Treatment With Novel Foam Dressing of NPWTi-D for Postoperative Necrosis Complicated by Critical Limb Ischemia

A 69-year-old man presented with ischemic ulcer against a background of diabetes and chronic renal failure. He showed skin necrosis of the right third toe and heel and had undergone below-the-knee amputation at another hospital. Postoperatively, the edge of the wound became necrotic, and debridement was performed, but the area of necrosis expanded, and the patient was referred to us (Figure 1). Skin perfusion pressure (SPP) at the distal thigh was 45 mmHg, but measurement below the knee was too painful. Angiography showed diffuse 90% stenosis of the superficial femoral artery in the distal thigh, so percutaneous balloon angioplasty of the same area was performed. Blood flow was resumed up to the bifurcation of the 3 main branches of the lower leg, but no wound blush was seen. Two days later, debridement was performed. A skin incision was made at the edge of the dark red area, and necrotic tissue and muscle with no apparent blood flow were debrided from the superficial layer. In consideration of the risk of ischemic limb, debridement was limited to the layer where necrotic tissue remained thin and little bleeding was evident (Figure 2).

After confirming hemostasis, we started negative pressure wound therapy with instillation and dwell time (NPWTi-d) using reticulated open cell foam dressings (ROCF-CC). To avoid disturbing blood flow to the tissue of the ischemic limb, negative pressure was initially set at -100 mmHg. We set a cycle time of 3.5 hours with an immersion time of 10 minutes. Negative pressure was changed to -125 mmHg after the first look 3 days later, after confirming no expansion of the necrotic area in the wound bed. When the foam was changed, some necrotic tissue was peeled off with the foam, the remaining necrotic tissue in the wound was softened and disintegrated, and the boundary between healthy granulation tissue was clearer, allowing easy debridement. Three weeks after starting NPWTi-d, all necrotic tissue had disappeared, and healthy granulation was observed over the entire surface of the wound bed, forming a macrocolumn (Figure 3a–c). NPWTi-d was temporarily interrupted to flatten the macrocolumn, and the patient was switched to once-daily washing, treatment with a trafermin preparation (Fibrast Spray; Kaken Pharmaceutical Co, Ltd), and purified white sugar povidone-iodine ointment (Isodine Sugar Paste Ointment; Mundipharma KK). Skin graft transplantation was performed 1 week later. Softened skin at the wound margin was removed, resulting in a 14×20-cm skin defect. Skin was harvested from the left lower abdomen in a 16×7-cm spindle shape and transplanted in separate layers with 25/1000-inch, 3 times mesh (Figure 4a, b). Grafts were sutured and fixed with VAC Ulta without washing function. One week later, the fixation was removed, and the graft was fully engrafted. The mesh pore was completely epithelialized after 4 weeks of treatment with Fibrast Spray and

alprostadil alfadex ointment (Prostandin Ointment; Ono Pharmaceutical Co, Ltd) after daily washing.

If the patient is bedridden, above-the-knee (AK) amputation in favor of early and certain wound healing can be a good choice. Otherwise, amputation at a high level should not be performed to preserve stable sitting position and better function. Covering a tibial stump with well-vascularized gastrocnemius and soleus muscles is important for preventing pressure ulcers. When extensive necrosis of the lower-leg muscles occurs, AK amputation is often chosen.

However, NPWT can be increasingly used for the wound, except exposed bone, to cover the bone stump with voluminous, blood-rich tissue by promoting granulation growth. It is enough for preventing pressure ulcers and keeping stable sitting position, so it is worthwhile to preserve the proximal lower leg, even with the complete loss of the lower-leg muscles.

In this case in particular, the muscles covering the bone stump were preserved, and the range of motion of the knee joint was good, so preservation of the proximal lower leg was significant. As of 4 months postoperatively, only mild pigmentation remained, with no pain or phantom limb sensation and no recurrence of ulcer (Figure 5). Although the patient declined to participate in rehabilitation, and making an orthosis and acquiring walking was difficult, he was able to maintain a stable sitting position.

As a principle of critical limb ischemia (CLI) treatment, the process needs to be implemented appropriately from debridement to wound healing in as short a time as possible, paying attention to infection control and blood flow. Blood circulation should be assessed based on values such as SPP and modalities such as angiography, and progression of necrosis by inadvertent debridement should be avoided. If sufficient blood flow is observed, lower limb salvage can be achieved by debridement and appropriate wound closure, but major amputation at a higher level is often necessary.

One issue that makes the treatment of ischemic limb difficult is the problem of proper debridement. SPP greater than or equal to 30 mmHg is considered necessary for wound healing.¹ Thus, if the SPP is close to 30 mmHg, repeated under-debridement is needed with attention given to the potential expansion of necrosis caused by debridement.

As an option for closure, NPWT is very useful and has often been used in the treatment of critical lower limb ischemia.² NPWTi-d has a cleaning function that allows safe treatment of cases with exposed tendons and bones, large amounts of necrotic tissue, or ischemic limbs with mild infection.³ Daniel et al⁴ reported good wound healing using ROCF-CC for ischemic ulcer on the plantar.

ROCF-CC facilitates surgical debridement by physically debriding necrotic tissue via foam material in addition to the conventional granulation promotion by NPWT (Figure 6). The time to complete wound healing can thus be shortened. In addition, necrotic tissue is better removed at the bottom of the wound than at the top of the microcolumn by the pressure strain at a minimum on the tops of the through holes of the ROCF-CC and at a maximum at the edges of the hole openings,² improving observation of the shape and condition of the wound bed and allowing more accurate assessment of the state of granulation and blood flow to the tissue. In this way, wound healing can be achieved without amputation at

a higher level.

The guidelines for the use of NPWTi-d and ROCF-CC recommend an immersion time of 2–20 minutes, a negative pressure time of 0.5–3.5 hours, and suction pressure of -125 or -150 mmHg. An algorithm is provided, but ischemia is not yet considered as a factor.²

Although a negative pressure of -125 mmHg is recommended for NPWTi-d,⁵ when negative pressure of -125 mmHg was applied to the foot of a healthy individual, transcutaneous pO2 reportedly decreased from 69.3 ± 8.1 mmHg before treatment to 60.0 ± 10.0 mmHg after treatment.⁶ In cases of ischemic limb, the difference is expected to be more pronounced, and the pressure should be lower than -125 mmHg because excessive negative pressure can contribute to necrosis of the wound surface.⁷ Judging from tissue condition, suction pressure of -125 mmHg, which is conventionally avoided in ischemic limbs, can be applied to promote granulation and shorten the treatment period.

In the present case, negative pressure was initially started at -100 mmHg, but no findings suggested any increase in the extent of necrosis in the wound bed or ischemia of the granulation tissue. Since a large amount of necrotic tissue remained in the wound bed, suction pressure was increased to -125 mmHg to prioritize more rapid debridement of necrotic tissue. This further accelerated the softening and decomposition of necrotic tissue, clarifying the boundary between viable and necrotic tissue and allowing easier and faster debridement. We suggest that NPWTi-d and ROCF-CC can be used on the ischemic limb for safe and efficient debridement if wound condition is carefully monitored and pressure is changed accordingly.

Affiliations: ¹Department of Plastic and Reconstructive Surgery, Kansai Medical University, Osaka, Japan

Correspondence: Yuki Matsuoka, MD; ykmatsuokayk@gmail.com

Disclosures: The authors have no relevant financial or nonfinancial interests to disclose.