Frostbite in Sable Antelope During Chemical Immobilization
The sable (Hippotragus niger) is a large African antelope of stout build with a long face, short neck, and dark mane.1Sable have very large, ringed horns which rise upward and curve backward. Both males and females have horns, but those of the females are shorter and slightly less curved. Sable change color as they grow older; calves are born with a reddish-brown color and almost no markings. White markings appear as they grow older and their coats become darker.1
Sable live in the southern savannas of Africa from the southeastern part of Kenya, in eastern Tanzania, Mozambique, Angola and in southern Zaire. They prefer a mixture of grassland and savanna woodlands and avoid open lands when they can.
There are four subspecies of sable, which include:
- Black sable (also Mastitis sable)—This is the most widespread subspecies of sable, with a habitat covering 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
Sable are diurnal, but they are less active during the day. They live in large herds, most often females with their young with one dominant male. Only the most dominant mature males can maintain territories, and these tend to be in the best feeding areas in order to attract females.1 While sable are generally timid like other antelope, they can become aggressive if attacked or provoked. This is particularly true of male sable. When herds are threatened by predators, they often confront them using their formidable horns. It has been reported that some predators, generally big cats, have died during such encounters.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
Risks for Frostbite in Sable
The chemical immobilization of sable can require extended periods of immobility in the captured animal. While hypothermia is an inherent risk to any animal undergoing chemical immobilization regardless of ambient temperature, frostbite is an even greater risk during cooler months, and at higher altitudes. Although the risk of frostbite as a complication of chemical immobilization tends to be significantly lower for African species in the field (as opposed to those in the Northern Hemisphere, for example), it still does present some risk.
Frostbite is a freezing injury that may be divided into four phases:
- Vascular stasis
- Late ischemic3
The first phase, prefreeze, involves tissue cooling with accompanying vasoconstriction and ischemia and without ice crystal formation. The freeze–thaw phase is represented by the intracellular or extracellular formation of ice crystals. This can give rise to protein and lipid derangement, cellular electrolyte shifts, cellular dehydration, cell membrane lysis, and cell death. In the vascular stasis phase, vessels fluctuate between constriction and dilation, and blood may leak from vessels or coagulate within them. The late ischemic phase results from progressive tissue ischemia and infarction from a cascade of events, including inflammation, vasoconstriction and emboli.4
Frostbite is classified into four degrees of injury which follow the classification schemes for thermal burn injury. The early stages of frostbite are to be differentiated from frostnip, which is a superficial nonfreezing cold injury associated with intense vasoconstriction on exposed skin. Frostnip may, however, precede frostbite.5,6
- First-degree frostbite causes numbness and erythema. A white or yellow, firm, and slightly raised plaque develops in the area of injury. There may be slight epidermal sloughing and mild edema is common.
- Second-degree frostbite injury causes superficial skin vesiculation. A clear or milky fluid will be present in superficial blisters surrounded by erythema and edema.
- Third-degree frostbite causes deeper hemorrhagic blisters, indicating that the injury has extended into the reticular dermis and beneath the dermal vascular plexus.
- Fourth-degree frostbite extends completely through the dermis and involves the comparatively avascular subcutaneous tissues, with necrosis extending into muscle and bone.3
One variation offered by McIntosh, et. al., involves a 2-tier classification scheme:
- Superficial—Minimal anticipated tissue loss, corresponding to first- and second-degree injury.
- Deep—Anticipated tissue loss corresponding to third- and fourth-degree injury.3
It should be noted that the severity of frostbite may vary within a single extremity.
