A third-degree burn, as seen here, causes damage beyond the dermis (deepest layer of skin), extending into subcutaneous tissues.
Photo: R. Reid Hanson, DVM, Dipl. ACVS
The night of May 31, 2011, a barn fire at Phillip Dutton's True Prospect Farm in Pennsylvania took six horses' lives. Five others were lucky enough to escape, but many of their burns were extensive and their recoveries slow. One of those survivors was Caitlin Silliman's top-level event horse Catch a Star, who sustained superficial burns over 80% of her body. She lost significant skin on her left shoulder and along her neck, and her wounds were a combination of first-, second-, and third-degree burns. Her treatment included weeks of pain medications and antibiotics, diligent wound care and cleaning, and hyperbaric oxygen therapy sessions.
Nearly a year later, in March 2012, Silliman and Catch a Star were back in the show ring, competing at Pine Top Farm's Spring Horse Trials in Georgia, with the help of a fitness-training program and a custom-made sheepskin saddle pad to prevent irritation over her permanently hairless spine area.
Tragic events like the True Prospect Farm barn fire are, fortunately, quite rare. But when they do happen, or when wildfire strikes, burns are injuries to be taken very seriously, as they can be deceptively deep. "Over the course of several days the wound might become larger and deeper than it appeared initially," explains Laura Riggs, DVM, PhD, Dipl. ACVS, assistant professor of Veterinary Surgery in Louisiana State University's Department of Veterinary Clinical Sciences. For this reason and others, a veterinarian should promptly evaluate any horse that has survived a fire or sustained a burn injury.
Just as in humans, burns are categorized by degree. First- and second-degree burns leave the deeper layers of skin intact. These wounds generally heal well without grafting--a process in which the veterinarian removes healthy skin from one part of the body and transfers it to the wound bed to enhance healing. Third-degree burns (in which the skin is completely gone) and fourth-degree burns (involving damage to tissues beneath the skin, such as muscle, tendons, and bone) are life-threatening if the affected area is extensive. Many serious cases are a combination of second-, third-, and sometimes fourth-degree burns.
First- and Second-Degree Burns
Reid Hanson, DVM, Dipl. ACVS, ACVECC, professor of equine surgery and lameness at Auburn University, has treated many equine burn injuries. "Most are first-degree burns similar to sunburn; only the top layers of skin are affected," he says. "They heal quickly, with very little treatment. Prognosis is excellent unless there is ocular (eye) or respiratory involvement."
The more serious second-degree burns impact deeper layers of skin. "These are usually painful because nerve endings are still intact, but are usually not life-threatening," explains David Wilson, DVM, MS, Dipl. ACVS, professor of equine surgery at the University of Missouri-Columbia. Pain in the affected area is actually a good sign, indicating the nerves are intact (while third- and fourth-degree burns generally destroy nerves).
Second-degree burns "develop vesicles and blisters--which should be left intact for the first 24 to 48 hours after they form," says Hanson. "Blister fluid provides protection from infection." Also, intact blisters are less painful than the exposed raw skin surface if they break.
"After 24 to 48 hours, we partially excise (remove) the blister and apply an antimicrobial dressing to the wound," he continues. "This allows the eschar to form. This collagen tissue (like a scab) helps protect the wound."
Riggs has observed that many equine barn fire survivors suffer burns over their topline. These burns are often easier to clean and treat than burns underneath the belly or on the legs. "There's more soft tissue over the back than on the legs, scarring is less, and the horse is not lying on the wounds," she explains. On the other hand, "lower limbs have very little tissue covering joints, bones, and tendons. If there's any thermal damage, it's immediately down to vital structures."
Third- and Fourth-Degree Burns
These burns are potentially life-threatening. A third-degree burn causes damage beyond the dermis (deepest layer of skin), extending into subcutaneous tissues. "Immediately after injury, we cool the burn with ice or (a) cold water bath and lavage with a weak, sterile chlorhexadine solution," says Hanson. He cautions, however, that too much water will increase edema (fluid swelling) in the skin. "We leave the eschar intact, but clip surrounding hair and debride (remove) the dead, burned tissues," he continues.
These types of burns only heal by the skin drawing in from the edges of the wound, a process known as contraction, or by grafting.
"Deep second-degree burns, or third- or fourth-degree burns have poor prognoses," says Wilson. "If more than 40 to 50% of the body is affected there will be many issues to deal with, such as significant fluid and protein losses" that are difficult to replace.
When treating severe third- and fourth-degree burns initially, Hanson says he cleans the area and then applies a water-based antibiotic ointment liberally over affected areas to prevent heat and moisture loss and to protect the eschar, which acts as a natural bandage. This also helps prevent bacterial invasion and potential resulting septicemia (bloodstream infection). Over time, these applications also help loosen necrotic (dead) tissue and debris.
