Aspiration in Elk During Capture and Chemical Immobilization

The elk (Cervus elaphus canadensis), also called wapiti, is the largest subspecies of red deer (Cervus elaphus) found in North America and in the high mountains of Central Asia. They are also called wapiti, a Native American (Shawnee) word that means white or light-colored deer. Elk are members of the deer family, (Cervidae, order Artiodactyla). Recent genetic studies suggest that this animal may indeed be three species: the European red deer, the Tibetan–West Chinese red deer, and the elk.¹

The North American elk (Cervus elaphus) is further split by some biologists into six subspecies, two of which are considered extinct:

• Rocky Mountain (Rocky Mountain West) – these elk have the largest antlers of all subspecies
• Roosevelt’s (Coastal Pacific Northwest) – these are the largest in body size of all subspecies
• Tule (Central California) – these have the smallest body size of all subspecies
• Manitoban (northern Great Plains)
• Merriam’s (Southwest and Mexico) – Extinct
• Eastern (east of the Mississippi) – Extinct²

Elk were once found throughout much of the Northern Hemisphere, from Europe through northern Africa, Asia and North America. It is believed that extensive hunting and habitat destruction have limited them to a portion of their former range. Today, large populations in North America are found only in the western United States from Canada through the Eastern Rockies to New Mexico, and in a small region of the northern lower peninsula of Michigan. Elk were reestablished in the eastern United States, including Michigan, with three transplantations throughout the 20^th-Century.

Exceeded in size only by the moose (the largest of the cervids), adult male elk average around 840 pounds. The body mass of elk populations varies considerably within and between populations and increases from south to north. The largest bulls can exceed 1,100 pounds in weight. Compared to other cervids, female elk are more similar to bulls in external appearance and body mass. During winter, both have well-developed, dark neck manes. Elk range in color from dark brown in winter to tan in summer and have a characteristic lighter-colored rump. The head, neck, belly, and legs are darker than both the back and sides. Elk have a long head with large ears and widely branching antlers as long as 3 to 5 feet from tip to tip; these are only found on the bucks.

Elk are browsers who feed on grasses, sedges, and forbs in summer, and woody growth during the winter months. They appear to be especially fond of dandelions, aster, hawkweed, violets, clover, and the occasional mushroom. Since elk are ruminants, they regurgitate their food and remasticate to aid in digestion.^1,2

Both males and females are sexually mature at sixteen months, although young males do not usually mate until they are a few year old and can compete with more mature males. Gestation generally lasts between 240 and 262 days and results in a single birth. Shortly before the fall rut (late September and early October), male elk lose the velvet on their antlers and begin to compete for access to females. Fights between dominant males and intruders can be intense and result in injury, exhaustion, or death.

Elk are social animals, and often live in herds with as many as 400 individuals. The herds are matriarchal and are typically dominated by a single cow. These herds will migrate elevationally, occupying higher elevations during the summer and lower elevations during winter. As the fall mating season approachs, bulls form harems. In the spring, the sexes separate with females leaving to give birth, while bulls form their own separate summer herds.

Elk, Chemical Immobilization and Aspiration

Researchers, wildlife managers and deer farmers are often called upon to perform routine procedures on elk, or to administer medical treatment. In nearly all cases, this requires the use of sedative and/or anesthetic drugs. Vomiting is one of the more common post-sedation and post-anesthesia complications in both domestic and exotic animals. Vomiting that occurs during a procedure can pose grave risks due to anesthetic aspiration.

Aspiration is described as when a foreign substance enters the airway or lungs; this can apply to food, liquid, or other materials. Aspiration can give rise to serious health problems, such as aspiration pneumonia. Aspiration can occur when a human or animal has difficulty swallowing normally (which is referred to as dysphagia), but in some instances it can be brought on during or after anesthetic events, as indicated above.

Aspiration pneumonia is a condition that is characterized by inflammation and necrosis of lung tissue due to the inhalation of foreign material. The most common material aspirated in large animals is a large volume of liquid, due to weakness from a pathological condition, during oral administration of fluids or as a result of chemical immobilization. The severity of the inflammatory response depend on the type and volume of material aspirated and the distribution of aspirated material in the lungs.

In severe cases in which large volumes of liquid have been aspirated, death can occur swiftly. Other cases will present later with clinical signs consistent with cranioventral bronchopneumonia.³ Cervids such as elk that are affected with chronic wasting disease may also develop aspiration pneumonia due to central nervous system dysfunction.³

Elk and Chemical Immobilization

At the beginning of the last century, the primary method used for the capture of many large wild animals such as elk was to chase them to the point of near-exhaustion—a labor-intensive method that was impractical and fairly inhumane.³ With the pioneering work on the chemical immobilization of wildlife that took place from the 1950s on, chemical immobilization techniques have improved greatly through the development of increasingly efficacious drugs and equipment.

