Aspiration in Barasingha Deer During Capture and Chemical Immobilization

The barasingha deer (Rucervus duvaucelii), also known as the swamp deer, is a deer species that is distributed across the Indian subcontinent. Formerly considered an endangered species, today there are large but fragmented populations in northern and central India, and the barasingha has been introduced into several countries.^1,2 In the U.S., this deer may be hunted on carefully-controlled ranches and reserves.

In the late 1960s, the total population of barasingha deer was estimated at less than 2,200 individuals in India and about 1,500 in Nepal. These losses leading up to the 1960s were due to overhunting and the conversion of large grassland areas into cropland.²

The barasingha differs from other deer species in India in that its antlers have more than three tines. It is from this feature that the deer derives its name, which loosely translates into "twelve-horned" in Hindi. In fact, mature stags often have 10 to 14 tines, and some have been known to sport up to 20.³

The barasingha is a relatively large deer with a shoulder height of approximately 45 inches and an overall length of nearly 6 feet. Stags weigh from 350 to 630 lbs., and females weigh from 290 to 320 lbs. Some larger stags have been reported as weighing up to 570 lbs.¹ The barasingha’s coat is woolly and yellowish brown with white spots along its spine. Its throat, abdomen, inside of the thighs and beneath the tail is white, and its coat becomes a brighter orange-brown color in summer. The females are a bit paler in color than males, and the young have faint spots.³

Barasingha deer are primarily grazing animals, eating a diet of grasses and aquatic plants. During the day, they feed with peaks during the mornings and late afternoons. In India, herds comprise from 8 to 20 individuals; large herds may have up to 60 individuals. During the rut, barasingha deer will form large herds of adults. Their breeding season lasts from September to April, and fawns are born after a gestation period of 240 to 250 days in August to November.^2,3

Barasingha Deer, Chemical Immobilization and Aspiration

Researchers, wildlife managers, veterinarians and deer farmers are often called upon to perform routine procedures on barasingha deer or to administer medical treatment. In most cases, this requires the use of sedative and/or anesthetic drugs. Vomiting is one of the more common post-sedation and post-anesthesia complications in both domestic and exotic animals. Vomiting that occurs during a procedure can pose grave risks due to anesthetic aspiration.

When a foreign substance enters the airway or lungs, this is described as aspiration. It can apply to food, liquid, or other materials. Aspiration is dangerous in that it can give rise to serious health problems, such as aspiration 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 sedation or anesthetic events.

Aspiration pneumonia is a condition that is characterized by inflammation and necrosis of lung tissue due to the inhalation of foreign material. The most common material aspirated in large animals is a large volume of liquid, due to weakness from a pathological condition, during oral administration of fluids or as a result of chemical immobilization. The severity of the inflammatory response depend on the type and volume of material aspirated and the distribution of aspirated material in the lungs.

In cases where large volumes of liquid have been aspirated, an animal’s death can occur swiftly. Other cases will present later with clinical signs consistent with cranioventral bronchopneumonia.⁴ Cervids that are affected with chronic wasting disease may also develop aspiration pneumonia due to central nervous system dysfunction.³

Barasingha Deer and Chemical Immobilization

The primary method used for the capture of large wild animals such as barasingha deer at the beginning of the last century was to chase them to the point of near-exhaustion, a labor-intensive method that was impractical and fairly inhumane.^4,5With the pioneering work on the chemical immobilization of wildlife that took place from the 1950s on, chemical immobilization techniques have improved significantly through the development of superior drugs and equipment.

The immobilization of wild animals with drugs is a method of rendering them tractable while using minimal restraint. Here, the objectives are usually to measure or weigh a live deer, 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.^4,5 These requirements have resulted in the development of increasingly safer methods of chemical immobilization.

Each species of deer has its own anesthesia recommendations with intra-species variations of dosages because of diverse individual responses to anesthetic agents.⁵ These variations are of course factors in the risk of anesthetic aspiration in these species, and attendant factors (e.g., stress, venue, individual animal and field conditions) must also be taken into account.

Practices and Procedures for Chemical Immobilization

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 barasingha deer 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 operations) 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.^4-7Intubation has been widely recommended for any anesthetized deer that needs to be transported or anesthetized for greater than one hour. Unfortunately, the literature suggests that intubation can increase the risk of vomiting during an anesthetic event.^4,8

Anesthetic Aspiration in Barasingha Deer

Until formulated drugs (such as combinations of α2-agonists like medetomidine, detomidine, xylazine and their reversal agents) came into use, opioids were the mainstay of large animal anesthesia in wildlife and captive care.⁵ As with other mammals, problems encountered with certain opioids (such as etorphine or carfentanil, which have been widely used in wildlife chemical immobilization) in barasingha deer are known to include vomiting or passive regurgitation that can lead to fatal aspiration pneumonia.

Periprocedural fasting (fasting prior to an anesthetic event) is routinely recommended by clinicians due to the risk of aspiration. Unfortunately, this is often impossible under field conditions. Additionally, much of the data on anesthetic aspiration relates to humans receiving general anesthesia, however, deer and other mammals have been known to aspirate during procedures while under sedation and where no intubation or general anesthesia have been employed.

For the prevention of anesthetic aspiration, the 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) which promote gastric emptying are also believed to reduce the risk of aspiration.⁶

In the event that aspiration occurs in barasingha deer during a procedure, the first step in managing the situation is the recognition of gastric content in the oropharynx or the airways.^5-8 The deer should be immediately positioned with the head down and rotated laterally if possible. Orotracheal and endotracheal suctioning should be performed, either before or after orotracheal intubation, depending on whether regurgitation continues and if the airway is visible. The airway should be secured to prevent further contamination and to facilitate airway clearance.⁴ Flexible bronchoscopy is an important adjunct to orotracheal and endotracheal suctioning; rigid bronchoscopy may be required if particulate matter is present in the deer’s airway.^4,7