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Overview of Wound Management:

Overview of Wound Management

  • Wound healing is the restoration of the normal anatomic continuity to a disrupted area of tissue. An understanding of the normal process of wound healing is essential to make sound decisions in the management of wounds.
  • Correctly using the principles of wound management help avoid premature wound closure and its potential complications.
  • Wounds may be classified as clean, contaminated, or infected. Clean wounds are those created under aseptic conditions, eg, surgical incisions.
  • The number of bacteria present can determine the difference between contaminated and infected wounds. As a guideline, >105 bacteria per gram of tissue is considered adequate to cause infection.
  • The level of contamination, blood supply, and the cause of the wound all contribute to the development of the necessary conditions for infection, and each case must be assessed individually.

 

General Principles of Wound Healing:

  • Although there are many types of wounds, most undergo similar stages in healing that are mediated by cytokines and other chemotactic factors within the tissue. The duration of each state varies with the wound type, management, microbiologic, and other physiologic factors. There are 3 major stages of wound healing after a full-thickness skin wound.
  • Inflammation is the first stage of wound healing. It can be divided into several phases, resulting in the control of bleeding and the resolution of infection.
  • During the initial phase, vasoconstriction occurs immediately to control hemorrhage, followed within minutes by vasodilation.
  • During the second phase, cells adhere to the vascular endothelium. Within 30 min, leukocytes migrate through the vascular basement membrane into the newly created wound. Initially, neutrophils predominate (as in the peripheral blood); later, the neutrophils die off and monocytes become the predominant cell type in the wound.
  • Debridement is the next phase of wound healing. Although neutrophils phagocytose bacteria, monocytes, rather than neutrophils, are considered essential for wound healing.
  • After migration out of the blood vessels, monocytes are considered macrophages, which then phagocytose necrotic debris.
  • Macrophages also attract mesenchymal cells by an undefined mechanism. Finally, mononuclear cells coalesce to form multin
  • cleated giant cells in chronic inflammation.
  • Lymphocytes may also be present in the wound and contribute to the immunologic response to foreign debris.
  • Proliferation is the second stage of wound healing. It consists of fibroblast, capillary, and epithelial proliferation phases.
  • During the proliferation stage, mesenchymal cells transform into fibroblasts, which lay fibrin strands to act as a framework for cellular migration.
  • In a healthy wound, fibroblasts begin to appear ∼3 days after the initial injury. These fibroblasts initially secrete ground substance and later collagen.
  • The early collagen secretion results in an initial rapid increase in wound strength, which continues to increase more slowly as the collagen fibers reorganize according to the stress on the wound.
  • Migrating capillaries deliver a blood supply to the wound. The center of the wound is an area of low oxygen tension that attracts capillaries following the oxygen gradient.
  • Because of the need for oxygen, fibroblast activity depends on the rate of capillary development.
  • As capillaries and fibroblasts proliferate, granulation tissue is produced. Because of the extensive capillary invasion, granulation tissue is both very friable and resistant to infection.
  • Epithelial cell migration begins within hours of the initial wound. Basal epithelial cells flatten and migrate across the open wound.
  • The epithelial cells may slide across the defect in small groups, or “leapfrog” across one another to cover the defect. Migrating epithelial cells secrete mediators, such as transforming growth factors α and β, which enhance wound closure.
  • Although epithelial cells migrate in random directions, migration stops when contact is made with other epithelial cells on all sides (ie, contact inhibition).
  • Epithelial cells migrate across the open wound and can cover a properly closed surgical incision within 48 hr. In an open wound, epithelial cells must have a healthy bed of granulation tissue to cross. Epithelialization is retarded in a desiccated wound.
  • Remodeling is the final stage of wound healing. During this period, the newly laid collagen fibers and fibroblasts reorganize along lines of tension. Fibers in a nonfunctional orientation are replaced by functional fibers.
  • This process allows wound strength to increase slowly over a long period (up to 2 yr). Most wounds remain 15–20% weaker than the original tissue. However, the urinary bladder and bone regain 100% of their original strength after wounding and repair.

 

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 the hemorrhage is controlled.
  • Use of a cuff avoids neurovascular complications that can be associated with narrow tourniquets.
  • 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:

  • 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 the 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.

 

Debridement:

  • After wound preparation and hair removal, debridement can be performed. Skin and local tissue viability should be assessed.
  • Blue-black, leathery, thin, or white skin are signs 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.
  • 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.

