Cardiac Arrest in Alpaca During Capture and Chemical Immobilization

The alpaca (Vicugña pacos) is a domesticated species of South American camelid (Camelidae). This group of animals, also called lamoids, includes llamas, alpacas, vicuñas, and guanacos. Like camels, these animals originated in North America over 40 million years ago, with camels later migrating east via the Bering Strait and becoming extinct in North America. At the same time, it is believed that lamoids migrated to South America.

While camels, llamas, and alpacas have been domesticated for thousands of years, guanacos and vicunas still roam freely in herds in the mountainous regions of Chile, Peru, and Bolivia. Lamoids vary by size and purpose, with some being used as pack animals and others—such as alpacas— being used for their fleece.¹ The alpaca encompasses two breed types: the huacaya and the suri. Huacayas are the more common type, and account for about 90% of all alpacas.² These two breed types differ primarily in terms of the properties of their fleece.

Alpacas are slender-bodied animals with a long neck and long legs, a short tail, a small head, and large tapering ears. They are the most limited in range and the most specialized of the four species of lamoids, being adapted to altitudes from 13,000 to 15,700 feet. Remains of alpaca found at elevations closer to sea levels suggest that alpaca once had a wider geographical distribution and that the reduction of its range started with the arrival of the Spanish conquistadores and their introduced livestock.²

Alpacas are distinguished from llamas (the largest South American camelids) by their smaller size, and they are the smallest of the domesticated lamoids. The weight of an adult alpaca ranges from 120 to 140 lbs, with a height ranging from 2 to 3 feet. They are even-toed ungulates with two toes on each foot and an unguligrade form of locomotion. This involves most of the weight of an animal being supported by the hoofs, as opposed to digitigrade, wherein the toes touch the ground, or plantigrade, where the entire foot is on the ground.²

The alpaca’s origin has long been a matter of debate. This was complicated by the fact that alpacas and llamas are able to breed with one another and produce fertile offspring. This suggested that both species stemmed from guanacos, the parent species of the llama. Genetic studies however, have concluded that alpacas are the domesticated descendants of vicuñas, and that this occurred between 6,000 and 7,000 years ago.³

Alpacas are the most widely-used lamoids for fleece production. The fleece of the alpaca is lightweight, strong, high in insulation value and resistant to moisture. It has been reported that during the height of the Incan civilization, the wearing of robes made of alpaca fleece was reserved for the nobility and royalty.³ Alpaca wool fibers are hollow, which gives them the ability to insulate very well, and to absorb moisture and wick it away. As a result, alpaca farming has become a worldwide cottage industry.

Alpaca Chemical Immobilization

Wildlife management personnel, biologists, veterinarians in zoos and alpaca farmers are regularly called upon to chemically immobilize alpacas for medical treatment, research and the like. Unfortunately, such procedures carry the risk for a variety of complications in these animals. These include, but are not limited to vomiting and aspiration, respiratory depression, respiratory arrest, bloat, capture myopathy and cardiac arrest.

The different species protocols and dosage variations for immobilizing drugs present an increased risk of complications during anesthetic events. Until the more recent use of formulated drugs (e.g., combinations of α2-agonists such as medetomidine, detomidine, xylazine and their reversal agents), opioids were the mainstay of alpaca anesthesia in wildlife and captive care, and are still widely utilized.⁵ Xylazine is often used to provide sedation or, in higher doses, restraint for lamoids such as llamas and alpacas. Xylazine can be used for sedation without recumbency. Higher dosages will result in recumbency and provide a light plane of anesthesia for 20–30 min. Simultaneous administration of xylazine, ketamine, and butorphanol usually provides 20–30 min of recumbent restraint.

Tolazoline has activity at both alpha-1and alpha-2 receptors, while the other two drugs are more selective having activity only at alpha-2 receptors. Although doxapram, an analeptic, will reverse xylazine sedation in cattle and dogs, it will not reverse xylazine sedation in camelids, even when given in doses as high as 2.0 mg/kgIV. Tolazoline can cause vasodilatation because of its alpha-1effect. Caution should therefore be exercised when tolazoline is given to animals with compromised cardiovascular status to avoid precipitating shock. Monitoring core body temperature is essential in alpaca anesthesia,^5,6 and it is recommended that alpacas be orotracheally intubated for procedures lasting more than 20 minutes.⁷

Cardiac Arrest as a Complication of Chemical Immobilization

Cardiac arrest, or cardiopulmonary arrest (CPA) is a sudden and complete failure of the respiratory and circulatory systems. The subsequent lack of oxygen transport can quickly cause systemic cellular death from oxygen depletion.⁵ If left untreated, cerebral hypoxia can result in death within four to six minutes of a CPA event.⁶ Prompt cardiopulmonary resuscitation is imperative in these cases.

Capture and/or chemical immobilization can result in CPA events in alpacas. 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)⁵ or a variety of comorbidities.

Signs of an impending CPA event 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.

Responding to Cardiac Arrest in Alpacas

Cardiopulmonary cerebral resuscitation in alpacas involves three stages:

• Basic life support (BLS),
• Advanced life support (ALS)
• Post resuscitation care

The first stage involves establishing an open and clear airway, providing assisted ventilation, and performing chest compressions. If the alpaca’s pulse becomes absent or weak, all administration of immobilizing drugs must be ceased and external cardiac massage should be initiated. Veterinary patients can usually be easily ventilated with a bag-valve mask,^5,7the caveat being that this may not be available under field conditions.

The veterinarian can establish venous access 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.⁵ Epinephrine at 0.2 mg/kg (concentrated at 1/10,000) should be given IV or intracardially (IC) while cardiac massage continues. If the alpaca 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.⁶

Alpaca that are restored to a perfusing cardiac rhythm may experience rearrest, especially if the original cause of the CPA event has not been identified. Therefore, resuscitated patients usually 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.⁷