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Managing wound exudate: finding the right dressing

Nicky Whitfield
RGN NDNCert BSc(Hons)
Tissue Viability Nurse Specialist
Leeds North West PCT
E:nicola.whitfield@ nhs.net

Exudate is a combination of the fluid that bathes cells in the extracellular space and additional fluid, which leaves the blood supply.(1) It is widely accepted that a warm, moist wound environment encourages healing and prevents tissue dehydration and cell death.(2) This article explores the action of dressings designed to absorb wound exudate and aims to provide practitioners with some guidance on the appropriate selection of wound dressings to absorb and contain exudate.
The inflammatory response resulting from tissue damage directs exudate to the wound site.(3) Wounds that may have heavy levels of exudate as part of this process include venous leg ulcers, surgical wounds, sinuses, cavities and pressure ulcers.
Factors that can affect the level of wound exudate include:(4)

  • Hydrostatic pressure - chronic venous ­hypertension.
  • Wound infection/colonisation by bacteria.
  • Lymphatic drainage problems.
  • Heart failure/circulatory problems.

Excessive amounts of wound exudate can cause maceration and breakdown of the surrounding tissues and increase the size of the wound. Both acute and chronic wounds can produce large amounts of exudate as part of the inflammatory process. Wound fluid can be beneficial in acute wounds, as it contains nutrients and growth factors to bathe the wound, actively cleansing the wound surface and thereby facilitating wound healing.(5) Wound exudate in chronic wounds can be detrimental to the healing of the wound as it can delay or block the proliferation of cells, such as keratinocytes, fibroblasts and endothelial cells.(6) The aim of exudate management is to achieve a balance between retaining moisture at the wound bed and preventing maceration to the surrounding skin.(1)
Morris points out that the assessment of levels of exudate by healthcare professionals is subjective and tends to be described in terms of "light, moderate and heavy",(7) as opposed to objective measurement of quantity.(8) It is useful to define the viscosity of the wound fluid as well as the volume.
 
Foam dressings
Natural sponges were used in the past to absorb exudate, stop bleeding and as simple wound cleaners. Some of the disadvantages of these were that they adhered to the wound bed, could be a source of wound infection, and were difficult to clean and to sterilise. The potential of foams in wound care was not really recognised until the 1970s when Silastic Foam (Dow Corning) and Lyofoam (Seton Healthcare) were developed.
Foam dressings vary in their composition and the amount of exudate they are designed to absorb. Some just absorb exudate, whereas others are able to transmit moisture vapour away from the wound and out through the back of the dressing (see Table 1).(1,9)

[[NIP19_table1_78]]

Foam dressings are hydrophilic (readily absorb moisture) so are able to absorb large amounts, often several times their own weight, of exudate, even when pressure is applied in the form of compression bandages. The fluid-handling capacity is assisted by a vapour-permeable membrane, which allows a significant proportion of the absorbed fluid to be disposed of by evaporation through the back of the dressing. This layer also helps to prevent the penetration of bacteria. As the level of exudate decreases, the backing also helps to prevent excessive drying out of the surface of the wound. Fluid does not pass out of the outer layer but moisture vapour can.
Recent innovations in foam dressings include dressings designed specifically for the amount of exudate: for example, Allevyn lite and Tielle lite for wounds with minimal levels of exudate, Allevyn and Tielle for moderate to heavy levels of exudate, and Allevyn plus and Tielle plus for wounds with heavy levels of exudate.
There are also foam dressings available that have been designed to be worn under compression bandages, but it is debatable how effective these dressings are and how much the exudate level is reduced by the presence of compression therapy rather than the dressing.
 
Hydrocolloids
Hydrocolloids are manufactured from gel-forming agents combined with elastomers and adhesives. They are available as a flexible foam or film sheet coated with a layer of hydrocolloid. The hydrocolloid base is also available as granules of paste, which can be used along with the wafers to increase the rate of absorption.
Hydrocolloid dressings are listed in Table 2.

[[NIP19_table2_79]]

Alginates
Alginates are presented in the form of sheets, ribbon or ropes (see Table 3).

