Alfaxalone is rapidly becoming the injectable anaesthetic of choice for reptiles, however little is known about its physiological effects. These studies explored the cardiovascular and respiratory effects of alfaxalone anaesthesia, as well as the associated effects of handling prior to and during anaesthesia. The latter have largely remained ignored in clinical research.
In the first study, pythons were administered alfaxalone via two routes, 20 mg/kg intramuscularly (IM) and 10 mg/kg intravascularly (IV - via an indwelling arterial catheter) and compared to an equivalent volume of saline. Animals were handled for IM injection, but remained undisturbed for IV administration of alfaxalone and saline. Heart rate and blood pressure increased dramatically immediately following IM injection, returning to baseline values after 25 minutes. Few differences in heart rate and blood pressure were observed between IM saline and IM alfaxalone administration. IV saline produced no response in heart rate or blood pressure, but blood pressure decreased in response to IV alfaxalone. Despite sufficient loss of reflexes, heart rate and blood pressure increased in response to endotracheal intubation.
In the second study, rattlesnakes were administered 15 mg/kg alfaxalone IV without prior handling. Heart rate approximately doubled 5 minutes post-injection and remained elevated throughout. Blood pressure also increased, but not as dramatically, and began to decrease towards baseline after 10 minutes.
These findings demonstrate that handling for injection and intubation can mask the physiological effects of anaesthetic drugs, even in the absence of reflexes and response to stimulation, and that physiological species differences are pertinent to consider.