Wound exudate is produced as a normal part of the healing process. During the inflammatory response blood vessel walls dilate and become more porous allowing leakage of protein-rich fluid into the wounded area (White, 2000). Managing exudate and maintaining a wound environment that is moist but not wet is a constant challenge.
VOL: 99, ISSUE: 05, PAGE NO: 51
Jacqui Fletcher, RGN, BSc, PGCert, ILT, is senior lecturer tissue viability, University of Hertfordshire, Hatfield
Exudate has several roles including:
- Maintaining the optimum moist environment necessary for cellular activity and movement (Winter, 1962);
- Carrying white blood cells;
- Forming part of the primary defence against invading micro-organisms;
- Facilitating the movement of other key cells such as macrophages (which have a major role in clearing debris from the wounded area) to where they are most needed.
In the normal process of repair, the volume of exudate gradually diminishes as a wound heals and fluid conservation may become important (Thomas, 1997). However, in chronic wounds or where the process of healing is disrupted, such as when a wound becomes infected, the exudate level is maintained or may increase.
Although it is generally believed that exudate plays an essential role in the healing process it is less clear when its detrimental effects begin to outweigh the benefits. Several studies have investigated the content of exudate and it is apparent that the constituents and quantities of individual components vary among individuals and at different times during the healing process (Baker and Leaper, 2000).
Acute wound fluid appears to play an important part in attracting the essential cells to the wounded area. It is rich in both leucocytes and proteases to clear debris, and growth factors to promote tissue regeneration and facilitate the migration of cells. It is also believed to have antibacterial properties (Kreig and Eming, 1997). However, the make up of the exudate is not consistent and differing constituents are found even between similar acute wounds (Baker and Leaper, 2000).
A different balance of cell types is found in chronic wound fluid, where there appears to be an imbalance between the amount of degradative substances such as the matrix metalloproteinases (MMPs) and their inhibitors, tissue inhibitors of matrix metalloproteinases (TIMPs). The resulting high levels of MMPs not only actively break down protein but also have an inhibitory affect on growth factor activity (Trengrove et al, 1999; Yager and Nwomeh, 1999).
In addition to the uncertainty about the constituents of exudate there is also a lack of consensus as to what is the normal amount, with considerable differences occurring between wound types. This problem is compounded by a lack of standardised terminology with regard to exudate and the fact that many practitioners use subjective descriptions of the amount.
Falanga (2000) proposed the terms; none/mimimal, moderate amounts and very exudative, while Sibbald et al (2000) used scant, moderate and copious as descriptors. While practitioners may believe they understand these terms, Thomas et al (1996) showed that even highly experienced practitioners were unable to objectively estimate the amount of exudate or agree on whether the amount was low, moderate or high.
A more objective measure was proposed by Mulder (1994) who suggested that the amount can be estimated based on the frequency of dressing change using a 10cm x 10cm gauze as the measure. Although similar terminology is used (absent, minimal, moderate and high), each of these descriptors is quantified (see Box). These definitions are limited in that the amounts described in the paper are based on the absorptive capacity of a simple gauze dressing. However, the principle could be adapted to a broader range of dressing types allowing for objective comparison of exudate levels within the same wound.
Care should be taken when reviewing the quantity of exudate to allow for increases in fluid levels due to other causes such as the debridement of necrotic tissue by autolysis/rehydration - or reduction in fluid levels where lower limb oedema is reduced by the use of compression bandaging. These two simple but common examples demonstrate how fluid levels in and around the wound may change without affecting the true exudate levels. They also demonstrate why it may be difficult to use levels of exudate to predict changes in healing status, as it is not clinically possible to differentiate between exudate and fluid seepage from severe oedematous legs.
Colour and consistency of exudate
The colour and consistency of exudate is also perceived to be important and, when coupled with quantity, may be used as an indicator of progress or deterioration in the wound. Again several authors have proposed descriptors. For example, Mulder (1994) used the terms serous, sanguineous, serosanguineous and purulent. Sibbald et al (2000) proposed serous-serum, sanguineous-blood, purulent-infection and a combination.
It is interesting to note that these authors all see consistency as a good indicator of the presence of infection. However, a large study reviewing the validity of the clinical signs and symptoms of infection in chronic wounds (Gardner et al, 2001) found that purulent exudate alone was less predictive of infection than other indicators such as increased pain, friable granulation tissue, wound breakdown and foul odour.
While moisture is necessary for healing, an overly wet environment may damage the wound bed as well as the surrounding skin (Cutting and White, 2002). This damage may be maceration (caused by the trapping of fluid on the skin), or excoriation related to the proteolytic enzymes contained within the exudate, however, in practice these frequently occur together. Damage may also occur due to increased frequency of dressing change, when adhesive products are being removed too often causing epidermal stripping. Patients frequently identify feelings of anxiety over possible leakage, and feel stigmatised at the smell of the wound. In many instances these factors cause patients to become withdrawn or isolated.
The first factor to consider is the reduction of anything that may be contributing to increased fluid levels. For example, the use of diuretics to treat heart failure or elevation of limbs to reduce dependant oedema may help to reduce exudate. Once these factors have been addressed local management of the exudate with dressing products or therapies may be considered.
A range of dressing products can be used to manage exudate, including absorbent products, those which allow transmission of exudate, those which interact with exudate, or a combination.
The majority of dressings used to manage exudate will be absorbers of some kind. They may also have the capacity to evaporate some fluid through the back of the dressing, although this is usually a very small amount of fluid. Where both these methods of fluid handling are present, the manufacturers may refer to the total fluid handling capacity of their product.
Absorbent products vary in their design and fluid-handling capacity. Simple absorbers such as gauze-based products will soak up the fluid and allow it to pass onto the back of the dressing. Other products such as alginates absorb the fluid and change in structure from a dry product to a gel. Some products claim to selectively absorb the liquid component of the exudate, concentrating the beneficial wound proteins on the wound surface (Achterberg and Meyer-Ingold, 1996). However, in light of the high levels of potentially detrimental MMPs in chronic wound fluid, this option needs to be considered carefully.
More sophisticated products not only take the fluid into the dressing but also hold on to it even when subjected to pressure, and so may be more suitable when applying dressings to heels and buttocks or for use under compression bandaging.
The amount of exudate a dressing can hold is also influenced by the way the material handles the fluid. Simple products such as gauze absorb exudate at the point of contact with the fluid. Other dressings spread the fluid across the whole of the dressing, giving a greater fluid-handling capacity.
Products that allow transmission of exudate provide a protective wound contact layer and then allow for free drainage of exudate into a collection system. This may be a simple and inexpensive absorber, a drainage bag or the more sophisticated negative pressure systems (Thomas, 1997). The latter two enable a more accurate measurement of fluid loss to be maintained. When the volume of fluid lost is high it is important to measure the loss as it will usually warrant fluid replacement therapy.
It is important to consider patient comfort. Very absorbent dressings and drainage bags can become heavy when filled with fluid and may pull on the surrounding skin and it may be necessary to change the dressing or empty the bag before it is completely full to maintain the patient’s comfort. However frequent the dressing change, the potential for damage to the surrounding skin should always be considered and keyhole dressings, skin protectants or barrier creams should be used to prevent the wound area from extending.
Managing patients with exuding wounds is complex and requires good assessment and critical thinking skills. The cause of the exudate and any potential complications should also be addressed. With careful planning most wounds can be successfully managed with dressing products that are widely available and the patient’s comfort and dignity need to remain paramount in the planning of care.