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Chemical restraint of native carnivores (Proceedings)
In wildlife medicine, it is often necessary to chemically restrain animals to perform even the most basic procedure.
In wildlife medicine, it is often necessary to chemically restrain animals to perform even the most basic procedure. This is certainly true when one is working with members of the Order Carnivora, a large and diverse group of mammals consisting of seven families (Canidae, Felidae, Ursidae, Procyonidae, Mustelidae, Viverridae, and Hyaenidae). It is, therefore, important to be familiar with the variety of immobilizing agents and equipment used in this field, as well as to understand when to use each of them. Because there is some overlap in the situations in which the various drugs and equipment may be used, personal preference and familiarity play a large role in determining which types of immobilization agents and equipment are used. Other factors involved in this decision include: facility design, the species involved, the attitude and behavioral characteristics of the animal, and the physiologic or pathologic condition of the animal.
Considerations for choice of restraint methods include: human safety, animal safety, environmental factors, knowledge and preference, and the preparation/planning involved.
Although physical restraint of native carnivores may be appropriate in some management and medical situations (and will be influenced by the animal's type, temperament, size [generally ≤ 5 kg], and physical/pathologic condition), it does effect patients in various physiologic and psychological ("stress") ways. In addition, physical restraint may precede an anesthetic procedure, especially when the proper use of physical restraint can preclude the use of additional anesthetic agents. To facilitate the physical restraint of nondomestic patients, therefore, one should have access to equipment such as protective gloves, towels, hoop nets, snares, plastic tubes, and ideally, a squeeze cage.
Most native carnivores, especially large (≥ 5 kg), wild, or fractious individuals, or those requiring extensive procedures or surgical manipulation, require chemical restraint. In these cases, pre-immobilization planning is essential for successful chemical immobilization. This involves having trained personnel, appropriate equipment, an equipment check-off list, a check-off list to refer to during the procedure, emergency drug doses calculated, and a preanesthetic assessment of the patient (may be visual/behavioral observations). Human and animal safety issues must also be addressed prior to the chemical restraint of an animal.
Prior to anesthesia, the patient needs to be fasted for appropriate periods (generally 24-48 hours for large, 24 hours for medium-sized, and 12 hours for small carnivores). Also, withhold water for 12 hours in large animals (unless dehydrated) and 2 hours in smaller patients.
Premedication/sedation of animals may have value in some cases, but may be unnecessary in others. Some medications (i.e., diazepam) can be administered PO prior to a procedure, often with beneficial results; results, though can be highly variable. To administer premedications parenterally, though, requires that an animal be handled or darted twice to achieve anesthesia. In some cases, this can result in an excited animal at the wrong time, negating any potential benefit from a sedative. Frequently, the anesthetic sparing effect of some sedatives can be retained by incorporating them with the anesthetic drugs (i.e., administering the drugs simultaneously). Following induction, maintenance of the animal using gaseous anesthetics is often indicated.
Once anesthetized, it is important to monitor cardiopulmonary functions (i.e., pulse oximeter, Doppler blood flow monitor, ECG, etc.) and temperature of the patient. Administering supportive care such as supplemental heat and fluid therapy to anesthetized patients may be required. Recovery of an anesthetized patient should occur in an undisturbed, quiet, dimly lit, secure area that is free from physical hazards. Animals are generally placed in lateral recumbency for recovery. Chemical reversal of the anesthestic agent is generally desirable. Unfortunately, postanesthetic monitoring of native carnivores is generally difficult.
The use of drugs for restraint and immobilization is an essential part of a veterinarian's role in managing native carnivores. Drugs permit manipulative procedures that otherwise would be impossible to perform. Although many of the commonly used agents have only been widely used during the past 20 years, restraint drugs are not new, and, in fact, have been around since ancient times.
In selecting an appropriate immobilizing agent, there are many areas to consider. An ideal restraint drug should have a high therapeutic index (lethal/effective) (in many cases, the therapeutic index increases in drug combinations), be compatible with other drugs, have a short induction period, have a reversal agent, be stable in solution, be effective in small volumes, be non-irritating, be economical, and could be administered intramuscularly. Obviously the ideal drug has not yet been found. However, for most species, select drugs are available that would meet most of the qualifications.
Commonly Used Drugs
Drugs commonly used in the chemical immobilization of native carnivores by most practitioners include: ketamine, zolazepam and tiletamine (Telazol®, Fort Dodge), medetomidine (Dormitor®, Pfizer Animal Health), xylazine, midazolam, and diazepam. Opioids such as butorphanol have occasionally been used in combination with other drugs to immobilize native carnivores; carfentanil has been used by some zoo/wildlife veterinarians to chemically restrain bears.
