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 choice 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 effects of zolazepam-tiletamine (ZT) with those of medetomidine-ketamine (MK) and medetomidine-zolazepam-tiletamine (MZT) in 93 free-ranging polar bears. The 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 of sudden recoveries during anesthesia with MK limited our use of this combination. MK and MZT sometimes caused apnea and bradycardia initially and hyperthermia at increased ambient temperatures. Hypoxemia occurred transiently with all combinations. When anesthesia with ZT and MK exceeded 1 hr, frequent necessary top-up doses caused irregular physiologic function. ZT is recommended for short duration anesthesia (< or = 1 hr), but MZT is better for anesthesia of longer duration and under circumstances where reversibility is desirable.