Nyala Antelope Aspiration During Capture and Chemical Immobilization
The nyala is found in the eastern part of southern Africa. There are two subspecies of nyala: The lowland nyala (Tragelaphus agasi), and the mountain nyala (Tragelaphus buxtoni). These antelope typically live near dense brush and on the fringes of forests where they are seldom far from water. The males are much larger than the females, grey in color, while the females and calves are a reddish-brown. The males also have spiral horns and a crest of longer hair down the back of the neck, down the throat and under the abdomen.1 Both the males, females and calves have vertical white stripes along the torso and flanks.
While nyala prefer thick vegetation, they often venture into open areas to graze on grasses. They prefer succulent, high-protein vegetation.1 It is thought that these animals are not widely spread chiefly due to their dietary preferences. Nyala do not have the explosive running ability of many other African antelope, thus they depend on blending into the vegetation to evade predators.2
Vomiting and Aspiration in Nyala
The chemical immobilization of nyala is sometimes necessary in the field as well as in the zoo setting for the purposes of medical evaluation and treatment, research or relocation. Vomiting during chemical immobilization events is one of the more common complications that can arise in nyala. This is potentially dangerous in that it can lead to aspiration (foreign substances entering the airway or lungs). Aspiration can give rise to serious health problems, such as pneumonia. Aspiration can occur when a human or animal has difficulty swallowing normally (which is referred to as dysphagia), but in some instances it can be brought on during or after anesthetic events.
In the case 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 much larger 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,3 aspiration during a surgical procedure is very dangerous and can prove fatal.4
Nyala and Chemical Immobilization
At the beginning of the last century, the primary method used for the capture of many large wild animals such as nyala was to chase them to the point of near-exhaustion—a method that was labor-intensive, impractical and fairly inhumane.5With the pioneering work in the chemical immobilization of wildlife that took place from the 1950s on, chemical immobilization techniques improved greatly through the development of increasingly efficacious drugs and equipment. Today, research or wildlife management objectives are usually to measure or weigh a nyala, collect blood or tissue for research or diagnostics, mark an individual or fit a radio transmitter for studying range requirements and behavior patterns.3,4
Each species of antelope has its own anesthesia recommendations with intra-species variations of dosages because of diverse individual responses to anesthetic agents.5,6 These represent risk factors for vomiting and anesthetic aspiration in nyala, and factors such as stress, venue, and field conditions must also be taken into account.
Reducing Risks for Aspiration
Basic veterinary knowledge can go a long way toward ensuring animal safety during capture and chemical immobilization events. Teams that handle wild mammals should have the appropriate expertise in wildlife anesthesia and should include an attending veterinarian whenever possible. Successful chemical restraint is not complete until the animal is fully recovered and back in its environment. Applying the appropriate pharmacological principles with an emphasis on drug reversibility can minimize the chances that the animal will be at a competitive disadvantage or inordinately disoriented following its release.3,5
Intubation has been widely recommended for any anesthetized antelope that needs to be transported or anesthetized for greater than one hour. Unfortunately, the literature strongly suggests that intubation can increase the risk of vomiting during an anesthetic event.3,6
Anesthetic Aspiration in Nyala
When foreign substances such as food, drink, or 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, opioids were the go-to drugs for antelope anesthesia.4 As with other mammals, problems encountered with certain opioids included vomiting or passive regurgitation that often led to fatal aspiration pneumonia.
Fasting prior to sedation or anesthesia has historically been recommended by clinicians because of the risk of aspiration. Unfortunately, this is very often impossible under field conditions. Additionally, 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 (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.4 Prokinetics (e.g., domperidone, metoclopramide, erythromycin and renzapride) promote gastric emptying and are also believed to reduce the risk of aspiration.6
In the event that aspiration occurs in nyala during an immobilization event, the first step in managing the situation is the recognition of gastric content in the oropharynx or the airways.6 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 In addition to orotracheal and endotracheal suctioning, flexible or rigid bronchoscopy may also be required if particulate matter is visible in the airway.4,7
3 Shaikh, Safiya Imtiaz et al. Postoperative nausea and vomiting: A simple yet complex problem. Anesthesia, essays and researches vol. 10, 3 (2016).
4Nason, K. Acute Intraoperative Pulmonary Aspiration. Thoracic surgery clinics vol. 25,3 (2015): 301-7.
5Lance, W. Exotic Hoof Stock Anesthesia and Analgesia: Best Practices. In: Proceedings, NAVC Conference 2008, pp. 1914-15.
6Ball, L. Antelope Anesthesia. Wiley Online Library, 25 July 2014, https://doi.org/10.1002/9781118792919.ch60.
7Kluger 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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