The field immobilization of wild animals with chemical agents is a method of rendering them tractable while using minimal restraint. Here, the research or wildlife management objectives are usually to measure or weigh the live elk, collection of blood or tissue for research or diagnostics, marking an individual or fitting a radio transmitter for studying migration patterns, range requirements and behavior patterns or the translocation of animals for a variety of reasons.^3,4These requirements have resulted in the development of increasingly safer methods of chemical immobilization.

Each cervid species have their own anesthesia recommendations with intra-species variations of dosages because of diverse individual responses to anesthetic agents.^3,4 These variations are of course factors in the risk of vomiting and anesthetic aspiration, and attendant factors (e.g., stress, venue, individual animal and field conditions) must also be taken into account.

Chemical Immobilization: Practices and Procedures

The utilization of basic veterinary knowledge can make a substantial contribution to animal safety during capture and chemical immobilization. Teams that are qualified to handle wild mammals should evidence the appropriate expertise in wildlife anesthesia and should include an attending veterinarian when appropriate. A successful chemical restraint exercise is not complete until the subject is fully recovered and (in the case of field operations) back in its environment. The application of appropriate pharmacological principles with an emphasis on drug reversibility will minimize the chances that the animal will be at a competitive disadvantage or inordinately disoriented following its release.^3-5

Hyperthermia and capture myopathy are commonly-encountered problems with elk anesthesia. Intubation has been widely recommended for any anesthetized elk that needs to be transported or anesthetized for greater than one hour. Unfortunately, the literature strongly suggests that intubation can increase the risk of vomiting during an anesthetic event.^1,4

Anesthetic Aspiration in Elk

Until formulated drugs (e.g., combinations of α2-agonists such as medetomidine, detomidine, xylazine and their reversal agents) came into use in recent years, opioids were the mainstay of large animal anesthesia in wildlife and captive care.⁴As with other mammals, problems encountered with certain opioids (such as etorphine or carfentanil, which have been widely used in wildlife chemical immobilization) in elk are known to include vomiting or passive regurgitation that can lead to fatal aspiration pneumonia.

Periprocedural fasting (fasting prior to an anesthetic event) has historically been recommended by clinicians because of the suspected risk of aspiration. Unfortunately, periprocedural fasting is very often impossible under field conditions. Additionally, much of the data on anesthetic aspiration relates to humans receiving general anesthesia, however, elk and other mammals have been known to aspirate during procedures while under sedation and where no intubation or general anesthesia were employed.

For the prevention of anesthetic aspiration, the literature recommends histamine (H2) antagonists such as cimetidine, famotidine, nizatidine, and ranitidine and proton pump inhibitors (PPIs) such as dexlansoprazole, esomeprazole, lansoprazole, omeprazole, pantoprazole, and rabeprazole, which have been shown to be effective in increasing the pH and reduce the volume of gastric contents.² Prokinetics (e.g., domperidone, metoclopramide, erythromycin and renzapride) promote gastric emptying and are also believed to reduce the risk of aspiration.⁴

In the event that aspiration occurs during a procedure in an elk, the first step in managing the situation is the recognition of gastric content in the oropharynx or the airways.^4-7 The elk should be immediately positioned with the head down and rotated laterally if possible. Orotracheal and endotracheal suctioning is indicated, either before or after orotracheal intubation, depending on whether regurgitation continues and if the airway is visible. It is recommended that the airway be secured as rapidly as possible to prevent further contamination and to facilitate airway clearance.² Flexible bronchoscopy is an important adjunct to orotracheal and endotracheal suctioning. Rigid bronchoscopy may be required if particulate matter is present in the elk’s airway.^2,5

¹britannica.com.
²rmef.org.
³Merck Veterinary Manual.
⁴ Shaikh, Safiya Imtiaz et al. Postoperative nausea and vomiting: A simple yet complex problem. Anesthesia, essays and researches vol. 10, 3 (2016).
⁵Nason, K. Acute Intraoperative Pulmonary Aspiration. Thoracic surgery clinics vol. 25,3 (2015): 301-7.
⁶Lance, W. Exotic Hoof Stock Anesthesia and Analgesia: Best Practices. In: Proceedings, NAVC Conference 2008, pp. 1914-15.
⁷Kluger M.T., et. al. Crisis management during anaesthesia: regurgitation, vomiting, and aspiration. Quality & safety in health care. 2005;14(3): e4.