WRNC 2018: Managing Wounds in Wildlife

Most wild birds, reptiles, and small mammals that are presented to veterinary practices have traumatic injuries, reported Kate E. Archibald, DVM, at the Wildlife Rehabilitators of North Carolina annual symposium held at North Carolina State University College of Veterinary Medicine in Raleigh.

Wounds in wild animals brought in for treatment are typically infected, contain debris, and/ or were inflicted by a predator, said Dr. Archibald, a zoological medicine resident at the college and the North Carolina Zoo. These wounds fall outside the “golden period”—the few hours after wound initiation during which they can be closed safely with sutures. Most wounds in wildlife heal by second intention: The edges are not apposed, and the wounds heal via granulation. In her presentation, Dr. Archibald discussed wound biology, wound dressings, factors affecting healing, and current therapies.

Phases of Healing

The phase of wound healing partly determines the choice of wound care product, according to Dr. Archibald. The initial inflammatory phase lasts about 4 days and is characterized by redness, swelling, and pain. Blood flow to the wound increases and platelets aggregate. Exudate forms as part of the natural debridement process.

Tissue granulation and reepithelialization characterize the repair phase. Beginning 3 to 5 days after wound initiation, fibroblasts contract the wound and granulation tissue forms. In the next days to weeks, a fragile layer of epithelial cells migrates across the granulation bed at a rate (in mammals) of about 1 mm per day.

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In the maturation phase, which lasts days to months after wound initiation, more layers of epithelium and connective tissue are laid down. The new tissue has about 80% of the strength of the original epithelium. Scars formed during this phase are a particular concern in wildlife, Dr. Archibald said. For example, scars that distort critical structures such as the eyelid or patagium (wing membrane) can impair an animal’s ability to function in the wild. Deep wounds that disrupt follicles can also cause loss of feathers or fur.

Initial Wound Care

When a wild animal arrives for treatment, the first step is to stabilize the animal and address life-threatening injuries. Chest wounds can be accompanied by pneumothorax, for example. For animals with limb wounds, Dr. Archibald recommends determining whether innervation and blood supply to the distal limb are intact and ligaments and tendons are still present.

“Ideally, every animal that’s coming in to have a wound evaluated is given some form of analgesia,” Dr. Archibald said. Some animals require sedation or general anesthesia. Although wounds in wildlife are dirty, they should be evaluated and treated using aseptic technique.

Debridement

The goals of debridement, which occurs mainly during the inflammatory phase, are to remove infected or necrotic tissue, ensure that wound edges have sufficient blood supply, and—ideally—maintain aseptic technique, Dr. Archibald said. She classified debridement techniques as nonselective (encompassing the entire wound) and selective (directed specifically at the tissue to be removed).

Nonselective Debridement

Dr. Archibald reviewed 2 nonselective debridement techniques: irrigation and application of a gauze contact layer.

Wound Irrigation

Nearly every wound is irrigated to remove contaminants and improve visualization of the wound. Although a variety of fluids can be used to flush wounds, Dr. Archibald noted that “volume is significantly more important” than fluid type.

“The current literature recommends high-volume and, ideally, high-pressure [irrigation] unless it’s very delicate tissue,” she said. The suggested lavage volume is 50 to 100 mL of fluid per centimeter of wound. Low-pressure irrigation is gentle to tissues and does not force bacteria deeper into the wound, but it does not debride as well as high-pressure irrigation, which can be performed with a pressurized fluid bag or a large syringe with an 18-gauge catheter attached.

The ideal lavage fluid is balanced electrolyte solution or sterile phosphate-buffered saline, Dr. Archibald said. Tap water is also acceptable, although because it is hypotonic it can be cytotoxic to fibroblasts. Adding an antiseptic such as chlorhexidine or povidone-iodine to lavage fluid does not enhance the mechanical removal of debris. If antiseptic solutions are used, they should be diluted properly. Dr. Archibald added that scrub preparations should be avoided because detergents are cytotoxic to open wound tissue; these products are intended for use on healthy skin before surgery. Hydrogen peroxide (3%) and vinegar are also cytotoxic and should not be used to flush wounds.

Gauze Contact Layer

Adherent contact layers, such as wet-to-dry dressings (gauze soaked in saline and allowed to dry on the wound), are no longer recommended and should never be used on granulation tissue, Dr. Archibald said. Although this type of dressing provides mechanical debridement, it can delay healing, and removing it can be painful for the patient.

Selective Debridement

Selective techniques include surgical, enzymatic, and autolytic debridement. Surgical debridement allows large amounts of necrotic tissue to be removed quickly. Enzymatic products (eg, those containing protease or trypsin) are also available.

