Wildlife Animal Immobilization

Chemical immobilization consists of the use of chemical anesthetic and/or sedation agents to subdue, restrain or immobilize wildlife. The reasons for employing chemical immobilization in the field generally include research studies, conservation and preservation, relocation and the treatment of ailments. Issues of public safety and animal welfare (either individual or within a population) also factor into the reasons chemical immobilization of wildlife are considered.

Occasionally, veterinarians and/or wildlife managers may be called upon to capture or restrain wildlife species that have been illegally obtained (confiscation) by a private individual, or in cases where an individual animal has escaped from a zoo, sanctuary, preserve or other facility. In other instances, an animal may have become trapped in an area of human habitation. In all of these cases, both public safety and the welfare of the animal come into play.

In the United States, most of the agents used in the chemical immobilization of wildlife will be regulated by the U.S. Drug Enforcement Administration (DEA). The mission of the DEA is “to enforce the controlled substances laws and regulations of the United States and bring to the criminal and civil justice system those organizations and principal members of organizations, involved in the growing, manufacture, or distribution of controlled substances appearing in or destined for illicit traffic in the United States; and to recommend and support non-enforcement programs aimed at reducing the availability of illicit controlled substances on the domestic and international markets” (dea.gov).

Thus, registration with the DEA for all principals (usually a veterinarian, wildlife manager or research study scientist) possessing, handling or dispensing these chemical agents is mandatory. DEA requirements for registered individuals and organizations include:

• A Perpetual Drug Log
• Chemical Immobilization Records
• Transfer of Controlled Substance Records
• Controlled Substance Biennial
• Reports of significant (drug) loss

Chemical vs. Physical Restraint

While methods of physical restraint for some wildlife species may be considered (such as traps, squeeze cages, etc.), in the case of larger species or those capable of inflicting injury to handlers, chemical immobilization will be the preferred method. Even in the case of more docile species, the stresses of capture often favor the use of chemical agents over physical restraint only. “When choosing between chemical and physical methods of capture or restraint, consideration must be given to pain, animal stress, and both human and animal safety. Capture- and anesthesia-related morbidity and mortality is inherent with field immobilizations. It is essential that the investigator and veterinarian evaluate all aspects of the protocol, including species, terrain, and capture and restraint methodology, to minimize animal risk. In some situations, it may be sufficient or preferable to physically immobilize an animal without inducing unconsciousness.”¹

Smaller and more sedentary species may be handled and anesthetized without the use of specialized equipment, most will require some sort of specialized equipment to allow safe and effective anesthesia. “For initial restraint of birds, reptiles, and small mammals, towels, hoop nets, and gauntlets are indispensible components. For larger animals squeeze cages, narrow corridors, chutes, and stockades may aid in the initial contact with the animal. Traps, either manually triggered or with built-in closing mechanisms, may aid in capturing shy and fragile animals such as mouse deer or animals that retreat to burrows.”²

In the field, remote injection systems (systems for administering drugs at a distance) are frequently used to immobilize evasive, large or potentially dangerous species. These usually consist of pole syringes (which are often unsuitable for use in the field unless the animal has been trapped), blow darts or commercially-available firearms that have been designed to deliver darts rather than cartridges. Depending on the species, terrain and capture conditions, this may involve vehicles, such as trucks, ATVs or helicopters to provide access.

Chemical Immobilization Agents

Drugs for the chemical immobilization of wildlife have been significantly refined since the 1950s, when remote delivery systems were pioneered and drugs used in veterinary medicine saw increasing use in wildlife. The main classes of drugs used in the field include:

• Cyclohexamines
• Neuroleptics
• Opioids
• Reversal Agents

Cyclohexamines (also known as Dissociatives) are motor inhibitors which produce an altered state of consciousness and dissociate the patient from environmental stimulation. When using these agents, the patient may retain certain vital reflexes; they cannot walk, but can move tongue, blink, and retain the swallowing reflex. The patient may also feel some pain. Common cyclohexamines include ketamine and tiletamine.

The available literature states that cyclohexamines are not reversible and should not be used alone, as they can cause rigidity and/or seizures; rather, they should be used in conjunction with other drugs. Cyclohexamines are most commonly combined with neuroleptics.³

Neuroleptics (tranquilizers or neuro-inhibitors) produce calmness and relaxation but do not cause loss of consciousness or alleviate pain. The literature states that neuroleptics are the drug of choice for carnivores and ungulates. Neuroleptics will cause death before they cause loss of consciousness, so caution should be used when employing this class of drug. Otherwise, neuroleptics have a fairly wide margin of safety, take effect immediately and are completely reversible. Commonly used neuroleptics include zolazepam (the active ingredient in Telazol), diazepam (Valium), xylazine (Rompun, Cervizine, Anased).³

Opioids have been used extensively in the immobilization of wildlife. They are relatively fast-acting, and provide analgesia and sedation, but lack the muscle relaxation seen with alpha-2 agonists. “Common side effects seen with opioid combinations include excitation, regurgitation, severe respiratory depression and hypoxemia, muscle rigidity, and renarcotization. Most opioids used in a field setting are ultrapotent and should be handled appropriately to decrease the chance of accidental human exposure. The appropriate opioid antagonist should be on hand for rapid reversal of the immobilization.”² Commonly used opioids include buprenorphine, tramadol and butorphanol.

