Cardiac Arrest in Eld’s Deer During Capture and Chemical Immobilization

Deer are among the most well-known of the large wildlife species globally. They belong to the order Artiodactyla, and the family Cervidae. Deer live in almost every country of the world; there are around a half dozen species that are common in North America, as well as other subspecies and non-native species.

The Eld's deer (Rucervus eldii) is native to areas of Southeast Asia. So named because of their discovery by Lt. Percy Eld in the Manipur Valley of India in 1838, there are three recognized subspecies of R. eldii, which include:

• Rucervus eldii eldii (native to Manipur),
• Rucervus eldii thamin (native to Burma/Myanmar), and
• Rucervus eldii siamensis, (native to Thailand, Annam, and Hainan island).

The Eld’s deer is a large deer that is considered elegant in appearance. They are similar in size to white-tailed deer, but differ somewhat in appearance. Their legs are long and thin, and they have slender bodies with a large head and ears. Their rough coats change color with the season. In summer, they are reddish-brown, and dark brown in winter. Stags often have darker coloring than hinds (females) and have a thick mane of long hair around the neck.¹

Eld’s deer stags have large bow- or lyre-shaped antlers; these sweep back in a curve of about 40 inches in length. One smaller tine grows toward the front of the head. Antlers are shed every year and reach their largest size during the breeding season.² Male Eld’s deer grow to about 71 inches in length and weigh from 276 to 386 pounds. They are taller and larger than the hinds, which stand about 60 inches tall.

In their native ranges, Eld’s deer inhabit suitable forest habitats, lowland valleys and plains, avoiding dense forests and coastal areas. This also includes monsoonal forests. Today, they occur in a number of protected areas throughout these areas and have been introduced to numerous countries as game animals, including the United States.²

Eld’s deer are associated with areas that are seasonally burned, and are fond of eating new grasses as they emerge after fires. Their diet consists largely of grasses, fruits, herbaceous and wetland plants. They are known to graze and to browse opportunistically on cultivated crops such as rice, lentils, maize and peas. On ranches and reserves, Eld’s deer are typically fed a low-protein herbivore diet and alfalfa hay.^1,3

Eld’s deer females can begin reproducing at two years of age and typically continue to do so until they are 10 years of age. They begin estrus in the late winter or early spring and have a long period of ovarian activity (225 to 342 days), during which they average 10 to 17 estrous cycles. After they have mated, the females enter anestrus, which usually occurs in the autumn months.²

Rucervus eldii are primarily nocturnal deer. Throughout most of the year, stags tend to be loners, except in the spring when mating commences. Females are generally found alone or in pairs with their young. They remain in close association with their fawns and other female-fawn pairs. Larger groups are often formed when males join groups of females prior to the breeding season, and groups of up to 20 animals are common.

Risks for Cardiac Arrest in Eld’s Deer

Wildlife management, farming and medical concerns sometimes require the capture of individual Eld’s deer. This may be carried out using either chemical immobilization or various forms of traps. Unfortunately, the stressors associated with capture (of any kind) can potentially lead to a host of complications, including cardiac arrest or cardiopulmonary arrest (CPA).

CPA is characterized by an abrupt, complete failure of the respiratory and circulatory systems. The subsequent lack of oxygen transport can quickly cause systemic cellular death from oxygen depletion. If left untreated, cerebral hypoxia can result in death within four to six minutes of a CPA event.⁴ In these cases, prompt cardiopulmonary resuscitation is imperative.

Signs of an impending CPA event in Eld’s deer can include dramatic changes in breathing effort, rate, or rhythm, significant hypotension, absence of a pulse, irregular or inaudible heart sounds, changes in the heart rate or rhythm; changes in mucous membrane color and fixed, dilated pupils.

Eld’s Deer and Chemical Immobilization

For reasons of safety and efficacy, chemical immobilization (sedation and/or anesthesia) has become the capture method of choice for most large hoofstock. In the field, remote drug delivery via dart is the administration method of choice, with darts being delivered from the ground, a ground-based vehicle or from a helicopter. In a captive situation (e.g., a zoo or farm), drugs may be delivered via pole syringe or dart.

Chemical immobilization can be induced with opioids, alpha-2 agonists combined with dissociative drugs⁴ or custom compounded preparations. Neuroleptic drugs should be used with caution, but can be useful in the management of wild and semi-domesticated deer. These drugs facilitate transport of deer and help to decrease stress in acutely captured deer. In zoos and farms, deer may also be handled in drop-floor or hydraulic squeeze chutes.

Chemical immobilization can result in CPA events in Eld’s deer, particularly under field conditions. In some instances, the stress of capture can significantly increase the likelihood of cardiac arrest in these animals. While under anesthesia, common causes of CPA can include vagal stimulation, unstable cardiac arrhythmias, severe electrolyte disturbances, exacerbated cardiorespiratory disorders (e.g., congestive heart failure, hypoxia)⁴ or a variety of comorbidities.

Techniques for cardiopulmonary cerebral resuscitation in Eld’s deer have been adopted from human emergency medicine, and involve three stages:

1. Basic life support (BLS)
2. Advanced life support (ALS)
3. Post resuscitation care⁵

The first stage involves establishing an open and clear airway, providing assisted ventilation, and performing chest compressions. If the deer’s pulse becomes absent or weak, all administration of immobilizing drugs must be suspended and external cardiac massage should be initiated. Veterinary patients can usually be easily and safely ventilated with a bag-valve mask,⁴ although this may not be available under field conditions.

Venous access can be established by using such methods as intraosseus catheter placement and venous cutdown, in which a small opening is created in a vein to allow passage of a needle or cannula.⁴ Epinephrine at 0.2 mg/kg (concentrated at 1/10,000) should be given IV or intracardially (IC) while cardiac massage continues. If the deer fails to respond, 0.1 ml/kg IV or IC calcium chloride may be given. If there is still no response, the epinephrine and calcium chloride may be re-administered with 10-20 mEq IV or IC sodium bicarbonate.⁵

An Eld’s deer that is restored to a perfusing cardiac rhythm may experience rearrest, especially if the original cause of the CPA event has not been identified. Therefore, resuscitated animals should have cardiovascular and ventilatory support during the period following CPA. Mild hypothermia after resuscitation from CPA decreases cerebral oxygen demand and has been shown to improve outcomes.⁶

¹animaldiversity.org.
²nationalzoo.si.edu.
³vetfolio.com.
⁴Caulkett, N., Arnemo, J. Cervids. Zoo Animal and Wildlife Immobilization and Anesthesia, Second Edition, 25 July 2014.
⁵Pablo L.S. Current concepts in cardiopulmonary resuscitation. World Small Anim Vet Assoc World Congr Proc:2003.
⁶Kreeger T., Arnemo, J., Raath, J. Handbook of Wildlife Chemical Immobilization, International Edition, Wildlife Pharmaceuticals, Inc., Fort Collins, CO. (2002).