Comparison of clinical signs and hemodynamic variables used to monitor rabbits during halothane- and isoflurane-induced anesthesia

Abstract

Objective - To characterize variable used to monitor rabbits during inhalation anesthesia. Animals - 8 male New Zealand White rabbits. Procedure - Rabbits were similarly anesthetized with halothane (HAL) or isoflurane (ISO) in a crossover study; half received HAL followed by ISO, and the protocol was reversed for the remaining rabbits. After induction, minimum alveolar concentration (MAC) was determined for each agent, using the tail- clamp method, and variables were recorded at 0.8, 1.0, 1.5, and 2.0 MAC (order randomized). Results - Mean ± SEM MAC was 1.43 ± 0.05 and 2.07 ± 0.09% for the HAL and ISO, respectively. Directly measured auricular mean arterial blood pressure was 52.8 ± 5.6 ± and 54.8 ± 6.1 mm Hg at 0.8 MAC for HAL and ISO, respectively, and decreased from these values in a parallel dose-dependent manner. Respiratory frequency remained constant (range, 69 to 78 breaths/min) over the range of HAL doses but incrementally decreased from a mean of 53 (at 0.8 MAC) to 32 breaths/min (at 2.0 MAC) for ISO. The PaCO2 was similar at 0.8 MAC for HAL and ISO and progressively increased with increasing doses of both agents; PaCO2 at 2.0 MAC for ISO was significantly greater than that at 2.0 MAC for HAL (79.8 ± 13.7 vs 54.9 ± 4.0 mm Hg, respectively). Eyelid aperture consistently increased in a dose-dependent manner for both anesthetics. Conclusions - Arterial blood pressure, PaCO2, and eyelid aperture consistently and predicatably changed in rabbits in response to changes in anesthetic doses. The magnitude of respiratory depression was greater for ISO than for HAL.