Antelope Vomiting During Capture and Chemical Immobilization

Vomiting is one of the more common post-sedation and post-anesthesia complications in both domestic and exotic animals. Vomiting 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. A far more serious complication involves vomiting that occurs during a procedure, as this can pose grave risks due to anesthetic aspiration. Many will be familiar with the admonition that humans facing surgical procedures receive regarding their abstaining from food for a period of time prior to surgery. This is because anesthesia/sedation does carry the risk of emesis (vomiting) during and after a surgical procedure.

Anesthetic Aspiration

Anesthetic aspiration involves a patient (human or animal) 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 is defined as 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.

Acute intraoperative aspiration (aspiration during a surgical procedure) 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

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

Advancements Mitigate Risk

The veterinary 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 are required to amass the requisite knowledge associated with safely anesthetizing and handling these animals.

The sedation and anesthesia of antelopes 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 major challenge—and one 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.³ 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 pasture enclosure.

Today, the quality of sedation, anesthesia and analgesia achievable in antelopes 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.

Antelopes and Chemical Immobilization

Antelope are a diverse collection of ruminants, “antelope” being a common name given to various members of the family Antilocapridae and Bovidae. The pronghorn antelope, Antilocapra americana, is the only member in the Antilocapridaefamily.³ Antelope males and the females of some species have unbranched horns attached to the frontal bones of the skull.² Until the advent of potent opiates, the pronghorn was very difficult to safely capture or anesthetize.³ Although carfentanil was reported as effective in many captures, more recently, the combination of butorphanol and azaperone have become popular in the chemical immobilization of pronghorn.

According to the available literature, each species of antelope has its own anesthesia recommendation with intra-species variations of dosages because of diverse individual responses to anesthetic agents.^2,3 These variations are of course factors in the risk of vomiting and anesthetic aspiration in these species, and attendant factors (e.g., stress, venue, individual animal and field conditions) must also be taken into account.

Monitoring core body temperature is essential in antelope anesthesia.³ Hyperthermia and subsequent capture myopathy is a commonly-encountered problems with antelope anesthesia. Intubation has been widely recommended for any anesthetized antelope that needs to be transported or anesthetized for greater than one hour. Until the more recent use of formulated drugs (e.g., combinations of α2-agonists such as medetomidine, detomidine, xylazine and their reversal agents), opioids were the mainstay of antelope anesthesia in wildlife and captive care.³

Preventing and Managing Anesthetic Aspiration in Antelopes

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

The first step in successful management of an intraoperative aspiration 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 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.^1,4