Earlier the best inhalation anesthetic available was halothane. This gas was being used on humans, and was quickly adopted for use in small animals and birds. One of the biggest advances in avian surgery was the introduction of isoflurane. This gas, while very expensive when compared with halothane, was much safer for birds. With both injectable anesthetics (most often ketamine, combined with other drugs, such as Valium or xylazine) and halothane, there was always the very real risk of anesthetic death, usually from an idiosyncratic reaction to a drug, heart problems, respiratory depression ...