Antelope Aspiration During Capture and Chemical Immobilization
Aspiration is described as 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 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.
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. Dysphagia can occur if there is a problem with the swallowing process as food and/or liquids pass through the mouth, pharynx, and esophagus. The pharynx is also involved in the process that transmits air into the lungs. Upon inhalation, 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 dysphagia, small amounts of food or fluids may be inadvertently aspirated. In the case of anesthetic aspiration, the human or 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,1 intraoperative aspiration (aspiration during a surgical procedure), is very dangerous and can prove fatal.2
Antelopes and Chemical Immobilization
At the beginning of the last century, the primary method used for the capture of many large wild animals such as antelopes was to chase them to the point of near-exhaustion—a method that was quite labor-intensive, impractical and fairly inhumane.3 With 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. The field immobilization of wild animals with chemical agents is a method of rendering wild animals tractable while using minimal of restraint. Here, the research or wildlife management objectives are usually to measure or weigh the live 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 safe methods in chemical immobilization.
Antelope are ruminants belonging to the family Antilocapridae and Bovidae. The pronghorn antelope, Antilocapra americana, is the only member in the former.4 Antelope males and the females of some species have unbranched horns attached to the frontal bones of the skull.3 Until the advent of potent opiates, the pronghorn was notoriously difficult to safely capture or anesthetize.4 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 attendant factors (e.g., stress, venue, individual animal and field conditions) must also be taken into account.
Chemical Immobilization: Practices and Procedures
The utilization of 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. A successful chemical restraint exercise is not complete until the subject is fully recovered and (in the case of field research) back in its environment. The application of appropriate pharmacological principles with an emphasis on drug reversibility will minimize the chances that the animal will be at a competitive disadvantage or inordinately disoriented following its release. Further, residual sedation and renarcotization should be avoided in the field unless absolutely necessary.3,5
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. Unfortunately, the literature strongly suggests that intubation can increase the risk of vomiting during an anesthetic event.1,4
Anesthetic Aspiration in Antelopes
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 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 antelope 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, periprocedural fasting is very often impractical or 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.
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.2 Prokinetics (e.g., domperidone, metoclopramide, erythromycin and renzapride) promote gastric emptying and are also 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. 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.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
1Shaikh, 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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