Vomiting in Elk During Capture and Chemical Immobilization

A very common post-sedation and post-anesthesia complications that can occur in both domestic and exotic animals is emesis (vomiting). If this occurs once or twice after a surgical procedure can be considered normal however, if the vomiting continues, it can be a sign of an emerging complication.

Vomiting that occurs during a surgical procedure is a far more serious complication, as this can pose grave risks due to anesthetic aspiration. Anyone who has had inpatient surgery will be familiar with the admonition to abstain from food for a period of time prior to surgery. This is because anesthesia and sedation carries the risk of vomiting during and after a surgical procedure.

Elk Background and Biology

The elk (Cervus canadensis) is the second-largest wild cervid after the moose. Also called wapiti, these animals are often confused with the moose, not only because they look somewhat similar, but because the moose is called “elk” in parts of Eurasia. The Roosevelt’s elk, Tule elk, Rocky Mountain elk, and the Manitoban elk are four of the six North American subspecies that still exist in the wild, while the Eastern and the Merriam’s Easter elk subspecies are extinct.¹

Elk are related to an ancient breed of red deer in Asia, and are still called “red deer” in regions of Asia. They came to North America across the Bering Strait about 120,000 years ago, as did the caribou and other hoofstock species. Between 5,000 to 10,000 years ago, they advanced as far as Colorado, and there may have been as many as 10 million elk in North America when European settlement began.²

Male elk are called bulls and female elk are called cows. They are some of the most social of the cervids, with group sizes during the summer reaching up to 400 individuals. Adult males and females segregate themselves into different herds during most of the year, with female herds being larger and males creating small groups or being solitary.¹ Younger bulls live in female herds or in groups of older, less aggressive bulls.

Male elk have antlers that are comprised of bone and grow about an inch a day. These can grow to over 20 inches in length. As they grow, a layer of velvet covers them, which is shed in the spring after the antlers are done developing. The North American and Siberian elk have the largest antlers, which can weigh up to 40lbs.^1,2

Vomiting and Anesthetic Aspiration in Elk

Anesthetic aspiration involves an elk vomiting food from their stomach during a surgical procedure which subsequently infiltrates into the lungs. This can lead to aspiration pneumonia. While modern protocols for anesthesia and sedation in wildlife are generally safe, respiratory complications such as anesthesia-related aspiration and pneumonia can be fatal.

Anesthesia-related aspiration involves the entry of liquid or solid material into the trachea and lungs. As indicated above, this occurs when patients without sufficient laryngeal protective reflexes (as a result of sedation or anesthetic agents) regurgitate gastric contents. “Pulmonary syndromes of differing severity can result, ranging from mild symptoms such as hypoxia to complete respiratory failure and acute respiratory distress syndrome (ARDS).”³ In extreme circumstances, cardiopulmonary collapse and death can occur. The related pulmonary syndromes can include acid-associated pneumonitis, particle-associated aspiration (airway obstruction) or bacterial infection. Which of these develops depends upon the composition and volume of the aspirate.

Aspiration during a surgical procedure (acute intraoperative aspiration) is a potentially fatal complication with significant associated morbidity. Animals undergoing thoracic surgery are at increased risk for anesthesia-related aspiration, largely due to the predisposing conditions associated with this complication. Awareness of the risk factors, predisposing conditions, precautions to decrease risk and immediate management options by the veterinarian is imperative to reducing risk and optimizing outcomes associated with this complication.^3,4

In the case of chemically immobilized wildlife, it is often impossible to perform the presurgical assessments that are routine and even required for veterinary and human patients. Therefore, attending wildlife and research veterinarians must be prepared for the possibility of anesthetic aspiration in elk.

Improved Care and Risk Minimization

The care of non-domestic hoofstock has become commonplace due to the integration of veterinary medicine in wildlife management programs, zoological collections, exotic animal ranching expansions and the private collection of wildlife species.³ As a result, research and wildlife veterinarians must have the requisite knowledge associated with safely anesthetizing and handling these animals.

The sedation and anesthesia of elk requires the knowledge the pharmacology of the drugs being used, as well as the wide variation in dose response among sub-species of these animals. A challenge which impacts potential complications such as anesthetic aspiration is correlating the available pharmaceutical tools with the environment and conditions, as well as the procedures and events preceding, during, and following the anesthetic event.^4,5 For example, an anesthesia protocol that’s practical in a fenced captive environment may not be appropriate in a free-ranging field environment or large enclosure.

Today, the quality of sedation, anesthesia and analgesia achievable in elk and other wildlife species has been made possible through the availability of new, receptor-specific and highly potent agonist-reversible pharmaceuticals and the improved knowledge of CNS receptors.

Preventing and Managing Anesthetic Aspiration in Elk

For the prevention of anesthetic aspiration, histamine (H2) antagonists such as cimetidine, famotidine, nizatidine, and ranitidine and proton pump inhibitors (PPIs) such as dexlansoprazole, esomeprazole, lansoprazole, omeprazole, pantoprazole, and rabeprazole have been shown to be effective in increasing the pH and reduce the volume of gastric contents.¹ Additionally, prokinetics (e.g., domperidone, metoclopramide, erythromycin and renzapride) promote gastric emptying and are believed to reduce the risk of aspiration.⁴

Should intraoperative aspiration occur in an elk, the first step in successful management is the immediate recognition of gastric content in the oropharynx or the airways.⁵ The animal 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 elk’s airway be secured as rapidly as possible to prevent further contamination and to facilitate airway clearance.⁵ Flexible bronchoscopy is an important adjunct to orotracheal and endotracheal suctioning, and having a flexible bronchoscope at the ready if possible is a sound prophylactic measure. If particulate matter is present in the airway, rigid bronchoscopy may be required.^3,5

¹britannica.com.
²rmef.org.
³Nason, K. Acute Intraoperative Pulmonary Aspiration. Thoracic surgery clinics vol. 25,3 (2015): 301-7.
⁴Lance, W. Exotic Hoof Stock Anesthesia and Analgesia: Best Practices. In: Proceedings, NAVC Conference 2008, pp. 1914-15.
⁵Kluger M.T., et. al. Crisis management during anaesthesia: regurgitation, vomiting, and aspiration. Quality & safety in health care. 2005;14(3): e4.