Creative Closure of Tunneling and Undermining Wounds with Negative Pressure Wound Therapy Protection Status

by Beth Hawkins Bradley RN, MN, CWON

Wounds treated with negative pressure wound therapy (NPWT) are not often straightforward. They occur in interesting places, have anything from slough to hardware visible in the bases, and have nooks and crannies that are not visible to the clinicians peering into the wound. A gentle probe is necessary during wound assessment to identify tunnels and undermined areas. I prefer to gently probe first with my gloved finger (I have small hands) because I can identify hidden structures and other oddities. Then I will use a swab to measure how far the tunnel or undermining extends. Once hidden dead spaces have been identified, clinicians can select the best strategy to bring them to closure. Herein are several techniques employed by clinicians to close undermined and tunneled areas.

White foam is a favorite choice. Some foam-based NPWT manufacturers offer white foam, but not all. White foam is hydrophilic. It is intended to hold moisture next to structures like tendon, bone and hardware. The extent to which wound fluid is able to move through hydrophilic foams depends on the material that the foam consists of. Some foams are made of polyvinyl alcohol (PVA) material. This foam must remain moist or it will become quite hard, and has limited ability to move moisture through it. Check clinical guidelines, typically it is recommended that pressures be increased with PVA foam. Other manufacturers’ white foam is polyurethane (PUA). This is soft even when dry, and does not require pressures be increased to move fluid.

When using white foam to fill tunnels or undermined wound areas, make sure that you do not overfill the dead space. Although you want to fill to within 1 cm of the back of the tunnel or undermined area, it is preferable to allow the volume to collapse around the foam to speed granulation. Make sure that a sufficient amount of white foam protrudes from the opening so that it is easily identified at the dressing change.

While white foam is useful, it is not always available. Medicare and other third party payers do not cover it, so clinicians in the outpatient and home care settings have to find alternatives when there is hidden dead space to fill in a wound. Two materials that are readily available in most settings include gauze packing strips and wound non-contact layers. These materials have an advantage of allowing tunnels to collapse around it easily, but prevent seroma formation. It is difficult to use these materials for large undermined areas, however. While black foam might be preferable, the risk of breakage is real. A great way to use black foam safely in undermined areas or long wound tunnels is to roll it in a single layer of gauze or wound non-contact material. This technique gives insurance that all of the black foam will be removed while minimally impacting its ability to move moisture.

Some clinicians choose not to fill tunnels and undermined areas at all; rather they bolster the hidden dead space from above to promote wound closure. Below are the steps that are usually followed when bolstering undermined areas or tunnels.

  1. Carefully assess the area to be certain how far it extends.
  2. Drape the skin overlying the dead space.
  3. Apply a full thickness piece of foam on the draped skin overlying the entire dead space. Make sure the foam connects onto foam used to fill the wound. Drape the foam bolster with the rest of the wound, and complete the NPWT dressing application as usual.
  4. As the dressing pulls down and achieves target pressure, gently press over the bolstered area to ensure that the wound underlying the bolster has sealed.

The risk of this technique includes seroma or abscess formation, so the prescribing provider should always approve of this technique being employed.

In conclusion, hidden dead spaces must always be thoroughly cleansed at each dressing change to remove debris and reduce bioburden. Since irrigation of the areas may be challenging, a syringe can be a useful tool to irrigate. Closure of undermined and tunneled areas is essential in achieving wound healing success.

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.

Practical Guide to NPWT


I was wondering what you thought of the channel dressing NPWT for tunnels. I have used this silicone star shaped tubing inserting it into a deep tunneled area and filling in around it with the gauze or if the wound is only the size of the tubing, just inserting the tubing and adding some gauze around the exit site before applying the transparent film cover. In rectal area wounds I have had good results but in abdominal wounds it hasn't been that successful.

Great information. Just one thought: PVA (white foam) is readily available to home care patients on KCI VAC therapy. It's vital that this type of foam is used in tunnels to prevent breakage, and subsequent retention.

Thank you. I found this very helpful, especially because I have been very interested in managing undermining and tunneling wounds.

Iodoform is great after the wound vac is of no use anymore. Keeps small tunnels open and clean!

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