Dosage Calculations

The responsibility for the correct use and storage of immobilizing drugs rests entirely with the user. This includes the worker, the veterinarian responsible for obtaining and dispensing the drug, and, finally, the agency.⁴ Drug manufacturers typically cannot be held liable or assume any responsibility for the use, misuse or possible abuse of their products.

Dosage calculations are usually determined by the following formula:

In order to correctly calculate the drug dosage required to immobilize a particular animal, the veterinarian and/or party preparing the immobilizing drugs must be aware of three factors:

Estimated weight. If the weight of the animal is estimated in pounds (lbs), it should be converted to kilograms (kg), as dosages are expressed in mg/kg (milligram of drug per kilogram of body weight) required to produce immobilization. One pound equals .454kg, and the conversion is made by multiplying the estimated pounds by .454. Thus, a 100lb animal weighs 45.4kg. Since 1lb is almost equal to 1/2kg, a simpler conversion can be made by dividing the estimated weight in pounds by 2. By this method the 100lb animal weighs 50kg. Because of the difficulty in accurately estimating the weight of an animal and the safety margin of the CNS drugs, this simpler conversion is acceptable for fieldwork.

Recommended dosage. This is the dosage recommended to produce immobilization in a particular species. Dosage recommendations may be provided by a veterinarian, by the drug package insert, or by consulting dosage tables in reference literature. The suggested dosage tables are given in mg/kg (milligram of drug per kilogram of body weight).

Drug concentration. The concentration (solution strength) of the drug is listed on the label of the vial, on the package, and in the package insert. It is given as mg/ml (milligram of drug per milliliter of liquid volume). To minimize the drug volume, the highest available concentration of a given drug should be used.⁴

Anesthesia records should, at a minimum, document drugs administered including dosage, time of administration, and success of delivery. “Detailed anesthetic recordkeeping, including heart rate, respiratory rate, and temperature, should be performed when feasible. In many situations, keeping a detailed record can detract from the actual monitoring of the patient and, in these situations, patient monitoring and treatment should take priority.”³ An accurate and detailed anesthetic record provides valuable information both during the anesthesia and later as data are being analyzed and interpreted.

¹Sathya K. Chinnadurai, S., Strahl-Heldreth, D., Fiorello, C., Harms, C. (2016) Best-Practice Guidelines for Field-Based Surgery and Anesthesia Of Free-Ranging Wildlife. I. Anesthesia and Analgesia. Journal of Wildlife Diseases: April 2016, Vol. 52, No. 2s, pp. S14-S27

²Bertelsen, M., DVM. Anesthesia - The Tall and the Small, One Size Does Not Fit All. Proceedings: NAVC Conference 2013.

³Smith, A., Orlando, A., Holmes, K. Safe Capture-Chemical Immobilization. FWC Division of Law Enforcement, Version 2018.1.

⁴pneudart.com.

About NexGen Pharmaceuticals

NexGen Pharmaceuticals is an industry-leading veterinary compounding pharmacy, offering sterile and non-sterile compounding services nationwide. Unlike other veterinary compounding pharmacies, NexGen focuses on drugs that are difficult to find or are no longer available due to manufacturer discontinuance or have yet to be offered commercially for veterinary applications, but which still serve a critical need for our customers. We also specialize in wildlife pharmaceuticals, including sedatives and their antagonists, offering many unique options to serve a wide array of zoo animal and wildlife immobilization and anesthesia requirements.

Our pharmacists are also encouraged to develop strong working relationships with our veterinarians in order to better care for veterinary patients. Such relationships foster an ever-increasing knowledge base upon which pharmacists and veterinarians can draw, making both significantly more effective in their professional roles.

Disclaimer

The information contained in this blog post is general in nature and is intended for use as an informational aid. It does not cover all possible uses, actions, precautions, side effects, or interactions of the medications shown, nor is the information intended as medical advice or diagnosis for individual health problems or for making an evaluation as to the risks and benefits of using a particular medication. You should consult your veterinarian about diagnosis and treatment of any health problems. Information and statements have not been evaluated by the Food and Drug Administration ("FDA"), nor has the FDA approved the medications to diagnose, cure or prevent disease. Medications compounded by NexGen Pharmaceuticals are prepared at the direction of a veterinarian. NexGen Pharmaceuticals compounded veterinary preparations are not intended for use in food and food-producing animals.

NexGen Pharmaceuticals, LLC does not recommend, endorse or make any representation about the efficacy, appropriateness or suitability of any specific dosing, products, procedures, treatments, services, opinions, veterinary care providers or other information that may be contained in this blog post. NEXGEN PHARMACEUTICALS, LLC IS NOT RESPONSIBLE NOR LIABLE FOR ANY ADVICE, COURSE OF TREATMENT, DIAGNOSIS OR ANY OTHER INFORMATION, SERVICES OR PRODUCTS THAT YOU OBTAIN THROUGH THIS BLOG POST.