Respiratory Arrest in Alpaca During Capture and Chemical Immobilization

The alpaca (Vicugña pacos) is a lamoid that is native to the Andes and which has been used for its fleece since it was domesticated approximately 4000-6000 years ago. Lamoids are a group of South American camelids (Camelidae) that includes llamas, alpacas, vicuñas, and guanacos. Over thousands of years, these species have been interbred and developed for various uses, such as pack animals, food or fleece. Lamoids are also referred to as New World camelids.

It is believed that both New World and Old World camelids originated in North America over 40 million years ago, with lamoids migrating to South America and the forerunners of camels migrating west via the Bering Strait and later becoming extinct in North America.¹

Alpacas are the smallest of the South American camelids. They are slender, with a long neck and long legs, a short tail, a small head, and large, tapering ears. They are the most specialized of the four species of lamoids, being adapted to altitudes from 13,000 to 15,500 feet.² They are distinguished from llamas (the largest South American camelids) by their size. The weight of an adult alpaca ranges from 120 to 140 lbs, with a height ranging from 2 to 3 feet. South American camelids vary by size and purpose, with some being used as pack animals and others (such as alpacas) being valued for their fleece.¹ Alpacas are the most widely-used lamoids for fleece production.

The huacaya and the suri are the two breeds of alpaca, although these are technically the same species. Huacayas are the more common type, and account for about 90% of all alpacas.² Chiefly, the two breed types differ in the properties of their fleece. The fleece of the alpaca is lightweight, strong, high in insulation value and very resistant to moisture. Alpaca wool fibers are hollow, which gives them the ability to insulate very well, and to absorb moisture. As a result, alpaca farming has become a worldwide industry.

Alpacas are known as pseudo-ruminants; these animals have a single stomach divided into three compartments rather than four, like true ruminants (such as cattle). They produce rumen, chew cud and are able to process food very efficiently. In the field, alpacas graze on grasses and plants. Alpacas have a split upper lip that is mobile and highly-sensitive. The split in the upper lip allows the alpaca to be a discriminating eater; as they graze, alpacas tend not to ingest undesirable foreign bodies. On farms, alpacas generally eat grass or hay. They consume approximately two pounds per 125 pounds of body weight daily in hay or fresh pasture. Some farmers feed extra alfalfa to alpacas that are leaner, or those which live in very cold temperatures, such as those that occur in North America and Europe.³

Alpacas mate from August through September. Their babies are called crias, which typically weigh 15-20 pounds at birth. Adult alpaca reach about 3 feet in height and 150 pounds in weight,² and live for 15 to 25 years.

Respiratory Arrest Risks in Alpaca

Wildlife management personnel, alpaca farmers veterinarians are often called upon to chemically immobilize alpaca for medical treatment, research and so forth. Respiratory arrest in alpaca during chemical immobilization can occur due to drug overdose, but it can happen as a spontaneous adverse reaction to immobilizing drugs. Central nervous system disorders can also cause hypoventilation leading to respiratory arrest, as can compression of the brain stem during a capture event.¹

In cases where respiratory arrest is brought on by chemical immobilization, the decreased respiratory effort reflects central nervous system (CNS) impairment due to the immobilizing drugs. Drugs that decrease respiratory effort include opioids and certain sedatives. Certain combinations of drugs can increase the risk for respiratory depression, although some of the newer species-specific formulations can actually lower the risk of complications, including respiratory depression and arrest. Opioid-induced respiratory depression (ORID) is usually most common risk factor in the immediate postoperative recovery period, but it can persist and lead to catastrophic clinical outcomes.¹

Chemical Immobilization and Respiratory Arrest in Alpaca

Respiratory depression (known as hypoventilation) is characterized by reduced or compromised breathing. Respiratory arrest is the cessation of breathing. There are several approaches available to alleviate respiratory arrest in alpaca as a result of chemical immobilization. Antagonists (also known as reversal agents) are able to reverse the effects of opioid anesthetics and tranquilizers; these have been some of the most notable pharmacological developments in wildlife immobilization. ^6-8 These drugs are able to completely reverse anesthetic effects and return an animal to a normal physiological state. The benefits of antagonists include preventing predation in the wild after anesthetic events and avoiding complications. Antagonists also decrease the personnel and equipment time needed for monitoring immobilized animals through their recovery. It should be noted that intubation is recommended for alpacas being anesthetized for longer than 20 minutes.⁴

In cases of respiratory arrest, the goal is to restore adequate ventilation and oxygenation without further compromising an already compromised cardiovascular situation.⁶ In the event of respiratory arrest in an immobilized alpaca, of course the administration of all immobilizing drugs should be ceased. Naltrexone is frequently used to fully reverse opioid-based immobilization after capture, especially if the animal needs to be released back into the field and must be fully alert. If residual analgesic or sedative effects are required, partial opioid antagonists or mixed agonists/antagonists can be used for the reversal of opioids such as diprenorphine, nalorphine or butorphanol.^7,8 Atipamezole is often used as a reversal agent for medetomidine and dexmedetomidine in order to reduce their sedative and analgesic effects. It has also been used for the reversal of other alpha-2 adrenergic agonists (e.g., xylazine, clonidine, tizanidine and brimonidine).⁶

Potassium channel blockers such as doxapram can be used to stimulate breathing in alpacas suffering from respiratory depression or arrest. Doxapram is widely used as a respiratory stimulant in veterinary medicine, and has been shown to increase the minute ventilation in large herbivores immobilized with etorphine.⁷ The use of oxygen is recommended during alpaca immobilization whenever possible, since it can lower the risk of respiratory arrest occurring. It can also be combined with partial opioid reversal agents to better alleviate hypoxia.⁶