The most useful combination of drugs used in chemically immobilizing nondomestic carnivores include: ketamine/medetomidine; ketamine/zylazine; zolazepam/tiletamine; zolezepam/tiletamine/medetomidine; and ketamine/midazolam. Of these, ketamine/medetomidine is probably the most commonly used, and results in a safe and rapid immobilization. Medetomidine has a 10x greater affinity for alpha2 receptor sites and is up to 30x more potent than xylazine, thereby allowing a 75% reduction in the ketamine dose. This combination is generally very safe and appears to be the most reliable in terms of predicted potency over the widest species range. Ketamine/xylazine has also been used in a variety of species, and is comparatively less costly than other combinations. Medetomidine and xylazine are reversible with atipamezole and yohimbine, respectively.
Telazol® is also commonly used and has the following advantages: only a small volume is required; rapid induction; and good muscle relaxation. Concerns in using Telazol® include: relatively slow recovery (sometimes "rough") and the drug is not completely reversible (only the zolazepam is reversible, but its antagonist, flumazenil, is very expensive and its use may predispose an animal to seizures secondary to the remaining tiletamine).
Other points to remember when immobilizing nondomestic carnivores include: diazepam may be useful in some cases as a premedication administered PO 30-60 minutes prior to administering the anesthetic drug; if additional parenteral drugs are required in an animal following the initial immobilization, ketamine (i.e., 1.0-1.5 mg/kg IV slowly) is generally the drug of choice; and reversal agents are usually administered 25% IV and 75% IM (although administering 50% IV and 50% IM, or 100% IM are also commonly done).
NOTE: K= ketamine; M= medetomidine; X= xylazine; T= Telazol®; A= acepromazine; B= butorphanol.
Badger, American a. 4.4 mg/kg (T) (supplement with 4.4 mg/kg [K])
b. 15 mg/kg (K) + 1 mg/kg (X)
Bear, black a. 1.5 mg/kg (K) + 0.04 mg/kg (M)
b. 7 mg/kg (T)
c. 4.4 mg/kg (K) + 2 mg/kg (X)
d. 2 mg/kg [T] + 0.05 mg/kg [M]
Bear, brown (grizzly) a. 8 mg/kg (T) (supplement with 4.4 mg/kg [K])
b. 4.5 mg/kg [T] + 0.025 mg/kg [M]
c. 3.8 mg/kg (T) + 2.5 mg/kg (X)
Bobcat a. 2.5 mg/kg (K) + 0.06 mg/kg (M)
b. 4.8 mg/kg (T), captive; 6-11 mg/kg (T), wild
c. 10 mg/kg (K) + 1.5 mg/kg (X)
Coyote a. 10 mg/kg (T)
b. 4 mg/kg (K) + 2 mg/kg (X)
c. 10 mg/kg (K) + 0.1 mg/kg (A)
Fisher a. 20 mg/kg (K) + 0.04 mg/kg (M) (supplement with 10 mg/kg [K])
b. 4 mg/kg (K) + 0.06 mg/kg (M)
c. 11 mg/kg (T)
Fox, arctic a. 2.5 mg/kg (K) + 0.05 mg/kg (M)
Fox, gray a. 4 mg/kg (K) + 0.08 mg/kg (M)
b. 10 mg/kg (K) + 2 mg/kg (X)
c. 9 mg/kg (T)
d. 10 mg/kg (T) + 1.5 mg/kg (X)
e. 20 mg/kg (K) + 0.2 mg/kg (A)
Fox, red a. 4 mg/kg (K) + 0.02 mg/kg (M) + 0.04 mg/kg (B)
b. 20 mg/kg (K) + 1 mg/kg (X)
c. 25 mg/kg (K) + 1 mg/kg (midazolam)
d. 10 mg/kg (T)
Marten a. 10 mg/kg (K) + 0.02 mg/kg (M)
Mink a. 15 mg/kg (T)
b. 5 mg/kg (K) + 0.1 mg/kg (M)
c. 40 mg/kg (K) + 1 mg/kg (X)
Mountain lion a. 2 mg/kg (K) + 0.075 mg/kg (M)
b. 4-6 mg/kg (K) + 0.03-0.04 mg/kg (M)
c. 6-11 mg/kg (T)
d. 10 mg/kg (K) + 2 mg/kg (X)
e. 4-6 mg/kg (K) + 1-2 mg/kg (X)
Otter, river a. 2.5 mg/kg (K) + 0.025-0.050 mg/kg (M)
b. 20 mg/kg (K) + 0.3 mg/kg (Midazolam)
Raccoon a. 2.5 mg/kg (K) + 0.075 mg/kg (M) (Everson, pers. com.)
