Piecing the puzzle back together: Wound management & basic reconstructive skin surgery
Written by Michael B. Mison, DVM, Diplomate ACVS Staff Surgeon - Seattle Veterinary SpecialistsAffiliate Assistant Professor - University of Washington School of Medicine
Irrigants are delivered at a pressure of 8 psi (35-mL syringe and 19-gauge needle) to be maximally effective. The use of a higher pressure lavage may be more effective in reducing bacterial numbers and removing foreign debris and necrotic tissue. However, such pressures may result in dissemination of bacteria and debris into deeper tissues, damage underlying tissues, and reduce resistance to infection. Commercial lavage units such as Surgilav (Stryker Co.) are available for clinical use. This disposable pressure lavage unit connects to an intravenous fluid bag and is effective for aggressive lavage of contaminated wounds.
Devitalized tissue may be removed by surgical excision, enzymes, or wet-dry bandages. The extent of surgical débridement varies with the type of wound and the degree of contamination. Devitalized tissue should be surgically excised in layers beginning at the surface and progressing to the depths of the wound. Evaluation of skin viability in the acute period may be difficult due to vasospasm and edema. Skin débridement may be delayed 48 to 72 hours to allow the tissues to declare their viability. Staged débridement allows for selectivity, and tissues that are initially questionable may recover and can be spared for facilitate wound closure. Alternatively, the entire wound can be excised en-bloc if sufficient healthy tissue surrounds the wound and vital structures can be preserved. Enzymatic débridement (trypsin and chymotrypsin) has a minor role in treatment of wounds in small animals. They may be beneficial in patients that are poor anesthetic risk or when surgical débridement may damage healthy tissue. These agents are generally not a substitute for surgical débridement of larger areas of necrosis.
The benefits of topical antimicrobial agents in the treatment of superficial wounds outweigh their potential cytotoxic effects. Clean or mildly contaminated wounds do not benefit from topical antimicrobials. However, combined systemic and local therapy is advantageous in heavily contaminated wounds. Antibiotics applied within 1 to 3 hours of contamination often are effective in preventing infection. Once infection is established, topical antibiotics have no beneficial effect in preventing suppuration of wounds. Commonly used topical antimicrobials in small animals include triple-antibiotic ointment (bacitracin-neomycin-polymyxin), silver sulfadiazine, nitrofurazone, and gentamicin sulfate. Systemic antibiotics may be used prophylactically or therapeutically. Selection of systemic antibiotics should be targeted against the microorganism most likely to cause wound infection or based on culture sensitivity.
Provision of adequate drainage is important in the management of wounds. Leaving the wound open provides optimal drainage for the patient’s injury. At the time of closure, drains may be used to minimize dead space and provide an outlet for removal of debris and tissue fluids. Drains can be divided into two types: passive and active drain systems. The most commonly used passive drain is the Penrose drain. This is a flat drain that functions through capillary action and gravity. Other types of drains include tube drains and multilumen drains. Active drainage is provided by closed suction drains, in which a vacuum created within the wound facilitaties continuous drainage. A vacuum of 80 mmHg is ideal. Closed suction drains allow dressings to remain dry, prevent ascending infection, and enable quantitative assessment of drainage.
Wound healing stimulants have application on chronic wounds, as well as severe acute wounds. Wound healing stimulants are topical preparations that stimulate wound healing cells to produce cytokines and growth factors which enhance wound healing. These stimulants do not have antimicrobial activity. Such medications available for clinical use include macrophage activators (Acemannan), hydrophilic agents (copolymer flakes, dextranomer, maltodextrin, and hydrolyzed bovine collagen), and tripeptide-copper complex medication (Iamin-Vet Skin Care Gel®). It has been found that these medications have their greatest effect during the first 7 days of use. Porcine collagen (Vet BioSISt®) has also been used for wound management. It has been reported that there is rapid incorporation of the Vet BioSISt into full-thickness wounds. Studies have shown that there is an earlier appearance of granulation tissue over exposed bone in wound treated with porcine collagen as compared to control wounds treated with only bandage. Experimentally, pulsed electromagnetic field treatment of open wounds has been shown to enhance wound epithelialization and possibly early wound contraction. There is also evidence that both ultrasonography and phototherapy (low-powered laser) shorten the inflammatory phase of healing and enhance the release of factors that stimulate the proliferative stage of repair. The use of a controlled sub-atmospheric pressure dressing (Vacuum Assisted Closure™) has also been shown to help remove interstitial fluid allowing tissue decompression, help remove tissue debris, and promote wound healing
Bandages provide wound cleanliness, control the wound environment, reduce edema and hemorrhage, eliminate dead space, immobilize injured tissue, and minimize scar tissue. They also provide comfort and absorb and allow for characterization of wound secretions. Bandages keep wounds warm, which improves wound healing and facilitates oxygen dissociation. Absorbent/adherent bandages are indicated for open contaminated and infected wounds. These assist in microdébridement with each dressing change, usually performed daily or more often if strike-through occurs. Absorbent/adherent bandages should be replaced by non-adherent bandages when drainage becomes serosanguenous and granulation tissue forms on the wound.