"This is a slow method of debridement, allowing removal of all the necrotic tissue and preventing removal of healthy germinal (growing) layers by mistake," Hanson explains.
When the burn starts to heal, newly formed cells migrate under the eschar and lift it off the burn bed. "Once that starts lifting, bacteria can get under it," says Wilson.
At this point, because it's nearly impossible to prevent bacteria from contaminating a large wound, caretakers should clean the area two to three times a day with a weak chlorhexidine solution, applying antibiotic ointment (e.g., silver sulfadiazine) after each cleaning. Veterinarians also sometimes apply aloe vera, which our sources say possesses properties that relieve pain and decrease inflammation while inhibiting bacterial and fungal activity.
"We rarely use systemic antibiotics because there is not enough (local) blood supply to carry them to burned tissues, and it may promote resistant organisms moving in," Hanson notes.
Fluid Loss If a third- or fourth-degree burn exceeds 15 to 20% of the horse's body surface area, he will need immediate intravenous (IV) fluid therapy to combat fluid loss and shock. "We don't use huge volumes of IV therapy because of the risk for overhydrating the horse," says Hanson. This could also increase lung damage if the horse has suffered heat or smoke inhalation; excessive edema in the lungs (pulmonary edema) essentially drowns the horse.
"We use about 20 liters of fluid, maximum, in an adult horse," says Hanson. "We also give Banamine (flunixin meglumine) to reduce pain/inflammation and pentoxifylline to help with circulation of blood through the vessels. We carefully monitor the horse's hydration status, lung sounds, and cardiovascular status."
He adds that, depending on the horse and the amount of protein loss through the burn wounds, he might also administer 10 to 20 liters of plasma. "We often give (intravenous) DMSO (dimethyl sulfoxide) during the first 24 hours to decrease inflammation and pulmonary edema, pulling fluid out of the lungs," he says. "If the veterinarian suspects pulmonary edema, and the horse is unresponsive to DMSO treatment, dexamethasone (a glucocorticoid that acts as an anti-inflammatory and immunosuppressant) might be given just once."
Respiratory Damage Nathan Slovis, DVM, Dipl. ACVIM, of Hagyard Equine Medical Institute, in Lexington, Ky., says it is very important for the veterinarian to listen to the horse's breathing to detect any respiratory stridor (abnormal breathing pattern). "The horse may need steroids, Lasix (furosemide, a diuretic), or some other medication to try to reduce airway swelling from thermal injury," he says. Otherwise, swollen tissues might restrict the horse's ability to breathe or even close off the airways. If airways begin to swell shut, the veterinarian might need to perform a tracheotomy (a surgically created opening through the skin into the trachea, allowing for insertion of a breathing tube).
If a veterinarian suspects respiratory damage or smoke inhalation (most facial burns are accompanied by smoke inhalation), he or she usually puts the horse on systemic antibiotics to treat the lungs. "Unlike burned skin, the lungs still have a good blood supply that can carry antibiotic to damaged areas," says Hanson. "We usually put these horses on intramuscular penicillin if they have an uninjured area where we can inject it. This helps deal with contaminants like soot in the airway. The body has to eliminate all that carbon, and penicillin helps keep the horse from getting secondary bacterial infections."
If respiratory signs worsen (e.g., the horse exhibits elevated respiratory rate or coughing), Hanson suggests the practitioner sample some lung fluid (via the trachea) for a culture and sensitivity test to determine if another antibiotic is needed.
"We generally do an endoscopy of the trachea after a burn, for prognostic purposes, because there may be sloughing of the mucosa inside the airway," he says. "We try to aspirate the sloughed mucosa (using suction tubing), but the procedure should last no longer than 15-second intervals because this is also aspirating oxygen, making it harder for the horse to breathe."
Ocular Damage Another potential post-burn problem is eye damage, such as corneal ulcerations and eyelid burns. "If the lids are swollen we apply an ophthalmic ointment to the cornea (the transparent outer coating of the eye) every six hours," Hanson says. "If the cornea is damaged, we carefully debride the necrotic cornea with the horse tranquilized, while using a topical anesthetic. We apply a topical antibiotic and atropine (which causes the pupil to dilate)."
Skin Problems The post-burn infections described earlier are also common. "We use silver sulfadiazine to cover raw areas," says Hanson. "It is effective against Gram-negative organisms such as pseudomonas and has antifungal activity as well."
