Nigel Caulkett1 and Jon M. Arnemo2 1 Faculty of Veterinary Medicine, University of Calgary, Calgary, Alberta, Canada 2 Inland Norway University of Applied Sciences, Campus Evenstad, Norway and Swedish University of Agricultural Sciences, Umeå, Sweden Chemical immobilization of free‐ranging wildlife can be challenging. The nature of the procedure dictates that veterinarians must alter or even ignore many of the principles that underlie good anesthetic practice in other settings. It is generally not possible to access the patients for a preanesthetic physical examination or laboratory work. Physical status of the patients cannot be accurately assessed, and animals are usually assumed to be healthy. Even if physical status and anesthetic risk could be determined, generally only a few effective protocols are available [1–3]. Induction of anesthesia in wildlife can be extremely stressful, and stress‐related conditions or injuries can result. Free‐ranging wildlife are subject to environmental hazards and are often at risk for hypothermia or hyperthermia. Appropriate supportive care, such as controlled ventilation, intravenous (IV) fluid therapy, or inotropic support, is often not possible in field situations. Veterinarians may be required to work on species for which there is very little information about their physiology or pharmacologic response to drugs. Extrapolation between similar species may be required but can result in unexpected complications. Issues of human safety must also be considered. Given the challenges that are encountered during wildlife capture, it is not surprising that morbidity and mortality of animals can be high and injury to people engaged in the capturing procedure more common. This chapter focuses on the major principles of wildlife capture and handling. It is beyond the scope of a single chapter to provide complete dose recommendations for terrestrial mammals. The Handbook of Wildlife Chemical Immobilization [1] and Zoo Animal and Wildlife Immobilization and Anesthesia [3] can be used to find detailed drug and dose information for individual species. Wildlife capture is often required for both research and management purposes. Capture events should be carefully planned because complications can often be anticipated and responses better prepared. Capture sites may be chosen based on their suitability and the timing chosen in an appropriate season of the year when environmental hazards are minimized. For example, ungulates may be captured in late winter or spring to decrease the risk of hyperthermia and enable tracking in snow or visualization of animals in deciduous forest. Often individual animals do not have to be targeted in management projects, and the capture team can choose any animal in a relatively safe capture environment. It is generally possible to adhere to strict pursuit time limits. If it is not absolutely necessary to capture the target animal, pursuit can be terminated to decrease the risk of stress‐related disease, such as exertional myopathy. Current literature and experts in the field can be consulted prior to the capture event to ensure that the most suitable technique is used. It may also be possible to close areas to the public where wildlife are captured. Finally, appropriate equipment for monitoring and supportive care should be obtained and taken into the field when possible. Weather conditions may dictate whether wildlife capture is possible. Safe helicopter flight is generally not possible in high winds or foggy conditions. Snow and rain can lead to hypothermia, particularly if wind is also present to enhance convective heat loss. Smaller mammals may be particularly prone to hypothermia. Hyperthermia is a serious complication that can be difficult to treat in field situations. Several of the drug regimens used for wildlife capture can impede thermoregulation and lead to hypothermia or hyperthermia [3,4]. When possible, captures should be planned for the cooler hours of the day during summer months. In remote locations, sudden changes in weather may also be a hazard to personnel. It is important to keep track of current and forecasted conditions during planned events. Capture for management purposes may occur at any time. Provisions should be made to prevent heat loss and actively cool animals, if required. Logistics generally dictate what type of equipment can be carried in a field situation. It is often difficult to carry all but the most necessary pieces. Fortunately, there are compact ambulatory monitors suitable for field use. Equipment should withstand field use and be as lightweight and compact as possible. Hypoxemia is a common complication of wildlife anesthesia, particularly with ruminants [3–7]. Oxygen is fundamental supportive care during field anesthesia. Aluminum E and D cylinders, combined with a sturdy regulator and flowmeter, are ideal for field use (Fig. 55.1). Oxygen concentrators may provide an attractive alternative to compressed oxygen cylinders as they do not require refilling and eliminate many of the risks of working with compressed gas [8] (Fig. 55.2). Often, nasal insufflation of oxygen is adequate to treat hypoxemia. However, equipment for airway management and ventilatory support is recommended for many scenarios. It is difficult to carry a wide range of emergency drugs or an adequate volume of crystalloid fluids to treat shock, but a basic emergency kit containing epinephrine, atropine, lidocaine, and reversal agents should always be carried. Ruminants are predisposed to ruminal tympany, so a suitably sized tube to desufflate the rumen should be available. Equipment should also be carried to treat lacerations and other incidental injuries during capture. An animal may be captured initially by physical or chemical means. The choice of capture technique depends on the species, the terrain, the facilities, and the experience of the capture crew. Many species of ungulates can be effectively captured and handled by experienced teams with physical techniques such as net guns [4,9]. Physical restraint can be very stressful for wild animals, but sedatives or anesthetics can be used to decrease the stress of handling once animals have been netted [4,9]. Figure 55.1 Oxygen delivery via intranasal supplementation in a brown bear Figure 55.2 Portable oxygen concentrators can be used instead of compressed gas cylinders in field situations. They have some advantages for use in remote locations. Net gunning can cause high rates of mortality if it is performed by inexperienced personnel. The risk to capture personnel can also be high. During a 10‐year period in New Zealand, there were 127 helicopter crashes and 25 human fatalities during net gun capture of red deer [10]. These figures stress the need for experienced pilots and capture personnel. The use of physical restraint will confine an animal’s movements during the induction of anesthesia, which may be a positive when terrain dictates a limited escape route. Physical restraint can induce greater stress than chemical restraint [11]. Generally, physical restraint should be of brief duration to avoid stress‐related complications. A number of hazards can be encountered during anesthesia of free‐ranging wildlife. It is important to perform a risk assessment prior to embarking on a project to identify and minimize the risks. The target species can pose a risk to personnel. In addition to the obvious risks of serious personnel injury from carnivores, ungulates can also act aggressively. Many deer species undergo a period of rut during the breeding season, during which stags are often more aggressive. Injury may also occur from flailing limbs or heads in lightly anesthetized animals. It is important to know how a species will act in a stressful situation, and to leave an exit for the animal (and for the capture personnel) if things do not go according to plan. The best way to avoid injury is to work with people who are familiar with animal behavior. Many species carry zoonotic disease, so capture personnel should be aware of this potential and handle the animal appropriately. During capture, the focus tends to be on the captured animal. It is always important to be aware of the surrounding environment because other animals may approach. This is particularly important with social carnivores, such as lions. It is also important with bears, particularly if members of a family group are captured. In these situations, an armed lookout should be posted to protect the capture team. A firearm backup is important with more dangerous species. The primary person performing the backup should be trained and experienced in the use of firearms, and an appropriate firearm should be used. If firearms are commonly used, all members of the capture team should receive firearm safety training. Similar training is advisable for people using dart rifles or pistols. Pepper spray may be considered as a non‐lethal alternative to firearms. Recent studies have demonstrated that pepper spray is as effective as a firearm in many situations [12] (Fig. 55.3). The environment itself can be hazardous since capture may occur in remote and rugged locations. In these situations, personnel must be prepared to look after themselves if they cannot return to a base area. A method of communication with rescue services should be established. In some environments, weather can change rapidly and often dictates whether capture should take place. There are hazards specific to the terrain and region; for instance, capture personnel should receive avalanche training before working in mountainous regions during winter when there is an avalanche risk. It is important to anticipate risks in any environment. Figure 55.3 Pepper spray has been proven to effectively deter