Wounds may be closed immediately (primary wound closure), within 1-3 days after injury when they are free of infection but before granulation tissue formation (delayed primary wound closure, after the formation of granulation tissue (secondary closure), or they may be allowed to contract and epithelialize (second intention healing). Factors that affect the decision to close wounds include the amount of time elapsed since the injury, degree of contamination, amount of tissue damage, completeness of débridement, status of the wound’s blood supply, animal’s health, extent of tension or dead space, and location of the wound. Delayed primary closure is indicated for mildly contaminated, minimally traumatized wounds. Wounds are first lavaged and débrided, and treated with bandages after injury before closure. Grossly contaminated or infected wounds or wounds with considerable tissue loss should not be closed primarily and should be treated as open wounds. Again, the goal is to convert the open contaminated wound into a surgically clean wound. They should be thoroughly explored and lavaged to remove debris and reduce bacterial numbers. The wounds will initially heal by contraction and epithelialization and may be allowed to heal completely. Alternatively, healthy wounds may be repaired by secondary closure or by use of a flap or graft.
Postoperative wound care should optimize healing. Wounds should be evaluated frequently for infection, tension, seroma formation, dehiscence, and necrosis. Sutures should be removed from wounds in 7 to 14 days. Scarring and suture associated infection is greater when sutures are left for longer periods.
Although many of the wounds seen in clinical practice are not life-threatening, delays in early effective management can have devastating consequences. Successful results require practice, careful attention to detail, and adherence to the basic principles of wound management.
Introduction to Reconstructive Surgery
Indications for reconstructive sugery include
The skin is composed of stratified squamous epithelium. The dermis, located under the epidermis is composed of connective tissue with an extensive vascular and nervous network. The subcutaneous tissue lies deep to the dermis.
The glands of the skin (apocrine sweat glands and sebaceous sweat glands, perianal glands, and merocirne sweat glands) extend through the dermis into the subcutaneous tissue. The cutaneous trunci muscle is found under the subcutaneous tissue and allows for skin movement. Innervation to the skin is by the cutaneous branches of the ventral branch of the 8th cervical nerve and the 1st thoracic nerve. The blood supply to the skin is provided by direct cutaneous arteries. Three plexuses develop from the direct cutaneous artery and include:
deep or subdermal plexus, middle or cutaneous plexus, and superficial or subpappilary plexus). The subdermal plexus provides the major blood supply to the skin and preservation of this vascular network is essential to skin flap survival. Since this plexus is located in the subcutaneous connective tissues, it is very important to undermine skin flaps such that the subcutaneous layer remains attached to the dermis. In areas where panniculus or cutaneous trunci muscles are under the skin, elevation of skin by dissecting under the muscle preserves the plexus. Remember that the skin is an organ. It provides a barrier to infectious disease, and to chemical or gaseous exchange, as well as insulation against thermal changes. Like many other tissues, as an organ, it does not regenerate when excised. Epithelial and connective tissue structural repair occurs but adnexal structures do not regenerate.
Sources of skin injury could be due to:
- Secondary skin defects
- Extensive surgical dissection
Surgical closure of cutaneous defect requires proper timing and planning. Infected wounds are generally treated and managed as on open wound so multiple debriding procedures can be done to allow formation of healthy granulation tissue. The location of the defect is also a factor that contributes to skin repair. The trunk of small animals is blessed with very mobile skin. In general, region of good skin mobility include the trunk, cervical region, and upper extremities, whereas skin around the eyes, ears, anogenital region, and distal extremities has limited mobility. Tension lines resulting from gravitational pull and muscle pull influence closure of cutaneous wounds. Incisions made across tension lines tend to separate. Incisions made parallel to tension lines gape less. Thus, when planning an incision, it is helpful to make your incision parallel to the tension lines.
