Cardiovascular tolerance of intravenous bupivacaine in broiler chickens (Gallus gallus domesticus) anesthetized with isoflurane

Objective To determine the median effective dose (ED50) of intravenous (IV) bupivacaine associated with a 50% probability of causing clinically relevant cardiovascular effects [defined as 30% change in heart rate (HR) or mean arterial pressure (MAP)] in chickens anesthetized with isoflurane. Study design Randomized up-and-down study. Animals A total of 14 Ross-708 broiler chickens (Gallus gallus domesticus) weighing 1.70-2.75 kg. Methods Anesthesia was induced and maintained with isoflurane. Monitoring included the electrocardiogram and invasive arterial pressures. Chickens were administered bupivacaine IV over 2 minutes using a dose based on the response of the previous animal. Dose was decreased when HR and/or MAP in the previous animal increased or decreased >= 30% after bupivacaine administration, or increased when HR or MAP changed <30%. The ED50 was defined as the dose resulting in >= 30% variation in HR or MAP in 50% of the population studied. Results The IV ED50 of bupivacaine was 1.94 mg kg(-1) using Dixon's up-and-down method and 1.96 mg kg(-1) by logistic regression. Conclusions and clinical relevance These results suggest that 1.33 and 1.96 mg kg(-1) of IV bupivacaine are associated with a respective 1 or 50% probability of a clinically significant change in MAP in isoflurane-anesthetized chickens. Identification of the cardiovascular changes associated with different doses of bupivacaine can be used as the basis for studies of therapeutic applications in the domestic chicken. Further studies are required to determine interspecies variation.