Wound care and wound management in companion animals

Management of wounds and the decision when to close a wound or how or continue to treat it as open represents a key question in small animal veterinary first opinion practice.

Factors to consider include time elapsed since occurrence, extent of tissue trauma, amount of local tissue loss, degree of contamination, clinical condition of the patient, degree of tissue ischemia and local blood supply, possibility of closure based on wound location, wound tension or dead space, and likelihood of possible complications such as contracture, or wound dehiscence.

Patients with non-healing or delayed healing of open wounds should be evaluated for conditions that may interfere with the process such as local ischemia, multi-resistant bacterial contamination, presence of necrotic tissue and tension. Systemic disease such as endocrynopathies, and malnutrition can also interfere with the healing process.

ANTIMICROBIAL TREATMENT

Bacterial infection can delay wound healing. Topical agents, indicated in the early wound management, in general cover a broad bacterial spectrum and include antimicrobial/ silver-based ointments (silver sulfadiazine), silver-based dressings, and hyperosmotic substances such as honey, sugar, and 20% hypertonic saline. Use of medical honey is recommended. Honey is available as raw honey in tubes or jars or impregnated dressings (Fig. 1). It has an osmotic effect that dehydrates microorganisms reducing oedema and inflammation and promoting granulation tissue formation and epithelialization. Honey can be used in the inflammatory and early repair phases of healing and discontinued when debridement is complete and healthy granulation tissue is present. A honey- soaked gauze dressing may need to be replaced 1 to 3 times daily in highly exudative wounds or once every 1 to 3 days if the wound produces a small amount of exudate. The gauze may adhere to viable tissues causing pain upon removal. This can be avoided using a hydrophilic dressing impregnated with honey.

Sugar has hypertonic effects similar to honey and also enhances granulation tissue formation and epithelialization. It does not have the same anti-inflammatory and wound stimulation effects as honey. Sugar is applied in a 1 cm thick layer on the wound covered by an absorbent bandage. Bandage changes are required 2-3 times daily to maintain the osmolality of the wound.

Diagnosis of wound infection should be based on culture and sensitivity of samples taken from the deep wound tissue, and these results should inform selection of systemic antibiotics. Acute wound infections are usually characterised by the presence of one dominating microorganism, whilst chronic infections are often polymicrobic and possibly multi-resistant. Systemic antimicrobial therapy is indicated for progressing cutaneous infections or infections involving the deeper tissues.

The use of antimicrobial treatment can be discontinued once healthy granulation tissue has formed because penetration into granulation tissue is limited.

Wounds that only have localised signs of infection may be treated by topical methods alone.

INITIAL ASSESSMENT

Animals with traumatic wounds should be accurately assessed for any further life-threatening injuries. Full consideration should be given to radiography of the thorax and ultrasonography of the abdominal cavity.

Pain management is mandatory in traumatised patients. Opioids such as methadone and NSAIDS are valuable choices. NSAIDS should not be administered in hypovolemic patients due to the possible renal and gastrointestinal side effects. Local analgesia using lidocaine or bupivacaine provides good local pain control with reduced systemic effects.

Traumatised patients should be monitored and reassessed regularly as they may destabilise rapidly.

INITIAL WOUND CARE

Contaminated wounds should not be surgically closed and should be managed as open wounds for days until they can be closed or heal by second intention. Irrigation of the wound has an important role as it allows physical removal of the gross contamination. Clinical studies evaluating tap water and sterile saline for wound irrigation in humans showed no difference in occurrence of wound infection after tap water or sterile saline irrigation. Valid alternatives for wound irrigation are:

• Balanced electrolyte solutions;
• Unbalanced electrolyte solution: 0.9% saline;
• Antiseptic irrigation solutions:
  •   0.05% chlorhexidine solution using 10 ml of Chlorhexidine Gluconate 5% added to 500 ml sterile water;
  •   0.1% Povidone-iodine solution using 50 ml of Povidine –iodine 10% added to 500 ml balanced electrolyte solution.

Very high pressure (such as that produced by pulsatile lavage instruments) may drive contaminants into deeper tissue planes, which could reduce the resistance to infection. A common technique is to use a 35-ml syringe with an 18-gauge needle to generate 7-8 psi pressure. Low-pressure irrigation can also be used by flowing fluid from a given set connected to a bag of sterile solution or pouring fluid from a sterile bottle or by use of a bulb syringe.

Initial wound care should also include covering the wound with a clean, dry bandage to prevent further contamination, haemorrhage, and to stabilise the injured area improving comfort for the patient and limiting further trauma. The covering remains in place until definitive treatment can be performed. In areas where the bandage may be difficult to place the dressing can be secured with a tie-over technique (Fig.2).

Wound debridement is indicated for removal of foreign material, devitalized, or necrotic tissue. Debridement may be selective or nonselective. Selective debridement involves the use of enzymes to remove only damaged tissue leaving the healthy tissue in place. Nonselective debridement involves physical removal of debris including some healthy tissue.

Selective debridement includes enzymatic debridement and autolytic debridement. Enzymatic debridement uses agents applied to the wound surface to selectively destroy necrotic tissue and bacterial biofilm. This technique can be used instead of surgical debridement in patients with anaesthetic risk or with other surgical contraindications. Enzymatic agents are available as ointments or gels containing streptokinase, trypsin, proteinase and collagenase. Enzymatic debridement occurs without pain or bleeding, it can be slow and expansive and it is not indicated to treat large areas.