Autolytic debridement refers to the body’s natural debridement. Enzymes, cytokines, and other components of wound exudate kill bacteria and remove dead tissue while preserving healthy tissue. This natural process occurs only in a moist environment, Dr. Archibald noted.

Wound Dressings

“Moist wound healing is the current standard of care for open wound management in humans,” Dr. Archibald said. Moisture promotes autolytic debridement, helps granulation tissue form, and decreases bacterial populations by reducing oxygen content and facilitating antibiotic penetration into the wound.

Because moist wounds reepithelialize faster than dry wounds, moist wound healing shortens the time wild animals must be held in captivity for treatment, Dr. Archibald noted. She discussed several types of agents and dressings that maintain a moist wound environment.

Hyperosmotic Agents

Hypertonic saline, honey, sugar, and other hyperosmotic agents draw out exudate, reduce edema, and inhibit bacterial growth. Dressings containing these agents should be changed frequently, Dr. Archibald said, noting that hypertonic saline can dehydrate healthy tissue surrounding a wound. Honey, which acts as an antioxidant and contains a low concentration of hydrogen peroxide, is more effective than sugar, she said. Medical-grade honey is available.

Hydrophilic Dressings

Hydrophilic wound dressings are absorbent, semiocclusive materials that create a moist wound environment and promote granulation, but do not adhere to wounds. Dressings containing alginate, a biomaterial derived from seaweed, are highly absorbent and useful for wounds that produce heavy exudate. Polyurethane foam and hydrocolloids work well for mildly to moderately exudative wounds. Hydrogel dressings provide moisture for dry wounds with little or no exudate.

Nonadherent Semiocclusive Dressings

Dressings such as polyurethane film and gauze coated with nonadherent material are not hydrophilic and may be drying. They should be used only in wounds that have had time to develop an intact epithelial layer unless they are used as a secondary layer, Dr. Archibald said.

Topical Antimicrobial Products

Silver sulfadiazine and triple antibiotic preparations reduce the concentration of bacteria at the wound surface. These products slow wound contraction and can be used during the inflammatory and possibly early granulation phases of healing.

Factors That Influence Wound Healing

Dr. Archibald reviewed a number of factors that affect wound healing, including infection, wound location, nutrition, the environment, the overall health of the patient, and the species involved.

She noted the distinction between infection and contamination: Infection involves a host response, but contamination does not—bacteria are present in the wound but have not yet colonized. Infection inhibits healing by disrupting the blood supply, lengthening the inflammatory phase, and producing enzymes that interfere with the healing process.

Wounds in areas that are subjected to tension, pressure, or motion may undergo ischemia or dehiscence. Splints can be used to limit joint motion.

Dr. Archibald emphasized the importance of good nutrition for animals with traumatic injuries. “Wound healing is a catabolic state,” she said, adding that wild animals presented for treatment are often already undernourished.

Enclosures for wildlife should be designed to minimize animal stress, as well as cleaned and disinfected properly to reduce hospital-acquired infections. Reptiles should be housed at the upper end of their optimal temperature zone to facilitate healing.

Current Treatments

Dr. Archibald concluded with a discussion of current wound care therapies that can be used in wildlife.

• Cold laser: Studies of this therapy in veterinary patients are ongoing, Dr. Archibald said. Cold laser therapy is thought to stimulate capillary growth and vasodilation. This treatment is costly, requires safety training, and should not be used in patients with cancer.
• Growthfactors: Recombinant platelet-derived growth factors are used to treat diabetic ulcers in humans. Like cold laser, this treatment is expensive.
• Platelet-rich plasma: This treatment uses the patient’s own platelets as a source of natural growth factors.
• Vacuum-assisted closure: Applying subatmospheric pressure across a wound improves perfusion; stimulates granulation tissue; and decreases edema, exudate, and bacterial load. Dr. Archibald described an inexpensive way to achieve a vacuum: Punch small holes in the tubing of a butterfly catheter, lay the catheter in the wound, cover it with an occlusive bandage, and attach the catheter needle to an evacuated blood collection tube or a syringe with negative pressure applied.

“There are many, many treatment options for wounds,” Dr. Archibald concluded. Considering the type of wound and the patient’s specific needs can help guide the veterinarian’s choice of treatment.

Dr. Walden received her doctorate in veterinary medicine from North Carolina State University in 1994. After an internship at Auburn University College of Veterinary Medicine, she returned to North Carolina, where she has been in companion animal general practice for over 20 years. Dr. Walden is also a board-certified editor in the life sciences and owner of Walden Medical Writing.