Anesthesia of polar bears (Ursus maritimus) with zolazepam-tiletamine, medetomidine-ketamine, and medetomidine-zolazepam-tiletamine

A 1:1 combination (by weight) of zolazepam and tiletamine is the drug of ch oice for anesthetizing polar bears (Ursus maritimus), but recovery time is prolonged when additional doses are administered. Recoveries may last 24 hr and may threaten the health of the bears. We compared the anesthetic effec ts of zolazepam-tiletamine (ZT) with those of medetomidine-ketamine (MK) an d medetomidine-zolazepam-tiletamine (MZT) in 93 free-ranging polar bears. T he MZT combination was administered in smaller dose and volume, resulted in more rapid, safer, and more predictable induction, provided more reliable anesthesia, and was safely reversed with atipamezole. Frequent occurrence o f sudden recoveries during anesthesia with MK limited our use of this combi nation. MK and MZT sometimes caused apnea and bradycardia initially and hyp erthermia at increased ambient temperatures. Hypoxemia occurred transiently with all combinations. When anesthesia with ZT and MK exceeded I hr, frequ ent necessary top-up doses caused irregular physiologic function. ZT is rec ommended for short duration anesthesia (less than or equal to 1 hr), but MZ T is better for anesthesia of longer duration and under circumstances where reversibility is desirable.