Impala Antelope Vomiting During Capture and Chemical Immobilization
The Impala (Aepyceros melampus) is the most common antelope of the savannas of eastern and southern Africa and the bushveld regions of South Africa. Like other antelopes, it is a member of the family Bovidae, and the only member of the subfamily (or tribe) Aepycerotini.1 It is a medium-sized antelope with slender, well-developed legs and a long neck. The impala stands 28–36 inches high and weighs 88–167 pounds. Impala males are approximately 20% heavier than females and have wide, winding horns that are 18–36 inches or longer.2
Impala males and females are similarly colored and have a tan coat with a reddish-brown saddle and white markings at the eyes, the inside of the ears, throat, the underside of the torso and tail. They also have black markings at the ears, tail and back feet. The darker, black-faced impala (Aepyceros melampus petersi) of southwest Africa is a less common subspecies.1
Like several other African antelope, the impala is an “edge” species that favors the ecotone between woodland and grassland. It is a mixed feeder that eats grass during the rainy season and switches to browsing during the dry season.1,2
This antelope is often seen in large breeding herds that are closely attended by a dominant male. It is a seasonal breeder that mates during the rainy season and given birth six months later. During the rut, large herds of up to 100 impalas enhance male sexual competition.1 Near the end of gestation, females leave the herds and seek secluded places to bear their fawns.
Vomiting as a Complication
Research and animal management concerns occasionally require the chemical immobilization of impala. One of the more common post-sedation and post-anesthesia complications in both domestic and exotic animals is vomiting. This may be considered normal if it occurs once or twice after a surgical procedure, but 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. Anesthetic aspiration involves an impala 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. 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 reported morbidity. Any animal undergoing thoracic surgery is 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 are essential in reducing risk and optimizing outcomes associated with this complication.3
In the case of chemically immobilized wildlife, it is often impossible to perform the 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 impala.
Risk Mitigation
Since the veterinary care of non-domestic hoofstock has become so commonplace (due to the integration of veterinary medicine in wildlife management programs, zoological collections, etc.), research and wildlife veterinarians are required to amass the requisite knowledge associated with safely anesthetizing and handling these animals.4 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 challenge that 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.
Unlike the pioneering days of field chemical immobilization, the improved quality of sedation, anesthesia and analgesia achievable in impala has been made possible through the availability of new, receptor-specific and highly potent agonist-reversible pharmaceuticals and the improved knowledge of CNS receptors.
Until the advent of potent opiates and more novel immobilization drug combinations, certain antelope species were known to be 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 risk factors for vomiting and anesthetic aspiration in antelope.
Monitoring core body temperature is essential in antelope anesthesia,5 and intubation has been widely recommended for any anesthetized impala 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.5
Preventing and Managing Vomiting in Impala
For the prevention of vomiting and 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.3 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 vomiting or intraoperative aspiration 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
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.
5Ball, L. Antelope Anesthesia. Wiley Online Library, 25 July 2014, https://doi.org/10.1002/9781118792919.ch60.
6Kluger M.T., et. al. Crisis management during anaesthesia: regurgitation, vomiting, and aspiration. Quality & safety in health care. 2005;14(3): e4.
About NexGen Pharmaceuticals
NexGen Pharmaceuticals is an industry-leading veterinary compounding pharmacy, offering sterile and non-sterile compounding services nationwide. Unlike other veterinary compounding pharmacies, NexGen focuses on drugs that are difficult to find or are no longer available due to manufacturer discontinuance or have yet to be offered commercially for veterinary applications, but which still serve a critical need for our customers. We also specialize in wildlife pharmaceuticals, including sedatives and their antagonists, offering many unique options to serve a wide array of zoo animal and wildlife immobilization and anesthesia requirements.
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