Respiratory Arrest in Kudu Antelope During Chemical Immobilization
The chemical immobilization of kudu antelope is often necessary for a variety of reasons, including physiological study, research, and for the purposes of wildlife management. However, 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.
There are two species of kudu antelope: The lesser kudu (Tragelaphus imberbis) and the greater kudu (Tragelaphus strepsiceros). The greater kudu is comprised of three subspecies: Tragelaphus strepsiceros, Tragelaphus chora and Tragelaphus cottoni.1 Greater kudus are common in Eastern and Southern Africa. The more elusive lesser kudu is common in northeast and East Africa.2
Causes of Respiratory Arrest
While respiratory arrest and cardiac arrest are different complications, 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 whereby respiratory function is restored.
Respiratory arrest during the chemical immobilization of kudu can occur due to drug overdose, but in many cases, it can come about as a spontaneous adverse reaction to immobilizing drugs (e.g., the animal was inordinately stressed, comorbidities existed, etc.). 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.3
In the case of respiratory arrest 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. 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 such as severe brain damage or death.3
According to the available literature, different 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 all antelope anesthesia, and intubation has also been recommended for any anesthetized antelope that needs to be transported or anesthetized for greater than one hour. Until the more recent use of formulated drugs, opioids were the mainstay of antelope anesthesia in wildlife and captive care.5
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 antelope as a result of immobilizing drugs, the probability is high that this is in reaction to opioids.
Respiratory Arrest in Kudu
Respiratory depression (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 antelope 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 typically 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.
When respiratory arrest occurs, the ultimate goal is to restore adequate ventilation and oxygenation without further compromising an already compromised cardiovascular situation.5 In the event of respiratory arrest in an immobilized antelope, 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.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 an antelope 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.5 The use of oxygen is recommended during the immobilization of kudu, as it can lower the risk of respiratory arrest occurring. It 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.
3Arnemo, J. Kreeger, T. (2018). Handbook of Wildlife Chemical Immobilization 5th Ed. Sunquest Publishing, 2007.
4Ball, L. Antelope Anesthesia. Wiley Online Library, 25 July 2014, https://doi.org/10.1002/9781118792919.ch60.
5Arnemo, 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.
6Van der Schier, R., et. al. (2014) Opioid-induced respiratory depression: reversal by non-opioid drugs. F1000 Prime Reports, 6, pp.1–8.
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