 

Wound Closure:

  • Although primary closure is the simplest method of wound management, it should be used only in ideal 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 a 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. These 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.
  • More recently, the concept of moist wound healing has emerged. In this technique, wound healing is combined with autolyticdebridement to advance wound healing.
  • The use of moist wound dressings keeps white cells healthier, allowing them to aid in the debridement process. Many dressings are available. Alginate dressings are commonly used in the exudative wound to stimulate granulation tissue.
  • Hydrocolloids are used to maintain moisture levels in drier wounds. Classically, moist wound dressings are changed only every 2 days.

Sugar Dressings:

  • Sugar has been used as an inexpensive wound dressing for over 3 centuries. The use of sugar is based on its high osmolality, which draws fluid out of the wound. Reducing water in the wound inhibits 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 or twice daily or more frequently as needed (eg, 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 epithelize. Because a large volume of fluid can be removed from the wound, the patient's hemodynamic and hydration status must be monitored and treated accordingly.
  • Hypovolemia and low collod osmotic pressure are complications that may be associated with this therapy.

Honey Dressings:

  • 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 may be changed daily or more frequently as needed.

Drains:

  • Drains are used to direct fluid out of a wound or body cavity. Passive drainage techniques require gravity or capillary action to draw fluid from the wound or cavity.
  • Penrose drains are soft, flat, commonly used passive drains made from latex. These drains must be placed in gravity-dependent locations to ensure proper function.
  • A firmer drain can be constructed from a red rubber or silicone tube. A double lumen or sump drain allows fluid to drain through the outer lumen, and air to enter from the inner lumen.
  • Active drains require some type of negative pressure to pull fluid from the wound. Red rubber or silicone drains can be used with a closed system and low-pressure suction maintained with the intermittent use of low-pressure pumps or handheld rechargeable devices.
  • The use of active, closed-drain systems decreases the likelihood of ascending infection that can be associated with passive drains.
  • Drains should be left in place until the draining fluid decreases in quantity and no longer appears purulent. The fluid can be evaluated by cytologic examination.

Bandages:

  • The goals of bandaging include limiting hemorrhage, immobilizing the area, preventing further trauma or contamination of the wound, preventing wound desiccation, absorbing exudate, and aiding in mechanical debridement of the wound. When constructing bandages, several principles must be followed to avoid complications.
  • The bandages should be sufficiently padded, applied evenly and snugly, composed of 3 layers (primary, secondary, and tertiary), and placed to avoid traumatizing the newly formed granulation tissue or epithelium.
  • The first or primary layer directly contacts the wound to allow tissue fluid to pass through to the secondary layer. The first layer may be adherent or nonadherent.
  • A nonadherent bandage is usually a fine mesh, nonstick material and is indicated when a healthy granulation bed has developed.
  • This layer prevents tissue desiccation and causes minimal trauma. An adherent bandage uses a wide mesh material allowing tissue to become incorporated into the bandage. This tissue is then removed with the bandage change.
  • Adherent bandages are classified as dry to dry, wet to dry, or wet to wet based on the composition of the primary layer. Dry-to-dry bandages consist of dry gauze applied to the wound.
  • The bandages are painful to remove but enable excellent tissue debridement. Wet-to-dry bandages are made with saline-moistened gauze placed directly on the wound. They are also painful to remove but result in less tissue desiccation than dry-to-dry bandages.
  • Wet-to-wet bandages tend to damage the tissue bed by keeping it too moist.
  • The secondary layer of a bandage absorbs tissue fluid, pads the wound, and supports or immobilizes the limb. This layer is frequently composed of cast padding or roll cotton.
  • The tertiary layer functions to hold the primary and secondary layers in place, provide pressure, and keep the inner layers protected from the environment. This layer is composed of adhesive tape or elastic wraps.

Surgical Techniques in Wound Management:

