation for Sevoflurane Minimum Anesthetic Concentration Determination in Green Iguanas (Iguana iguana)

This study aimed to compare the minimum anesthetic concentration (MAC) of sevoflurane in green iguanas using electrical stimulation and tail clamping as noxious stimuli. Seven adult green iguanas (Iguana iguana) weighing 580 to 1,300 g were enrolled. Each iguana was anesthetized twice after a 1-week washout period, with MAC being determined using a tail clamp (MAC<sc>t</sc>) or electrical stimulation (MAC<sc>e</sc>) techniques. After sevoflurane mask induction and endotracheal intubation, the fraction of expired sevoflurane (F<sc>e</sc>'Sevo) was maintained at 3.1% for 15 min before noxious stimulation. In a bracketing design, the subsequent F<sc>e</sc>'Sevo values were increased or decreased by 10% after positive or negative responses, respectively. Each targeted F<sc>e</sc>'Sevo was kept constant for 15 min before stimulation. In MAC<sc>t</sc>, the noxious stimulus involved closing a Kelly hemostatic curved forceps to the first ratchet at the base of the tail. At the same site, in MAC<sc>e</sc>, 2 30 × 0.8–mm hypodermic needles inserted 1 cm apart were connected to an electrical stimulator set to deliver 30 mA at 50 Hz at a 6.5-ms interval. The hemostat and the needles were repositioned 2 cm distally and on alternate tail sides at each stimulation round. Individual MAC was obtained when 2 consecutive crossover events occurred (a positive response preceding a negative response or vice versa), with the MAC of each group represented by the average of the individual MAC values. Median (interquartile range) values for the sevoflurane MAC did not differ significantly between groups (2.2 [2.2 to 2.8%] in MAC<sc>e</sc> and 2.2 [1.8 to 3.5%] in MAC<sc>t</sc>; P = 0.812). Time to anesthesia induction, time to MAC measurement, heart rate (HR), end-tidal carbon dioxide (ET'CO₂), and cloacal temperature were not different between groups. Both the tail-clamping and the electrical stimulation techniques yielded resembling sevoflurane MAC values in green iguanas, which makes the tail clamp a reliable alternative to electrical stimulation-based MAC research in this species.