The first step in wound management is assessment of the overall stability of the animal. Obvious open wounds can detract attention from more subtle but potentially life-threatening problems. After initial assessment, the animal should be stabilized. First aid for the wound should be performed as soon as safely possible. Active bleeding can be controlled with direct pressure. A pneumatic cuff, instead of a tourniquet, should be used in cases of severe arterial bleeding; the cuff should be inflated until hemorrhage is controlled. Use of a cuff helps avoid neurovascular complications that can be associated with narrow tourniquets.
Treatment for any local wound should be guided by the fundamentals of debridement, infection or inflammation control, and moisture balance. The wound must be protected from further contamination or trauma by covering it with a sterile, lint-free dressing. The delay between examination and definitive debridement should be minimized to decrease bacterial contamination. If the wound is infected, a sample should be collected for culture and sensitivity testing. Antibiotic therapy should be instituted in all cases of dirty, infected, or puncture wounds. A broad-spectrum bactericidal antibiotic, eg, a first-generation cephalosporin, is generally recommended pending culture results. Analgesia is also indicated for pain relief.
Wound lavage serves two purposes. Irrigation of the wound washes away both visible and microscopic debris. This reduces the bacterial load in the tissue, which helps decrease wound complications. The lavage also allows better examination of underlying tissues. Assuming the solution is nontoxic, the most important factor in wound lavage is use of large volumes to facilitate removal of debris. Wound lavage is most effective when delivered under appropriate pressure. A recommended lavage system delivers moderate pressure with a 35-mL syringe and a 19-gauge needle to generate 8 lb/sq in. of pressure. Excessive pressure causes a detrimental side effect by driving debris deeper into the healthy tissue. The use of antibiotics in the lavage fluid is controversial.
The ideal lavage fluid should be antiseptic and nontoxic to the healing tissues. Although isotonic saline is not antiseptic, it is the least toxic to healing tissue. Surgical scrub agents should not be used because the detergent components are damaging to tissue. Dilute antiseptics can be used safely. Chlorhexidine diacetate 0.05% has sustained residual activity against a broad spectrum of bacteria while causing minimal tissue inflammation. However, gram-negative bacteria may become resistant to chlorhexidine. Stronger solutions of chlorhexidine are toxic to healing tissue. Povidone-iodine is an effective antiseptic, but it has minimal residual activity and may be inactivated by purulent debris. Although an effective antiseptic Antiseptics and Disinfectants , hydrogen peroxide is toxic to healthy tissue and should not be used for lavage of wounds.
After wound preparation and hair removal, debridement can be performed. Debridement may involve removal of large segments of tissue (nonselective) or may be performed in a more selective manner, enabling preservation of specific tissues. Skin and local tissue viability should be assessed before any attempted debridement. Skin that is blue-black, leathery, thin, or white is usually not viable. This necrotic tissue should be sharply excised. The debridement may be done in layers or as one complete section of tissue (en bloc resection). Tissues that have questionable viability or are associated with essential structures such as neurovascular bundles should be treated conservatively. Staged debridement is indicated in some situations. In addition to sharp dissection, debridement may be performed mechanically, enzymatically, or biologically (maggot therapy).
After initial inspection, lavage, and debridement, a decision must be made whether to close the wound or to manage it as an open wound. Considerations include the availability of skin for closure, wound location, and the level of contamination or infection. If the wound is left open, it should be managed for optimal healing.
Although primary closure is the simplest method of wound management, it should be used only in appropriate situations to avoid wound complications. Wounds may be closed with suture, staples, or cyanoacrylate. Clean wounds that are properly debrided usually heal without complication. With a primary closure, the layers should be individually closed to minimize “dead space” that might contribute to seroma formation. The types of suture and suture patterns used depend on surgeon preference, the size of the wound, the location of the wound, and the size of the animal.
Primary closure may not be appropriate for a grossly contaminated or infected wound. Therefore, if closure is a goal, it may be delayed until the contamination or infection is controlled. The wound can be managed short-term as an open wound until it appears healthy. At that time, the wound can be safely closed with minimal risk of complications. The time between initial debridement and final closure varies according to the degree of contamination or infection. Minimally contaminated wounds may be closed after 24–72 hours. Longer periods may be required for heavily infected wounds.
Wounds closed >5 days after the initial wounding are considered to be secondary closure. This implies that granulation tissue has begun to form in the wound before closure.
Open Wound Management
When a wound cannot or should not be closed, open wound management (ie, second-intention healing) may be appropriate. Such wounds include those in which there has been a loss of skin that makes closure impossible or those that are too grossly infected to close. Longitudinal degloving injuries of the extremities are especially amenable to open wound management. Open wound management enables progressive debridement procedures and does not require specialized equipment (such as may be needed with skin grafting). However, it increases cost, prolongs time for healing, and may create complications from wound contracture.