Prevention of Frostbite in Sable
The preponderance of literature suggests that prevention is a far better methodology than treatment for frostbite, which is usually preventable but often not improved by treatment. Underlying medical problems and the chemical immobilization event itself can increase risk of frostbite, so prevention must address both health-related and environmental aspects.5
Preventive measures to ensure local tissue perfusion include:
- Maintaining adequate core temperature
- Maintaining adequate body hydration
- Minimizing the effects of any known diseases that might decrease perfusion
- Covering the body and head to insulate from the cold
- Minimizing any blood flow restriction
- Using supplemental oxygen in severely hypoxic conditions3,6
Measures should also be taken to minimize exposure of the animal’s tissues to cold, such as:
- Avoid environmental conditions that predispose to frostbite if possible (e.g., below -15°C, even with low wind speeds
- Protecting exposed skin from moisture, wind, and cold
- Avoiding perspiration or wet extremities
- Increasing insulation and skin protection
- Using chemical and/or electric warmers to maintain peripheral warmth (These should be close to body temperature before being activated and must not be placed directly against skin or constrict flow)
- Regularly checking the animal’s temperature
- Recognizing frostnip or superficial frostbite before it becomes more serious
- Minimizing duration of cold exposure3,7
Treating Frostbite in Sable
If an animal’s body part is frozen in the field, the frozen tissue should immediately be protected from further damage.3,4 A decision must be made whether to thaw the tissue. If environmental conditions are such that thawed tissue could refreeze, it is safer to keep the affected part frozen until a thawed state can be maintained. Frostbite thaws spontaneously and should be allowed to do so if rapid rewarming cannot be easily achieved.
Hypothermia can accompany frostbite; this causes peripheral vasoconstriction that impairs blood flow to the extremities. Mild hypothermia may be treated concurrently with frostbite injury. Moderate and severe hypothermia should be treated prior to treating frostbite injury.6
Hydration Following Frostbite
Frostbite injury can result in vascular stasis, so appropriate hydration and avoidance of hypovolemia are important for frostbite recovery. Intravenous normal saline should be given to maintain normal urine output. IV fluids should optimally be warmed before infusion and infused in small, rapid boluses, as slow infusion can result in fluid cooling and even freezing as it passes through tubing. Fluid administration should be optimized to prevent clinical dehydration.5,6
Treatment With Low Molecular Weight Dextran
Intravenous low molecular weight dextran (LMWD) decreases blood viscosity by preventing red blood cell aggregation and formation of microthrombi and can be given in the field once it has been warmed. In some animal studies, the extent of tissue necrosis was found to be significantly less than in control subjects when LMWD was used, and was more beneficial if given early.3,7
The use of LMWD has not been evaluated in combination with other treatments such as thrombolytics. LMWD should be given if the animal is not being considered for other systemic treatments, such as thrombolytic therapy.4
Treatment With NSAIDS
Nonsteroidal anti-inflammatory drugs (NSAIDs) block the arachidonic acid pathway and decrease production of prostaglandins and thromboxanes. These can lead to vasoconstriction, dermal ischemia, and further tissue damage.3 No studies have demonstrated that any particular anti-inflammatory agent or dosing is clearly related to outcome, however. One rabbit ear model study showed 23% tissue survival with aspirin vs 0% in the control group.6 However, aspirin can block the production of certain prostaglandins that are beneficial to wound healing.7 Thus, ibuprofen has been recommended rather than aspirin in cases of frostbite.
3McIntosh, S., et. al. Clinical Practice Guidelines for the Prevention and Treatment of Frostbite: 2019 Update. Wilderness Medical Society Clinical Practice Guidelines, Volume 30, Issue 4, Supplement S19-S32, December 01, 2019.
4McIntosh, S.E., et. al. Wilderness Medical Society practice guidelines for the prevention and treatment of frostbite: 2014 update.Wilderness Environ Med. 2014; 25: S43-S54
5Mazur P. Causes of injury in frozen and thawed cells. Fed Proc. 1965; 24: S175-S182
6Lange K., et. al. The functional pathology of frostbite and the prevention of gangrene in experimental animals and humans.Science. 1945; 102: 151-152.
7Cauchy E., et. al. Retrospective study of 70 cases of severe frostbite lesions: a proposed new classification scheme. Wilderness Environ Med. 2001; 12: 248-255.
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