Clinical Care Wound Bed Preparation

Is wound bed preparation a critical part in advanced therapeutic products?

This area of wound care, i.e. preparation of the wound bed, is emerging as critical to our assessment and evaluation of new advanced technologies.

Does necrotic tissue have to be removed from the wound?

Certainly, it is highly unlikely that a wound will heal when covered by necrotic tissue. Indeed, there is evidence that more aggressive surgical debridement of diabetic ulcers leads to improved results with the use of a topically applied growth factor (PDGF).⁷¹ It is generally accepted that pressure ulcers need to be extensively debrided and their undermined tissue removed. The removal of the lipodermatosclerotic tissue in venous ulcers is beneficial.

What other techniques can be used to debride a wound?

Besides surgical debridement, there are enzymatic ways to debride wounds. Collagenase and similar preparations are commonly used, particularly after the surgical removal of extensively necrotic tissue and eschars, which may prove difficult to eliminate by enzymatic means alone.

Autolytic debridement can often be effective, particularly with the use of hydrocolloids. However, formal studies using debridement as an endpoint have not been done with these occlusive dressings.

Does edema affect wound healing?

There is little question that edema interferes with the healing process. The reasons remain unclear, but may represent a combination of impaired blood flow, increased bacterial colonization due to the accumulation of interstitial fluid, and perhaps trapping of growth factors and other key peptides and matrix proteins by the macromolecules (which leak from the extravascular space).

How can a well-vascularized wound bed be achieved?

In aiming to prepare a well-vascularized wound bed, much can be achieved by:

• Removing necrotic or fibrinous tissue
• Controlling edema
• Decreasing colonization of bacteria
• Compression therapy (especially for venous ulcers)
• Offloading

Further improvements in the vascularization of the wound bed can also be achieved by the application of growth factors, such as PDGF⁷¹, cellular therapies,^72,73 or even the use of occlusive dressings.⁷⁴

What is the purpose of an occlusive dressing for a chronic wound?

Stimulation of granulation tissue may be one of the most important effects of occlusive dressings in a chronic wound, in addition to pain relief and absorption of exudates.

How should bacterial burden be removed from a chronic wound?

Bacterial colonization can often be dealt with by the fundamental procedure of surgical debridement. Some topical therapies are useful in decreasing the bacterial load, containing wound exudates, and improving the appearance of granulation tissue. One of the ways we have achieved these goals is by applying cadexomer iodine, a slow-release iodine-releasing agent.

How does debridement further induce epithelialization?

Surgical debridement may have advantages in addition to its beneficial effects on bacterial burden through the removal of necrotic and infected tissue. Clinicians have often commented that extensive debridement turns a chronic wound into an acute wound. While this notion is probably an over-simplification, extensive debridement of ulcers may remove some of the cells that no longer respond to growth factors and cannot synthesize the right mix of extracellular matrix materials.⁷⁵

How do wound exudates halt wound healing?

Over the last several years, evidence has accumulated that wound exudates, particularly produced by chronic wounds, have a number of deleterious effects. Chronic wound fluid (in contrast with acute wound fluid⁷⁶) blocks the proliferation and activity of certain cell types, including fibroblasts and keratinocytes.⁷⁷ Metalloproteinases and other proteases are abundant in chronic wound fluid; there is evidence that these enzymes can break down extracellular matrix materials as well as growth factors.

What are the best ways to treat exudate?

There are direct and indirect approaches to treating exudate. Direct approaches include the use of compression bandages, highly-absorbent dressings, or mechanical (vacuum-based) systems. Indirect approaches require recognition of what is causing the exudate in the first place. For example, the wound may be heavily colonized with bacteria, which would need to be addressed for the exudate to diminish or be eliminated. Direct approaches alone are unlikely to control exudate effectively, if the underlying cause of that exudate has not been addressed.

Can the usage of cellular therapies achieve complete wound closure in venous ulcers?

When combined with standard therapy and near elimination of wound exudate, cellular therapies, consisting of cultured human keratinocytes and fibroblasts can achieve complete wound closure in the majority of difficult-to-heal venous ulcers. In a study conducted in two medical centers, 37 out of 54 venous ulcers (on 33 patients) treated with Apligraf® had complete wound closure. They were previously unresponsive to conventional therapy. Interestingly, the rates of closure were similar at the two centers, where different methods of wound debridement and exudate control were used. Thus, given a therapeutic goal of optimal wound bed preparation and elimination of wound exudate, conditions that are ideal for the successful use of advanced therapeutic modalities can be created.

How will these advanced therapeutic products affect our patients?

Technological and laboratory advances in the last two decades allow us to offer our patients better and more effective therapeutic approaches. As we use these new approaches for treating difficult-to-heal wounds, we must not forget the lessons from the past. Optimization of the wound bed and removal of exudate can be used to improve the efficacy of new therapeutic agents.