Most thermal injuries (burns) in horses are caused by barn fires, lightning, electricity, caustic chemicals, or friction (eg, due to rope burns). Most burns are superficial, easily managed, inexpensive to treat, and quick to heal. Serious burns can be life-threatening or life-changing, require intensive management, and have high associated costs.
The severity of a burn is directly proportional to its size and depth. Large burns that damage all layers of tissue result in the greatest morbidity and mortality rates because of fluid and electrolyte losses, as well as secondary infection.
Initial evaluation of the burn patient must include the following:
classifying the burn according its depth
approximating the total body surface area affected
assessing the patient's cardiovascular and pulmonary status
determining the need for systemic support and analgesia
estimating the cost of treatment and eventual prognosis for recovery
Classification of Burns in Horses
As with humans, burns of horses are classified according to the depth of the injury (see the table Classification of Burns in Horses).
Classification of Burns in Horses
Burn Classification | Tissue Layers Involved | Clinical Characteristics |
|---|---|---|
First degree | Superficial layers of epidermis | Nonexudative, erythematous, tissue edema, painful. Usually heal without complication. |
Second degree (superficial) | Epidermis and superficial dermis | Exudative, erythematous, blister formation, painful. Usually heal without complication. |
Second degree (deep) | Epidermis and deep dermis | Erythema, tissue edema, eschar formation, not painful. Can progress to full thickness, delaying healing. |
Third degree | All layers of skin, extending into subcutaneous tissue | Variable color (white/black), marked fluid loss from tissue, eschar formation, not painful. Susceptible to infection and complications. |
Fourth degree | All layers of skin, extending into muscle, bone, ligament, fat, and fascia | Charred appearance of tissue, large tissue defects, not painful. Prognosis guarded; persistent tissue defects likely. |
First-Degree Burns
First degree-burns are limited to the most superficial layers of the epidermis. These burns are painful and characterized by erythema, edema, and desquamation of the superficial layers of skin. The germinal layer of the epidermis is spared, and burns heal without complication.
Second-Degree Burns
Second-degree burns involve the epidermis and can be superficial or deep.
Superficial second-degree burns involve the stratum corneum, stratum granulosum, and a few cells of the basal layer (see superficial second-degree burn image). Tactile and pain receptors remain intact. Because the basal layers are relatively uninjured, superficial second-degree burns heal rapidly (within 14–17 day), with minimal scarring.
Courtesy of Dr. R. Reid Hanson.
Deep second-degree burns involve all layers of the epidermis, including the stratum basale and stratum spinosum layers (see deep second-degree burn image). These burns are characterized by erythema and edema at the epidermal-dermal junction, necrosis of the epidermis, accumulation of white blood cells at the base of the burn zone, formation of eschar, and minimal pain.
Courtesy of Dr. R. Reid Hanson.
The only germinal cells spared in deep second-degree burns are those in the ducts of sweat glands and hair follicles. These burns can heal spontaneously in 3–4 weeks if care is taken to prevent further dermal ischemia that can lead to full-thickness necrosis.
Third-Degree Burns
Third-degree burns are characterized by loss of the epidermal and dermal components, including the adnexa (see third-degree burn image). When fresh, these burns range in color from white to black. There is fluid loss and a marked cellular response at the margins, eschar formation, lack of pain, shock, wound infection, and sometimes bacteremia and septicemia.
Courtesy of Dr. R. Reid Hanson.
Third-degree burns heal by contraction and epithelialization from the wound margins, or acceptance of an autograft. These burns are frequently complicated by infection.
Fourth-Degree Burns
Fourth-degree burns involve all of the skin and underlying muscle, bone, ligaments, fat, and fascia (see fourth-degree burn image). Fourth-degree burns result in tissue defects that can be life-threatening. Grafting could be required to facilitate formation of a functional scar.
Courtesy of Dr. R. Reid Hanson.
Because heat is slow to dissipate from burn wounds, it is often difficult to accurately evaluate the amount of tissue damage in the first 24–72 hours after injury. The extent of the burn depends on the size of the area exposed. The severity relates to the maximum temperature that the tissue attains and the duration of overheating. The mechanism of burn injury explains why skin damage often extends beyond the boundaries of the original burn.
Pathophysiology of Thermal Injuries in Horses
Severe burns (large, deep second-degree, third-degree, and fourth-degree burns) are accompanied by a dramatic cardiovascular effect termed "burn shock," which resembles hypovolemic shock. Local and systemic capillary permeability increases dramatically in response to heat and release of cytokines, prostaglandins, nitric oxide, vasoactive leukotrienes, serotonin, histamine, and oxygen radicals.
Treatment of Thermal Injuries in Horses
Burn patients' fluid deficit can be calculated as 4 mL/kg × burn area as a percentage of total body surface area. For example, a 500-kg horse with a 10% body surface burn would need 20 L. Half of this deficit is administered in the first 8 hours; the remaining half can be titrated as needed to maintain stable and adequate blood pressure. An alternative is to administer hypertonic saline solution (4 mL/kg) followed by isotonic fluids.
If the horse has smoke or heat inhalation injury, crystalloid administration should be limited to the amount that normalizes circulatory volume and blood pressure, because the injured lung could be susceptible to pulmonary edema after fluid administration.
Continuing to administer electrolyte solutions at the same rate after burn shock resolves leads to edema, which counters any improvement in cardiovascular dynamics. The attending veterinarian should carefully monitor hydration, lung sounds, and cardiovascular status during fluid administration via clinical assessment and measurement of PCV and total protein concentration.
The severe pain experienced by burn victims necessitates a careful, multimodal analgesia plan.
Flunixin meglumine (0.25–1.0 mg/kg, IV, every 12–24 hours) is an effective analgesic and anti-inflammatory.
