Chemical Immobilization: Post-Capture Approach, Monitoring, and Procedures

Many situations are encountered in the field and in zoos where the capture and restraint of wildlife is required. Improved understanding of the margins of safe capture, chemical immobilization, and handling of animals for research and management has been greatly enhanced over the years due to documentation and examination efforts involving various species, study designs, and environmental conditions.¹ The capture of free-ranging and captive exotic animals is an important foundation of wildlife research. Minimizing harm, especially mortality, is a principal ethical concern therein.

The San Diego Zoo Wildlife Alliance (SDZWA) currently offers a variety of courses in safe capture chemical immobilization techniques for those who are interested in or who are pursuing careers in veterinary medicine, wildlife management, biology, zoology, animal control and related disciplines. Among these are in-depth modules on the pharmacology of chemical immobilization drugs and their use. Chemical Immobilization Pharmacology: Post-Capture Approach, Monitoring, and Procedures is one such module.

Chemical Immobilization Basics

Chemical immobilization involves the use of anesthetic drugs to immobilize an animal for the purpose of capture. Chemical capture is most commonly accomplished by the projection delivery of a dart containing anesthetizing drugs from a remote delivery system such as a rifle, pistol, blowpipe or pole syringe.² There has been a dramatic evolution of both capture equipment and drugs in recent years. There are now many manufacturers of safe capture equipment and remote delivery systems. Immobilizing drugs have undergone a similar transformation, with compounded drugs specially designed for the chemical immobilization of wildlife being offered by veterinary custom compounding pharmacies. These formulations are far safer and more efficient that the drugs and drug combinations used in years past.

Capture events, whether in a zoo or field setting, should be carried out according to proven, established protocols that are species-specific. All personnel executing actions during the capture event should be adequately trained and under the guidance of a veterinarian or wildlife manager.

Post-Capture Procedures

After immobilizing drugs are delivered to an animal, those on the capture team should remain still and calm while assessing the situation. While many animals will bolt after darting, personnel should do nothing to cause an animal to bolt. Immobilizing drugs do not act instantaneously, or even very rapidly.^3,4 It may take two to three minutes for an adequate amount of the drugs to be absorbed and metabolized. If the animal is highly-stressed or threatened, it may take even longer.

When the animal appears immobilized, it should be approached slowly and calmly from behind. Those approaching should make no sudden movements nor sounds. If immobilized, the animal should be gently and quietly assessed, and restraint gear applied if appropriate.

Immediate monitoring of temperature, pulse, and respiration should be conducted and continued throughout.⁴ Covering the animal’s head and eyes with a towel or cloth is often recommended to help keep it calm. Immediately ensure that the animal’s airway is open and free from obstruction, and that the animal is breathing. Ruminants should be placed in sternal recumbancy with the head lifted until recovery to avoid breathing problems.^2,4

The capture team must be prepared to take immediate corrective action if any of the animal’s vital signs stray from the normal range, or if capture-related emergencies occur (e.g., hyperthermia, hypothermia, capture myopathy, respiratory or circulatory failure or bloat).⁴ Preferably, a chart showing observations and each of the animal’s vital signs should be maintained. This will make it easier to determine trends for the future.

In optimal circumstances, animals recovering from an immobilization event (whether allowed to recover naturally or via anesthetic antagonists) should remain under care until they are fully recovered and able to return to their habitat and normal behavior.

Practitioners of chemical capture should consult with a veterinarian to help determine which drugs are best for a particular need. In the US, immobilizing drugs may only be used under the supervision of a licensed veterinarian. Exotic (wildlife) veterinarians will usually be able to determine the best dosages for the target species. Each species will have different sensitivities to various drugs and will have different recommended dosages.

Interested in learning more about safe capture? The San Diego Zoo now offers courses in safe capture techniques and best practices. Learn reliable, safe, and effective techniques for the species you work with and the scenarios you encounter!