Bongo Antelope Aspiration During Capture and Chemical Immobilization
The bongo antelope is a large, forest-living antelope that lives in the lowland forests of Zaire and West Africa to southern Sudan, with small populations also living in the highland forests of Kenya and also in the Congo. Currently, all bongo are considered endangered species. There are two sub-species of this antelope: the Lowland (or Western) bongo, and the Mountain (or Eastern) bongo. Bongo are nocturnal, shy and elusive, with males living a solitary life and socializing only for mating purposes. The females often group together for protection in herds of up to 50 females and their young.
Aspiration in Bongo Antelope
Wildlife managers, researchers and veterinarians in zoo settings sometimes need to chemically immobilize bongo to mark them for identification, to provide veterinary treatment or for relocation. There are a number of risks and potential complications associated with the capture and chemical immobilization of bongo, and aspiration is one of these.Aspiration occurs 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; in the short term, it may lead to asphyxia.
When food is swallowed, it passes from the mouth into the pharynx (throat). It then progresses through the esophagus into the stomach via peristaltic action. When an animal inhales, air enters through the nose or mouth and progresses into the pharynx. It then moves into the trachea and into the lungs. Over the top of the trachea, there is a small flap of tissue called the epiglottis which blocks food and drink from moving into the trachea during the process of swallowing. In some cases, these substances can enter the trachea, causing aspiration.
In cases of anesthetic aspiration, an animal vomits food from their stomach during a surgical procedure, which is then aspirated into the lungs. This potentially represents a fairly large volume of food and/or fluids being aspirated, which can lead to serious complications. While postoperative nausea and vomiting (PONV) is common in humans and other mammals,1 intraoperative aspiration (aspiration during a surgical procedure), is very dangerous and can prove fatal.2
At the beginning of the last century, the primary method used for the capture of many large antelopes was to chase them to the point of near-exhaustion—a method that was quite labor-intensive, impractical and less than humane.3 With progress in chemical immobilization that took place from the mid- 20th Century on, techniques have improved greatly through the development of increasingly efficacious drugs and equipment. The field immobilization of wild animals with chemical agents is a method of rendering wild animals tractable while using minimal of restraint. Usually, research or wildlife management objectives are to measure or weigh an antelope, 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 for a variety of reasons.3,4 These requirements have resulted in the development of increasingly 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.3,4 These variations are of course factors in the risk of vomiting and anesthetic aspiration in these species, and factors such as stress, venue and field conditions must also be taken into account.
Bongo Antelope Aspiration: Prevention & Treatment
Using basic veterinary knowledge can make a substantial contribution to animal safety during capture and chemical immobilization. Teams that are qualified to handle wild mammals should evidence the appropriate expertise in wildlife anesthesia and should include an attending veterinarian when appropriate. The application of appropriate pharmacological principles with an emphasis on drug reversibility minimizes the chances that an animal will be at a competitive disadvantage or inordinately disoriented following its release. Residual sedation and renarcotization should be avoided in the field unless absolutely necessary.3,5
When the various components of stomach contents make their way into the lungs, 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.4 As with other mammals, problems encountered with certain opioids (such as etorphine or carfentanil, which have been widely used in wildlife chemical immobilization) in bongo are known to include vomiting or passive regurgitation that can lead to fatal aspiration pneumonia.
Periprocedural fasting (fasting prior to an anesthetic event) has historically been recommended by clinicians because of the suspected risk of aspiration. Unfortunately, this is impractical if not impossible under field conditions. Additionally, much of the data on anesthetic aspiration relates to humans receiving general anesthesia, however, antelope and other mammals have been known to aspirate during procedures while under sedation and where no intubation or general anesthesia were employed.
For the prevention of anesthetic aspiration, the available literature recommends histamine 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.2 The use of prokinetic drugs (e.g., domperidone, metoclopramide, erythromycin and renzapride) promote gastric emptying and are believed to reduce the risk of aspiration.4
In the event that aspiration occurs during a procedure, the first step in managing the situation is the immediate recognition of gastric content in the oropharynx or the airways.2 The animal should be immediately positioned with the head down and rotated laterally if possible. It is recommended that the airway be secured as rapidly as possible to prevent further contamination and to facilitate airway clearance.2 Flexible bronchoscopy is an important adjunct to orotracheal and endotracheal suctioning. Rigid bronchoscopy may be required if particulate matter is present in the airway.2,5 Orotracheal and endotracheal suctioning is indicated, either before or after orotracheal intubation, depending on whether regurgitation continues and if the airway is visible.
1 Shaikh, Safiya Imtiaz et al. Postoperative nausea and vomiting: A simple yet complex problem. Anesthesia, essays and researches vol. 10, 3 (2016).
2Nason, K. Acute Intraoperative Pulmonary Aspiration. Thoracic surgery clinics vol. 25,3 (2015): 301-7.
3Lance, W. Exotic Hoof Stock Anesthesia and Analgesia: Best Practices. In: Proceedings, NAVC Conference 2008, pp. 1914-15.
4Ball, L. Antelope Anesthesia. Wiley Online Library, 25 July 2014, https://doi.org/10.1002/9781118792919.ch60.
5Kluger 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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