Wound Bed Preparation and Negative Pressure Wound Therapy

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By Beth Hawkins Bradley RN, MN, CWOCN

Negative pressure wound therapy (NPWT) has become a mainstay in wound management. During the advent years of its use, NPWT was only used to treat large, difficult wounds. Now it is a standard treatment for a wide range of wounds. As a clinician interested in wound management, you are likely using this therapy frequently. But how knowledgeable are you about important aspects of NPWT? The author’s hope is that, as you read these NPWT-focused articles, you will become interested in filling in any “knowledge gaps” that you identify.

When is the best time to begin NPWT for a given wound? There is no protocol for answering this question. The answer must be derived from an understanding of the indications, contraindications, and precautions for NPWT. If a wound is indicated for NPWT, then the best time seems to be “anytime.”

Let’s review : Below are the generally accepted indications, contraindications and precautions for NPWT as outlined by Debra Nestch in Ruth Bryant’s text, Acute and Chronic Wounds, 4th edition. Some of these vary by manufacturer:

Indications: Acute, chronic, sub-acute, traumatic, and dehisced wounds, ulcers, partial-thickness burns, flaps and grafts.

Contraindications: Untreated osteomyelitis, malignancy in the wound, exposed organs, exposed blood vessels, non-enteric or unexplored fistulas, necrotic tissue.

Precautions: Active wound infections, potential for bleeding, treated osteomyelitis, surgical excision of malignancy, anticoagulant therapy, and poor patient compliance.

Do any of these surprise you? Many clinicians question waiting to use NPWT until all necrotic tissue is removed from the wound. It seems that the black open-cell reticulated foam (OCR) foam would help to debride necrotic tissue. Or adding an enzymatic debridement ointment into the wound base prior to applying the NPWT dressing will help. However, understanding a few characteristics of black foam may change your mind about using negative pressure before the wound bed is free of necrotic tissue.

Black foam consists of open-cell, reticulated polyurethane. The pores that are visible in the foam help to not only move fluid away from the wound base (thus the foam is hydrophobic), but also distributes negative pressure across the wound base and any existing dead space. These two functions are key properties of effective NPWT. Therefore, it is important to keep the foam pores open.

Applying black foam over slough or other non-viable tissue can be counter-productive. The tissue, even as it breaks down, has the potential to clog the foam pores. This prevents the movement of fluid and the distribution of negative pressure. Since bacterial load is higher in the presence of non-viable tissue, the wound fluid becomes a bacteria laden “soup” with the potential for causing infection. Matrix metalloproteinases (MMP) levels will likely be increased, slowing wound granulation.

Enzymatic ointments can lead to the same result: clogged pores. Additionally, most manufacturers recommend that the ointment remain in contact with the wound base for prolonged periods of time so that the cuff at the base of the slough can be broken. When the ointment is used with NPWT, it is likely moved away from the base very quickly, clogging foam pores to boot.

The likely conclusion, then, is to delay negative pressure until the wound base is clean. One feature of some NPWT devices may make the therapy acceptable if scattered slough is present, the irrigation feature. Adding irrigation simultaneously with negative pressure will move a stream of fluid across the wound base, then moves it through the foam for a cleansing effect that keeps pores open. Bacterial load is likely decreased. The additional moisture may help with slough removal. In the absence of the ability to use irrigation, however, you may rethink starting this therapy until non-viable tissue is removed.

Netsch D. Negative Pressure Wound Therapy. In: Bryant R. Acute and Chronic Wounds: Current Management Concepts. 4th ed., St. Louis, Mo:Mosby Elsevier; 2012:337-344.

About the Author
Beth Hawkins Bradley, RN, MN, CWON is the director of Clinical Operations at Cardinal Health. She has been certified in the specialty of Wound, Ostomy, Continence nursing since 1990.

The views and opinions expressed in this blog are solely those of the author, and do not represent the views of WoundSource, Kestrel Health Information, Inc., its affiliates, or subsidiary companies.

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