Immobilization Anesthesia For Veterinarians

Since wild animals are, well... wild, this dictates that any manipulation requiring handling will also necessitate chemical immobilization. Wildlife veterinarians are not only required to possess the normal complement of skills and qualifications of veterinarians working in a practice or research facility, but they must also be familiar with the unique anatomy and physiology of wildlife species and the challenging field conditions they will inevitably encounter in performing their work. Additionally, they must be readily able to adjust the general principles of anaesthesia to the physiological parameters of the species with which they are working.

Unlike working with small animal patients, veterinarians planning to anaesthetize wildlife are seldom afforded the opportunity to physically examine patients or acquire biological samples to assess their physical status prior to anaesthesia, and that sometimes translates to choosing anaesthetic cocktails with a wider safety margin while sacrificing other parameters such as recovery time. Additionally, capture and chemical immobilization of wildlife can pose some significant human safety considerations.

Variables in Working With Wildlife

In the field, specific anatomical and physiological details pertaining to the species at hand are not always available to the wildlife veterinarian. While anaesthetic protocols may have been adjusted from doses in domestic species, rarely are detailed pharmacokinetic studies available.² In response to this challenge, custom compounding pharmacies have created wildlife-specific anesthetic medications.

These premixed formulations are derived from the available knowledge on species with which the wildlife veterinarian is likely to encounter, but are available in concentrations that are more safe, effective and economical than executing "on-the-fly" formulations of existing medications. Nominally, these are medications that have been formulated through the engagement of knowledgeable veterinarians and veterinary pharmacists with expertise in wildlife management.

In addition to the above, there are many benefits to using such medications for the veterinarian, the capture team and the animal alike. Among these are access to relevant and accurate drug dosages and volume calculations, safe capture techniques, strategies of approach, medication delivery techniques and capture pharmacology, to name a few.

Administration and Injection Sites

To have any effect on the animal, the immobilizing drug must be absorbed from the vascular tissue of the injection site and conveyed in sufficient volume through the circulatory system to the brain. The time (in minutes) from injection to a satisfactory level of immobilization is known as the induction time. The drug response in individual animals is influenced by a variety of factors.

Administration of an immobilizing drug by remote delivery is by intramuscular injection. The aim is to hit the animal in a specifically-selected site, causing injection into vascular tissue and thereby facilitating rapid absorption of the drug.

The neck is a suitable injection site for large animals with muscular necks (such as deer). Care should be taken to avoid hitting the jugular vein, the upper end of the neck, and the head, with the best injection site being the trapezius muscle mass at the upper base of the neck. The shoulder is also a suitable injection site for larger species.

General Recommendations and Precautions

General recommendations for minimizing the effects of long-term stress of confinement and field sedation include:

• Knowing the species. Information regarding specific biological and sociological needs, flight distance, dependency on cover, and food preferences is of paramount importance.
• Ensuring the area of confinement is appropriate in size, quality, and furnishings for the species, the flight distance is important in this regard. With some species, the flight distance may be reduced with the creative use of opaque barriers. Provide sufficient shade structures for all species.
• Provision of adequate cover for nervous species. Animals are more at ease when in cover, and it permits them to withdraw from human observation at will. Covering open fencing— including gates—with opaque material will prevent animals from injuring themselves by trying to crash through fencing.
• Avoiding stimulation of newly-caught animals by placing the area of confinement away and upwind from the center of human activities, by screening the enclosure with opaque material, and by avoiding unnecessary human interaction with the animals.
• Provision of an appropriately contained source of clean, fresh water in enclosures. In the case of animals that must be caged and/or transported (as opposed to being worked on in the field), it is important to be aware that many species require surface-level water and will not drink from a bucket, barrel, or aboveground container. Other species are suspicious of water containers and will destroy them.
• Provision of appropriate food for the species. Large enclosures with natural forage and surface water are best for herbivores. Cut supplemental food should be natural as is possible to acquire.
• Minimizing unnecessary stimulus. When feeding, watering, or checking on confined animals, workers should always approach the enclosure from the same direction, while talking gently to warn of their approach. While working with the animals, talking or singing softly can habituate animal to the presence of humans, thereby lowering stress.
• Monitoring of confined animals for signs of injury, illness, undue anxiety, loss of condition, refusal to eat or drink, and abnormal bodily functions or social interactions.

Drug Combinations and Synergy

Prior to the advent of custom compounded formulations, veterinarians were relegated to using single drugs or combinations prepared by the veterinarian. For animals such as deer, this typically meant drugs such as xylazine or carfentanil.³ Although many drugs may be used alone for the immobilization of wildlife, combinations of two or more synergistic drugs are often safer as well as being more effective. It is for this reason that such combinations have become more widely used in this regard.

For larger wildlife species such as deer, it has been found that medetomidine provides superior pain relief and muscle relaxation to other compounds employing alpha-2 adrenergic agonists, with Ketamine HCL supplying an effective paralytic. In combination, the two medications provide safe, smooth induction times and excellent recovery results when working with larger wildlife species.