Basic Wound Management

. Bandages, Dressings and Dressing Techniques

After any emergency treatment, such as arresting serious hemorrhage, the horse should, if possible, be moved to a more suitable environment for assessment and treatment. All wounds must be promptly and thoroughly examined to determine the exact site, depth and direction of the wound, and which anatomical tissues and structures are involved and to what extent. It is essential to determine whether important structures, e.g. joints, tendons, nerves, or blood vessels have been damaged. The risk of complications may thereby be minimized and the owner appraised of possible complications in healing at the outset of treatment.

History

The cause and time of the injury should be determined; sometimes they can only be surmised. The cause of the wound and the time delay between injury and veterinary attention will have important implications for the subsequent management.

Tetanus status should always be determined and appropriate protection ensured.

Horses that are receiving drugs for other purposes may have healing problems (either from the underlying disease or from the drugs themselves).

Restraint

Sedatives, opioid analgesic drugs with non-steroidal anti-inflammatory drugs make initial assessment far easier. Suitable drug doses for initial wound management are available.

Initial Examination

Hemorrhage Control

Provision of a Moist Environment

A moist wound healing environment has become standard practice. Wounds heal better when maintained in this fashion ¹⁰. Hydrogels, hydrocolloids, and collagen dressings support a moist environment. Hydrophilic, gas permeable, waterproof polymeric foam dressings should be used in the initial stages of wound management. These foams are available in various shapes to allow cavity management. Alginate or highly absorptive dressings may be required if exudate is excessive.

Wound Closure

Primary Closure

Incised wounds (see p. 8) frequently lend themselves to suturing. Suturing should only be carried out when so doing will have a positive advantage and minimal harmful effects. Careful selection of suture patterns will make a considerable difference to wound healing. The standard patterns and their advantages and disadvantages are described on p. 48 and in standard surgical texts. No wound should be completely closed unless the deeper tissues are effectively sterile.

Factors that are likely to result in wound breakdown (dehiscence) after suturing include:

1. Gross contamination.

2. Infection.

3. Significant skin loss/tension in suture line

4. Marked swelling.

Note

Delays in closure may result in primary contraction of the skin flaps that may preclude closure. Primary closure will almost always fail when tissue necrosis and swelling disrupt the suture line.

Notwithstanding the presence of obvious complication factors, wounds involving the lower parts of the limbs usually present the greatest challenges. There is considerable controversy over the necessity to suture lower limb wounds. In general, a limb wound may be sutured if the wound is clean, free of complicating factors, and in the longitudinal plane (i.e. running up-down the limb). If the wound is not in a suitable site that makes suturing without undue tension feasible, then it is probably best to use second intention healing (see p. 18) or delayed primary intention healing (see p. 20).

Delayed Primary Closure

This is used in relatively clean but contaminated wounds with extensive tissue damage. The wound is cleaned, debrided and dressed with a hydrogel (Intrasite Gel or Intrasite Conformable; Smith and Nephew), and a polymeric foam dressing (e.g. Allevyn, Smith and Nephew) applied. Cavity dressings (Allevyn Cavity or Intrasite Conformable; Smith and Nephew) or shaped dressings (e.g. Allevyn Heel; Smith and Nephew) can be used in awkward sites.

Reexamination and redressing continues at appropriate intervals until the wound is free of obvious infection and necrotic tissue, and the wound bed contains healthy granulation tissue. The wound is then freshened using careful superficial sharp debridement and closed using a suitable suture technique (possibly with tension relieving quills or tension relieving lateral incisions).

Second Intention Healing

The wound is left open after initial treatment and allowed to granulate. Healthy granulation tissue fills the wound from its depth, and once it reaches the wound margin the epithelium should be able to migrate across the wound. Wound contraction is a significant aspect of second intention healing. It occurs at a rapid rate and is responsible for over 95% of second intention healing on the body and neck.

Contraction is very weak in the distal limb regions of horses in particular (see p. 20). Second intention healing is faster in ponies than in horses, and faster on the body trunk than on the limbs where, at least in a proportion of larger horses, the inflammatory process is weak and prolonged and so the wound never heals¹¹.

Note

In most horses over 140 cm in height there is no significant contraction in limb wounds, i.e. below the stifle and the elbow, and in particular below the knee (carpus) and the hock (tarsus).

Antibacterial Support

Failure to control potential and actual infection will inevitably result in retarded healing. Removal of bacteria before adhesion occurs is a useful aid to wound healing. Antibiotics are used to treat known or suspected infections, and as prophylaxis for various types of medical and surgical procedures. Antibiotics seldom eliminate infection; rather they reduce the rate of bacterial replication to a degree, which allows the host’s defence systems to eliminate the infectious agent.

The side-effects of antibiotics include:

1. Bacterial resistance.

2. Anaphylactic reactions.

3. Overgrowth of bacteria and gastrointestinal disturbances.

4. Specific toxicity on organs and systems.

Tetanus vaccination status should be established in all cases. If the horse has had a recent vaccination then there should be no risk of the disease, as the vaccine is highly effective. Where the vaccination history is dubious, either a tetanus toxoid booster vaccination or antiserum (or both) should be administered.

