While negative pressure wound therapy (NPWT) has been acknowledged as a significant advance in helping to heal chronic wounds in the lower extremity, there are potential complications that clinicians may need to address. With this in mind, this author surveys the literature to discuss complications ranging from bleeding and periwound issues to excessive exudate removal and pain.
Complications of diabetes involving the lower extremity represent a significant and increasing burden on both the global and United States health care systems. These events have a devastating impact on the individuals affected as well as their closest friends and relatives. It is estimated that up to 25 percent of patients with diabetes will develop a foot ulcer at some point during their lifetime, and nearly one in five requires an amputation.1,2 In fact, every seven seconds around the world, someone dies from diabetes-related complications and every 20 seconds, someone undergoes an amputation.3
When examining the overall economic impact of diabetic foot complications as well as the relative five-year mortality rates associated with diabetes, lower extremity amputations, and peripheral arterial disease (PAD), diabetes rivals many forms of cancer.4 Furthermore, wound healing is not truly an “end goal.” In fact, it is in many ways the beginning of a long, difficult journey toward continued remission. Health care providers and patients must both adopt strategies for prevention of recurrence and further complications.5
Negative pressure wound therapy (NPWT) has emerged as a valuable and dynamic tool in the treatment of many types of wounds, including diabetic foot ulcers (DFUs). The indications and applications of NPWT continue to evolve. This occurs as the need for reliable, reproducible and validated forms of advanced wound care modalities becomes paramount to decreasing the number of wound complications and reducing lower extremity amputations in the U.S. and abroad.
A Quick Primer On Uses For And Applications Of NPWT
The mechanism of action for NPWT is multifactorial. Researchers have shown that NPWT decreases wound margins and promotes granulation tissue formation and perfusion.6 NPWT also maintains a moist wound healing environment and stimulates wound healing through microstrain and macrostrain properties via mechanical stimulation. NPWT additionally facilitates the removal of exudate and infectious materials.
NPWT involves the application of local, subatmospheric pressure to a wound. Typically, one applies a foam or gauze interface directly to the wound site and it is connected to a pump via external tubing. The clinician can secure the wound interface in place with an adhesive dressing. It is common to use a pressure of 75-125 mm Hg in a continuous or intermittent fashion, but one may adjust the pressure based on the needs of the patient and health care team. Factors to consider may include the need for granulation tissue formation, wound closure by secondary intention, skin graft bolstering and clinical appearance of the wound.
Novel uses include NPWT with fluid instillation, closed-incision NPWT and ultra-portable NPWT systems that may or may not rely on electrical power to maintain topical pressure. Despite the reported benefits of and advances in NPWT, significant challenges remain in selecting proper patients and wound types for this therapy. Additionally, it is essential that one possesses the technical skill required for safe and effective use. Lastly, the health care provider should exercise caution and avoid over-reliance on NPWT as a cure-all for complex ulcers.
A Closer Look At NPWT And Excessive Bleeding
Bleeding. Researchers have noted bleeding as a serious complication of NPWT. White and colleagues reported an erosion and hemorrhage of the left anterior tibial artery associated with a vacuum-assisted closure device in a young patient who sustained a traumatic open lower leg fracture/dislocation. Following the injury, surgeons performed emergent ORIF along with debridement of the open fracture site. Following a second irrigation and debridement of the open fracture, physicians applied NPWT on the fifth day after the injury had occurred. Nearly two weeks later, they noted severe bleeding at the wound site and exploration of the wound revealed erosion of the lateral wall of the anterior tibial artery as the source of the hemorrhage. The patient underwent emergent arterial repair and physicians discontinued use of NPWT. Of note, the patient was undergoing concomitant anticoagulant therapy for a suspected pulmonary embolism.7
Petzina and coworkers described bleeding as a major complication of NPWT following poststernotomy mediastinitis.8 In a retrospective analysis of 69 consecutive patients with this condition, the authors reported that 7.2 percent sustained major complications during NPWT due to excessive bleeding.
Of course, these are rare cases in which physicians applied NPWT directly over exposed heart or blood vessels. For the purposes of this publication and readership, the vast majority of NPWT application will not involve these structures.
