Cardiac Arrest in Deer During Capture and Chemical Immobilization

Cardiac arrest, or cardiopulmonary arrest (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.¹ In these cases, prompt cardiopulmonary resuscitation is imperative.

Signs of an impending CPA event in 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.

The Chemical Immobilization of Deer

Deer are among the most well-known of the large wildlife species, and are popular among hunters and wildlife enthusiasts alike. They belong to the order Artiodactyla, a group also known as cervids. 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. Deer are valued aesthetically, as well as by hunters. Venison is not only the most popular game meat, but is one of the most nutritious meats for human consumption.

Most deer prefer forested areas where they can find plenty of vegetation for eating and hiding, but they readily adapt to other environments. Deer are primarily herbivores that browse for roots, twigs, bark, grass, leaves, and other vegetation. They are also partial to fruits, vegetables, and flowers—a fact to which many suburban gardeners can attest. Deer have a four-chambered stomach, and are cud-chewing herbivores (ruminants). Most deer have 32 teeth, although they lack upper incisor teeth, and most species also lack upper canines.¹

Cervids differ from other ruminants in that males grow antlers that are comprised of bone. These are shed and regrown annually, and increase each year in size and intricacy. Except in the case of caribou, female deer do not grow antlers. While the antlers grow, they are covered by a thin layer of downy skin known as velvet. When the antlers are fully grown, the velvet dries and is typically rubbed off by the animal.² Antlers serve as ornamentation for breeding purposes, as well as weapons during the mating season.

There are an estimated 35 million deer in the U.S., with the white-tailed deer (or whitetail deer, Odocoileus virginianus)being the most common. These deer weigh from 150-300 pounds, and stand from 37-87 inches at the shoulder.

White-tailed deer are primarily distributed east of the Rocky Mountains and in most of Mexico, although in recent years, they have expanded farther west in the United States and into western Canada. Also called the Virginian deer, whitetails get their name from the white underside of their tail. Upon seeing predators, they raise their tail and flash the white underside to let the predator know it has been seen, thus reducing the possibility of an actual attack. The whitetail’s coat changes from a reddish-brown for the spring and summer to a gray-brown in the winter.

White-tailed deer are what are known as “short-day” breeders. During the fall, their breeding season starts with the decline in the length of the day. This results in hormonal events stimulating the reproductive organs of the males and females. Females have the ability to come into heat multiple times during the breeding season, and a female white-tailed deer can have one to three young.

Responding to Cardiac Arrest in Deer

The management of and research involving wild or captive deer routinely call for the use of chemical immobilization(sedation and/or anesthesia). In the field, remote drug delivery via dart is the modality 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.

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. Chemical immobilization can be also induced with opioids, alpha-2 agonists combined with dissociative drugs⁴ or custom compounded preparations. In zoos and farms, deer may also be handled in drop-floor or hydraulic squeeze chutes. Free-ranging deer are sometimes captured with net guns, drive nets, or clover traps.⁴

Capture and/or chemical immobilization can result in CPA events in deer, particularly under field conditions. In some instances, the stress of capture (depending upon the method 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)¹ or a variety of comorbidities.

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

• Basic life support (BLS)
• Advanced life support (ALS)
• Post resuscitation care³

The first stage involves establishing an open and clear airway, providing assisted ventilation, and performing chest compressions. If a 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,¹ the caveat being that 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.¹ 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.⁴

A deer that is restored to a perfusing cardiac rhythm can 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.³

¹safariclub.org.
²wildlifeinformer.com.
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).