This is particularly crucial in horses, whose wounds tend to be “heavily contaminated” with necrotic debris that can significantly interfere with healing, said Reid Hanson, DVM, Dipl. ACVS, ACVECC, professor of equine surgery and lameness at Auburn University’s College of Veterinary Medicine, in Alabama.
Considering key factors such as wound location, the extent of tissue damage, the horse’s temperament, the veterinarian’s own skill, and the owner’s budget can help steer clinicians toward the best approach, Hanson said during the 2021 American Association of Equine Practitioners’ convention, held Dec. 4-8 in Nashville, Tennessee, and virtually.
Hanson said veterinarians can use six forms of debridement, either alone or in combination::
- Biological; and
- Negative pressure.
Autolytic debridement is a technique that allows the body to eliminate contamination through its own natural processes, which are enhanced by keeping the wound moist. “It is slow; it is selective; it is accurate,” Hanson said. “Only the devitalized tissue is liquefied, while the normal tissues remain unharmed in the wound. And the great thing is that it is virtually painless.”
Occlusive gauzes and films effectively keep moisture in the wound, he said. But that also means they won’t let exudate—seeping bodily fluids—out.
Mechanical debridement involves applying gauzes (dry on wet wounds, wet on dry wounds) that will take the top layer of tissue with them when the practitioner peels them off the wound a day or two later, he said. They can be soaked with saline—which works very well—or other dressings, such as antimicrobial solutions. An important downside to this technique, however, is it’s entirely nonselective. The dressing clings to the wound surface as it dries, Hanson said, and he emphasized that it will indiscriminately remove tissue that is adhered to that .
Hypertonic saline is often a better choice because it also desiccates bacteria and necrotic tissue through the process of osmosis, he said. “Hypertonic saline in a 20% solution applied in a gauze dressing is ideal for that necrotic, old, heavily infected, exudating wound,” Hanson said. Even so, caretakers must use hypertonic saline with caution, because it can be caustic to the surrounding healthy skin if applied for too long, he added.
Certain kinds of honey can also be used for this approach, he said. Their thickness makes them easy to apply, and they form a protective barrier against infection. Honey “also has growth-factor-like effects: It’s anti-inflammatory, promotes moist wound healing, and will facilitate that debridement,” said Hanson.
Surgical debridement—“the one we all think about when we think about debridement,” said Hanson—involves removing unwanted tissue directly with a scalpel, water jet, or other surgical methods. While fast and highly effective, especially for removing large amounts of devitalized tissue, this “heal with steel” method, as Hanson calls it, comes with the inevitable limitation of being nonselective at a microscopic level.
“You and I as practitioners can’t tell (on) a cell-by-cell basis which tissue is dead versus alive,” he said. Still, the surgeon’s precision can allow for careful removal of anything visibly necrotic or infected—thereby making the technique “very selective” in a larger sense, he added.
Generally, surgeons should aim to not remove any pink, red, or even purple tissue, but debride anything of other colors—including white, tan, black, and green—as well any poorly attached tissues that look unlikely to survive, as well as the surface of any exposed bone, Hanson said.
In some cases, such as a wound that won’t stop draining, surgeons should perform en bloc debridement, which involves removing the entire wound, including its margins, he said. Piecemeal debridement, meanwhile, is a more delicate surgical technique in which the veterinarian cuts carefully around important anatomical structures.
Enzymatic debridement techniques enhance the process of mechanical debridement in wounds that can’t benefit from surgical debridement, such as those close to nerves or blood vessels, he explained. The dressings contain enzymes that digest nonviable protein matter without harming healthy tissue. However, study results suggest that, at least in horses, enzymatic debridement isn’t as effective as saline-soaked gauze dressings for removing fibrin and blood clots from wounds, for example.
Biological debridement techniques involve using living insects—specifically, “our friend the green bottle fly … Lucilia sericata,” Hanson said, grown in a sterile environment. The fly’s first-stage larvae—more commonly known as maggots—feed on dead tissue and pathogens, including certain methicillin-resistant bacteria.
“(This technique) is used to enhance healing of subacute and chronic nonhealing wounds when complete surgical debridement is difficult and ineffective,” he said.
The wound dressing should be able to breathe in this case, to allow the maggots to thrive, he added. This also ensures the exudates can continue to clear from the wound.
Negative pressure wound therapy is a relatively new debridement technique that offers an ideal method for controlling wound infection and enhancing wound contraction, said Hanson. It involves essentially trimming an open-cell foam piece to the shape of the wound, sealing it with an adhesive drape, and then establishing negative pressure with a pump, so fluids get sucked up out of the wound and into a tube where they collect in an attached container. Negative pressure wound therapy reduces the risk of infection and the size of the wound, and it upregulates the gene expression of cytokines associated with wound healing. In addition, granulation tissue forms earlier and is of better quality, he said.
Any combination of these techniques may be combined and/or used successively to reach better results, Hanson said. “Being open to utilizing more than one debridement method, I have found, will promote healing, reduce the risk of infection, improve patients’ outcomes, and provide consistency in wound bed preparation toward healing,” he said.