Dressings for chronic wounds

The principles outlined for acute wounds remain true for chronic wounds including leg ulcers or surgical wounds healing by secondary intention.

In a full-thickness wound, the dermis must be recreated before re-epithelialization can begin. These wounds heal from the base as well as from the edges so the development of some fibrinous exudate in the wound bed is a positive sign.

Occlusive options
Occlusion of chronic wounds:

    Allows macrophages and fibroblasts to enter the wound
    Promotes autolysis mediated by enzymes released from leukocytes.
    Favours cell proliferation because of low pH and hypoxia.
    Enhances growth factors and cytokines within wound fluid.

The occlusive dressings may be divided into five categories:

    Hydrogels
    Hydrocolloid
    Foams
    Films
    Alginates.

Hydrogels are composed primarily of water, fixed in a cross-linked polymer (sodium carboxymethylcellullose, or starch). They may be hydrated or in a dehydrated state requiring moistening with water or saline. They are used to rehydrate dried-out necrotic eschar. Hydrogels are also useful for exudative wounds because they have high absorptive capacity and are nonadherent. They cool the wound and can provide excellent pain relief. They are also useful for partial thickness wounds from resurfacing procedures and skin graft donor sites.

The hydrogel should be covered by an absorbent layer, made of gauze or cotton, and an outer layer of tape, netting or roll bandage.

Hydrocolloid dressings are a mixture of a hydrophilic base and adhesive, often with an outer covering of polyurethane. They adhere directly to the wound and do not usually require a secondary dressing to keep them in place. In addition, they absorb mild to moderate wound exudate so they can be worn for three to seven days without changing.

Hydrophilic foam dressings are permeable to oxygen and water vapour. They usually have a hydrophobic backing that provides occlusion and some have an adhesive surface, which makes application easier. They can absorb only limited amounts of wound exudate so may need to be changed every two to three days or even more frequently during early wound healing when exudation is greatest.

Foam dressings are ideally suited for superficial and dry wounds eg after ablative resurfacing procedures and chronic ulcers since they provide padding that can relieve pressure over bony prominences.

Thin transparent film dressings are not very absorptive, so they are not useful for wounds with significant exudate. They can be used to keep other dressings in place, including as top layer of an acute surgical wound dressing. They are often used to cover sites of IV insertion, superficial abrasions and as temporary dressings e.g. over local anaesthetic cream prior to venepuncture.

Alginates are highly absorbent and are indicated when a wound is very exudative. They release calcium ions, which help haemostasis so are useful applied to a surgical wound in a patient with excessive bleeding. In chronic wounds, the exudate combines with the alginate gel to form green or yellowish goo. The alginates are nonadherent unless the wound dries out. They can be soaked off to avoid unnecessarily debriding the wound.

Curasol™ hydrogel wound dressing    
Duoderm™ hydrocolloid dressing    
Allevyn™ foam dressing

Opsite™ film dressing    
Sorbsan™ alginate dressing    
Dressings for chronic wounds

Honey
Honey has been used as a traditional remedy for burns and wounds, and more recently several studies have demonstrated that it has antibacterial activity. Honey can clear infection from cutaneous wounds and improve healing. Honey from New Zealand manuka (Leptospermum spp) has enhanced antibacterial activity. It is available in a jar (also for oral consumption), a tube, or impregnated on a wound dressing. The antibacterial effect is labelled with its UMF (Unique Manuka Factor) according to Waikato University's honey research unit tests.

Proposed mechanisms include:

    Physicochemical properties (eg, osmotic effects and pH)
    Antiinflammatory activity stimulates immune responses
    Hydrogen peroxide concentration.


Active UMF10+ Manuka honey    
Medihoney™ wound dressing    
Activon™ tulle wound dressing
Honey for wounds
Choice of dressing

The most suitable dressing depends on the type of wound.

    Necrotic wounds have a dry black eschar composed of dead epidermis
    Sloughy wounds contain yellow viscous adherent slough
    Granulating wounds contain deep red vascularised granulation tissue
    Epithelialising wounds have a pink margin to the wound or isolated pink islands on the surface
    Infected wounds.

It also depends on the location and size of the wound. Some dressings are easier to use and remove than others. Modern dressings are relatively hypoallergenic and non-adherent but sensitisation may occur to iodine, antibiotics, rubber, adhesives and preservatives. Tape cannot be applied if the skin is treated with emollient or topical steroid creams. Cost and availability must also be considered.

Necrotic wounds
The aim is to rehydrate the dry scab so that it will separate off. Options are: Wet dressings using saline or hypochlorite (Eusol). Hydrogel covered by perforated plastic film absorbent dressing (Melolin or Telfa) or vapour permeable film. Hydrocolloid dressing.

Sloughy wounds
These need debriding to remove the abnormal matrix of fibrin, exudate, inflammatory cells and bacteria. This can be done by surgical debridement or by an agent that soaks up debris and forms a moist gel. Options are:

    Polysaccharide dressing as beads or paste.
    Hydrocolloid dressing if wound less exudative.
    Alginate dressing.
    Enzymes.

Granulating wounds
Granulation tissue is a highly vascular matrix collagen and proteoglycans.

    Cavity wounds are packed with alginate fibre ribbon, silicone foam dressing or foam chips
    Shallow but heavily exuding ulcers are dressed with alginate dressings or hydrophilic foam product
    Less exudative ulcers are dressed with hydrocolloid or thin foam dressing

Epithelialising wounds
Superficial wounds that exude fluid (burns and donor sites):

    Paraffin gauze covered with gauze and cotton tissue (Gamgee)
    Alginate
    Hydrocolloid.

Dry superficial wounds:

    Hydrocolloid
    Film dressing
    Perforated plastic film dressing
    Knitted viscose non-adherent dressings.

Infected wounds
Infected wounds need to be covered because they may have an unpleasant odour, and to prevent the spread of the organisms, particularly if they are resistant to standard antibiotics. Several dressings include antibacterial agents. Their use is controversial.

    Framycetin
    Fusidic acid
    Chlorhexidine
    Povidone iodine

Bioengineered skin substitutes

Skin autografts are commonly used to cover acute surgical wounds and chronic ulcers. However, harvesting skin grafts creates another wound that must heal, and suitable skin is unavailable in some cases such as extensive thermal burns. Sterilised cadaver allografts provide temporary wound dressings but eventually slough off. There has been intensive research and development in recent years to provide a satisfactory substitute for healthy skin. Replacement of dermal matrix and epidermis is required.

Cultured keratinocyte autografts can provide permanent coverage of large area from a skin biopsy. However, 3 weeks are needed for graft cultivation.

Keratinocyte allografts cultured from neonatal foreskins are available immediately. They can be cryopreserved and banked, but are not currently commercially available.

Applying a substitute dermal matrix has been shown to improve the likelihood that cultured epidermal cells (or an autologous split skin graft) will take. Several immunologically inert systems are now under investigation for management of refractory venous and diabetic ulcers.

Alloderm™ dermal matrix    
Apligraf™ artificial skin in culture