Horses sometimes seem almost single-mindedly bent on hurting themselves, so proper wound care is an important part of any equine practitioner’s responsibilities. To help with those responsibilities, a seemingly endless number of products are said to help promote wound healing. Unfortunately, many of them lack evidence of safety or effectiveness, and some can even cause harm.
At the American Association of Equine Practitioners conference in December, Colorado State University’s Dean Hendrickson, DVM, MS, Dipl. ACVS, gave a presentation on “What You Should and Should Not Put on Wounds,” from which most of this article is drawn.
It’s always a good idea for any practitioner to know what effect a wound care product will have on a wound prior to using it.
Proper wound care includes removal of any necrotic tissue and debris while, at the same, time reducing bacterial contamination on the surface. While undoubtedly important, cleaning a wound causes additional mechanical trauma, and the cleaning process may introduce potentially cytotoxic agents to the wound surface. Thus, the risks, benefits and costs of various techniques must be considered prior to using any approach.
In human medicine, it’s been said that you should never put anything onto a wound that you wouldn’t put into your own eye. Using procedures and products that minimize wound trauma and chemical damage to cells should be the goal of every equine practitioner.
A solution of approximately 0.9 percent sodium chloride (isotonic saline) has been shown to reduce infection rates in human emergency rooms, as has 1 percent povidone-iodine solutions. Even so, isotonic solution is acidic, and a polyionic solution such as lactated Ringer’s solution arguably would be even better. Hypertonic saline solution (20 percent) is very effective at reducing bacterial numbers, but it is traumatic to normal tissue and probably should be avoided for lavaging wounds in most cases.
A good body of research in human medicine, most recently complied in 2012 by the UK Cochrane Collaboration, indicates that tap water—perhaps counterintuitive due to the fact that it is hypotonic—is a good lavage solution. There’s some evidence that it might even reduce the rate of infection.
Povidone-Iodine (“tamed” iodine) and chlorhexidine are probably the most commonly used cleansing agents in equine wound care. However, research indicates that these agents are not particularly good choices; in fact, they do not appear to be more effective than isotonic saline irrigation in reducing bacterial load. Further, both can cause some tissue necrosis, which can lead to infection. Both products are best when used on intact skin.
Hydrogen peroxide is a popular wound cleansing agent. It foams when contacting a wound, perhaps adding to the impression that is effective. However, hydrogen peroxide has not been shown to have antibacterial effects and is of limited benefit in debriding wounds.
Dilutions of distilled vinegar (0.25 or 0.5 percent solution) applied for 15 minutes create an acidic environment that certain bacteria (e.g., pseudomonas) cannot tolerate. Vinegar-treated wounds should be rinsed with saline when treatment is completed. Surfactant-based cleaners such as polysorbate-20 or pluronic F-68 are less commonly used but are very safe for wound cleaning. When used, they are allowed to sit for one to two minutes, then rinsed off and reapplied as needed.
Topical Antimicrobial Agents
Elemental silver is extremely effective as an antibicrobial. Most commonly, it’s applied as silver sulfadiazine (SSD) cream. At least one study shows that SSD cream reduces exuberant granulation tissue.
Silver-impregnated dressings are being formulated, and one study showed that their use decreased the length of hospital stay, the rate of wound infection, inflammation and the use of analgesics when compared to SSD.
Nitrofurazone ointment is readily available as an over-the-counter wound dressing, though research indicates that it retards healing. Dr. Hendrickson recommends against its use in open wounds.
Combinations of polymixin B, bacitracin and neomycin (“triple antibiotic ointment”) have been used since the 1950s, but bacterial susceptibility to them essentially is unchanged since its inception, and the mixture remains an excellent choice for topical wound treatment.
Innumerable wound dressings exist, but there appears to be no single dressing that is appropriate for all stages of sound healing. Wound dressings, usually applied after wound closure, provide physical support and protection from bacterial contamination and absorb exudate. Current thought is that open wounds should be kept moist throughout any of the healing stages, as moist wounds appear to heal more quickly than do dry wounds.
However, the Cochrane Collaboration in 2014 found insufficient evidence as to whether covering surgical wounds healing by primary intention with wound dressings reduces the risk of surgical site infection.
In the initial stages of wound care, dressings may be applied to remove bacteria and necrotic tissue from wounds, usually in combination with physical debridement. Hyper-tonic saline dressings draw fluid from wounds and wound bacteria and lift bacteria from wounds when the dressings are changed. An effective solution can be made by dissolving 200 grams of sodium chloride in one liter of boiling water. Saline dressings should be discontinued when bacterial infection appears to be under control.
Polyhexamethylene biquanide (PHMB) dressings are antimicrobial, effective and readily obtained, but they’re not inexpensive. These dressings should be moistened with saline before use and are best used to help limit bacterial penetration into a healing wound bed.
Honey has been investigated extensively as a wound treatment. It acts as a debridement dressing because of its high sugar content, but it also is very acidic and contains small amounts of hydrogen peroxide. It prevents a formidable barrier to bacteria attempting to penetrate wounds.
Honey-impregnated bandages are available. While most research has been done on manuka honey—produced in New Zealand by bees that pollinate the native manuka bush—other honeys are shown to have beneficial effects on wound healing, including those that can readily be purchased at food stores.
Necrotic, dry wounds should be treated with gel dressings that donate moisture to wounds. Gel dressings typically contain water, glycerin and a polymer. Once wounds are moist, another dressing should be used.
While granulation tissue (“proud flesh”) typically has been a feared sequel to equine wounds, encouraging granulation tissue may be a treatment goal in certain circumstances. Calcium alginate dressings encourage an effective inflammatory process that promotes granulation tissue in wounds with tissue loss (such as overexposed bone). These dressings also provide calcium to the healing wounds, which encourages wound contraction.
Once a wound has filled with granulation tissue, another dressing should be used. Corticosteroid-containing ointments or creams can be used to help control excessive granulation tissue.
Dressings of semi-occlusive foam may be used at the end of wound healing to help encourage epithelialization. Foam dressings increase wound surface temperature, which assists the epithelialization process. These dressings also contain PHMB, which helps limit bacterial growth. On the other hand, corticosteroid dressings can inhibit epithelialization.
Dr. Ramey is a 1983 graduate of the Colorado State University College of Veterinary Medicine and Biomedical Sciences. An author, lecturer and Southern California equine practitioner, he specializes in the care and treatment of sport and pleasure horses. His website is www.doctorramey.com.
Originally published in the April 2016 issue of Veterinary Practice News. Did you enjoy this article? Then subscribe today!