by Chloe Fay BSc (Hons) RVN CertVN ECC VTS (ECC)
Wounds
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 stabilised and definite wound management may need to be delayed as the treatment of life-threatening injuries takes priority. Emergency management should prevent any additional injury and minimise contamination. Open wounds may be covered with a sterile dressing until the patient is stabilised. Many patients may be in pain from their injuries, so appropriate analgesia is important. Fractious patients may require sedation or general anaesthesia for wound evaluation to be performed.
Wounds can be classified by their cause and the type of tissue damage caused:
- Abrasion: Skin damage with a loss of epidermis and a portion of the dermis
- Avulsion (degloving): Tearing of tissue from its attachments
- Incision: Wound created by a sharp tool, resulting in wound edges with minimal tissue trauma
- Laceration: Irregular wound caused by tearing, which produces superficial and underlying tissue damage
- Puncture: Penetrating wound caused by a sharp object; punctures cause minimal skin damage but underlying tissue damage may be severe, resulting in a higher risk of subsequent infection by contamination introduced at time of puncture
Wounds can be classified further into degrees of contamination and duration (although the degree of contamination trumps the importance of duration):
Class 1: Clean wound with minimal contamination and a 0 to 6 H duration
Class 2: Wound with significant contamination or 6 to 12 H duration
Class 3: Wound with gross contamination or > 12 H duration
There are 3 phases of wound healing; healing can take place on its own or with medical or surgical intervention.
- Phase 1 — Inflammatory Phase: This phase occurs immediately after injury and is mainly directed at minimizing blood loss from the injured area by haemostasis—vasoconstriction, platelet aggregation, and clot formation—followed by vasodilation and phagocytosis.
Phase 2 — Proliferative Phase: In this phase, granulation, contraction, and epithelialization of the injured tissues occurs.
Phase 3 — Remodelling Phase: This phase involves formation of new collagen, wound tissue strengthening, and scar formation.
Treatment
Treatment for any wound should follow the following steps: debridement (+ lavage), 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 minimised to decrease bacterial contamination. If the wound is infected, a sample should be collected for culture and sensitivity testing. In traumatic and infected wounds, antibiotics should be administered as soon as possible. A first-generation cephalosporin or clavulanic acid potentiated amoxicillin are good first line choices.
Bleeding should be controlled. Direct pressure is applied using sterile swabs or by bandaging. Addition of diluted adrenaline to swabs may help by causing vasoconstriction, but should not be used on extremities or in the presence of cardiac arrhythmias. Pressure can be applied to brachial or femoral arteries if arterial haemorrhage is present.
A tourniquet can be applied above the wound if it is on a limb. Narrow elastic tourniquets put significant pressure on neurovascular structures and should only be used for up to 5 minutes. Bands 5–10cm wide can be used for up to 30 minutes. Blood pressure cuffs can be placed proximal to the wound and inflated to 20–30cm H2O higher than arterial pressure and can be left in place for up to 6 hours. Ligation may be needed for larger vessels.
After achieving haemostasis, the wound should be covered with a sterile dressing. Using aseptic techniques, the wound is packed with sterile gel or soaked swabs and hair clipped from the wound outwards. The wound can then be lavaged with copious saline or lactated Ringer’s solution (Hartmann’s) and a protective bandage applied.
Once the patient is stable a more thorough evaluation may be carried out. Appropriate chemical restraint may be required for examination. Prior to their administration, it is important to evaluate distal neuromuscular and motor function. Diagnostic imaging may be used to check for foreign material, penetrating injuries, associated fractures, dislocations and tendon or ligament damage. A management plan should take into account the wound’s location, size, damage to local structures and the amount of tissue loss.
Lavage reduces the number of bacteria present, and helps to loosen necrotic tissue and debris.
Lavage solutions containing antibacterials or deter gents should be avoided; they can cause cell damage, slow wound healing and may result in bacterial resistance. Lactated Ringer’s solution (LRS) is the best choice, it is the least cytotoxic and has a near neutral pH. In heavily contaminated wounds tap water is adequate. The initial tap water lavage should be followed by sterile LRS.
The pressure for lavage solution needs to exceed the adhesive and cohesive forces of the contaminant, yet avoid pushing debris into the tissues and causing damage to vital tissues. The suggested force is 5–10 psi. In practice this can be achieved by using a bag of fluid with an 18–20 gauge needle fitted to the end of an attached giving set. The volume of lavage solution is equally important. For small, superficial wounds, 0.5–1l is generally used; for larger wounds several litres of sterile lavage solution may be needed.
Any traumatic wound will require the debridement of devitalised tissues and foreign material in order to prevent infection and necrosis and to promote optimal wound healing. Debridement may be performed using a number of different methods.
Sharp debridement involves the use of a scalpel blade or scissors and may be carried out carefully in stages in order to preserve as much healthy tissue as possible. Subcutaneous tissue, fat, skin, fascia and muscle can generally be freely debrided. Tendons, vessels, nerves and bone should be debrided much more conservatively. In some situations, necrotic tissue close to vital structures may be left in place until there is a line of demarcation.
Mechanical debridement involves the use of dressings (e.g. wet to dry, irrigation or hydro surgery). Wet to dry dressings are commonly used in veterinary practice but their use requires sedation or anaesthesia as removal is painful. Autolytic debridement involves the use of wound dressings and solutions, e.g., hydrogels, and is not recommended in infected wounds.
Following debridement, a decision needs to be made about wound closure. In clean and clean contaminated wounds, surgical closure to allow rest intention healing may be the best option. If there is any doubt about the tissue viability or the risk of infection, the wound should be allowed to heal using open wound management. Damage to underlying structures such as tendon and bone may delay the healing of the overlying tissue and require specialist treatment. If there has been significant skin loss then skin aps or grafts may be needed.
