Anthony Tickner, DPM, FACCWS, FAPWCA, FAPWH
Elizabeth Ansert, MA, DPM, MBA
Since the development and Food and Drug Administration (FDA) approval of negative pressure wound therapy (NPWT) in 1995, it has been used in a wide range of wound types.1 Clinical applications have increased and undergone extensive study in various settings.2 The currentstandard setting for NPWT is -125 mmHg.3
One area that varies among clinical uses is the setting of pressure applied by the NPWT system. A study by Kairinos, Solomons and Hudson examined the effect of increased pressure on soft tissue using various materials and pressure sensors.4 In this study, pressures ranged from -100 to -500 mmHg. The base of the wound showed a proportional increase in wound pressure as the negative pressure setting increased.4 However, as the authors moved the sensors farther from the base of the suction, the pressure did not proportionally increase. In fact, the authors noted little change with the sensors at two and three cm from the base of the wound with increased pressure.4
Another study by Saxena and colleagues noted the peak average strain of a wound was experienced at pressures of -125mmHg.5 This peak cellular strain was about five to 20 percent.5 However, the strain increased with increased pressure applied by the NPWT system.5
The physiological effect NPWT has on wounds is not completely understood. However, some postulate that the increase in pressure dissipates extracellular fluid away from the wound.4 This could allow for increased perfusion of oxygen and nutrients into the area. Furthermore, the literature notes that allowing cells to “stretch,” presumably by decreasing extracellular pressure, proliferate more rapidly.6 This five to twenty percent cellular strain generated by NPWT indeed promotes cell proliferation.7
In very edematous wounds or wounds with increased drainage, increasing NPWT pressure to accommodate for these clinical variables may be warranted. Here we present three patients in the authors’ clinical setting with edematous wounds, large defects and increased drainage from the wound bed.
When Physicians Choose Increased NPWT Pressure: Case Examples
Case 1.This patient is a 60-year-old male who presented to the emergency department with foot and leg pain, swelling and systemic symptoms of infection. He subsequently underwent emergent extensive incision and drainage for necrotizing fasciitis. After clearing all infection from the wound, he began NPWT with an initial setting of -150mmHg. After one week of NPWT at -150mmHg settings, the wound area measured 60.7cm2 (see first photo above). At this time, we increased pressure to -175mmHg. After one week of increased pressure, the area of the wound decreased to 58.5cm2 (see second photo above). The NPWT continued until achieving substantial granulation tissue. The wound went on to heal (see third photo above) with NPWT, collagen and antibiotic dressings.
Case 2. Patient 2 is a 60-year-old male admitted for a diabetic foot infection. He underwent extensive debridement and continued to have purulence and malodor, requiring additional surgical intervention. After the infection was well controlled, NPWT was applied at the standard -125mmHg with a wound area of 73cm2 (see fourth photo above). Upon examination at the second week, the wound area increased to 75.5cm2, and we increased the NPWT pressure was increased to -150mmHg. After doing so, the wound area decreased substantially to 60cm2. After a 55 percent decrease in wound area, we stopped NPWT and the patient continues to heal without complication (see fifth and sixth photos above).
Case 3. Patient 3 is a 69-year-old male who presented with a chronic, infected fifth metatarsal wound. Surgical and clinical debridements resulted in minimal wound changes, and NPWT at -125mmHg was initiated. The wound area at this time was 15cm2 (see seventh photo above). After two weeks of NPWT, we increased the pressure to -175mmHg. This resulted in a significant reduction in wound area to 11.4cm2 after one week of increased pressure (24 percent area decrease, see eighth photo). NPWT continued until the wound bed was level with the periwound skin level. This patient continues to heal without complication.
Three patients in our health system have anecdotally shown significant improvement after one week of NPWT settings above the standard -125mmHg. On average, there was an approximately 38 percent reduction in wound area with increased pressure. Each patient had a history of significant infection, osteomyelitis and significant wound drainage.
Based on current literature, the increased pressure setting is thought to physiologically decrease extracellular pressure placed on wound bed cells. This decrease in pressure allows for the cells to stretch and increases microtension, which causes an increase in cell proliferation mechanisms.6 This increase in microtension has also been thought to allow for increased angiogenesis due to peaking cellular stretch and pressure.6,8
Physicians can safely apply increased NPWT to patients who have substantially draining wounds, increased edema and who are able to tolerate a higher level of pressure. While the exact mechanism of action of NPWT is not known, current literature supposes the theory of reduced edema to allow for cell proliferation. While the optimal NPWT setting is still controversial, barrier dressings and edematous wounds studied justify using increased pressure in these clinical settings.9
Dr. Tickner is the Medical Director of the Saint Vincent Hospital/RestorixHealth Wound Healing Center in Worcester, Mass. He is a global wound care consultant and is involved in podiatric wound care education at Saint Vincent Hospital.
Dr. Ansert is a second-year podiatric surgical resident at Saint Vincent Hospital in Worcester, Mass.
Originally Published- Podiatry Today, June 2021