bear attacks. It is a potential less‐lethal option for personal defense against dangerous wildlife. Pharmaceuticals used for wildlife immobilization and anesthesia can present a serious human health hazard because of their high potency and concentrated formulations. Handling of potent opioids, such as etorphine and thiafentanil, carries the risk of lethal toxicity in people [1,13]. These drugs must be handled with extreme caution. Protective clothing, such as disposable gloves and face shields, should be used to prevent skin or mucous membrane contact. A pharmacologic antagonist should be available to treat human exposure. Potent opioids receive a great deal of attention, but any concentrated sedative or anesthetic must also be handled carefully. Medetomidine can be formulated at a concentration of 40 mg/mL for use in wildlife. Dexmedetomidine, which is used at a dose of 0.5–1 μg/kg IV in people [14], is twice as potent as medetomidine [15]. This dose is equivalent to 1–2 μg of medetomidine per 1 kg of body weight or a total of 75–150 μg in a 75 kg person. The high end of this dose range is equivalent to a 0.0038 mL volume of concentrated medetomidine. Obviously, there is serious risk of toxicity from exposure to a very low volume of a 40 mg/mL medetomidine formulation. Tiletamine–zolazepam is another immobilizing mixture that can be delivered in a concentrated form and therefore must be handled with caution. Everyone working on a capture team should be trained in first aid, and equipment should be available to provide respiratory and airway support. Wildlife anesthesia should never be performed by a single person. At least two trained people should be present whenever potent drugs are handled. Loading and charging of darts is a time of high risk for exposure to drugs. Darts should be charged under a protective cover to decrease the risk of accidental drug exposure. Antagonists, such as naloxone or naltrexone, should always be immediately available in case of inadvertent human exposure. Dart delivery equipment should be handled with care and only by trained individuals. Darts have the potential to induce significant tissue injury and death. Firearm safety rules apply to darting equipment, and individuals handling this equipment should be appropriately trained. Helicopters present a significant hazard. Wildlife capture requires a very skilled pilot to decrease the risk of injury to the target animal and the capture personnel. Anyone working around a helicopter must receive training in helicopter safety [16]. Prior to any capture, it is advisable to meet with local medical personnel and discuss an evacuation and treatment plan in case of inadvertent human exposure. A meeting of this nature will familiarize physicians and emergency medical services personnel with the drugs that are being used and the potential treatments. In the event of an emergency, this can save valuable time and someone’s life. Wildlife capture often requires drug delivery over relatively long distances. Generally, it is difficult to deliver drugs accurately at distances greater than 40 m, but there have been major advances in the equipment available for remote drug delivery. It is important to realize that these systems have the potential to produce serious injury or death if they are used inappropriately. The major sources of injury arise from dart impact trauma, high‐velocity injection of dart contents, and inaccurate dart placement. Dart impact trauma results from dispersion of energy on dart impact. Impact kinetic energy (KE) is represented by the following equation: where M is mass (kg), and V is velocity (m/s) [1]. High velocity is the major factor that will cause trauma. A good general rule is to use the lowest velocity that will provide an accurate trajectory at a given distance. Practice with a darting system at a variety of distances is vital to minimize velocity. The other major factor is the mass of the dart. Darts with a lower mass will have less impact energy at a given velocity. This should be a consideration in the choice of a darting system, particularly when dealing with smaller animals that are more prone to trauma. Inaccurate dart placement can cause injury. This most frequently occurs if the dart penetrates the abdomen, thorax, or other vital structures of the head and neck. The major factors that can lead to inaccurate dart placement include lack of practice with the darting system, an attempt to place a dart over an excessive range, inherent inaccuracy of the darting system, and wind, including down‐wash from the helicopter rotor during aerial darting. The final source of injury is related to high‐velocity injection of dart contents. Systems that expel drug via an explosive charge can disrupt tissue and produce trauma. These systems should only be used on large, well‐muscled animals (Fig. 55.4). Injection volume should be minimized