Respiratory Arrest in Camels During Chemical Immobilization
The chemical immobilization of camels is may become necessary for a variety of reasons, including physiological study, research, and for the purposes of wildlife management. The drugs used for chemical immobilization can 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 different 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.1 Cardiac arrest almost always follows without respiratory function being restored.
Causes of Respiratory Arrest
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.1
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.1
Chemical Immobilization in Camels
There are currently three recognized species of camel: the dromedary camel (Camelus dromedarius), the Bactrian camel (C. bactrianus) and the wild Bactrian camel (C. ferus). Approximately 90% of the world's camels are dromedary camels (also known as Arabian camels) and nearly all of these are domesticated.2 Camels are found in northern Africa and southwestern Asia, and were introduced into Australia in the 1840's nearly two centuries ago.
The dromedary camel has one back hump, while the domesticated Bactrian and wild Bactrian camels have two humps. Arabian camels have been domesticated for approximately 3,500 years and have been long valued as pack animals that can carry large loads (over 100 lbs.) for up to 25 miles a day.2 Camels have long been used by humans for their wool, milk, meat, leather, and dung.2
Camels are camelids, which includes camels, alpacas and llamas. They are members of the biological family Camelidae, and the only family in the suborder Tylopoda.3 Camels differ from other ruminants in several ways: They have a three-chambered digestive tract rather than a four-chambered one. Their upper lip that is split in two, with each part separately mobile. They also have an isolated incisor in the upper jaw. Their red blood cells 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
All three camel species are approximately 10 feet long and 6-1/2 feet high at the hump. Males weigh in at 900 to 1,400 pounds; females are about 10% smaller and lighter.2 Their color is light brown to medium gray. Bactrian camels are slightly darker and stockier, and have more hair than wild Bactrian camels.2 All camels have heavy eyelashes which protect their eyes from blowing sand, and their nostrils can be squeezed shut.
Camels spend much of their days eating. Their split upper lips allow them to forage short grass very near to the ground. These lips can break off and eat tough vegetation such as thorns or salty plants.3 Camels can go a week or more without water, and a camel can last for several months without food. Their humps can store up to 80 pounds of fat, which camels break down into water and energy when food is not available.2,3
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 1840's to assist in the exploration of inland Australia. Today, there are over one million feral camels in the rangeland ecosystems of Australia.4 Unfortunately, these animals are causing significant damage to the natural environment as well as having a negative social, cultural and economic impact across their extensive range.
Radio-collared camels are currently being used today in Australia as a part of camel population control programs.5 This procedure, which includes chemical immobilization, carries the risk of inducing a wide range of complications in these animals, including respiratory depression and respiratory arrest.
Respiratory Arrest in Camels
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 camel, 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 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 whenever possible, as it can lower the risk of respiratory arrest occurring. It can also be combined with partial opioid reversal agents to better alleviate hypoxia.6
1Izrailtyan I, et. al. Risk factors for cardiopulmonary and respiratory arrest in medical and surgical hospital patients on opioid analgesics and sedatives. PLoS One Mar 22;13(3):e019455, 2018.
6Arnemo, J. Kreeger, T. (2018). Handbook of Wildlife Chemical Immobilization 5th Ed. Sunquest Publishing, 2007.
7Arnemo, J., et. al. Field Emergencies and Complications. In: G. West, D. Heard, & N. Caulkett, eds. Zoo Animal and Wildlife Immobilization and Anaesthesia. Oxford: Wiley Blackwell, pp. 139–147.
8Van der Schier, R., et. al. (2014) Opioid-induced respiratory depression: reversal by non-opioid drugs. F1000 Prime Reports, 6, pp.1–8.
About NexGen Pharmaceuticals
NexGen Pharmaceuticals is an industry-leading veterinary compounding pharmacy, offering sterile and non-sterile compounding services nationwide. Unlike other veterinary compounding pharmacies, NexGen focuses on drugs that are difficult to find or are no longer available due to manufacturer discontinuance or have yet to be offered commercially for veterinary applications, but which still serve a critical need for our customers. We also specialize in wildlife pharmaceuticals, including sedatives and their antagonists, offering many unique options to serve a wide array of zoo animal and wildlife immobilization and anesthesia requirements.
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