Guinea pigs are an anesthesic challenge.
They lack accessible blood vessels for IV administration and display great variability in response. It is not uncommon for two guinea pigs of the same sex, age, weight, and strain to respond quite differently to the same anesthesia. Guinea pigs can also exhibit a swimming motion with their legs during the surgical plane of anesthesia. Halothane is considered high risk for guinea pigs as they hold their breath and then gasp. Isoflurane has been used with great success in guinea pigs.