Basic principles of wound management (Proceedings)

Dogs and cats are very commonly presented for management of acute or chronic wounds in veterinary practice. The goal of wound management is to accelerate the healing process and not to interfere with it.  Therefore, the management of the wounds requires a good understanding of the healing process of wounds to be able to treat them effectively.

Stages of wound healing

Wound healing includes four different phases: inflammatory phase, debridement phase, granulation phase and maturation.  It is very important to be able to recognize each the phases because the management of the wound is conditioned by the phase of wound healing.  The duration of each stage is a function of an individual wound, the degree of contamination, the degree of ischemia, and the extent soft tissue damage.  More likely, the stages overlap with time.

Wound management

When an animal is presented for the management of an acute or chronic wound precautions should be taken not to further contaminate the wound. While a physical examination is performed to evaluate for any life threatening injury the wound should be covered with a light sterile bandage.  This will help prevent contamination wit resistant bacteria present in the clinic.  After the animal has been stabilized, the wound should be evaluated and cleaned.  Sterile gloves are required to manipulate the wound.  Pain medication should be delivered appropriately to the animal.

Preliminary evaluation

The wound needs to be covered with a water-soluble lubricant or a wet sterile sponge before starting clipping.  A large clipping is performed with a # 40 blade.  After completion of the clipping, the water-soluble gel is eliminated with sterile saline.  If the wound is important, tap water can be used first to eliminate the gross contamination and sterile saline should be used for the last flush.  Any obvious foreign material should be removed manually.

After the wound has been flushed, a deep sample should be taken for culture and sensitivity.  While results of the culture are pending, the animal should be placed under broad-spectrum antibiotics.  The most common bacteria in a wound are skin contaminant unless the trauma happened in a specific environment that may contaminate the wound with different bacteria.  Usually a first generation cephalosporin is offering an adequate coverage.

The wound should then be evaluate for exposure of vital structure such as artery, vein, nerve, and joint.   If the femoral artery or the sciatic nerve are exposed it is recommended to move tissue to cover these structures.  Joints if exposed need to be aggressively flushed to remove the foreign material and closed over a drain.

Deep tissue cultured should then be taken.  It will give a good idea of what kind of bacteria are left in the wound after flushing. Clavamox should be administered to the patient until the culture-sensitivity is back.

Wound closure

The decision of closing a wound is made on the amount of contamination present in the wound, the time since injury happened, the amount of devitalized tissue.  Four options are available to the surgeon; primary wound closure, delayed primary wound closure, secondary wound closure, and second intention healing.  As a general rule, the wound is better left unsutured if a surgeon doubts the success of primary or delayed primary closure.

Primary wound closure

Primary wound closure entails closure of the wound relatively soon after it has been inflicted. Ideally, primary closure should be performed when the animal is otherwise in good condition.  Additional requirements are a short time lap (< 6 hours) since injury and a minimal degree of contamination and tissue trauma.  A thorough surgical debridement and lavage to provide tissue suitable for suturing are required for a successful outcome.  Closure should be possible in the presence of good hemostasis without tension and dead space.

Surgical debridement consists of removing non-bleeding tissue.  Surgical debridement is not performed immediately after the injury.  During the first 24 hours after an injury, the blood vessels are vasoconstricted. If surgical debridement is performed while intense vasoconstriction is present, viable skin might be removed.  This might be a serious issue later when the wound is closed.  It is preferable to let the ischemia demarcate itself and then perform a surgical debridement.  However, the debridement phase can be helped with bandage technique.

Most wounds created by a sharp object have low levels of bacteria and minimal soft tissue damage.  They are amenable to primary closure.  Crush wounds have more severe soft tissue trauma and contamination.  They are usually closed with delay primary or secondary closure.

Primary closure should eliminate dead space and provide a good anatomical apposition of tissue.  The amount of suture should be maintained to a minimum because it can act as a nidus for bacteria.  Monofilament absorbable sutures of a small size are recommended.

Delayed primary closure

Delayed primary wound closure is wound closure 3 to 5 days after the time of infliction of the wound during which time the wound is medically managed to improve its chances of healing.  Delayed primary closure is indicated for recent wounds with severe contusion, heavily contaminated wounds, or wound from a sharp object of several days duration.  Mechanical debridement and lavage should be applied daily to the wound until closure is judged appropriate.

