Evaluation of medetomidine-ketamine anesthesia with atipamezole reversal in American alligators (Alligator mississippiensis)

摘要

Sixteen captive and wild-caught American alligators (Alligator mississippiensis), seven juveniles (51 m total length [TL]; 6.75 +/- 1.02 kg), and nine adults (greater than or equal to2 m TL; 36.65 +/- 38.85 kg), were successfully anesthetized multiple times (n = 33) with an intramuscular (i.m.) medetomidine-ketamine (MK) combination administered in either the triceps or masseter muscle. The juvenile animals required significantly larger doses of medetomidine ((x) over bar = 220.1 +/- 76.9 mug/kg i.m.) and atiparnezole ((x) over bar = 1,188.5 +/- 328.1 mug/kg i.m.) compared with the adults (medetomidine, (x) over bar = 131.1 +/- 19.5 mug/kg i.m.; atipamezole, (x) over bar = 694.0 +/- 101.0 mug/kg i.m.). Juvenile alligators also required higher (statistically insignificant) doses of ketamine ((x) over bar = 10.0 +/- 4.9 mg/kg i.m.) compared with the adult animals ((x) over bar = 7.5 +/- 4.2 mg/kg i.m.). The differences in anesthesia induction times (juveniles, (x) over bar = 19.6 +/- 8.5 min; adults, (x) over bar = 26.6 +/- 17.4 min) and recovery times (juveniles, (x) over bar = 35.4 +/- 22.1 min; adults, (x) over bar = 37.9 +/- 20.2 min) were also not statistically significant. Anesthesia depth was judged by the loss of the righting, biting, corneal and blink, and front or rear toe-pinch withdrawal reflexes. Recovery in the animals was measured by the return of reflexes, open-mouthed hissing, and attempts to high-walk to the opposite end of the pen. Baseline heart rates (HRs) were significantly higher in the juvenile animals ((x) over bar = 37 +/- 4 beats/min) compared with the adults ((x) over bar = 24 +/- 5 bpm). However, RRs (juveniles, (x) over bar = 8 +/- 2 breaths/min; adults, (x) over bar = 8 +/- 2 breaths/min) and body temperatures (juveniles, (x) over bar = 24.1 +/- 1.1degreesC; adults, (x) over bar = 25.2 +/- 1.2degreesC) did not differ between the age groups. In both groups, significant HR decreases were recorded within 30-60 min after MK administration. Cardiac arrhythmias (second degree atrio-ventricular block and premature ventricular contractions) were seen in two animals but were not considered life-threatening. Total anesthesia times ranged from 61-250 min after i.m. injection. Although dosages were significantly different between the age groups, MK and atipamezole provided safe, effective, completely reversible anesthesia in alligators. Drug-dosage differences appear to be related to metabolic differences between the two size-classes, requiring more research into metabolic scaling as a method of calculating anesthetic dosages.