Exotic Animal Immobilization

Veterinarians are regularly called upon to anesthetize a wide variety of exotic animals. For the purposes of this discussion, exotic animals are those non-domesticated species that are encountered in the field, in a zoo setting or those which have found their way into homes as companion animals (such as the larger psittacines, some of the smaller felids, reptiles, etc.).

Access to some of the more dangerous or free-ranging species and determining anesthetic protocols can be difficult, because more often than not, neither exact weight nor actual health status can be predetermined. “Additional factors such as nutrition, disease, parasite load, infection, estrus, pregnancy, and lactation are also major anesthetic considerations, but usually cannot be assessed with certainty at a distance.”¹

Drug Delivery, Protocols and Routes

In the case of exotic animals in the field, the environment in which the veterinarian is required to work is necessarily far less controlled than that of a zoo or the traditional veterinary practice. Thus, in many cases, particularly if the individual animal cannot be assessed prior to procedures, drug doses must be estimated. In some instances, particularly with larger or inherently dangerous individuals, the remote delivery of anesthetics or sedation drugs must be considered.

“In the late 1950s, the first complete remote delivery system designed for the sedation of exotic animals became available, but the concept was not new. People of South America, Asia, and Africa have for centuries used arrows and spears with plant or animal poisons for hunting. Poison-coated darts have been used by South American Indians for hunting of birds and small mammals by the means of a blow pipe.”¹

Improvements in design over subsequent decades have of course improved the effectiveness of remote delivery devices, and the refinement of anesthetic and sedation drugs and related protocols have increased the veterinarian’s efficiency in treating exotic animals in the field, as well as increasing safety margins for animals and human handlers alike.

The preferred route for the administration of an immobilizing drug by remote delivery is via intramuscular injection. The aim is to hit the animal in a specifically-selected site, causing injection into vascular tissue and facilitating rapid absorption of the drug. Not all areas of an animal's body are equally well-suited for injection by remote delivery; thus, the injection site should be carefully chosen.

The neck is generally a suitable site for large animals with muscular necks. Care should be taken to avoid hitting the jugular vein, the upper neck and the head. The ideal injection site is the trapezius muscle mass at the upper base of the neck. This injection site is suitable for species such as elk, moose, buffalo, bear, the equids and larger antelopes, rhinoceros, hippopotamus and elephant (if the ears can be avoided). Animals with slender necks, such as gazelle, gerenuk, giraffe and impala should not be darted in this area.

Drug Classes and Combinations

In general, the requirements of an ideal anesthetic drug for exotic animal anesthesia are:

• Large therapeutic index to compensate weight estimation errors and lack of preanesthetic evaluation of the patient
• High concentration to permit one-dart application (if remote delivery is required)
• Long durability
• High compatibility (if combined with other drugs)
• Rapid induction time
• Good sedative, muscle relaxant, and analgesic qualities
• Minimal local or systemic side effects
• Safe intramuscular application
• Availability of an antagonist

Practice and field experience have often demonstrated that a combination of compatible and complementary drugs may constitute the safest and most effective method to meet the ideal requirements for anesthesia for selected species.¹

Many of the anesthetic and sedation agents available to veterinarians in practice settings have been integral to the protocols devised for exotic animals in the field, zoos and in other settings. Typically, the classes of drugs used are the same, although custom formulations provided by custom compounding pharmacies have gained popularity in recent years, since these can be tailored to the species encountered by veterinarians in such circumstances.

Dissociative anaesthetics such as ketamine, tiletamine and etorphine are classified as cyclohexamines. Anaesthetics are used when an animal needs to be unconscious and unaware for an extended period of time, such as for surgery or performing assisted reproductive techniques. When used singly, these agents can cause rough inductions and recoveries and convulsions may be experienced. Therefore, they are usually used in combination with sedatives or tranquilizers that produce synergistic effects to yield good induction and smooth recovery.²

As in traditional veterinary practices, dissociatives such as ketamine are often combined with alpha-2 adrenergic agonists such as xylazine and medetomidine for the synergistic effects that have proved to be functional and highly effective in immobilization for many years.

Sedatives such as acepromazine, diazepam, xylazine and medetomidine produce calmness, loss of aggression and loss of alertness which is generally required during transportation. Animals do not become fully immobilized with these agents, and can be aroused by slight disturbances. Therefore, they are used primarily as adjuncts to dissociative anesthetics for hastening smoother induction and to reduce the quantity of anesthetic for achieving more effective immobilization. “This combined synergistic effect of tranquilizer and anesthetic is far greater than the individual effect of either of the two drugs with respect to smooth induction, good muscle relaxation and smoother recovery.”²

Opioids and opioid agonist/antagonists are also used in a variety of species as analgesics and for premedication in the sedation and immobilization of exotic species. “Opioids continue to be the cornerstone of effective pain treatment in veterinary medicine. The opioids are a diverse group of naturally occurring and synthetic drugs used primarily for their analgesic activity. Despite some well-known adverse effects and disadvantages, opioids are the most effective analgesics available for the systemic treatment of acute pain in many species, particularly dogs and cats.”³

There are potent synthetic opiates, primarily oripavine derivatives or 4-amino-piperidine compounds. They are commonly used for immobilization of ungulates, elephants, and rhinoceroses.⁴ The opioids have good analgesic but only limited muscle relaxant properties. They have a wide margin of safety, are predictable in action, and can be reversed with the administration of a suitable antagonist (diprenorphine, naloxone or nalorphine).¹

Butorphanol tartrate is one synthetically derived opioid agonist-antagonist analgesic of the phenanthrene series, with a potency of about four to seven times that of morphine. In combination with agents such as medetomidine and ketamine, the veterinarian can rely on a safe and gentle induction with excellent recovery results. Formulations such as these provide reversible sedation, with shorter induction times and longer working times, an indispensible benefit in the field, the zoo or practice when treating exotic species.