Cardiac Arrest in Sable Antelope During Capture and Chemical Immobilization

The African sable (Hippotragus niger) is an antelope that inhabits the savannah of East Africa below Kenya and into South Africa. They are members of the Hippotraginae family, 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, which include:

• Black sable (also Mastitis sable)—This is the most widespread sable. Its habitat covers south of the Zambezi River through Zimbabwe and Botswana into South Africa.
• Giant Sable (also Royal sable)—These have the longest horns of any other sable subspecies.
• Common (also southern sable)—This antelope is sometimes called the West Zambian sable.
• Eastern sable—This is the smallest of the sable family, with a range that includes the costal lands of southern Kenya, eastern Tanzania and into Mozambique.²

On average, a mature male sable weighs approximately 520-600 pounds, with females being shorter and weighing around 30 to 50 pounds less. The sable has a thick neck and heavy hide. While both males and females have large, backward-curving horns, those of females are shorter. The horns of the males can reach 65 inches in length.¹

Sable live in grasslands and woodlands, where they eat grass and leaves. They typically stay nearby sources of water that are close to where they feed. Living in herds of 30 or more animals, sable bulls are very territorial and will fight other bulls for territory and breeding rights. Subadult males are chased out of 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

Cardiac Arrest: Risks

Cardiac arrest, sometimes called cardiopulmonary arrest (CPA), is described by a sudden, complete failure of the respiratory and circulatory systems. The subsequent lack of oxygen transport can quickly cause systemic cellular death from oxygen depletion.³ Cerebral hypoxia can result in death within four to six minutes of a CPA event if left untreated.⁴

Capture and/or chemical immobilization can result in CPA events in sable, particularly under field conditions. Sometimes the stress of capture can significantly increase the likelihood of cardiac arrest in these animals. While under anesthesia, common causes of CPA can include vagal stimulation, unstable cardiac arrhythmias, severe electrolyte disturbances, exacerbated cardiorespiratory disorders (e.g., congestive heart failure, hypoxia)³ or other comorbidities. Clinical signs of an imminent CPA event can include dramatic changes in breathing effort, rate, or rhythm, significant hypotension, irregular or inaudible heart sounds, changes in the heart rate or rhythm, changes in mucous membrane color and fixed, dilated pupils.

Chemical Immobilization in Sable Antelope

Due to the diverse individual responses to anesthetic agents, each species of antelope has its own anesthesia recommendation with intra-species variations of dosages.^5,6 These variations present an increased risk of complications during anesthetic events. It has been widely reported that until the advent of potent opiates, some antelope species were very difficult to safely capture or anesthetize.⁵ Although carfentanil was reported as effective in many captures, more recently, the combination of butorphanol and azaperone have become popular in the chemical immobilization of pronghorn.

Monitoring core body temperature is essential in sable anesthesia,^5,6 and intubation has been widely 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 (e.g., combinations of α2-agonists such as medetomidine, detomidine, xylazine and their reversal agents), opioids were the mainstay of antelope anesthesia in wildlife and captive care.⁵

Responding to Cardiac Arrest in Sable

Cardiopulmonary cerebral resuscitation in sable involves three stages:

• Basic life support (BLS)
• Advanced life support (ALS)
• Post resuscitation care.⁵

The first stage involves establishing an open and clear airway, providing assisted ventilation, and performing chest compressions. If the animal’s pulse becomes absent or weak, all administration of immobilizing drugs must be suspended and external cardiac massage should be initiated. Most sable can be easily and safely ventilated with a bag-valve mask,³the caveat being that this may not be available under field conditions.

The veterinarian may establish venous access using such methods as intraosseus catheter placement and venous cutdown, in which a small opening is created in a vein to allow passage of a needle or cannula.³ Epinephrine at 0.2 mg/kg (concentrated at 1/10,000) should be given IV or intracardially (IC) while cardiac massage continues. If the animal fails to respond, 0.1 ml/kg IV or IC calcium chloride may be given. If there is still no response, the epinephrine and calcium chloride may be re-administered with 10-20 mEq IV or IC sodium bicarbonate.⁶

Sable that are restored to a perfusing cardiac rhythm can experience rearrest, especially if the original cause of the CPA event has not been identified. As such, resuscitated animals should have cardiovascular and ventilatory support during the period following the CPA episode. Mild hypothermia after resuscitation decreases cerebral oxygen demand and has been shown to improve recovery.³