Protocol for Best Practice Use of Antibiotics (Figure 37)

Wound Lavage

Wound lavage is an essential part of the management of fresh and older wounds. It is used to remove adherent and non-adherent bacteria and foreign matter from the wound without compromising the physiological status of the tissues involved. The two major factors are the type of fluid used and the pressure of the fluid used.

Given the essential need for a physiologically sound fluid, the pressure is more important than the actual fluid used; in order to overcome bacterial adhesion the ideal pressure is 10–15 psi (as achieved by commercially available lavage instruments such as a ‘Water-Pic’. However, a 35/50 ml syringe with a 19G needle attached will provide about 8 psi.

The Mills wound irrigator is an ideal safe and convenient wound irrigation system. It can be attached to a bag of sterile saline without any difficulty or delays, so that the wound can be lavaged with an ideal solution at an ideal pressure.

Figure 38 The Mills wound irrigator system provides physiologically sound, sterile irrigation at an ideal pressure. It is both convenient and efficient.

Lavage Fluids

Saline (Physiological Saline)

Saline is the ideal irrigation solution because of its physiological compatibility. It can be delivered from a sterile injection bag, but a working solution in large volumes can be made by adding a flat teaspoonful of salt to 0.6 liters (1 pint) of warm (previously boiled) water. Saline can be used to restore physiological normality after water irrigations have been used.

Water

Fresh clean (drinking) water is probably sterile enough as an initial wound lavage fluid, but it lacks physiological compatibility and has the potential to cause cell swelling. Prolonged and repeated water irrigation can cause significant cell destruction. It should not be used apart from initial ‘washing of gross contamination’ if saline is available, and in any case its use should be followed by saline to restore normal physiological status.

Povidone Iodine

Povidone iodine is commonly supplied as a 10% solution. The active ingredient is free iodine; dilute (0.1–1%) solutions have greater bactericidal activity than the full strength product. Serum can reduce activity (by binding free iodine) and there is only a short-lived residual effect, hence if used to maintain cleanliness of a wound, 4–6 hourly repetition is necessary.

Strong solutions of povidone iodine can be detrimental to healing, even causing necrosis; 0.1–0.5% solutions can be used for lavage purposes.

The benefit of povidone iodine in controlling bacterial infection may be limited. Povidone iodine solutions can cause nerve damage if they are repeatedly applied to exposed nerves.

Chlorhexidine

Chlorhexidine is a broadly active antiseptic. It is usually supplied in 10% solution in a soap base as a surgical scrub. When mixed with saline it forms a precipitate within only 12–24 hours. If solutions must be stored, deionized water should be used as the diluent. The advised concentration is 0.05% to avoid adverse effects on the tissues. Irrigation with 0.05%–1% chlorhexidine solutions probably leads to fewer infections when compared to 0.1%–0.5% povidone iodine. It also has a significant residual activity, being bound to cells.

Hydrogen Peroxide

Hydrogen peroxide is available in various strengths measured in volumes of oxygen released (the strongest solution is 30 volumes). Solutions over five volumes will cause tissue damage. While various solutions have been used for wound lavage, it is now generally considered unsuitable for this purpose because of the tissue damage it causes. Hydrogen peroxide can however, be used as a debriding agent and for flushing out anaerobic wounds (e.g. in the sole of the foot).

Acetic/Malic/Salicylic Acid

Commercial mixtures of these (and other) acids are available as wound irrigation solutions, but they are very acidic and highly tissue toxic. They are totally unsuitable as initial wound lavage solutions and should be reserved for special purposes only. Application of the solutions to a fresh wound results in the wound turning black due to formation of acid hematin. These solutions should be used only when Pseudomonas spp. infection is suspected or proven. Under these conditions they can be very effective.

The ointment forms can be useful debriding agents in the early stages of management of neglected, infected, and highly contaminated wounds.

Soluble Antibiotics

Dilute antibiotic solutions, e.g. penicillin, ampicillin, neomycin, kanamycin, and gentamicin, have been beneficial when added to lavage solutions. However, the solutions usually have an inappropriate pH for wound healing, and so some cell damage is expected. Suspensions of antibiotics and ointments are not appropriate for wound lavage. Antibiotic creams used for bovine mastitis treatment are not suitable for wound management and should never be applied to a healing wound.

Skin Wound Repair

Suture Patterns

Sutures are used to close a wound and are used for first intention (primary union) healing (Table 3). Sutures are also used in delayed primary healing. The decision to suture a wound must be based on sound understanding of the likely healing processes involved. Primary closure is the best method of closing and healing a skin wound, but is only applicable to a relatively narrow range of accidental wounds that fulfill certain criteria: the wound should be fresh, clean, and there should be no foreign matter within the wound bed. In addition, once closed by suturing there should be no tension on the wound (unless suitable tension relieving mechanisms can be applied), including during movement or swelling, and there should be no dead space within the wound.

Table 3

Suture materials for skin closure