However, there are cases in which surgeons apply NPWT in lower extremity wounds with significant depth and exposed deep structures. It is critical that providers exercise caution in these cases to decrease the likelihood of bleeding complications. Applying a rigid barrier between the foam and deep structure is reportedly a beneficial protective measure in wounds with exposed structures such as blood vessels, vascular grafts, and nerves.9
What You Should Know About Retained Foam
Retained foam. The foam or gauze interface clinicians typically use with NPWT provides a suitable conduit for granulation tissue formation and tissue ingrowth. However, especially in deep wounds with irregular margins, areas of undermining and tunneling, foam pieces may be difficult to visualize and retrieve during dressing changes. In addition, if NPWT dressing changes occur beyond the recommended time period, the dressing can become embedded in the wound and may tear into small pieces during extraction. Similar to a foreign body, the retained dressing material can act as a potential infection source, further complicating wound healing.
A report by Mazoch and Montgomery describes two cases in which patients who utilized NPWT for traumatic wounds developed severe infections.10 The authors point out that the foam sponge used in NPWT is radiolucent and undetectable by X-ray, thus delaying a potential diagnosis. The report also highlights the challenges faced by the health care team in identifying and removing foam if, for example, one has used a white, hydrophilic foam to cover deep structures, such as bone, tendon and nerve. In these cases, the foam may blend into the surrounding tissue, making it difficult to visualize in the wound. In addition, different personnel may be involved with NPWT dressing changes due to varying schedules and resources. For example, one may initiate NPWT in a hospital setting but upon discharge, subsequent dressing changes may be performed at a skilled nursing facility or in the home by a visiting nurse.
The authors make several recommendations for decreasing complications of NPWT associated with retained foam, including a “surgical-like count” of the foam sponges during dressing changes.10 This count would record and make readily available in the medical record the amount, number of pieces, size and type of foam providers have placed or removed. Furthermore, when it comes to patients with a history of NPWT for a chronic wound, clinicians should have a heightened awareness for the possibility of previously retained dressing materials as a source of wound healing complications.
When NPWT Is Accidentally Unplugged
Device malfunction. Another reported complication of NPWT is interruption of therapy due to device malfunction. Collinge and Reddix evaluated 123 consecutive orthopedic trauma patients treated with NPWT between May and November 2008, and found a significant number (12/123) of cases in which therapy was unintentionally interrupted.11 In all of these cases, the authors noted that the NPWT device had become unplugged from the primary power source, setting the stage for battery depletion and eventual therapy interruption. Of these cases, the study authors observed wound complications in seven patients, including five who were treated for infection and one patient who actually died secondary to complications of necrotizing fasciitis.
To clarify, the timeframe in which the cases were reported occurred shortly after new modifications to the device were made by the manufacturer and the article was published nearly a decade ago.11 However, it is not difficult to envision many of these scenarios in our own clinical practices, in which power cords are removed, batteries remain uncharged and depleted, or dressings are left on for prolonged periods.
Key Considerations With Periwound Complications
Periwound complications. While most of the attention regarding NPWT is focused on the wound itself, practitioners must be mindful of the periwound area and take precautions to protect surrounding, healthy skin. Clinicians typically cover the foam- or gauze-wound interface with an adhesive dressing. However, there may be situations in which the use of certain adhesives is contraindicated and another dressing type is recommended.
Researchers have previously noted the formation of blisters on the surrounding skin of wounds undergoing NPWT. In 2011, Howell and colleagues published the results of a prospective, randomized trial comparing the number of days to complete wound/incision site healing in 51 patients undergoing total knee arthroplasty (TKA) that had NPWT versus standard gauze dressings.12 The authors reported 63 percent (15/24) of these patients developed surrounding skin blisters after application of NPWT over a closed surgical incision, and the researchers subsequently stopped the study. In the referenced cases, the authors noted the lack of protective barrier or dressing between the NPWT foam sponge and surrounding skin.
The abrupt discontinuation of the study and extremely high number of complications prompted a letter to the editor, published in the same journal later that year.13 In the letter, Vaez-zadeh addressed the high rate of complications and development of skin blisters: “If the skin is not adequately protected, skin irritation, including blisters, may potentially result from the effect of negative pressure at the interface of the foam edge and drape with intact skin.”13 Vaez-zadeh concludes, “NPWT over clean, closed incisions can provide important benefits and should be applied carefully and correctly according to the product’s clinical guidelines and labeling.”13
What Studies Have Revealed About Infection, Contamination And Wound Exudate-Related Complications
Infection and contamination. As I previously discussed, complications of NPWT such as retained foam and interruption of therapy, have resulted in cases of severe infection. The ability of NPWT to reduce bacteria counts remains controversial.14 Anagnostakos and Mosser published an interesting study in which 101 NPWT dressings were cultured along with tissue of the corresponding treated wound.15 The authors concluded that in nearly 20 percent of cases, the bacteria identified on the NPWT dressing was either different from the wound or present on the dressing, but not in the wound.