Autolytic debridement occurs when a moist environment is maintained at the wound surface. This moisture allows normal cellular processes to destroy bacteria and remove or repair damaged tissue. Autolytic debridement is promoted by using hydrophilic, occlusive or semi-occlusive bandages, which allow some wound exudate to remain in contact with the wound surface and keep it moist. Wound exudate contains endogenous enzymes, and growth factors that stimulate angiogenesis, granulation tissue formation and epithelialisation. Bandages also keep the wound surface warm, which enhances enzymatic activity. Proper wound preparation is needed to create an optimal environment for autolytic debridement.

The principle of moist wound healing is put into practice by the use of hydrophilic dressings such as polyurethane foam, hydrogel, and hydrocolloid (Tab.1).

Tab. 1. Bandage dressings.

The previously mentioned wound irrigation and surgical debridement represent techniques of non-selective debridement.

Sterile instrumentation and aseptic technique should be used for surgical debridement. Foreign debris not removed by wound irrigation can be removed with thumb forceps scissors, scalpel blade and curette. Excessive excision of healthy tissue could however delay wound healing. The intent of debridement is to have a well-vascularized wound bed to support wound healing.

Tissue viability can be difficult to assess, initial tissue debridement should therefore be conservative. Skin circulation in fact may deteriorate for  days after trauma or surgery because of edema and other factors, so repeated debridement may be required as the extent of tissue necrosis becomes more evident. Skin viability is clinically assessed by colour, warmth, pain sensation, and bleeding. Nonviable necrotic skin is black or white, and the area may be non pliable, cool, and devoid of sensation. Normal skin is warm, pliable, and pink with pain sensation. Areas of questionable viability are blue or purple and sensation is poor.   

Layered debridement describes sequential removal of devitalised tissue at the surface of the wound, progressing to the wound depth. Exposed cortical bone, fat, and fascia are not well-vascularised tissues. Forage of exposed cortical bone (penetration of the bone in multiple sites with a pin creating multiple holes) allows the vascular medullary canal to communicate with the wound bed inducing formation of granulation tissue. Excess fat should be removed and intact fascia opened to expose underlying vascular muscle tissue.                                                                                                                                                                                                  

WOUND CLOSURE

There are four different options of wound healing: first intention healing (primary wound closure), delayed primary closure, second intention healing (healing by contraction and epithelialization), and third intention healing (secondary closure). First intention healing consists in apposing the wound edges with sutures, staples, or glue. It occurs in surgical wounds and is indicated in clean or minimal contaminated wounds. Class 1 (Tab. 2) wounds can be closed with primary wound closure. Delayed primary closure consists of apposing the wound edges 3 to 5 days after wounding, before granulation tissue has been formed. Class 2 wounds or mildly contaminated (Tabs. 2 and 3 ) wounds requiring some debridement and open wound management can be managed with delayed primary closure. Second intention healing occurs when the wound is left open allowing formation of granulation tissue until wound closure happens by contraction and epithelialisation. This healing is indicated for dirty wounds (Tab. 3) in which debridement and cleansing is necessary but primary or delayed closure is not permitted. Third intention healing occurs when appositional closure of a wound happens 3-5 days after wounding following formation of granulation tissue. In the author’s experience each wound is different and it is therefore not easy to give a precise rule about timing of wound closure. Contaminated wounds should never be closed primarily and should be revisited during the course of the management in order to choose the most appropriate timing and wound closure option.

Tab. 2. Classification of traumatic wounds

Tab. 3. Classification of surgical wounds

In some patients wound care for several days before the wound environment is suitable for closure is required. Vacuum-Assisted Closure (VAC) or NPWT (Negative Pressure Wound Therapy) is a wound healing strategy that improves wound environment, and speeds up wound healing. NPWT involves the use of topical negative pressure, or suction, applied to an open wound that has been covered with porous foam and then covered by an adherent, occlusive sheet to achieve an airtight seal (Fig. 7). Applied controlled negative (subatmospheric- -80 to -120 mm Hg) pressure pulls exudates through the foam into a reservoir resulting in active drainage and decreased edema. Negative pressure increases blood perfusion and neoangiogenesis to the wounded tissue allowing delivery of oxygen, nutrients, cells (fibroblasts) and growth factors. In addition, increased blood perfusion benefits the wound by removing free radicals and waste products and also increases the delivery of antimicrobials to the wounds in patients receiving antibiotics. Reduced bacterial burden in the wound has been proposed as a mechanism that leads to improved wound healing with NPWT. Indications for NPWT include chronic non-healing wounds, infected wounds, dehisced wounds, ulcers, skin grafts and skin flaps. NPWT should not be used in the presence of any local malignancy, because of the risk of local tumour recurrence. It should not be used over exposed vessels, tendons, ligaments, and nerves because damage could occur and severe haemorrhage could result if NPWT is placed over arteries or veins.

Appropriate monitoring of the NPWT is important. The system needs to be monitored at least every two hours for any evidence of suction loss. The character and volume of the fluid suctioned from the wound needs also to be monitored to determine the effectiveness of NPWT in controlling infection and to verify that drainage volume is declining. The canister needs to be emptied or changed when it approaches its maximum capacity. Dressings can be left in place for up to 3 days before changing, even though loss of suction and loss of the airtight seal require anticipation of the dressing change. NPWT seems to offer great benefit for the patient in terms of speed of wound healing, such as the speed and improvement in vascularity, decreased edema, an increased rate of granulation tissue formation, an increased rate of wound contraction, and a potential decrease in bacterial contamination.

CONCLUSION

Most wounds heal uneventfully. The goal of open wound management is to limit any further contamination and maintain the wound moisture for infection control and faster wound healing. Dressing selection changes with the progress of the wound healing, and amount of exudate. Management of chronic nonhealing wounds can be more complex and may require advanced adjunctive therapies.