Open wound management is based on repeated bandaging and debridement as needed until the wound heals. Traditional therapy calls for wet-to-dry dressings initially. The initial wide meshed gauze dressings help with mechanical debridement at every bandage change. Until a granulation bed forms, the bandage should be changed at least once daily. In the early stages of healing, the bandage may need to be changed as often as twice daily. After granulation tissue develops, the bandage should be changed to a dry, nonstick dressing so the granulation bed is not disrupted. Both the granulation bed and the early epithelium are easily damaged, and disruption of the granulation bed delays wound healing.
With the concept of moist wound healing, bandaging is combined with autolytic debridement to promote wound healing. The use of moist wound dressings keeps white cells healthier, allowing them to aid in the debridement process. A variety of dressings are available. With these newer dressing options, some consider traditional wet-to-dry dressings to be outdated.
A decision to use open wound management or delayed wound closure is based on several factors. These may include patient morbidity, cost, wound location, and the technical expertise required for closure. In certain patients, surgery may not be an option given their health status. For those patients, open wound management is a better choice. Although the initial cost of surgery is higher than bandage changes, the overall cost may be less expensive depending on the nature and length of wound care required without surgical intervention. Wound location also has a significant impact on the decision to surgically intervene. As the open wound heals, contracture of the wound begins to occur. Contracture of a wound on the lateral thorax may not result in any long-term complications. However, a wound spanning or adjacent to a joint may result in loss of longterm joint function or range of motion due to scarring.
To avoid this loss of function, the wound should be surgically closed. An important component of decision making in these cases relates to the clinician's abilities. If the techniques required for closure exceed the clinician's expertise, referral to another location for closure may be advisable to avoid unnecessary complications. Finally, the owner may have a specific request regarding cosmetics. Closure with open wound management will result in a hairless scar. For various reasons, this may not be acceptable. In those cases, surgical intervention is required.
Sugar has been used as an inexpensive wound dressing for more than three centuries to control odor and infection. The use of sugar is based on its high osmolality, drawing fluid out of the wound and inhibiting the growth of bacteria. The use of sugar also aids in the debridement of necrotic tissue while preserving viable tissue. Granulated sugar is placed into the wound cavity in a layer 1-cm thick and covered with a thick dressing to absorb fluid drawn from the wound. The sugar dressing should be changed once daily or more frequently whenever “strike-through” is seen on the bandage. During the bandage change, the wound should be liberally lavaged with warm saline or tap water. Sugar dressings may be used during the inflammatory phase. Because a large volume of fluid can be removed from the wound, the hemodynamic and hydration status of an animal with a large wound must be monitored to avoid hypovolemia and low colloid osmotic pressure.
Honey has also been used for wound dressings for centuries. Some of the beneficial effects of honey are a result of high osmolality, low pH, and hydrogen peroxide activity. However, the major contribution to honey’s antibacterial activity is methylglyoxal. Honey varieties with higher methylglyoxal levels are more bioactive. Leptospermum honey from the manuka bush in New Zealand has the highest methylglyoxal levels and is believed to the most effective for medicinal purposes. Honey may be placed directly into the wound or soaked in the contact dressing. The use of honey should be limited to the inflammatory phase. Once a granulation bed is present, continued use may desiccate the wound or traumatize the healing tissue during removal. Whereas topical usage has beneficial antibacterial effects, oral administration has not been shown to have similar benefits.
Silver has been used as a topical agent in various formulations for several hundred years. It is available in a cream (silver sulfadiazine) or in the newer form as nanocrystalline silver, which is generally embedded within the dressing. The primary benefit of silver is its antimicrobial effects and therefore is indicated for use in the inflammatory phase. The newer formulations may also have some antiinflammatory benefits by stimulating angiogenesis. The nanocrystalline form may also be useful in the proliferative phase. The use of silver-containing dressings to prevent infection is controversial.
Topical antibiotics may have two benefits. The antibacterial efficacy may be beneficial with topical infections. Zinc-containing antibiotics (eg, bacitracin-zinc) may also be beneficial for wound healing by the donation of zinc into the wound bed. Zinc has been shown to have both antimicrobial and antiinflammatory properties. When infection involves the deeper tissues, systemic antibiotics are indicated. Given limited ability of topical antibiotics to penetrate deeper tissue, the overall use of topical antibiotics is controversial.
Enzymatic agents (usually in ointment formulation) are proteolytic compounds used to liquefy necrotic tissue. These agents are used in the inflammatory phase of healing. Their application is indicated in cases where surgical debridement may be detrimental. In addition to the expense, enzymatic debridement action can be slow. Enzymatic agents can cause maceration of healthy tissue if left in prolonged contact.
Medicinal maggots are used during the inflammatory stage of wound healing to remove necrotic tissue and debris. The maggots debride necrotic tissue by secreting several proteolytic enzymes to liquefy the debris. Maggots also have a beneficial effect by ingesting bacteria. Finally, some of the secretions may also inhibit biofilm formation.
Maggot therapy may be contraindicated in dry wounds and should not be the primary therapy in a septic patient. The common green bottle fly (Lucilia sericata) is used as the source of medical grade maggots. Maggot therapy is not commonly used at this time and may be expensive. In addition to the maggots, a biobag must be used to prevent their movement off the patient.