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The colour of wounds and its implication for healing

The colour of wounds
Photo: The colour of wounds
Wounds are very common across the spectrum of health care settings, with a range of presentations including traumatic or surgical wounds and chronic wounds such as diabetic foot ulcers and leg wounds (in particular venous stasis ulcers and arterial ulcers), ischemic wounds (gangrene) and pressure injuries. Less common wounds may include vasculitic ulcers, necrotising fasciitis, pyoderma gangrenosum and calciphylaxis.

With any wound it is important to understand the aetiology in order to develop an appropriate management plan, but also to properly manage any comorbidities that may be associated with the development of the wound or limit the healing potential. Locally, the type of tissue in the wound bed may give important clues about the stage of healing or whether the wound will heal. Wound assessment must therefore be holistic and incorporate key aspects of both the patient and the wound to ensure the best possible outcome for the individual. While holistic assessment is the foundation for thorough wound assessment, this article will focus on wound characteristics, in particular tissue types and the condition of the surrounding skin.

More reading - Aging skin and the importance of skin integrity assessment 

Related CPD Training: Pressure Injury Module - endorsed by ACN, RACGP and Australian College of Rural & Remote Medicine

Healthy Skin
As the outer layer of the body, skin provides a protective barrier to environmental influences allowing us to respond to a myriad of environmental stimuli. Skin forms an impervious barrier to changing weather conditions as well as chemical and bacterial assault. Skin contains thousands of sensory nerve endings that detect changes in temperature, pain and pressure, and facilitate thermoregulation. Skin has metabolic functions producing vitamin D in response to sunlight and secreting salts through sweating.  Skin plays an important cosmetic role,influencing how we view ourselves and communicate with others. Any failure in skin integrity results in a wound. All wounds, regardless of their cause and healing intention (discussed in a future article), must progress through the stages of healing in order to close and restore skin integrity. The following provides a guide to understanding various tissue types associated with wounds.

Tissue types and wound healing
Management of a patient’s wound will be determined by the wound tissue present and exudates. The different types of tissue can easily be remembered by colour.Necrotic tissue, termed eschar, is easily identified as black or dark brown in colour. Eschar may be dry or moist and presents as thick and sometimes leathery necrotic tissue cast off from the surface of the wound. Eschar inhibits the proliferative and maturation phases of wound healing by preventing the formation of healthy granulation tissue and inhibiting wound contraction and epithelialisation (new skin growth).

Moist eschar supports bacterial growth increasing the risk of infection and ideally should be debrided. Dry eschar, on the other hand, forms an impervious barrier to external microbial contamination. In patients with compromised circulation, for example patients with peripheral arterial disease or diabetes, it is best to leave the eschar in place until investigations can determine the degree of arterial disease. Wounds with a poor blood supply have minimal oxygen and nutrients being delivered to the wound bed and surrounding tissues, limiting wound healing potential and removal of a dry eschar may cause further deterioration of the wound and increase the risk of infection. 

Slough (also necrotic tissue) is a non-viable fibrous yellow tissue(which may be pale,greenish in colouror have a washed out appearance)formed as a result of infection or damaged tissue in the wound. The presence of slough may indicate the wound is stuck in the inflammatory phase (chronic wounds) or the body is attempting to cleanthe wound bed in preparation for healing. Slough is usually a combination of leucocytes, bacteria, devitalised tissue or debris and usually has a moist, shiny stringy appearance or may be firmly attached to the wound bed.

Granulation tissue is a collagen rich tissue forming at the site of an injury during the proliferative phase. As the wound heals this tissue fills in the wound deficit replacing the blood clot formed during haemostasis and eventually forming scar tissue. Healthy granulation tissue is bright red with a grainy appearance, due to the budding or growth of new blood vessels into the tissue. This tissue is firm to touch and has a shiny appearance. It is essential to protect the granulation tissue to allow the epithelialisation process to proceed in order to close the wound. Granulating wounds require adequate tissue perfusion; a slightly acidic environment; a stable wound temperature; good bioburden control; moisture balance; a reduction of factors which may prevent healing (e.g. the underlying cause of the wound);and protection from physical trauma.

