The broad term “anesthesia” typically covers simple immobilization and recovery via heavy sedation as well as general anesthesia, despite these two modalities being distinctly different. The latter involves central nervous system depression resulting in the loss of consciousness and sensation, and includes the complement of technological means that allow for monitoring and maintaining a stable patient during procedures. Sedation (or chemical immobilization) involves the use of drugs for sedation and analgesia, and is the method preferred in the field.
Immobilization and recovery involving heavier sedation can produce far less stress, risk and a more expeditious procedure overall. With the current technology and variety of medications available today, it is now possible to design appropriate anesthetic and analgesic protocols for nearly any field situation. With careful planning and adequate communication, field team members will be able to smoothly execute most immobilization protocols, as well as anticipate and prepare for potential complications.
Drugs Used for Wildlife Immobilization
There is no single drug that is ideal for the chemical immobilization of wildlife. However, the desired properties for such drugs and drug combinations are as follows:
High therapeutic index: The drug should be safe for the animal and produce zero or minimal side effects.
Rapid absorption and induction: The animal should be immobilized quickly to avoid losing the animal in the field.
High concentration: Utilizing drugs in high concentration facilitates the use of smaller darts in remote delivery.
Specific antagonist: The antagonist should rapidly and fully reverse the effects of the immobilizing agent and should outlast the effects of the immobilizing agent.
Stability: In adverse conditions, and in conditions where a substantial length of time will pass between preparation and administration, drug solutions should remain stable over time and at a wide range of temperatures.
Safety: The drug should be safe enough that small volumes or accidental exposures do not cause serious problems; it should be possible to fully antagonize the effects of the drug (in animals or handlers) in the event of an accidental exposure.
Analgesia should be provided for any penetration of the 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 (which, in the field, would necessitate immobilization and transportation of the animal to a surgical facility). Intraoperative analgesia that continues after anesthetic recovery should be provided in some form to every surgical patient.1
Minimally invasive surgical procedures, including biopsies and dental extractions can be performed on conscious patients if general anesthesia would put the patient under extreme risk. When general anesthesia is not used, preemptive analgesia is of paramount importance. Analgesic drugs used in field settings include opioids, nonsteroidal anti-inflammatory drugs (NSAIDs), and local anesthetics.2
Ketamine and Medetomidine
Ketamine is a fast-acting dissociative anesthetic that is often used in combination with a tranquilizer-sedative, usually a benzodiazepine or an α-2 agonist. Immobilizations with combinations including ketamine provide a rapid onset of action, immobilization within 10 min, and long duration (up to 2 hours). Ketamine provides excellent somatic analgesia, but poor visceral analgesia, and therefore it should not be used as the sole analgesic for procedures expected to cause visceral pain. When used alone, side effects include increased muscle tone, hyperthermia, excessive salivation, catecholamine release, and convulsions. Ketamine has no known antagonist; for this reason the use of a reversible drug in combination with ketamine for field immobilizations is commonly recommended.3
Medetomidine (medetomidine hydrochloride) is a synthetic α-2-adrenoreceptor agonist with sedative and analgesic properties. Medetomidine is used by veterinarians as both a surgical anesthetic and analgesic. The pharmacological restraint and pain relief provided by medetomidine facilitates handling and aids in the conduct of diagnostic or therapeutic procedures. It also facilitates minor surgical procedures (with or without local anesthesia) and dental care where intubation is not required.
The MK Kit for the Field
The MK Kit by NexGen Pharmaceuticals is a premixed formulation developed to provide veterinarians and wildlife handlers with a field-tested immobilization anesthesia option that can be effectively used to immobilize a broad range of exotic animal species. This formulation consists of medetomidine (5mg/ml), which provides superior pain relief and muscle relaxation to other compounds employing α-2 adrenergic agonists, and ketamine HCL (150 mg/ml), which supplies an effective paralytic. In combination, the two provide safe, smooth induction times and excellent recovery results.
MK2 was originally developed by NexGen as a superior solution for anesthetizing wildlife species in a more efficient manner. The MK Kit includes the MK formulation with accompanying reversal agent (and a manufacturer discount for purchasing the two in combination).
For those who are new to utilizing MK to manage their exotic animals, it is important to understand the level of anesthesia you are administering with Medetomidine/Ketamine sedation. MK is a deep sedation, not to be confused with other sedations that are moderate.
Routes of Administration and Dosages
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.
The shoulder is a suitable injection site in many larger species. This region is well-muscled, presenting a flat, perpendicular target. It is surrounded by relatively resilient areas and presents a fair-sized target in animals that are robust enough to be darted with remote delivery equipment.
To prevent the needle from becoming embedded in cartilage, the upper end of the scapula should be avoided. In sensitive species, the sight and smell of a dart in the shoulder may cause panic and flight. Some carnivores will destroy the dart by pulling it out with their teeth. The shoulder is not a suitable injection site for smaller species, due to their lesser size and limited muscle mass.
Recommended dosages for large animal sedation with NexGen’s MK formulation are as follows:
- White Tail doe/sm buck – 1.0-2.0cc
- White Tail large buck – 2-2.5cc
- Bison cow/small bull – 2cc
- Bison Bull – 2.5cc
- Fallow deer doe – 1.0cc
- Fallow deer buck – 2-2.5cc
For reversal dosages, please consult MK Kit reversals documentation.
1Whiteside DP. 2014. Analgesia. In: Zoo animal and wildlife immobilization and anesthesia, 2nd Ed., West G, Heard D, Caulkett N, editors. John Wiley & Sons, Inc., Ames, Iowa, pp. 83–108.
2Chinnadurai, Sathya & Strahl-Heldreth, Danielle & Fiorello, Christine & Harms, Craig. (2016). Best-practice guidelines for field-based surgery and anesthesia of free-ranging wildlife. I. Anesthesia and analgesia. Journal of wildlife diseases. 52. S14-S27. 10.7589/52.2S.S14.
3Caulkett N, Arnemo J. 2007. Chemical immobilization of free-ranging terrestrial mammals. In: Lumb and Jones’ veterinary anesthesia, 4th Ed., Thurmon J, Tranquilli W, Grimm K, editors. Blackwell, Ames, Iowa, pp. 807–831.
