Impala Antelope Aspiration During Capture and Chemical Immobilization
Known for their spectacular and iconic leaps when alarmed or pursued by predators, the impala (Aepyceros melampus) is a widely-distributed African ungulate comprised of several subspecies. The most common in East Africa is Aepyceros melampus rendilis; Aepyceros melampus petersi, the black-faced impala, is distributed further south. There are other proposed subspecies (up to 4 additional) that are less well known; controversy as to their designation is ongoing.1 Impala are most often found in Kenya, Zimbabwe, Uganda, Zambia, Botswana, and Southern Angola to northern South Africa. They are one of the most dominant species of antelope on the African savannah.
Impala are fawn-colored with white underparts and a black stripe that extends from the top of the rump down the back of each thigh.2 Rams have horns which are lyre-shaped, and reach a length of around 30 inches. The impala stands 28–36 inches high and weighs 88–167 pounds. Impala males are approximately 20% heavier than females.
Impala are able to adapt to different environments of the savannas. In some areas, they are grazers and browsers in others. Impala herds typically stay within a few miles of water sources. Younger rams live in bachelor herds, while those strong enough establish or take over breeding herds.3
Vomiting and Aspiration
The chemical immobilization of impala is sometimes required due to research or animal management concerns. One of the more common and dangerous post-sedation and post-anesthesia complications in these animals is aspiration following vomiting during the immobilization event. Aspiration is when a foreign substance enters the airway or lungs; this can apply to food, liquid, or other materials. Aspiration can give rise to serious health problems, such as pneumonia. Aspiration can occur when an animal has difficulty swallowing normally (referred to as dysphagia), but in some instances it can be brought on during or after anesthetic events.
Normally, when food is swallowed, it passes from the mouth into the esophagus. It then progresses into the stomach via peristaltic action. Dysphagia can occur if there is a problem with the swallowing process as food and/or liquids pass through the mouth, pharynx, and esophagus. While postoperative nausea and vomiting (PONV) is common in humans and other mammals,4 intraoperative aspiration (aspiration during a surgical procedure), is very dangerous and can prove fatal.5
Impala and Chemical Immobilization
The field immobilization of wild animals with chemical agents is a method of rendering wild animals tractable while using minimal of restraint. At the beginning of the 1900s, the chief method used for the capture of large wild animals was to chase them to the point of near-exhaustion—a method that was quite labor-intensive, impractical and fairly inhumane.6With the pioneering work on the chemical immobilization of wildlife that took place from the 1950s on, chemical immobilization techniques have improved greatly through the development of increasingly efficacious drugs and equipment.
In most cases, research or wildlife management objectives usually include the measurement or weighing of a live impala, collection of blood or tissue for research or diagnostics, marking an individual or fitting a radio transmitter for studying migration patterns, range requirements and behavior patterns or the translocation of animals.6,7 These requirements and their increased practice have resulted in the development of safer methods in chemical immobilization.
Each species of antelope has its own anesthesia recommendations with intra-species variations of dosages because of diverse individual responses to anesthetic agents.6,7 These variations are 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.
Prevention and Preparation
Teams that are trained in the handling of wild mammals should display the appropriate expertise in wildlife anesthesia and should include an attending veterinarian when appropriate. A successful chemical restraint exercise is not complete until an animal is fully recovered and (in the case of field immobilization) back in its environment. Applying appropriate pharmacological principles with an emphasis on drug reversibility minimizes the chances that the animal will be at a competitive disadvantage or inordinately disoriented following its release. Residual sedation and renarcotization (re-dosing) should be avoided in the field unless absolutely necessary.6,8
When stomach contents make their way into the lungs as a result of aspiration, they can significantly damage the lung tissues, resulting in acid-associated pneumonitis or other bacterial infection. Until formulated drugs (e.g., combinations of α2-agonists such as medetomidine, detomidine, xylazine and their reversal agents) came into use in recent years, opioids were the mainstay of antelope anesthesia in wildlife and captive care.7 As with other mammals, problems encountered with certain opioids (such as etorphine or carfentanil, which have been widely used in wildlife chemical immobilization) in antelope are known to include vomiting or passive regurgitation that can lead to fatal aspiration pneumonia.
Fasting prior to an anesthetic event (periprocedural fasting) has historically been recommended by clinicians because of the suspected risk of aspiration. Unfortunately, this is very often impossible under field conditions. While much of the data on anesthetic aspiration relates to humans receiving general anesthesia, impala and other mammals have been known to aspirate during procedures while under sedation and where no intubation or general anesthesia were employed.
In general, for the prevention of anesthetic aspiration the available literature recommends histamine (H2) antagonists such as cimetidine, famotidine, nizatidine, and ranitidine and proton pump inhibitors (PPIs) such as dexlansoprazole, esomeprazole, lansoprazole, omeprazole, pantoprazole, and rabeprazole, which have been shown to be effective in increasing the pH and reduce the volume of gastric contents.5 Prokinetics (e.g., domperidone, metoclopramide, erythromycin and renzapride) promote gastric emptying and are also believed to reduce the risk of aspiration.7
Intubation has been widely recommended for any anesthetized impala that needs to be anesthetized for greater than one hour. Unfortunately, the literature strongly suggests that intubation can increase the risk of vomiting during an anesthetic event.4,7
Should aspiration occur during a procedure, the first step in managing the situation is the 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 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. Rigid bronchoscopy may be required if matter is present in the airway.5,8
4Shaikh, Safiya Imtiaz et al. Postoperative nausea and vomiting: A simple yet complex problem. Anesthesia, essays and researches vol. 10, 3 (2016).
5Nason, K. Acute Intraoperative Pulmonary Aspiration. Thoracic surgery clinics vol. 25,3 (2015): 301-7.
6Lance, W. Exotic Hoof Stock Anesthesia and Analgesia: Best Practices. In: Proceedings, NAVC Conference 2008, pp. 1914-15.
7Ball, L. Antelope Anesthesia. Wiley Online Library, 25 July 2014, https://doi.org/10.1002/9781118792919.ch60.
8Kluger 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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