Kinetics and potency of halothane, isoflurane, and desflurane in the Northern Leopard frog Rana pipiens

Equilibration between delivered and effect site anesthetic partial pressure is slow in frogs. The use of less soluble agents or overpressure delivery may speed equilibration. Ten Northern leopard frogs were exposed to 3-4 constant concentrations of halothane, isoflurane or desflurane and their motor response to noxious electrical stimulation of the forelimb evaluated every 30 minutes until a stable proportion of frogs were immobile. Each frog received each anesthetic and concentration in random order and allowed at least 14 hours to recover between anesthetic exposures. An overpressure technique based upon the kinetics in the first study was then tested with 4 concentrations of desflurane. For halothane, isoflurane and desflurane respectively; the proportion of frogs immobile in response to stimulus became stable after 510, 480 and 180 minutes, and ED50 values were 1.36, 1.67 and 6.78 % atm. Desflurane ED50 delivered by overpressure was not significantly different at 6.85 % atm. Halothane, isoflurane and desflurane are effective general anesthetics in frogs with potencies similar to those reported in mammals. The time required for anesthetic equilibration is fastest with desflurane and can be hastened further by initial delivery of higher partial pressures.