  • Advancement flaps can be used to move skin and relieve tension. The simplest type of advancement flap involves sliding skin to cover an adjacent defect. These flaps are elevated without regard to their vascular supply.
  • Flap survival depends on the subdermal vascular plexus from the flap base and revascularization from the recipient bed.
  • With subdermal plexus flaps, the vascular supply is affected by the width of the flap base. A high length/width ratio decreases the likelihood of survival as blood supply will not reach the distal end of the flap. Any flap placed in tension carries a high risk of failure.
  • The basic advancement flap technique is known as the single pedicle advancement flap. Two slightly divergent incisions are made perpendicular to the defect.
  • The tissue is undermined, advanced, and sutured to close the original defect. For larger wounds, two single pedicle flaps are safer than one large flap. Two advancement flaps are combined to form the “H” plasty.
  • There are several other well-described flap techniques, including the bipedicle advancement flap and the “V-Y” advancement flap. In each of these techniques, the coverage depends on stretching the skin over the defect.
  • For this reason, the use of these techniques may be limited by the regional anatomy, such as the region around the eyelids.
  • Flaps designed to incorporate a direct cutaneous artery are known as axial pattern flaps (arterial pedicle graft). The flaps can be used to cover a large area of tissue and carry along a new blood supply to ensure flap survival.
  • Muscle-based pattern flaps can also be used to reconstruct a body wall defect in addition to covering a loss of skin. The surviving area of axial pattern flaps is 50% greater than a corresponding subdermal plexus flap and therefore allows coverage of a larger area.
  • Because axial pattern flaps are based on arteries, they must have consistent landmarks and do not cover all regions of the body.
  • The best described of the axial pattern flaps is based on the caudal superficial epigastric artery. Based in the caudal aspect of the abdominal wall, this flap can extend cranially to include mammary glands 2–5.
  • Free skin grafts are used for cases with massive tissue loss such as large burns or degloving injuries. The grafts are best used as a split mesh. This allows drainage and helps prevent seroma formation.
  • Skin grafts will not remain viable if laid over squamous epithelium, denuded bone, cartilage, or tendon. The grafts must have a healthy, vascularized bed.
  • Initially, nutrition for the flap is maintained as capillary action pulls serum into the dilated capillaries of the skin graft, creating graft edema. Anastomosis with recipient bed vessels (inosculation) begins within 48–72 hr of surgery.
  • The edema may worsen immediately after inosculation, as venous return is not adequate initially. The edema should resolve as normal blood flow returns to the flap by day 4–6 after surgery.
  • All skin flaps and grafts require a clean, healthy recipient bed for survival. This is especially important for subdermal plexus flaps and free tissue transfers because they do not contain a direct cutaneous arterial supply.
  • The recipient bed must be free of debris, infection, and necrotic tissue.
  • While flaps may have well-described anatomic markers, determining their viability may not be as easy.
  • The simplest, but least accurate, methods for the assessment of a flap's viability are subjective measures, including the assessment of color, warmth, sensation, and bleeding. Purple color cannot be used as a predictor of viability.
  • Contused, purple skin is often viable. Progression from deep purple to black indicates necrosis. Skin temperature may be affected by the state of vasodilation and is therefore not an accurate method of assessing viability.
  • Bleeding from a cut surface may occur in viable flaps as well as nonviable flaps that still have some arterial function but poor or no venous return.
  • After movement of a flap, a flap may develop edema for the first few days until venous vascularization is completed.
  • Factors that interfere with wound healing may be divided by source into physical, endogenous, and exogenous categories.
  • Physical factors are environmental issues. Temperature affects the tensile strength of wounds. Ideal conditions allow wound healing to occur at 30°C. Decreasing the temperature to 12°C results in a 20% loss of tensile wound strength.
  • Adequate oxygen levels are also required for appropriate wound healing. Because of vessel disruption, wounds contain lower oxygen levels than surrounding healthy tissue.
  • Low levels of oxygen interfere with protein synthesis and fibroblast activity, causing a delay in wound healing. Oxygen levels may be compromised for many reasons, including hypovolemia, the presence of devitalized tissue, and excessively tight bandages.
  • Endogenous factors typically reflect the overall condition of the animal. Anemia may interfere with wound healing by creating low tissue oxygen levels. Nutrition has a significant overall effect on the body, although the ideal nutritional level for wound healing is unknown.
  • Hypoproteinemia delays wound healing only when the total serum protein content is <2.0 g/dL. Because wound healing is a function of protein synthesis, malnutrition may alter the healing process.
  • The addition of dl-methionine or cysteine (an important amino acid in wound repair) prevents delayed wound healing. Uremia can interfere with wound healing by slowing granulation tissue formation and inducing the synthesis of poor quality collagen.
  • Although diabetes is a known problem with wound healing in people, it has not been demonstrated to cause a problem in animals.
  • Obesity contributes to poor wound healing, primarily as a consequence of poor suture holding in the subcutaneous fat layers.
  • Decreased wound perfusion may also contribute.
  • Exogenous factors include any external chemical that alters wound healing. Cortisone is commonly implicated in wound complications.
  • Corticosteroids markedly inhibit capillary budding, fibroblast proliferation, and the rate of epithelialization. Similar to cortisone, vitamin E adversely affects wound healing by slowing collagen production.
  • This effect may be reversed with vitamin A. Additional vitamin A will not improve wound healing in the absence of vitamin E or cortisone. Vitamin C is required for the hydroxylation of proline and lysine. Zinc is required for epithelial and fibroblastic proliferation; however, excessive zinc delays wound healing by inhibiting macrophage function.
  • Radiation is detrimental to wound healing. Given 7 days before wound creation, healing is impaired. Cytotoxic drugs may also delay wound healing. Alkylating agents (eg, cyclophosphamide, melphalan) slow wound healing by blocking DNA synthesis.
  • Though most NSAID are thought to be safe in wound healing, recent work suggests that agens selective for COX-2 inhibition may slow wound healing.