to decrease the degree of tissue trauma. When possible, the use of darts that deliver their contents via compressed air should be considered. The choice of system depends on the range required, the dart size, and individual characteristics of the target animal. A more complete review and manufacturer information can be found elsewhere [1,3,16]. Darts must deliver their contents into a muscle group on impact for induction to be rapid and smooth. Choice of a system will depend on the situation and the size of the animal. Figure 55.4 Dart‐induced trauma in a lynx; note the extensive subcutaneous hemorrhage at the dart site. Darts that use an explosive discharge mechanism can produce considerable muscle trauma and should be reserved for large, well‐muscled animals. These darts have an aluminum or plastic body into which a small explosive cap is placed between the plunger and the tail. Upon impact, a firing pin inside the cap is forced forward, against the resistance of a spring, detonating the charge. The expanding gas pushes the plunger forward and the drug is expelled through the needle. The short duration of injection (e.g., 0.001 s) can result in high injectate velocity, which may cause tissue damage [16]. The explosive caps are very sensitive to moisture and must be kept dry. When placed in the dart, the cap must have its open end against the tail. If it is turned around, detonation and expulsion of the drug will occur at the moment the projector is fired. If reusable darts are used, the fit of the dart should be tested by inserting the dart in the muzzle. If it slides in and out with ease, the dart is not significantly deformed, and it can be reloaded. If the dart jams in the muzzle, the dart should not be reused. With repeated use, the dart body may expand to the point where the aluminum is weakened by the threads cut into it. This is caused by the high pressure created in the dart when gases from the explosive charge push the plunger forward. All of the darts with explosive discharge mechanisms inject through the tip of the needle. The needle should be barbed so that it stays in the animal during injection. If there is no barb or if the barb is removed, the force of the frontal expulsion of the drug is often sufficiently powerful to drive the dart out of the animal, resulting in only partial injection. These darts consist of an aluminum or plastic body into which compressed air is introduced through a one‐way valve in the tail piece. At impact, a silicone seal is displaced, exposing a port in the side of the needle. The plunger is pushed forward by air pressure, and the drug is expelled through the open port. Depending on the type and usage, plastic darts can be used repeatedly, but will eventually begin to leak or lose air pressure. In extreme cold, the drug may freeze inside the dart; therefore, darts should be kept warm in a secure container placed in an inside pocket or in a heated vehicle or helicopter. Wildlife immobilization has progressed a great deal in recent years. A variety of drugs are available to facilitate capture and handling, and new techniques continue to develop. An ideal drug or combination thereof would possess the following properties. A rapid effect is one of the most important attributes required in a capture drug. The induction period is a hazardous time. Handlers and bystanders may be at risk of injury if induction is prolonged. Rapid onset will limit the risks of trauma, hyperthermia, and possibly capture myopathy. Ideally, the animal should be immobilized within 1–5 min after injection. Practically, most current combinations can take longer than 5 min to induce anesthesia. Drugs used for wildlife capture must have a high margin of safety. It is difficult to transport supportive equipment into the field so capture drugs should produce minimal cardiopulmonary depression. Wild animals are not weighed prior to capture, and it is common to overestimate weight. Capture drugs must have high safety margins or therapeutic indices to decrease the risk of mortality from overdose. Precautions must always be taken to avoid human exposure to drugs. Ideally, drugs should be relatively safe to handle, with minimum risks of intoxication if the handler contacts the drug. The ability to antagonize the effects of any drug is also desirable in field situations. Capture drugs should be potent and concentrated enough to facilitate delivery at low volumes, ideally less than 3 mL. This decreases the risk of injection trauma from high‐velocity injection and facilitates accurate dart flight. The animal should rapidly lose motor function and ideally become unconscious and unaware of its surroundings. Free‐ranging wildlife often live in an environment full of potential hazards, so they must be cared for until they are fully awake. A pharmacologic antagonist will speed recovery and is also of value in emergency