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

Objective-To characterize variables used to monitor rabbits during inhalati on anesthesia. Animals-8 male New Zealand White rabbits. Procedure-Rabbits were similarly anesthetized with halothane (HAL) or isofl urane (ISO) in a crossover study; half received HAL followed by ISO, and th e 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 (o rder randomized). Results-Mean +/- SEM MAC was 1.42 +/- 0.05 and 2.07 +/- 0.09% for HAL and I SO, respectively. Directly measured auricular mean arterial blood pressure was 52.8 +/- 5.6 and 54.8 +/- 6.2 mm Hg at 0.8 MAC for HAL and ISO, respect ively, 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 Paco(2) was similar at 0.8 MAC for HAL and ISO and progressively increased with increasing doses o f both agents; Paco(2) at 2.0 MAC for ISO was significantly greater than th at 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, Paco(2), and eyelid aperture consisten tly and predictably changed in rabbits in response to changes in anesthetic doses. The magnitude of respiratory depression was greater for ISO than fo r HAL.