A month or two after the initial burn, the horse might become very itchy. If he rubs or chews the healing areas, he can destroy all healing progress. "Antihistamines may be effective in some cases, and reserpine (an antipsychotic) may help decrease the urge to scratch," Hanson advises.
Once healed, the horse's skin might lack pigment and, thus, be more susceptible to sunburn. And if the veterinarian had to graft the wound area, the new skin will be thinner and more fragile and won't have oil glands, sweat glands, or hair follicles.
Weight Loss Burned horses might lose weight due to stress and resulting extra energy requirements. "Caloric expenditure and protein breakdown are greater in burn injuries than in any other physiologic stress state," explains Hanson. "With burns greater than 30% of body surface, energy expenditure doubles."
Thus, "to keep the horse from losing weight we gradually increase the grain and add fat, such as 4 to 8 ounces of vegetable oil, and offer free-choice alfalfa hay to increase caloric intake," he says. "Occasionally we'll use an anabolic steroid." He says the steroid promotes a better appetite as well as muscle development.
A horse might also require nutritional considerations if he inhaled smoke or burned his face. For horses with damage to mucosa in the mouth and upper airways, "We soak the hay with water (to soften it) and feed on the ground to encourage drainage from the airways," says Hanson.
Other burn complications include colic and laminitis (inflammation of the laminae connecting the hoof to the coffin bone), particularly if the horse requires extended stall rest due to systemic complications.
Therapy After Injury
Post-burn rehabilitation is a huge commitment, especially if the horse needs therapy to regain range of motion in a limb. For instance, if a burned limb heals with fibrosis (scarring) over a fetlock joint, knee, or hock, the horse might develop a career-ending or life-threatening mechanical lameness, says Kathleen Anderson, DVM, of Equine Veterinary Care, in Elkton, Md.
To avoid this complication, the owner and veterinarian should institute a range of motion therapy early in the healing process so the tissue can heal with flexibility rather than scar tissue. "The underwater treadmill is an ideal rehabilitation tool to aid range of motion and tissue strength, but you can't risk contamination of the wound (with water) until there is a solid bed of granulation tissue (see page 26 to learn more) to protect the underlying structures from infection," says Anderson.
Hyperbaric oxygen therapy (HBOT) can be helpful for treating skin injury, smoke inhalation damage, and carbon monoxide poisoning. "Hyperbaric oxygen will also decrease edema formation in thermal injury to the throat, lung, or skin," explains Slovis, who is a certified hyperbaric therapist. He explains that the resulting increased oxygen tension in the bloodstream causes inflamed blood vessels to constrict.
Any damaged blood vessels beneath burned skin might be unable to transport oxygen and nutrients to the burned area for healing. "Hyperbaric oxygen (treatment) superoxygenates the blood," Slovis continues. "The oxygen is under such high pressure that it leaches into tissue from adjacent intact blood vessels. At the same time, the oxygen helps release growth factors in these tissues that can help with new blood vessel growth."
Hyperbaric oxygen also helps white blood cells fight bacteria. "The biggest problem is fighting off bacterial infections when skin has been destroyed and deprived of proper blood flow," says Slovis. "HBOT supplies the necessary amount of oxygen to the damaged tissue bed. This oxygen can be utilized by white blood cells to aid in the formation of free radicals, which are necessary for the destruction of harmful bacteria. At the same time, the oxygen can be utilized by a variety of other cells to help with the formation of collagen that is necessary for proper wound healing."
Many horses can survive burn wounds and recover sufficiently to lead a comfortable life or even go back to work--Silliman's hardy event mare is proof of that. But such an outcome requires early veterinary assessment and intervention, and treating and rehabilitating such a horse is a major, time-consuming commitment.
"Caitlin is riding (Catch A Star) carefully and making sure she's comfortable," explains Silliman's mother, Jenna. "(The soft tissue surgeon) said the hair over her spine won't grow back, and the skin pigment won't come back in some areas. But it's wonderful that (she and the other survivors) have been able to recuperate from their severe injuries."
About the Author
Heather Smith Thomas ranches with her husband near Salmon, Idaho, raising cattle and a few horses. She has a B.A. in English and history from University of Puget Sound (1966). She has raised and trained horses for 50 years, and has been writing freelance articles and books nearly that long, publishing 20 books and more than 9,000 articles for horse and livestock publications. Some of her books include Understanding Equine Hoof Care, The Horse Conformation Handbook, Care and Management of Horses, Storey's Guide to Raising Horses and Storey's Guide to Training Horses. Besides having her own blog, www.heathersmiththomas.blogspot.com, she writes a biweekly blog at http://insidestorey.blogspot.com that comes out on Tuesdays.
POLL: Radiographs for Hoof Care