Management of Specific Wounds:

Lacerations:

Uncomplicated simple lacerations are usually managed by complete closure if they are not grossly contaminated. The wound should be thoroughly lavaged and debrided as necessary before closure.

If tension is present on the wound edges, it should be relieved by tension-relieving suture techniques, sliding tissue flaps, or grafts. Deep lacerations may be treated according to the same principles, depending on the extent of the injury.

Damage to underlying structures (eg, muscles, tendons, and blood vessels) must be resolved before closure. If a laceration is grossly contaminated with debris, primary closure of the wound may not be indicated. Contaminated wounds may be closed with drains or treated as an open wound.

Bite Wounds:

Bite wounds are a major cause of injuries, especially in free-ranging animals. Cat bites tend to be small, penetrating wounds that frequently become infected and must be treated as an abscess with culture, debridement, antibiotics, and drainage.

Dog bites have a more varied presentation. Because of the slashing nature of dog bite injuries, the major tissue damage is usually found beneath the surface of the wound. While only small puncture marks or bruising may be evident on the surface, ribs may be broken or internal organs seriously damaged.

The animal should be thoroughly examined and stabilized before definitive wound care is begun. The wound should be surgically extended as far as necessary to allow a thorough examination and determination of its extent before a decision on the repair can be made. After a proper assessment, debridement can be performed.

Unless en bloc debridement is performed, complete wound closure is usually not recommended because the sites are usually contaminated. Closure can be accmplished with drains, as a delayed closure, or by second intention depending on the extent of the injury.

Degloving Injuries:

Degloving injuries result in an extensive loss of skin and a varied amount of deeper tissues. These injuries are a result of a shear force on the skin. Sources include fan belt injuries and loss of tissue during an accident with a motor vehicle.

With a physiologic degloving injury, the skin is still present but completely freed from the underlying fascia. If the injury results in a loss of blood supply to the skin, necrosis may develop later. In an anatomic degloving injury, the skin is torn off the body.

Anatomic degloving injuries frequently require marked and repeated debridement. Differentiating viable and nonviable tissue may be a problem in the early wound debridement process. An attempt should be made to salvage tissue in which viability is questionable.

Subsequent debridement can be used to remove any necrotic tissue. In orthopedic injuries that typically accompany degloving injuries, final stabilization may be delayed until local infection is under control.

Gunshot Injuries:

In gunshot injuries, most of the damage is not visible. As the projectile penetrates, it drags skin, hair, and dirt through the wound. If the projectile exits the body, the exit wound is larger than the entrance wound.

The amount of damage caused by the projectile is a function of its shape, aerodynamic stability, mass, and velocity. High-velocity projectiles tend to produce more damage as a result of impact-induced shock waves that move through the tissue.

The shock waves create blunt force trauma resulting in tissue and vascular damage.

Gunshot wounds are always considered to be contaminated, and primary closure is generally not recommended. These wounds should be managed as open wounds or by delayed primary closure.

After initial assessment and stabilization of the animal, the wound may be explored to evaluate the extent of damage and to determine a plan for repair. If the projectile caused a fracture, the method of repair depends on the location and type of fracture.

External fixation or bone plates are common choices for rigid stabilization of the fracture so that the soft tissues may be appropriately managed. Gunshot wounds to the abdomen are an indication for an exploratory celiotomy.

Gunshot wounds to the thorax may require a thoracotomy if hemorrhage or pneumothorax cannot be conservatively managed.

Pressure Wounds:

Pressure wounds or decubital ulcers develop as a result of pressure-induced necrosis. Pressure wounds can be extremely difficult to treat and are best prevented.

Preventive measures include changing the position of the animal frequently, maintaining adequate nutrition and cleanliness, and providing a sufficiently padded bed.

Factors that predispose to pressure wounds include paraplegia, tetraplegia, improper coaptation, and immobility. Mild ulcers may be managed with debridement and bandaging to prevent further trauma to the affected site.

More severe wounds require extensive surgical management. After debridement and development of a granulation bed, an advancement flap or pedicle graft may be required for closure.