b. 20 mg/kg (K) + 4 mg/kg (X)
c. 12 mg/kg (T)
d. 3 mg/kg (T) + 2 mg/kg (X)
Skunk, striped a. 10 mg/kg (T)
b. 15 mg/kg (K) + 0.2 mg/kg (A)
Wolf, grey a. 3-4 mg/kg (K) + 0.06-0.08 mg/kg (M)
b. 4-10 mg/kg (K) + 1-3 mg/kg (X)
c. 10 mg/kg (T) + 1.5 mg/kg (X)
Wolverine a. 5-8 mg/kg (K) + 0.1 mg/kg (M)
b. 20 mg/kg (K) + 0.2 mg/kg (A)
Most darts used in remote delivery systems consist of five main parts: the needle, the syringe barrel, a separating plunger, the injection delivery media, and the tailpiece. Each manufacturer and system has its own material and design for each of these dart components.
Needles come in a variety of lengths, gauges, and designs. Lengths and gauges vary with the animal to be darted, depending on its size and skin thickness. Some needles have barbs or collars that help the dart stay in the animal to prevent premature bouncing out or loss of the dart.
Needles, other than those used in syringes with internal charges, generally consist of a relatively blunted, sealed tip with ejection ports drilled into its sides. These ports are covered with a plug or sleeve during preparation and firing of the dart. On impact, the sleeve is forced back on the needle and the contents of the dart are forcibly injected into the animal because of the high pressure within the syringe.
The injection delivery system is an integral component of the dart and must be capable of producing sufficient pressure on the plunger to deliver varying amounts of liquid drug into the animal in an extremely short period of time. Some of the methods that have been used, or are currently used, include compressed air, butane, gun powder charges, and springs built into the syringe barrel.
Remote Drug Delivery Systems
The development of remote delivery systems (RDS) are a fairly recent development and is considered one of the major advances in zoo and wildlife medicine in the last 20 years. The RDS allows the administration of immobilizing agents, vaccines, etc., without the need for physical restraint and is, thus, generally safer and less stressful for both animals and people. Historically, however, remote drug delivery dates to pre-Columbian times when aboriginal natives of Africa and South America dipped arrows, spears, and blow darts in preparations of muscle-paralyzing drugs derived from plant and animal sources. Darts, propelled by a variety of means, are the usual means of delivering drugs remotely to animals.
The use of RDS has a number of advantages over traditional approaches of chemically immobilizing animals. Firstly, the specific animal can be targeted, as opposed to indiscriminate baiting or trapping techniques. Secondly, drugs can be administered on a body weight basis, permitting fairly precise doses to be administered under field conditions. Third, most of the RDS are capable of delivering a wide range of volumes. And, fourth, some RDS can both treat and mark individual animals. For example, some projectiles can be equipped with marking dyes and others can deliver electronic identification devices along with the drug.
It should be recognized, however, that most RDS are inherently complex, some are loud (rendering subsequent shots at other animals difficult or impossible), and that adequate training and experience is required to ensure safe and optimum performance of the system. Also, most RDS using projectiles are not terribly accurate and the preferred target area on smaller animals may be quite small. Therefore, the shot could either be misplaced causing injury or death, or it could miss the animal entirely. Even the impact energy or penetration depth of correctly placed darts could be injurious or lethal to smaller animals.
A pole syringe is a syringe on the end of a pole. This equipment is generally inexpensive, quiet, and is most useful in administering drugs to trapped or caged animals, or for giving additional drugs to animals not completely immobilized but approachable. Pole syringes are usually limited to administering 10 ml of drug because the animal will usually not hold still long enough to receive larger volumes.
Blow Pipes (Blow Guns)
Blow pipes operate by propelling a dart through a pipe or tube by rapid expulsion of one's breath. Advantages of the blow pipes are that it is a silent projection and result in only minimal trauma upon impact. It is adaptable for use on small animals. Disadvantages of the blow pipes are its length, short range, and that it generally requires a lot of experience or skill to be fully successful.
The most widely used and versatile of the RDS are dart-shooting guns. These guns propel darts by either gas generated from a .22 caliber blank cartridge, compressed CO2, or compressed atmospheric air. The ranges using selected types of this equipment can be up to 50 m or more, although it is more commonly used at much shorter distances. In most zoo and private practice settings, dart guns using compressed CO2 or compressed air are preferred.
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