[[NIP19_table3_80]]

Calcium alginate dressings are derived from seaweed and form a moist gel in the presence of exudate. Alginates containing mannuronic acids, such as Sorbsan, form soft gels, whereas alginates containing glucuronic acids, such as Kaltostat, form firmer gels.(5) They act via an ion exchange mechanism, absorbing serous fluid or exudate to form a gel that conforms to the shape of the wound.(2) They are often used to dress cavity wounds and should only be lightly packed into the wound to allow the dressing to swell when it comes into contact with exudate. They should not be packed too tightly as this may prevent free drainage from the wound.
An alginate dressing should be changed as soon as it reaches full absorbency, to prevent the exudate bypassing the dressing and macerating the surrounding skin.
All alginate fibres should have formed a gel if they have been in contact with the wound bed. If the fibres are dry then the alginate is not an appropriate use of dressing. Alternatively, this could mean that the length of time between dressing changes should be extended.
 
Others
Another type of dressing for the management of wound exudate is Vacutex (Pro-Tex). This consists of three layers and is a rapid capillary action dressing. The layers are made up of: a reversible wound contact layer to lift and transport exudate and/or necrotic/sloughy tissue; a middle layer that exudate moves into and wicks laterally to prevent "strikethrough"; and a final layer that "pulls" exudate from the saturated middle layer. Vacutex should not be used on arterial bleeds or extremely vascular, bleeding fungating wounds.(10)
Another recent innovation is vacuum-assisted closure (VAC) therapy. This applies controlled levels of negative pressure to remove interstitial fluid, decrease localised oedema and increase blood flow. It has been used to treat soft tissue injuries, donor sites, infected sternotomy wounds and various soft tissue injuries before surgical closure, grafting or reconstructive surgery.(11) There are issues relating to the cost-effectiveness of VAC therapy in comparison with more conventional treatments.

Conclusion
Unfortunately, there is a lack of robust evidence to help clinicians in their choice of dressing, and more research is needed.(1) Studies that have been carried out often compare dressings of different generic groups, so it is difficult to apply the findings to clinical practice.
It would be useful to have studies conducted using patients as subjects rather than having studies carried out in the laboratory setting. This would provide more information for nurses on the ability of dressing products to absorb exudate while patients are going about their daily activities. It is more difficult for practitioners to translate the findings of laboratory studies in order to inform the appropriate choice of dressing for their patients, particularly when they are to be worn under clothing or shoes.
Critically colonised or clinically infected wounds often present with an increased bacterial load and an increased level of exudate. As the bacterial load is decreased by the use of oral or topical antimicrobials, the exudate level will also decrease. Dressings are now being manufactured that contain antimicrobials in the form of silver or povidone iodine, although it is important that these are used appropriately to prevent resistance developing in future.
The most important aspect of wound management is the assessment of the type and amount of wound exudate and its effects upon the surrounding skin. This highlights the importance of accurate wound assessment and documentation of the progress of the wound, to inform practice and facilitate the selection of a dressing that is appropriate for the wound and the level of exudate.

References

  1. Young T. Managing exudate. Essential wound healing. Community Nurse 2000;6 Suppl:2-5.
  2. National Prescribing Centre. Modern wound management dressings. Nurse Prescribing Bull 1999;1(2):5-8.
  3. Thomas S. Wound management and dressings. London: The Pharmaceutical Press; 1990.
  4. Miller M, Glover D. Wound ­management theory and practice. London: NT Books; 1999.
  5. Flanagan M. Access to clinical ­education. Wound management. London: Churchill Livingstone; 1997.
  6. Chen WY, Rogers AA, Lydon MJ. Characterisation of biologic properties of wound fluid collected during early stages of wound healing. J Investig Dermatol 1999;99:559-64.
  7. Morris L. Descriptive evaluation of Alione hydro capillary dressing.Br J Nurs 2003;12:630-5.
  8. Thomas S. Assessment and ­management of wound exudate.J Wound Care 1997;6:327-33.
  9. BMA, RPSGB in association with CPHVA and RCN. Nurse Prescribers' Formulary for district nurses and health visitors. Incorporating BNF 46. (2003-2005).
  10. Deeth M. Review of an ­independent audit into the clinical ­efficacy of Vacutex(TM). Br J Nurs 2002;11 Suppl.
  11. Thomas S. An introduction to the use of vacuum assisted closure. 2001 Available from URL: http://www.worldwidewounds.com

Resources
World Wide Wounds
W:www.worldwidewounds.com
An online resource for dressing materials and practical wound ­management information
National Electronic Library For Health
W:www.nelh.nhs.uk

Practice ­pointers
Exudate ­management is concerned with maintaining a moist wound environment
Effective exudate management prevents ­maceration to surrounding tissues
Effective exudate management allows the ­dressing to attain its full absorptive potential to promote cost-effectiveness
Effective exudate management allows free drainage of ­cavities to promote healing