Respiratory Arrest in Sable Antelope During Chemical Immobilization
The sable (Hippotragus niger) is a large antelope that inhabits the savannah of East Africa below Kenya and into South Africa. They are members of the Hippotraginae subfamily, due to their horse-like build and erect mane that is found on the neck of most species.1
There are four subspecies of sable that are currently recognized, with common designations that can vary depending on the source:
- Zambian (Hippotragus niger kirkii)
- Common or Southern (Hippotragus niger niger)
- Eastern (Hippotragus niger roosevelti)
- Giant or Angolan (Hippotragus niger variani)
Mature male sable weigh approximately 520-600 pounds; females are shorter and weigh around 30 to 50 pounds less.2The sable has a thick neck and heavy hide. Both males and females have horns, but those of the females are shorter and slightly less curved. Sable change color as they mature; calves are born with a reddish-brown color and almost no markings. White markings on the face and undersides appear as they grow older and their coats become darker.1
Sable favor grasslands and woodlands, where they eat grass and leaves. They stay near sources of water that are close to where they feed. Living in herds of 30 or more animals, sable bulls are territorial and will fight other bulls for territory and breeding rights. Subadult males leave the herd when they reach three years old, after which they form small bachelor herds. Young females typically stay with the main herd. When sable herds encounter predators, the dominant male will stand its ground and use its horns to fight off the threat.1
Chemical Immobilization and Respiratory Arrest
The chemical immobilization of sable may be necessary for a variety of reasons, including physiological study, research, and for the purposes of wildlife management. Immobilizing drugs can adversely affect the cardiovascular and respiratory systems of these animals and, in certain circumstances, can lead to complications such as respiratory depression and/or respiratory arrest.
Respiratory arrest and cardiac arrest are different complications, but if left untreated, the former inevitably leads to the latter. Interruption of pulmonary gas exchange (respiration) for more than five minutes can irreversible vital organ damage, particularly in the brain.3 Cardiac arrest almost always follows without an intervention restoring respiratory function. 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.3
Drugs that decrease respiratory effort include opioids and certain sedatives. In the area of wildlife immobilization, the most significant group of drugs that carry the potential to depress ventilation are opioids, which include both the natural derivatives, semisynthetic opioids and synthetic opioids.6 When respiratory arrest occurs in an immobilized sable as a result of immobilizing drugs, the probability is high that this is in reaction to opioids.
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. Until the more recent use of formulated drugs, opioids were the mainstay of antelope anesthesia in wildlife and captive care.5 The risk for opioid-induced respiratory depression (ORID) is usually most common in the immediate postoperative recovery period but it can persist and lead to catastrophic outcomes.3
Clinical Signs of Respiratory Arrest
The available literature holds that the various species of antelope each have their own anesthesia recommendations with dosage variations due to their diverse individual responses to anesthetic agents.4,5 These variations are factors in the risk of complications. Monitoring core body temperature is widely recommended in antelope anesthesia, and intubation has also been recommended for any anesthetized antelope that needs to be transported or anesthetized for greater than one hour.
Respiratory depression (or hypoventilation) is characterized by reduced and/or ineffective breathing. Respiratory arrest is the cessation of breathing. There are several approaches available to alleviate respiratory arrest in sable 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.4,6 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.
Treating Respiratory Arrest in Sable
When respiratory arrest occurs, the goal is to restore adequate ventilation and oxygenation without further compromising an already compromised cardiovascular situation.7 In the event of respiratory arrest in an immobilized sable, the administration of all immobilizing drugs should be immediately 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 analgesic or sedative effects are still required, partial opioid antagonists or mixed agonists/antagonists can be used for the reversal of opioids such as diprenorphine, nalorphine or butorphanol.4,6 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).
Potassium channel blockers such as doxapram can also be used to stimulate breathing in sable suffering from respiratory depression. 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.5 The use of oxygen is recommended during antelope immobilization whenever possible, since it can lower the risk of respiratory arrest occurring. Oxygen can also be combined with partial opioid reversal agents to better alleviate hypoxia.3
3Izrailtyan 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.
4Arnemo, J. Kreeger, T. (2018). Handbook of Wildlife Chemical Immobilization 5th Ed. Sunquest Publishing, 2007.
5Ball, L. Antelope Anesthesia. Wiley Online Library, 25 July 2014, https://doi.org/10.1002/9781118792919.ch60.
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.
7Van 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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