Respiratory Arrest in Bactrian Camels During Chemical Immobilization
The chemical immobilization of Bactrian camels can become necessary for wildlife management, physiological study and research. 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 discrete complications however, if left untreated, respiratory arrest always leads to cardiac arrest. Interruption of pulmonary gas exchange (respiration) for more than five minutes can result in irreversible organ damage, particularly in the brain.1 Unless respiratory function is restored, cardiac arrest will follow.
Causes of Respiratory Arrest
Respiratory arrest during chemical immobilization can occur due to an overdose of the drugs being used, but it can also come about as a spontaneous adverse reaction to these 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 of respiratory arrest brought on by chemical immobilization, the decreased respiratory effort reflects impairment of the central nervous system (CNS) due to the immobilizing drugs. Drugs that decrease respiratory effort include opioids and certain sedatives. Combinations of some 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 the 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
Bactrian Camels: Background and Biology
The Bactrian camel (Camelus bactrianus) inhabits western China and parts of central Asia. These animals are set apart from their more western-ranging relative, the dromedary camel (Camelus dromedarius), in that Bactrian camels have two humps on their backs, whereas dromedary camels have only one.2 Both Bactrian camels and dromedary camels are large animals with an average height of 7 feet. Males weigh 900 to 1,400 pounds; females are about 10% smaller and lighter. Bactrian camels are also noted for their shaggy coats, which they shed during the summer months.
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. 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
Like dromedary camels, most Bactrian camels alive today have been domesticated. There are however, herds of wild Bactrian camels in China and Mongolia. Wild Bactrian camels live in herds of about 6 to 20, although they sometimes gather in groups of up to 30 individuals. Herds typically consist of one alpha adult male leading adult females and their calves. Bactrian camels are not territorial; occasionally, multiple herds will cross paths and form a larger herd which can reach up to 500 individuals. Herds spend the majority of their days migrating and grazing. During the winter months, Bactrian camels migrate to the Gobi desert steppe, returning to the desert when the snow melts in the spring.1
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
Both camel species are polygynous, meaning that the dominant male in a herd will mate with any of the females in the herd. The Bactrian camel's breeding season takes place in March and April. The calves are fully mobile within the first 24 hours after birth. Calves in the wild are typically weaned within the first two years.2,4
Treating Respiratory Arrest in Bactrian Camels
Respiratory depression (hypoventilation) is significantly reduced or compromised breathing. Respiratory arrest is the complete 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 one of the most notable pharmacological developments to wildlife immobilization; these drugs 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. It should be noted that intubation is recommended for any camel being anesthetized for longer than 20 minutes.5
When respiratory arrest in a camel occurs, 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 Bactrian 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.
Our pharmacists are also encouraged to develop strong working relationships with our veterinarians in order to better care for veterinary patients. Such relationships foster an ever-increasing knowledge base upon which pharmacists and veterinarians can draw, making both significantly more effective in their professional roles.
Disclaimer
The information contained in this blog post is general in nature and is intended for use as an informational aid. It does not cover all possible uses, actions, precautions, side effects, or interactions of the medications shown, nor is the information intended as medical advice or diagnosis for individual health problems or for making an evaluation as to the risks and benefits of using a particular medication. You should consult your veterinarian about diagnosis and treatment of any health problems. Information and statements have not been evaluated by the Food and Drug Administration ("FDA"), nor has the FDA approved the medications to diagnose, cure or prevent disease. Medications compounded by NexGen Pharmaceuticals are prepared at the direction of a veterinarian. NexGen Pharmaceuticals compounded veterinary preparations are not intended for use in food and food-producing animals.
NexGen Pharmaceuticals, LLC does not recommend, endorse or make any representation about the efficacy, appropriateness or suitability of any specific dosing, products, procedures, treatments, services, opinions, veterinary care providers or other information that may be contained in this blog post. NEXGEN PHARMACEUTICALS, LLC IS NOT RESPONSIBLE NOR LIABLE FOR ANY ADVICE, COURSE OF TREATMENT, DIAGNOSIS OR ANY OTHER INFORMATION, SERVICES OR PRODUCTS THAT YOU OBTAIN THROUGH THIS BLOG POST.