Wildlife Animal Sedation Reversals
Field wildlife anesthesia is often necessary for both invasive (e.g., surgical) and noninvasive (e.g., blood collection, collaring, metabolic) procedures. Anesthesia for noninvasive procedures is commonly utilized for the safety of the investigators and the animals.1
The terms “anesthesia” and “sedation” are often used interchangeably, but there are distinct differences when speaking in the clinical sense. Those differences speak to important practical aspects of the requirements for the procedures being performed. For example, in the case of less invasive procedures or procedures in which the veterinarian has deemed that general anesthesia may introduce unnecessary risk to the patient, heavier sedation may be prescribed prior to procedures being performed rather than general anesthesia.
The preparation of the wild animal for chemical restraint, sedation or anesthesia most often must be made without the benefit of a physical examination to determine physiological condition or specific needs. In many cases, the animal must receive the initial medication via propelled dart or other systems used from a point distant from the animal.2 Since it is difficult to measure preanesthetic responses in wild animals, attempts are often made to evaluate specific responses to certain medications in domestic animals and relate these to the gross responses seen in both domestic and exotic (wild) animals.3
Basic Definitions:
Anesthesia: Central nervous system depression that provides amnesia, unconsciousness and immobility in response to a painful stimulation. Drugs that produce anesthesia may or may not provide analgesia.4,5
Analgesia: Reduced or absence of pain in response to stimulation that would normally be painful. An analgesic drug can provide analgesia by acting at the level of the central nervous system (CNS), or at the site of inflammation or injury to diminish or block pain signals.4,5
Sedation: A state of mental calmness, decreased response to environmental stimuli and muscle relaxation. This state is characterized by suppression of spontaneous movement with maintenance of spinal reflexes.4
According to Chinnadurai, et. al.: “General anesthesia is inherently a veterinary medical endeavor and thus should be conducted under the supervision and guidance of a licensed veterinarian. In almost every case, the drugs needed for an immobilization are controlled substances or prescription drugs and must be acquired by a licensed veterinarian. All anesthetic protocols should be designed by a licensed veterinarian and ideally with the guidance of a board-certified anesthesiologist or wildlife veterinarian. Unlike domestic animal anesthesia, many field immobilizations are conducted by biologists and field technicians. Nonveterinary personnel should only perform and monitor anesthesia when properly trained by veterinarians or other specialists, and such training should be regularly reviewed and maintained.”
Analgesics and Reversals
Whether general anesthesia or sedation has been indicated, reversal agents are often required to neutralize sedation or anesthetic agents, thus allowing the treated animal to completely recover from being anesthetized. This is even more important in the field (than in a clinic or zoo setting) because a chemically-compromised animal will be in danger of injury, predation and other hazards. A familiarity with the efficacy of reversal agents used and their effect on a given species on the part of the attending veterinarian is essential in order to ensure sufficient recovery and to minimize the aforementioned risks.
Analgesia should be considered as essential for any penetration of the patient’s skin by a tool larger than a hypodermic needle, including biopsy instruments. Exceptions would be when it is impractical to do so, such as during biopsy using a projectile device. Invasive surgeries should be conducted using general anesthetics with the animal at a surgical plane; intraoperative analgesia that continues after anesthetic recovery should be provided in some form to every surgical patient.1
For analgesic drugs, doses and frequencies of administration are more difficult to gauge, even with close clinical observation for discomfort.4 These observations can be even more difficult to make in the field than in a clinic or zoo setting, compounding the difficulty in such assessments.
While a majority of field applications will necessitate the release of the animal once procedures are completed and the patient has fully recovered, one example of the importance of considering administration frequency in analgesic use is allowing for overnight pain management.Most of the opioid analgesics (Buprenorphine, Fentanyl, Butorphenol, Oxymorphone, etc.) administered in the early evening, for example, will not be effective the next morning. Thus, administration after normal business hours, use of extended release formulations, and/or trans‐dermal patches can be considered, depending on the species.4
Longer‐lasting, non‐steroidal anti‐inflammatory analgesics (NSAIDs) such as Meloxicam, Carprofen, Flunixin, Ketoprofen,etc. have longer durations of action than opioids, and can be administered in conjunction with opioids to increase potency of effect and duration of action.5
Reversal Agents for Wildlife
Duration of anesthesia is influenced by the drugs used, strain, age, sex, body weight, procedure performed and the amount of stimulus during the procedure. Due to all the factors that influence duration of anesthesia, the literature maintains that anesthetic drugs should always be titrated to effect. If anesthesia is being maintained by a gas anesthetic (eg., Isoflurane), titration of anesthetic depth can be controlled almost immediately by adjusting the amount of anesthetic gas being administered to the animal. In addition, anesthetic duration can be extended for as long as the anesthetic gas is administered.5
In contrast, injectable anesthetics and sedatives (which may be used for less invasive or higher-risk procedures) do not have this flexibility; once a dose has been administered, it cannot be “un-administered” to facilitate the end of anesthesia to coincide with the end of the procedure.6 Here, reversal drugs are used to bring about the desired effect.
Atipamezole is a synthetic α2-adrenergic antagonist. Developed to reverse the actions of compounds such as medetomidine and dexmedetomidine, Atipamezole for veterinary use safely and reliably reverses the effects of these compounds and is widely used in small and large animal practices, as well as in wildlife applications, such as deer.
Naltrexone hydrochloride is an opioid receptor antagonist that is used in veterinary medicine to block receptors as a reversal agent for opiate agonists such as butorphanol. It is also used for the treatment of recurring, compulsive animal behavior disorders such as tail-chasing and self-mutilation such as acral lick dermatitis.7 Naltrexone is currently under study for possible application in a wide range of other therapeutic areas within veterinary medicine, such as in treating lymphoma, adenomas, nasal/sinus cancer, inflammatory bowel disease and degenerative myelopathy.
Tolazoline belongs to the synthetic group of alpha-adrenergic blocking agents known as the imidazoline derivatives. It is typically used as a Xylazine reversing agent and antagonist for intravenous use in horses, with minimal adverse effects typically presenting. Onset of arousal is generally apparent within 5 minutes of Tolazine administration, depending on the depth and duration of sedation.
1Chinnadurai, 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.
2Rosenfield, D. (2017). Introduction to Technical Aspects of Remote Drug Delivery Systems with Telemetric Support in Free-Ranging Wildlife. ABRAVAS Technical Bulletin. II.
3Short, C. Anesthesia, Sedation and Chemical Restraint in Wild and Domestic Animals. Bull. Wildlife Disease Assoc. Vol. 5, July, 1969.
4Fish R.E., Brown M.J., Danneman P.J., Karas A.Z., editors. Anesthesia and Analgesia in Laboratory Animals. 2nd Ed. New York: Academic Press; 2008.2.
5Institute for Laboratory Animal Research (ILAR). Recognition and Alleviation of Pain in Laboratory Animals. 1st Ed. Washington DC: The National Academies Press; 2009.
6University of Colorado Anschutz Medical Campus Pub. Veterinary Anesthetic and Analgesic Formulary, 3rd Edition, Version G.
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.
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