situations. Because it can be difficult to provide supportive care, complications such as hyperthermia can quickly become life‐threatening and drug antagonism may be the only viable option in managing unexpected complications. Wildlife managers often deal with a variety of species. Thus, an ideal drug or combinations thereof should have predictable effects in a wide range of species. The use of a single protocol in a variety of species limits the variety of drugs required to be kept on hand and increases familiarity with the pharmacodynamics of the drug or drug combination. Wildlife capture may need to be performed in a wide range of ambient temperatures. Ideally, drugs should remain stable, in solution, over a wide range of temperatures. It has become more common to perform potentially painful procedures during wildlife handling. These procedures can include ear tagging, tooth removal, biopsies, and even surgery for abdominal or subcutaneous implant placement. These procedures dictate that appropriate intraoperative and postoperative analgesia be provided. A variety of opioids have been used for wildlife capture. Opioids can be used in a wide range of species but are particularly effective in ungulates. The opioids produce analgesia and sedation but lack muscle‐relaxant properties. They have been used alone or, more often, with a neuroleptic agent, the inclusion of which potentiates the opioid’s sedative effects, resulting in a smoother induction and decreased muscle rigidity. Opioids are predictable, act relatively fast, and can be reversed with the administration of a suitable antagonist. If not reversed, the duration of immobilization is lengthy, often several hours, during which the animal is at risk from opioid‐induced respiratory depression, thermoregulatory problems, and environmental hazards. Underdosing of opioids can result in a prolonged induction time characterized by central nervous system (CNS) excitation, which can cause hyperthermia, exhaustion, lost animals, and/or death of the animal. The adverse effects of opioid‐induced immobilization include: Potent opioids, such as etorphine and thiafentanil, are several thousand times more potent than morphine in humans and must be handled carefully to avoid accidental exposure [1–3,13]. Carfentanil was used for capture of free‐ranging ungulates and some large carnivores beginning in the early 1980s but is no longer available due to human drug abuse. Etorphine has been used successfully in many species, but has been particularly effective in ungulates, rhinoceroses, and elephants. Etorphine can be used alone or in combination with a suitable neuroleptic or sedative agent. Induction course and immobilization duration are dose dependent. Underdosing can cause excitation with its associated problems. At optimum doses, the first effects may be observed 3–8 min after intramuscular (IM) injection. The full effect may be reached in 20–30 min. Recovery is slow (up to 7 or 8 h) if no antagonist is given. When an antagonist is administered, animals will recover in 1–3 min after IV injection and in 5–10 min following IM injection. The most serious adverse effect is respiratory depression. For that reason, an animal should not be kept immobilized longer than necessary, and drug effect should be reversed as soon as possible. Other side effects are often dose or species dependent and may include excitement, muscle tremors, convulsions, regurgitation, bloat, bradycardia, tachycardia, hypertension, hyperthermia, and resedation. Thiafentanil has some potential advantages over etorphine, such as rapid induction, greater therapeutic index, shorter half‐life, lower incidence of resedation, and less respiratory and cardiac depression [19]. Thiafentanil is commercially available only in South Africa and the United States, but its use has been described in a variety of species [1,3,19]. It has been used alone or in combination with an α2‐adrenergic receptor agonist. Reports have detailed the use of thiafentanil combined with medetomidine and ketamine [20]. This is a promising drug combination that appears to be efficacious and have fewer side effects than high‐dose single opioid immobilization [3,20].
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Comparative Immobilization and Anesthesia – Free‐Ranging Terrestrial Mammals
Introduction
Field anesthesia
General considerations
Weather
Equipment
Capture technique
Hazards
Remote drug delivery equipment
Darts
Explosive discharge mechanisms
Air‐activated mechanisms
Pharmacology
Ideal drug combination for wildlife capture
Rapid onset of activity
High margin of safety
Handler safety
Small volume of delivery
Level of central nervous system effect
Ability to antagonize immobilization
Species versatility
Drug stability
Analgesia
Opioids
Carfentanil
Etorphine
Thiafentanil
Butorphanol
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