Initial Wound Management
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 avoids 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.
Irrigation of the wound washes away both visible and microscopic debris. This reduces the bacterial load in the tissue, which helps decrease wound complications. Assuming the solution is nontoxic, the most important factor in wound lavage is use of large volumes to facilitate removal of debris. The recommended lavage is a moderate pressure system using a 35-mL syringe and a 19-gauge needle that delivers lavage fluid at 8 lb/sq in. The use of antibiotics in the lavage fluid is controversial.
The ideal lavage fluid would 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 component is 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 1% is an effective antiseptic, but it has minimal residual activity and may be inactivated by purulent debris. (Also see Antiseptics and Disinfectants.)
After wound preparation and hair removal, debridement can be performed. Skin and local tissue viability should be assessed. Skin that is blue-black, leathery, thin, or white is associated with nonviability. Necrotic tissue should be sharply excised. The debridement may be done in layers or as one complete section of tissue. Tissues that have questionable viability or are associated with essential structures such as neurovascular bundles should be treated conservatively. Staged debridement may be indicated. In addition to sharp dissection, debridement may be performed mechanically (with wet-to-dry dressings), 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 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 the size and location of the wound and on the size of the animal.
Primary closure may not be appropriate for a grossly contaminated or infected wound. Therefore, if closure is a suitable 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 vary according to the degree of contamination or infection. Minimally contaminated wounds may be closed after 24–72 hr. Longer periods may be required for heavily infected wounds.
Wounds that are 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.
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 is available. Alginate dressings are commonly used in the exudative wound to stimulate granulation tissue. Hydrogels are used to maintain moisture levels in drier wounds. Foam dressings may be used to absorb excessive exudate or protect granulation beds. These newer dressings are changed only every 2−5 days.
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 until granulation tissue is seen. Once all infection is resolved, the wound may be closed or allowed to epithelialize. Because a large volume of fluid can be removed from the wound, the animal's hemodynamic and hydration status must be monitored and treated accordingly. Hypovolemia and low colloid osmotic pressure are complications that may be associated with this therapy.
Honey has also been used for wound dressings over the centuries. Honey’s beneficial effects are thought to be a result of hydrogen peroxide production from activity of the glucose oxidase enzyme. The low pH of honey also may accelerate healing. Honey used for wound healing must be unpasteurized, and the source of the honey appears to be a factor in its effectiveness. Manuka honey may be the best option for wound care. The contact layer wound dressings should be soaked in honey before application. The bandage should be changed daily or more frequently as needed.