Other anti-inflammatory drugs, such as phenylbutazone (2–4 mg/kg, IV or PO, every 12 hours) or fibrocoxib (0.1 mg/kg, PO, every 24 hours) can also be considered; however, the clinician should be wary of the longterm effect of NSAIDs on the colon, kidney, and stomach.
For more serious burns, morphine (0.1 mg/kg, IV or IM, every 6–24 hours) and/or ketamine (0.4–0.8 mg/kg/hour, IV as CRI) should be considered.
Pentoxifylline (8.0 mg/kg, IV, every 12 hours) improves perfusion by decreasing blood viscosity.
Dimethyl sulfoxide (DMSO; 1 g/kg, IV) administered in the first 24 hours can decrease inflammation and pulmonary edema.
If pulmonary edema is present and is unresponsive to DMSO and furosemide treatment, dexamethasone can be administered once at 0.5 mg/kg, IV.
Maintenance of airway patency, adequate oxygenation and ventilation, and stabilization of hemodynamic status are the cornerstones of treatment for smoke inhalation injury. Antimicrobials and corticosteroids do not affect survival rates and should not be routinely administered to smoke inhalation patients.
Pearls & Pitfalls
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Systemic antimicrobials are indicated only for confirmed infections, which increase in incidence 2–3 days after smoke inhalation. Procaine penicillin (22,000 IU/kg, IM, every 12 hours) is effective against oral contaminants colonizing the airway. If clinical signs of respiratory disease worsen, a transtracheal aspirate should be submitted for culture and susceptibility testing, and the antimicrobial regimen should be adapted accordingly. Patients with suspected substantial smoke inhalation should be observed closely for several hours (see bronchial alveolar wash image).
Courtesy of Dr. Reid Hanson.
Successful treatment of thermal injuries in horses depends on continual patient reassessment, as well as early and aggressive patient care. General principles of wound management should be adhered to, including the following:
prevent and control infection
manage contamination via wound debridement where appropriate
prevent further damage to tissue
Superficial burns can be left to heal by second intention; full-thickness wounds, however, usually require surgical closure or tissue grafting. First-degree burns are generally not life-threatening and can be simply managed.
Second-degree burns are associated with vesicles and blisters. Vesicles should be left intact because blister fluid provides protection from infection, and an intact blister is less painful than the denuded, exposed surface. An antibacterial dressing such as silver sulfadiazine should be applied to wounds while an eschar is allowed to form.
Third-degree burns can be difficult to manage. The patient’s systemic condition should be stabilized as rapidly as possible before wound management is undertaken. Destruction of the dermis leaves a primary collagenous structure called an eschar. The eschar does not prevent bacterial contamination or evaporation of heat or water. It should be covered with a topical antimicrobialtwice daily. Wound contraction does not occur while the eschar is intact. The eschar is sloughed by bacterial collagenase activity within 4 weeks. The exposed bed can then be grafted or allowed to contract.
Pearls & Pitfalls
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Although bacterial colonization of large burns in horses cannot be prevented, wounds should be cleansed every 8–12 hours, and a topical antimicrobial should be reapplied to decrease the bacterial load. Occlusive dressings should be avoided because of their ability to produce a closed wound environment that can both encourage bacterial proliferation and delay healing.
Amnion (the amniotic membrane from a placenta) can decrease the pain of the wound and is antibacterial. It is more useful in areas of the body, such as the distal limbs, where it can be firmly pressed into the wound. In addition, circulation to the burned areas is often compromised, thus substantially impairing delivery of parenterally administered antimicrobials within the wound.
The most commonly applied topical antimicrobial to treat burns is silver sulfadiazine in a 1% water-miscible cream. It is a broad-spectrum, antimicrobial agent able to penetrate eschars. Silver sulfadiazine is active against gram-negative bacteria, especially Pseudomonas spp; it is also effective against Staphylococcus aureus, Escherichia coli, Proteus spp, Enterobacteriaceae, and Candida albicans. Silver sulfadiazine causes minimal pain; however, it must be applied twice a day because it is inactivated by tissue secretions.
Another good topical option is manuka honey. The high sugar concentration of honey exerts osmotic pressure on bacterial cells and draws out intracellular fluid, making it bactericidal. In addition, honey helps maintain the moist wound environment that is essential for eventual tissue healing.
Many equine burn patients suffer pruritus to such an extent that measures must be taken to prevent self-mutilation of wounds. Reserpine (2.5 mg per 500-kg horse, PO, for 7–10 days), typically administered to horses as a long-acting tranquilizer, can be effective in decreasing the urge to scratch by successfully breaking the itch-scratch cycle.
Pearls & Pitfalls
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Weight loss of 10–15% during the course of illness due to thermal injury is indicative of inadequate nutritional intake. Gradually increasing dietary concentrate, adding fat in the form of vegetable oil, and offering free-choice alfalfa hay can help increase the horse's caloric intake.
Key Points
Large and/or deep burns can be associated with systemic compromise that must be addressed.
Smoke inhalation and lung injury should be considered as a possibility in burn patients.
Topical wound care, pain management, and nutritional support are important aspects of burn management in horses.
For More Information
Hanson RR. Management of burn injuries in the horse. Vet Clin North Am Equine Pract. 2005;21(1):105-123.
Vaughn L, Beckel N. Severe burn injury, burn shock, and smoke inhalation injury in small animals. Part 1: Burn classification and pathophysiology. J Vet Emerg Crit Care (San Antonio). 2012;22:179-186.
Vaughn L, Beckel N, Walters P. Severe burn injury, burn shock, and smoke inhalation injury in small animals. Part 2: Diagnosis, therapy, complications, and prognosis. J Vet Emerg Crit Care (San Antonio). 2012;22:187-200.
