Vomiting in Deer During Capture and Chemical Immobilization

One of the more common post-sedation and post-anesthesia complications 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.

Vomiting and Anesthetic Aspiration

Anesthetic aspiration involves a deer 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).”¹ 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.¹

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 deer.

Procedures, Improvements and Risk

The medical 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.² 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 deer 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.^1,2 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 deer 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.

Deer and Chemical Immobilization

Deer include any of over 40 species of hoofed ruminants belonging to the order Artiodactyla, which includes numerous species, among them pigs, camelids, deer, giraffe, antelopes, sheep, goats, and cattle.³ Deer are cervids (family Cervidae), and are noted for having two large and two small hooves on each foot. Deer are considered to be native to all continents except Australia and Antarctica, although many species have been widely introduced outside of their original habitats as game animals. In all save one species of deer, only the males carry antlers; in the reindeer or caribou (Rangifer tarandus), both sexes have antlers.⁴

The deer family (Cervidae) is further divided into two groups—Old World deer (subfamily Cervinae) and New World deer (subfamily Capreolinae). This distinction reflects where these animals evolved, but is not a geographical one. Instead, it references the differing foot structures of the two subfamilies. In Old World deer, the second and fifth hand bones (metapodia) have almost completely disappeared except for proximal, terminal remnants. In New World deer, these remnants are distal.^3,4

Obviously, all of the cervids occurring naturally in the Western Hemisphere are New World deer. These deer evolved from forebears that colonized North America, South America and Eurasia. Among these are the moose (Alces alces), the white-tailed deer (Odocoileus virginianus), the elk (Cervus canadensis), the caribou (R. tarandus), the mule deer (O. hemionus) and nearly a dozen other native species.

Deer are specialized herbivores, typically feeding on young grasses, herbs, lichens, foliage, buds, aquatic plants, woody shoots, fruit. They rely little on coarse, fibrous grasses, since they have not evolved a digestive system comparable to those found in bovids.³ Other distinguishing characteristics of deer include scent glands and lack of a gall bladder.⁵

Preventing and Managing Anesthetic Aspiration in Deer

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.³

Should intraoperative aspiration occur in a deer, the first step in successful management is the immediate recognition of gastric content in the oropharynx or the airways.¹ 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 deer’s airway be secured as rapidly as possible to prevent further contamination and to facilitate airway clearance.⁴ 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.^1,6