Debridement can be performed with an adherent bandage. An adherent bandage material used as the contact bandage layer has wide mesh openings without cotton filler.  The wide mesh entraps loose necrotic tissue and foreign bodies, which are then removed when the dressing is changed.  In addition, exudate penetrates the dressing and dries by evaporation, attaching the dressing to the crust that forms. Then at each bandage changes, some necrotic tissue that adhered to the bandage is going to be mechanically removed.  Wet-to-dry or dry-to-dry bandage can be used.  Wet to dry is recommended for wounds with a thick exudate.  The wet environment will loosen the exudate that will then adhere better to the bandage.  The secondary layer should soft and bulky to be able to absorb the exudate.  Adherent bandage should be changed at least every day or even twice a day in a severely contaminated wound.

At each bandage changes, the wound is flushed with sterile saline to eliminate foreign material, bacteria and loose necrotic tissue.  The mechanical effect is the most important effect.  Therefore, a high dilution of betadine can be used to perform the lavage.  The solution should be delivered at 7 to 8 PSI to avoid to create barotraumas and push foreign material and bacteria deeper in the tissue.  This pressure is achieved with a 30 ml syringe and 18-gauge needle.  A plastic spray bottle can also be used safely to perform the lavage.

When the wound is considered ready for closure, it is inspected again and surgical debridement performed if needed.  A minimal amount of granulation tissue is present at the time of closure.  The granulation tissue can be left in the wound.  A deep sample is again taken at the time of closure for culture and sensitivity.  The wound edges are debrided and sutured with minimal tension.  Skin flaps or releasing incisions can be performed to decrease the amount of tension on the wound edges.  A drain might be placed at the time of closure to eliminate dead space and allow drainage of any exudate that would increase the risk for an infection.

Secondary closure

Secondary closure of a wound is closure 5 days or longer after the time of injury, when the wound has form a bed of granulation tissue.  Severely infected wound at the time of presentation or wounds with severe necrosis are amenable to this technique.

Adherent bandages and aggressive flushing of the wound are going to be performed to debride the wound until granulation tissue is coming into the wound.  Severely contaminated wounds may require a bandage change twice a day at the beginning.  When the granulation tissue is appearing it means that the infection is under control and the necrotic tissue has been removed.  When granulation tissue is present, non-adherent bandage needs to be used to preserve it. Non-adherent semi occlusive bandages are Telfa pads or petrolatum impregnated sponges.  The non-adherent bandages are usually changed every other day.

When the wound is ready to be closed, the edges of the wound are debrided and the closed over the granulation tissue.  The granulation tissue is left in place and the wound edges pulled over it.  Secondary closure is usually associated with tension on the skin edges.  Undermining of the skin has to be performed.  Walking sutures, releasing incision, and mattress sutures can be used to reduce the tension.   A deep sample is taken for culture and sensitivity. Skin flaps can be performed to decrease the amount of tension on the wound edges. The amount is limited because the granulation tissue covered the entire wound at the time of closure. Secondary closure is rarely used and second intention healing is performed.

Secondary wound healing

Wounds can be left to heal completely by second intention or wound contraction and epithelialization.  Such a decision is based on a number of considerations: extension soft tissue damage, devitalization of skin edges, presence of severe tissue infection, and important skin defect. Cosmetic results are not optimal with secondary healing.

Second intention healing relies on granulation tissue formation, contraction and epithelialization to achieve closure.  Adequate debridement, proper application of bandage materials and dressing, and control of infection aid in formation of a healthy granulation tissue.  Adherent bandage is used for the debridement phase.  When granulation tissue is present in the wound non-adherent semi occlusive bandages are used to preserve the granulation tissue. If wound contraction fails to completely cover the wound because of excessive tension, a skin flap has to be considered. 

Releasing incisions can be performed to help contraction.  If there is laxity in the surrounding skin, wound contraction can occur unimpeded.  The wound can then be completely covered with skin and minimal amount of new epithelium. If contraction might interfere with joint motion then a skin flap is considered to stop the contraction. Non-adherent bandage such as hydrocolloid hydrogel and calcium alginate can be used to enhance epithelialization.  Those bandage are occlusive bandages.  They are not commonly used in veterinary practice mostly because of the risk of infection associated.

Wound management requires then a good understanding of the physiology of wound healing.  The major goal of the surgeon is not to interfere with normal mechanism but to help it. Wound closure following extensive tumor resection or trauma may require reconstruction surgery. Skin can be borrowed from another location to accomplish closure without tension. Free skin grafts have been used with good success, but this procedure requires healthy granulation tissue, is technically demanding and requires intensive postoperative care.  Skin flap is more applicable to veterinary surgery