Wound Dressings

The aim of wound management is to restore the integrity of the skin as rapidly as possible, with the best physiological result, and at a reasonable cost in terms of time and finances. This lecture is designed to help you overcome confusion with dressing selection while introducing you to the principles of 'advanced' wound care.

Advanced wound care became established after George Winter's research in 1962 began to highlight that a moist wound environment both supports cellular activity, assists natural debridement and ensures rapid proliferation of healthy granulation tissue and subsequent epithelial migration. His experimental wounds healed around 30% faster than those left open to the air.

More recent challenges with resistant species of bacteria in human healthcare have seen a call for topical dressings that are able to combat local infection, contamination and bio-burden within the wound. Historical treatments for wound infection have since been rediscovered. Silver and honey are now frequently used and a vast array of presentations means that, in those wounds that need their benefits, choice should combine antimicrobial effects within the provision of an ideal moist wound environment.

Despite over 2000 products and medical devices being available, it must be remembered that as advanced as some dressings may appear in the literature, none of them provide a miracle solution for healing.

Wounds that are considered challenging, unresponsive, chronic or 'non-healing' must be addressed by using the 12 factors of healing delay (Figure 1). Only some of these factors, such as moisture balance, management of local infection and removal of necrotic material are assisted using modern dressings; further investigation may need to be done, therefore, to identify other reasons for failure and to find an effective route to wound closure.

Figure 1. 12 factors of healing delay.

 Necrotic tissue

 Foreign body

 Infection/infestation

 Movement

 Altered local pH

 Paucity of blood supply

 Paucity of oxygen supply

 Poor nutritional and health status

 Local factors

 Iatrogenic factors

 Genetic factors

 Cell transformation

Conclusion

Not all wounds present with simple closure options and may require a period of open wound management to encourage healthy granulation for reconstruction, grafting or second intention healing, and the nurse's role and potential to enhance wound management in these instances cannot be underestimated. Careful dressing selection, correct application with an optimum wear time for the stage of healing, as well as identification and management of the factors that may delay healing will ensure the wound is given every chance of rapid closure.

The Purpose of Modern Dressings

Haemostatic Dressings

Several recent advances have brought improvements in this area. Traditionally Kaltostat® (Convatec), an alginate dressing with a haemostatic quality is useful for minor bleeds. A more impressive haemostatic quality has been achieved using chitin derived from shrimp shells. Celox® is an example that was developed for army use and rapidly stems bleeding, even from major arterial bleeds.

Physical Debridement

Historically, wet-to-dry dressings have been used to achieve debridement in wounds presenting with heavy contamination. Thought to be an outdated method in equine practice, this method is considerably destructive to healthy tissue. On the other hand, it does need to be included in a list of dressing types, as it may be commonly used in small animal wounds in mixed practice.

Hydrosurgical debridement via the Versajet® (Smith + Nephew) is a more recent advance that aims to give the clinician a precision approach to removal of dead and contaminated tissue in the wound. A pump (power console) and hand-piece provides the user with a small water jet that when passed across the surface of the wound creates a Venturi effect. This effectively sucks up debris and surface contamination into a reservoir leaving the wound surface debrided. A range of settings allows the user to be more or less aggressive in their debridement. This is an expensive alternative to traditional methods, but it is a capital investment that may be justified in busier or referral practices. It is thought to enable a significantly faster route to a clean wound for surgical wound closure which may be considered cost effective in the longer term.

Enzymatic agents have historically been used to assist in the breakdown of necrotic and sloughy tissue. Their action is to dissolve proteinaceous material in the wound, much in the same way as maggots do! This method of debridement is expensive in comparison to surgical debridement, takes longer and is considered damaging to healthy tissue.

Dry Dressings

Typical dry dressings include Melolin®, Rondopad® (Millpledge) and Release® (Systagenix), and are designed purely to protect the wound while being lightly absorbent. Most commonly used postoperatively for 24–48 hours, they wick fluid from the wound in order to keep the wound dry. They may stick to the wound bed in which case they effectively act as a wet-to-dry dressing on removal.

Non-Adherent Dressings

Non-adherent dressings (NA dressings) are used as a primary contact layer to protect fragile wound tissue. They are usually in a mesh format and allow the passage of exudate to an absorbent secondary dressing. NA dressings were originally made of knitted viscose and may also include a layer of paraffin (Jelonet® Smith + Nephew). More recent advancements in the form of silicone mesh have given a contact layer that is superior and is gentle on removal as well as being inert.

Moisture Control or 'Advanced' Dressings

The majority of products regularly available in practice, such as foam and gel dressings, are designed to create the optimal environment for healing and maintenance of a healthy environment. They do this by absorbing exudate (e.g., foams) or hydrating the environment to which they are applied (e.g., hydrogels). Any type of product used to maintain moisture balance is considered an 'advanced' approach.

'Infection Control' Dressings

Dressings may either be antimicrobial in action or protect the wound from cross-contamination through barrier / vapour-permeable film coverings. Some dressings do both. Dressings that reduce the topical risk of infection and help to manage contamination have grown in number. Silver and honey dressings are typical of those that have gained credibility in recent times, and are effective against a range of common wound pathogens including resistant strains. Ideally, dressings that provide antimicrobial properties should also be available in formats that support the moist wound-healing environment, such as those that combine an antimicrobial action with absorbency or hydration.

'Scaffold' Dressings

These products require a greater knowledge of wound physiology and timing for best results. They work by offering a scaffold or 'matrix' for cell growth, encouraging migration across the wound bed. These types of dressing may be used successfully providing the wound bed is at the granulating stage and failing to contract and epithelialise. Examples include collagen dressings and physiological membranes such as Veterinary Biosist®.

Protective Dressings

Surrounding tissue can often become damaged due to high levels of wound exudate, adhesives or environmental factors such as urine, pressure or friction. Protecting tissue will prevent unwanted deterioration and promote elasticity. Protective dressings include barrier sprays and creams, such as Cavilon® (3M).

Acknowledgements

I would like to thank Professor Dick White and particularly Professor Derek Knottenbelt for his continued support and kind words. I am not alone in being indebted to him and his specialism in this area.

References

1.  For further information and support on the use of dressings in practice contact Georgie Hollis through The Veterinary Wound Library, www.vetwoundlibrary.co.uk

2.  Knottenbelt DC. Handbook of Equine Wound Management. 2nd ed. Edinburgh: Saunders Elsevier Ltd, 2007.

3.  Molan PC. Honey as a topical antibacterial agent for treatment of infected wounds. World Wide Wounds, 2001. www.worldwidewounds.com

4.  Winter GD. Formation of the scab and the rate of epithelisation of superficial wounds in the skin of the young domestic pig. Nature 1962;193:293.