There are a few basic principles to remember when suturing skin flaps.
Suture placement must be done with care when securing skin flaps to the recipient area. Few sutures, if any, should be placed under the flap for dead space control. Place too many sutures under the flap may compromise blood supply. Sutures should be placed atraumatically at the periphery (subcuticular pattern) of flaps and then simple interrupted skin sutures are placed. And remember to limit tension.
Cutaneous Reconstructive Surgery:
The purpose of “walking sutures” is to take advantage of the normal elasticity of the skin when stretching skin over a cutaneous defect. The skin is undermined deep to the subdermal plexus to facilitate movement of skin. Using an absorbable monofilament suture material, the “walking suture” is placed through the dermis away from the proposed line of closure, and then subsequently through fascia closer to the proposed line of closure. The technique effectively disperses tension over the entire surface area of the flap, closes dead space, and advances surrounding skin over the defect to be covered.
Closure by local skin mobilization:
In the following procedures described, the skin defect is closed by utilizing tissue in the area of the defect. Examples of techniques include:
- Undermining – Dissecting under each edge of a defect to allow the skin to be stretched over the defect without tension.
- Relaxing incision – After an incision is made in juxtaposition to the defect, the intervening skin is undermined and moved over the defect. The resulting new defect is closed by an alternative technique or allowed to heal by second intention.
- Local skin flaps – These are full thickness flaps that are incised, undermined, and transposed over a cutaneous defect. They are based on the subdermal plexus blood supply. Examples include:
- Rotational flaps
- Transposition flaps
- Advancement flaps
- Closure by distant skin mobilization – These techniques often require multiple procedures. The additional procedures are required to allow the blood supply within a flap to increase and allow collateral circulation to develop. Techniques involving distant skin transposition are based on redirection of blood flow or incorporation of direct cutaneous arteries into the flap. Examples include:
- Axial pattern flap – Based on direct cutaneous arteries. Since these flaps contain an arterial supply, then can be made in long lengths, and subsequently mobilized to cover large distant trunk or extremity defects.
- Island arterial flap – This flap is dissected completely free of surrounding skin but the direct cutaneous artery and vein that supplies the flap is left intact. The technique results in increased flap mobility.
- Tube flaps – Based on the subdermal plexus. After parallel incisions, the skin is tubed on itself and the skin defect remaining is closed under the tube. After 14 days, the blood supply in the tubed skin is redirected in a longitudinal flow and one end of the tube can be safely excised and moved to a distant cutaneous defect. After adequate collateral circulation develops within the transferred pedicle, the tubed portion can be excised.
- Pouch flaps – These are flaps located on the lateral aspect of the trunk and based on the subdermal plexus. Used to cover defects on distal extremities. The extremity is immobilized to the flap by bandaging for 14 days. The base of the flap is excised at that time and sutured to the remaining defect. The cutaneous defect on the trunk is then closed primarily.
Free skin grafts:
Skin grafts are free avascular tissue that are transferred to a distant site that has a healthy granulation bed. Free grafts depend on tissue fluid from the graft recipient bed (plasmatic imbibition) for nutrition during the first 48 hours after transposition. During this period, capillary anastamosis or ingrowth (inosculation) form the granulation bed to the donor skin occurs. Movement, hematomas, seromas, or infection all decrease the likelihood of “graft take”.
Several methods of free skin grafts are possible and include:
- Full thickness skin graft – Full thickness skin that is transferred to a recipient bed of granulation tissue. This graft results in complete hair growth is it is important to note the direction of hair growth prior to transfer. Strict immobilization is required.
- Split thickness skin graft – The skin is split with a dermatome or a scalpel blade creating a thin graft. The split thickness skin graft can be placed over more undulating areas than the full thickness grafts. This graft is devoid of adnexal structures.
- Split thickness meshed skin graft – A split thickness graft that is meshed by scalpel or by a skin mesher to allow an accordion-like expansion of the graft. Doing so allows coverage of greater area with a smaller piece of skin. It can be placed over mobile, undulating defects and the meshed areas provide a route for escape of blood and serum.
- Sieve graft – A full thickness graft with holes punched in the center to allow drainage of serum and blood in hopes of better graft-granulation tissue contact.
- Strip graft – Strips of full thickness skin placed parallel to each other to cover a skin defect.
- Seed or Punch grafts – Circular areas of full thickness skin removed with a biopsy punch and set into holes of like diameter made in granulation tissue.
Published on December 3, 2007.