Respiratory Depression in Dromedary Camels During Chemical Immobilization
Camels are native to northern Africa and Asia, and are known for their ability to go for long periods without both food and water. The dromedary camel (Camelus dromedarius) has one back hump, whereas the domesticated Bactrian camel (C. bactrianus) and the wild Bactrian camel (C. ferus) have two.
Camels have been domesticated for approximately 3,500-4,000 years. As such, the dromedary camel—also called the one-humped camel or Arabian camel—is generally understood as being extinct in the wild. A large feral population (estimated at around one million individuals) exists in the Australian outback, descended from pack animals imported for exploration of the interior of the continent during the 1840s.
All three camel species are approximately 10 feet long and 6-1/2 feet high at the hump. Males typically weigh approximately 900 to 1,400 pounds; females are about 10% smaller and lighter. Camels are diurnal and spend much of their days eating. Their upper lips are split in half, with each half moving independently. This allows them to forage short grasses and plants that are very near to the ground.2,3
The ability of the dromedary camel to survive in desert conditions without water for long periods of time is legendary. The physiological adaptations of this animal have earned it the title "Ship of the Desert." Dromedary camels obtain much of their water from desert vegetation, and can survive after losing over 40% of their body weight in water. When water is available, camels can drink up to 30 gallons at a time. Camels also have an internal “thermostat” and normally do not start sweating until their body temperature reaches around 107oF.3 Their back humps store up to 80 pounds of fat, which they break down into energy when food is scarce.3
As previously mentioned, dromedary camels were introduced into Australia in the 1800's to assist in the exploration of inland Australia, which is similar to this animal’s native habitat. At present, there are over one million feral camels in the rangeland ecosystems of Australia. Unfortunately, feral camels are now negatively impacting the natural environment to a significant degree. Today, radio-collared camels are being used in Australia to enhance population control programs.4 The procedures involved in their capture, including chemical immobilization, carry the risk of inducing a wide range of complications in these animals.
Dromedary Camels and Chemical Immobilization
Chemical immobilization has become the preferred method of capture for large wildlife species for the purposes of translocation, diagnostic testing and medical treatment. In most cases, it has proven to be a safer, superior method to traps, capture with nets and the mass-capture of herds of animals.
In zoos, farms, breeding facilities and some free-ranging situations, the chemical immobilization of dromedary camels is usually carried out from the ground. In some circumstances, animals are located and darted from a helicopter. It should be noted that any capture method can cause significant stress and trauma to target animals, potentially giving rise to complications.
Remote drug delivery systems are typically used for the purpose of chemical immobilization, usually via a dart gun or blowpipe. Drugs are injected by means of a dart syringe which is fired from the dart gun at a distance. Since dart volume can be a limiting factor, immobilizing drugs must be highly potent and concentrated. They must also have a high therapeutic index and wide safety margin since animals cannot be examined and weighed prior to immobilization. The ideal drugs must be fast-acting to limit stress and the likelihood of escape following darting. They should also be reversible, since animals are often released immediately after the capture event.
Chemical Immobilization and Respiratory Depression
Even in the case of highly-domesticated animals such as dromedary camels, individuals are often highly-stressed and can run long distances after being darted. Furthermore, most of the drugs used for immobilization have side effects; they not only cause sedation by influencing the central nervous system, but also influence cardiovascular, respiratory and thermoregulatory functions.5 The most commonly-encountered problems during wildlife immobilization events include respiratory depression, cardiovascular disturbances, bloat, compromised thermoregulation, hypoxia and capture myopathy.5-7
In many cases, opioids are used for the chemical immobilization of camels and other wildlife. A chief disadvantage of using these drugs however, is that they cause clinically significant respiratory depression due to their potent effect on mu-opioid receptors.5 Activation of mu-opioid receptors in the respiratory centers of animals depresses neurons that generate the normal respiratory rhythm. At the same time, activation of these receptors activate other receptors in the brain stem, on the aortic arch and carotid bodies, which depresses normal respiratory function.6 Other classes of drugs also have the potential to compromise respiratory function (e.g., through causing hypoxia).
Treating Respiratory Depression in Dromedary Camels
There are several approaches that are typically used to mitigate opioid-induced respiratory depression in camels undergoing chemical immobilization. Endotracheal intubation is widely recommended for camelids undergoing procedures longer than 20 minutes. Assisted ventilation and oxygen insufflation may be used to combat hypoxia brought on by some immobilizing agents,5 while agents such as opioid antagonists or partial antagonists can also be used. Unfortunately, the latter also reduce the desirable effects of immobilizing drugs (e.g., the degree of immobilization, sedation and analgesia). Respiration can also be improved by administering respiratory stimulants which act on non-opioid receptor systems such as potassium channel blockers, ampakines and serotonin receptor agonists.7
Oxygen supplementation is recommended during wildlife immobilization and can be combined with a partial opioid reversal agent to better alleviate hypoxia.5 Naltrexone may be 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.
Partial opioid antagonists or mixed agonists/antagonists may be used for the reversal of opioids such as diprenorphine, nalorphine or butorphanol if residual analgesic or sedative effects are required.6,7 Signs of recovery after naltrexone administration typically consist of increased respiratory depth, followed by ear twitching, eye movement and lifting of the head.5
Partial mu-receptor antagonists (e.g., butorphanol) can be used to alleviate respiratory depression caused by strong mu-agonistic immobilization drugs.5,8 Some of these partial antagonists, however, also reduce the immobilization effects of opioids. Potassium channel blockers such as doxapram can also be used to stimulate breathing. Doxapram is widely used as a respiratory stimulant by veterinarians. It has been shown to increase the minute ventilation in large herbivores immobilized with etorphine.5
While efficacious drug combinations used for darting were not always commercially available as pre-mixed solutions, some of these can now be purchased as highly-concentrated drug formulations for this purpose from compounding pharmacies. Many of these formulations are often species-specific, more reliable and are less likely to bring about complications such as respiratory depression in camels than drugs and combinations used in the past.
5Arnemo, J. Kreeger, T. (2018). Handbook of Wildlife Chemical Immobilization 5th Ed. Sunquest Publishing, 2007.
6Arnemo, 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.
7Bailey, P.L., et. al. (1985) The ED50 of carfentanil for elk immobilization with and without the Tranquilizer R51703. The Journal of Wildlife Management, 49(4), pp.931–934.
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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