WOUNDS can be difficult to deal with in animal patients due to factors such as motion, maceration and mutilation. Simple wounds can often be dealt with using straightforward materials, creating an environment that allows healing by secondary intention.
In recent years there has been a trend toward using new techniques, dressings and topical applications to handle more complex cases involving contamination, infection or devitalised tissues, or those requiring a good cosmetic result quickly.
Dressing techniques
The first layer in contact with a wound can be adherent or non-adherent. A non-adherent dressing is applied to healthy granulation tissue, prevents tissues from drying out and causes minimal trauma. An adherent dressing can be dry to dry, where dry gauze is
applied to the wound; or dry to wet, using, for instance, saline soaked gauze applied to the wound.
Dry to wet has long been the standard treatment for contaminated and necrotic wounds but the technique does have drawbacks: fibres from the dressing stick to the wound, slowing healing, and also this “stickiness” makes the dressing difficult to remove, with healthy and unhealthy issues lifted off with the dressing. The frequent dressing changes needed to prevent infection and the need to sedate or anaesthetise the patient each time can make this an expensive and time-consuming process.
Moist wound healing (or wet to wet dressing) has gained widespread support in recent years. Despite concerns that moist wound healing increases the chances of infection, studies have found that it is lower than with dry dressings and that the repair phase of healing is stimulated using wet to wet dressing.
As importantly, the lack of adhesion means that dressing changes are less painful and patients do not generally have to be sedated or anaesthetised for removal, which should be taken into account when looking at costs and benefits, as some of the materials available to use as moist dressings can be expensive.
Honey
With the arrival of medical grade manuka honey, honey dressings have become a serious option in wound healing. Manuka honey is from bees feeding on the pollen of the manuka (or tea tree) bush that has its own antibacterial properties.
The effects of honey are sometimes attributed to the osmotic effect of sugar in honey but dilution by wound exudate may reduce the osmolarity to a level that does not control infection, although the osmotic effect will still draw fluid from the wound bed.
The antibacterial effects are more likely to be due to an enzyme in honey that, on dilution, produces hydrogen peroxide and prevents growth of S. aureus, as well as activating phagocytosis.
Hydrofibres and alginates
Hydrofibres are similar in appearance to cotton and made of carboxymethylcellulose. Alginates are derived from seaweeds and share similar properties. Hydrofibre dressings are lightweight but strongly hydrophilic, capable of absorbing heavy exudates and will rapidly absorb fluid, holding it within the structure of the fibres.
Upon absorbing the fluid, the fibres transform into a clear, soft gel but maintain their structure. They also conform to the wound. This type of dressing is less suitable for use in wounds with reduced exudate, as the fibres can adhere to the wound surface.
Hydrocolloids
Similar to hydrofibres, hydrocolloids contain gel forming agents such as sodium carboxymethylcellulose and gelatin and react with wound exudate to form either a solid, or more viscous mobile gel which is retained within the dressing. They are useful in wounds with moderate to low exudates.
Hydrogels
Available as gels or sheets, hydrogels are used to rehydrate dry necrotic or granulating wounds and to promote wound debridement. They may also be applied topically to minor injuries.
DACC
Dialkylcarbomoyl chloride (DACC) is a fatty acid derivative with hydrophobic properties. Fabric dressings impregnated with DACC are used in infected, contaminated wounds.
In an aqueous environment, hydrophobic particles aggregate together and are held in place by the surrounding water molecules.
When bacteria and microorganisms come in contact with the wound dressing they bind to the surface and are removed with the dressing. The dressing needs to be placed in direct contact with wound and insufficient exudate can cause adhesion at the wound site.
Foam
Foam dressings are strongly hydrophilic polyurethane foams, both absorbing and retaining fluid. They can be used in cavitating wounds or as semi-adhesive foam pads for smaller wounds. As they are flexible and comfortable they make good primary and secondary dressings which are comfortable and provide protection of the wound.
Collagen matrix
These dressings are usually made of animal collagen in a matrix coated with a bio-absorbable adhesive. Collagen-based dressings can absorb wound exudates and help maintain a moist environment. They are thought to be especially suited for use in chronic wounds.
Elevated levels of matrix metalloproteinases (MMPs) found in chronic wounds degrade viable and non-viable collagen. It is thought that collagen dressings may act as a sacrificial substrate. The resulting collagen breakdown products attract a variety of cell types needed for the formation of granulation tissue.
There are a variety of refinements available on the straight-forward collagen dressing, such as the inclusion of EDTA to deactivate a portion of the MMPs and prevent them being re-released, silver or a mix of denatured and type 1 collagen which is said to attract a wider variety of types of MMPs.
Soft silicone
Dressings coated in soft silicone can be removed without causing trauma to the wound.
They are comfortable for the patient but not absorbent, although they can be used to provide a facing layer to dressings containing absorbent components.
Silver
Several studies show that silver kills antibiotic strains of bacteria and silver dressings have become popular as a means of treating infected wounds in hospitals. However, the presence of organic matter is said to reduce efficacy and a report in April this year claimed there was little scientific evidence to back up efficacy.
It is also suggested that silver dressings can be damaging when used for acute wounds where they may delay healing. In the NHS, silver dressings are said to account for one in every seven dressings.
Choosing the right dressing
Many of these products are available in combination – alginate and honey impregnated dressings, for instance – or are designed to be used with compatible secondary dressings