This raises the important question of whether the NPWT dressing is susceptible to bacterial contamination, or if bacteria present in the wound exist and thrive under the conditions of NPWT. Further studies are certainly warranted.
Protein loss and malnutrition. Wound exudate contains large amounts of protein, glucose and other nutrients necessary for wound healing. While removal of this fluid is a critical part of the NPWT mechanism, excessive removal can have serious implications for nutrition and wound healing. Hourigan and colleagues reported a significant loss of protein in wound exudate samples collected from both open abdominal and soft tissue wounds.16 The authors noted similar losses for electrolytes and immunoglobulins. Nutritional status is a key part of any comprehensive strategy for wound healing involving NPWT.
Pertinent Insights On Pain Management With NPWT
Pain. Due to the large number of patients with neuropathy who are treated with NPWT for lower extremity wounds, pain is often overlooked as a significant complication. However, many patients undergoing NPWT for treatment of wounds secondary to trauma as well as those without neuropathy may experience severe pain during therapy and dressing changes. In addition, there may be differences in level of pain or pain perception with the various types of dressing interfaces.
Fraccalvieri and colleagues compared the level of pain before NPWT, during therapy and after dressing changes in two groups who had NPWT and foam, and NPWT and gauze for the treatment of acute, traumatic wounds.17 Observing less pain at the dressing change in the group being treated with NPWT with gauze, the study authors attributed this to the “more adhesive property of the foam probably because of the ingrowth of the granulation tissue in the micropores present on the foam.”17
Administration of oral or intravenous pain medication may be indicated in certain cases to decrease the level of pain before, during and after NPWT dressing changes. In addition, local anesthesia may play a key role in addressing pain. Franczyk and colleagues reported decreased pain in patients undergoing NPWT who were administered 0.2% lidocaine through the NPWT tubing 30 minutes prior to dressing change in comparison to a placebo group.18
Other Factors To Consider With NPWT
Anxiety. Despite all the potential benefits of NPWT and with the risks associated with delayed or prolonged wound healing, some patients refuse this therapy due to anxiety. Some of the factors that may increase patient anxiety include fear of pain during therapy and dressing changes, restriction of activity, and unfamiliarity with the device.19
Rare complications. While this complication is perhaps too rare to merit further study, it may be too unusual to omit. In a letter published by Plastic and Reconstructive Surgery in 2006, Henry noted a “curious side effect” of NPWT, new and “exuberant” hair growth following wound healing as well as rapid nail growth on the ipsilateral foot after a patient had NPWT for an anterior knee ulcer.20 The author offered no clear explanation.
Complications of diabetes involving the lower extremity, particularly DFUs, remain a challenging and growing problem. NPWT has emerged as an effective and useful modality for wound healing, but podiatric physicians and surgeons must be aware of the risks for potential complications. Appropriate patient and wound selection is critical, and clinicians should follow manufacturer instructions closely. It is simply unacceptable to say “just VAC it” in complex wound cases without understanding the potential pitfalls of NPWT.
While only a paucity of evidence exists specific to lower extremity NPWT complications, the available literature is worth noting and further studies are needed.
Dr. Isaac is the Director of Research at Foot and Ankle Specialists of the Mid-Atlantic (FASMA) in Rockville, Md. He is a Diplomate of the American Board of Foot and Ankle Surgery (ABFAS).
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14. Li Z, Yu A. Complications of negative pressure wound therapy: a mini review. Wound Repair Regen. 2014:22(4);457-461.
15. Anagnostakos K, Mosser P. Bacteria identification on NPWT foams: clinical relevance or contamination? Wound Care. 2012:21(7);333-339.
16. Hourigan LA, Hourigan L, Linfoot JA, et al. Loss of protein, immunoglobulins, and electrolytes in exudates from negative pressure wound therapy. Nutr Clin Pract. 2010:25(5);510-516.
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18. Franczyk M, Lohman RF, Agarwal JP, Rupani G, Drum M, Gottlieb LJ. The impact of topical lidocaine on pain level assessment during and after vacuum-assisted closure dressing changes: a double-blind, prospective, randomized study. Plast Reconstr Surg. 2009:124(3);854-861.
19. Upton D, Stephens D, Andrews A. Patients’ experiences of negative pressure wound therapy for the treatment of wounds: a review. J Wound Care. 2013:22(1);34-39.
20. Henry SL. A curious side effect of negative pressure wound therapy. Plast Reconstr Surg. 2006:117(7);2534-2535.