Respiratory Arrest in Dromedary Camels During Chemical Immobilization

Once called “The Ships of the Desert”, the dromedary or Arabian camel (Camelus dromedaries) was first domesticated beginning approximately 3,500 years ago. At this point, the dromedary camel has been so widely domesticated that there are no longer naturally-occurring dromedaries left in the wild. The dromedary camel’s range includes northern Africa, the Middle East and western Asia. This species differs from the Bactrian camel (Camelus bactrianus), which has two humps instead of one and is native to east Asia.

The ancestors of modern camels evolved in North America during the Palaeogene period and later spread to Asia, subsequently becoming extinct in North America.¹ Both dromedary and Bactrian camels were used extensively on the Silk Road, the 6,400 kilometer Eurasian trade route that was active from the 2^nd Century BCE until the mid-15th Century.^2,3 This was because they could carry heavier loads than horses or donkeys and could go for long distances and periods of time without food or water.

Dromedary camels have a long neck, a deep chest and (as mentioned above) a single hump. The hump is composed of fat and fibrous tissue, which allows the camel to store energy when food is scarce.¹ As a result, the size of the hump varies based on the camel’s nutritional status, becoming smaller during times of scarce food.

The dromedary camel has other unique adaptations that make them well-suited to living in the desert. A double row of long eyelashes protects their eyes from blowing sand and dust. During sandstorms, they can close their nostrils to prevent sand from entering the nose and throat.² They are also able to conserve water in a variety of ways. Dromedary camels can fluctuate their body temperature throughout the day, which allows them to conserve water by not sweating as the ambient temperature increases.³

The red blood cells of dromedary camels are oval shaped, which helps to facilitate their flow when the animal is dehydrated. The red blood cells are also more stable in order to withstand high osmotic variation without rupturing when these animals drink large amounts of water, which may be up to 30 gallons at a time.^2,3 The dromedary camel’s split upper lips allow them to forage short grass very near to the ground. These lips can break off and eat tough vegetation like thorns and salty plants.³

Risks for Respiratory Arrest in Dromedary Camels

The chemical immobilization of dromedary camels is often necessary for a variety of reasons, including physiological study, research, and for the purposes of management. The drugs used for chemical immobilization have the potential to adversely affect the cardiovascular and respiratory systems of these animals and, in some cases, can lead to complications such as respiratory depression and/or respiratory arrest.

Respiratory arrest and cardiac arrest are discrete complications however, if left untreated, the former nearly always leads to the latter. Interruption of pulmonary gas exchange (respiration) for more than five minutes can irreversible vital organ damage, particularly in the brain.⁵ Cardiac arrest almost always follows without respiratory function being restored.

Respiratory arrest during chemical immobilization can occur due to drug overdose, but in many cases, it can come about as a spontaneous adverse reaction to immobilizing drugs. Central nervous system disorders that affect the brain stem can also cause hypoventilation leading to respiratory arrest, as can compression of the brain stem during a capture event.⁵

When 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 outcomes such as severe brain damage or death.⁵

Wildlife management personnel and veterinarians are regularly called upon to chemically immobilize camels for medical treatment, research and the like. Additionally, dromedary camels were introduced into Australia in the 1840s to assist in the exploration of the inland continent. Today, there are over one million feral camels in the Australian interior. Unfortunately, these animals are causing significant damage to the natural environment. As a management practice, radio-collared camels are now being used in population control programs, which involves immobilizing individual camels.⁴This procedure carries the risk of giving rise to a variety of complications in the immobilized animals, including respiratory arrest.

Addressing Respiratory Depression and Respiratory Arrest

Respiratory depression, or 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 camels as a result of chemical immobilization. Antagonists, or reversal agents, are some of the notable pharmacological developments to wildlife immobilization that are able to reverse the effects of opioid anesthetics and tranquilizers.^6-8 These drugs are able to completely reverse anesthetic effects and return an animal to a normal physiological state. The chief benefits of antagonists include preventing predation in the wild after anesthetic events and to avoid or overcome complications. Antagonists also decrease the personnel and equipment time needed for monitoring the immobilized animal through its recovery. Intubation is recommended for camels being anesthetized for longer than 20 minutes.

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 dromedary camel, 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 also be used to stimulate breathing in camels suffering from respiratory depression/arrest. Doxapram is widely used as a respiratory stimulant by veterinarians and has been shown to increase the minute ventilation in large herbivores immobilized with etorphine.⁷ The use of oxygen is recommended during camel immobilization, as it can significantly lower the risk of respiratory arrest occurring. It can also be combined with partial opioid reversal agents to better alleviate hypoxia.⁶