Hyper-granulation tissue (often called over-granulation) is an excess of granulation tissue over and above that required to fill the wound cavity. Hyper-granulation tissue may appear dark red and devitalised (due to poor oxygenation) or pale due to lack of oxygen. Hyper-granulation tissue inhibits the migration of epithelial cells across the wound surface and increases the risk of scar tissue formation by preventing the wound edges from closing. Hyper-granulation tissue may be the result of prolonged inflammation due to infection or the presence of an irritant or foreign body; overuse of occlusive dressings; constant rubbing of dressings or tubes against the skin causing an inflammatory response (e.g. a peg tube or supra pubic catheter); allergy to dressings; or imbalance of cellular activities that regulate the production of healthy tissue.

With any hyper-granulation tissue it is important to identify and treat the cause and to eliminate malignancy. If occlusive dressings have been used change to a vapour permeable dressing. The application of light pressure to the wound bed using a foam dressing with tubigrip compression may reduce the overgrowth of tissue. Additionally, hypertonic dressing (e.g. Mesalt) may dehydrate the overgranulation. In case of infection, antimicrobial dressings such as silver, iodosorb or medical honey may also help to dehydrate the wound. Apply light pressure to the wound bed.  It is important to swab the wound to determine bacterial burden and to eliminate infection as a causative agent.

Epithelialisation is the regeneration of new skin (epithelium) over a wound and signifies the final stage of healing. Epithelial tissue, light pink in colour, usually migrates inwards from the wound margins or may appear as small islands of tissue over the surface of the wound. Requisites include maintenance of a warm, moist healing environment and protection from irritants and physical damage.

Exudate
While not the focus of this topic, exudate plays a critical role in wound healing providing a moist healing environment, nutrients and oxygen to newly developing tissues while facilitating the removal of waste products and toxins. However in highly exudating, non-healing wounds exudate can become problematic as the build-up of degrading proteins and other toxic substances delays healing by prolonging inflammation.At the other end of the scale a wound that is too dry will fail to epithelialise. The colour of the exudates may also provide clues as to the healing potential of the wound. Serous (a clear yellow or straw colour) and haemoserous (light pink or red and watery) exudates are normally present in a wound. A purulent discharge (characterised by a viscous dull red, gray or greenish fluid) may signify infection especially if malodour is present. Frank blood, also called sanguineous exudate,indicates bleeding and along with a purulent discharge must be investigated.

Surrounding skin
The condition of the periwound tells a great deal about the state of a wound and its potential for healing. Maceration, inflammation, undermining and tunnelling, oedema, induration and pain are all signs and symptoms of a potentially non-healing wound. Further afield the surrounding skin may provide clues as to the aetiology of a wound. Trophic changes such as abnormal pigmentation; atrophie blanche; lipodermatosclerosis; neuropathy; calluses; shiny hairless appearance; thickened discoloured nails; along with skin temperature and adequacy of peripheral perfusion may point to the underlying disease processes involved in wound pathology and guide management. For example, trophic skin changes in chronic ischemia secondary to peripheral arterial disease (PAD) may include a dusky appearance, cool peripheries and shiny, pale and often hairless skin. Tissue loss with gangrenous changes may also be present.Thickened and discoloured toenails may also signify PAD or a fungal infection often associated with diabetes. Similarly, haemosiderin stain (brown in colour) to the lower limbs, dry scaly skin, champagne legs, atrophe blanche (white star shaped scar tissue) and dependent oedema are indicative of peripheral venous disease (PVD).

Conclusion
Accurate wound and patient assessment provides useful clinical information that not only guides management but also provides baseline data for subsequent assessments. Wound characteristics such as tissue types present in the wound bed and the nature and volume of exudate are key aspects that assist the clinician to implement appropriate treatment to facilitate healing. Equally, documentation that clearly describes the wound features; the condition of the peri-wound and surrounding skin; and the effectiveness of any treatment helps to ensure good continuity of care through interdisciplinary management with better patient outcomes.

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Bonnie Fraser

A mother to three girls, previously Bonnie was an educator in the NSW secondary school system for 20 years before retraining to become a registered nurse. Bonnie has a Bachelor of Science with a Graduate Diploma in Education from the University of New England; and several certificates from TAFE NSW including Certificate IV in Workplace Training and Assessment and a Graduate Diploma in Management Communication. In 2009 Bonnie  attained a Bachelor of Nursing from Newcastle University, and is currently undertaking a Masters Degree in Wound Care though Monash University, this being her final year.  Currently Bonnie is employed as a registered nurse at the Port Macquarie Base Hospital located on the mid north coast of NSW. During her time as an RN she has worked in the areas of orthopaedic and general surgical nursing and fulfilled the roles of both clinical nurse educator for new and transitioning nurses and clinical nurse specialist wound management.