Sable Antelope Vomiting During Capture and Chemical Immobilization

The sable antelope (Hippotragus niger) is one of Africa’s most visually impressive antelopes. Its inclusion in the “horse antelope” genus (Hippotragini) is due to its compact, sturdy build, erect mane and thick neck.¹ Sable bulls have glossy black coats contrasted by white undersides, rump, throat, and facial markings and large scimitar-shaped horns. As such, they are a favorite among trophy hunters. Both male and female sable have horns, although those of the females tend to be slightly shorter and less curved. The females and young are a chestnut to dark brown in color; in the H. niger nigersubspecies which inhabit areas south of the Zambezi River, females can appear very dark.

The sable’s range includes the southern savanna from central Tanzania to South Africa.² It is an “edge” species that favors the ecotone between wooded savanna and grassland. From September to April (the rainy season), sable forage grasses and foliage of the woodlands; during the dry season, they come out onto grasslands where it grazes on green plants that emerge after the annual fires. Sable are water-dependent and visits pools daily during the dry season.¹

The sable is territorial but highly sociable. Herds of females and young of over 50 animals congregate in ranges of 4 to more than 20 square miles. In some areas, these can number in the hundreds. Female offspring generally remain in the home range, but established adult males drive out subadult males as they mature. These young males typically join bachelor herds until they are ready to compete for their own territory.²

Vomiting as a Complication of Capture

Vomiting is a common post-sedation and post-anesthesia complication in both domestic and exotic animals. While vomiting once or twice after a surgical procedure can be considered normal, it can be a sign of an emerging complication if it continues. A far more serious complication involves vomiting that occurs during a procedure, as this can pose grave risks due to anesthetic aspiration.

Anesthetic aspiration involves an animal vomiting food from their stomach during a surgical procedure, after which the vomitus 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).”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.

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.³

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.

Mitigating the Risk of Vomiting

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.⁴ 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.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 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.

Sable Antelope and Chemical Immobilization

Until the advent of potent opiates, some species of antelope were known for being notoriously difficult to safely capture or anesthetize.⁵ 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.^4,5 These variations are factors in the risk of vomiting and anesthetic aspiration in these species.

Monitoring core body temperature is essential in the chemical immobilization of sable.⁵ Hyperthermia and subsequent capture myopathy are 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, xylazineand their reversal agents), opioids were the mainstay of antelope anesthesia in wildlife and captive care.⁵

Preventing and Managing Anesthetic Aspiration in Sable

To prevent 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.³Additionally, prokinetics (e.g., domperidone, metoclopramide, erythromycin and renzapride) promote gastric emptying and are believed to reduce the risk of aspiration.⁵

The first step in successful management of an intraoperative aspiration in sable is the immediate recognition of gastric content in the oropharynx or the airways.³ 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.⁶ 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.^3,6