The Role of Personal-use Negative Pressure Wound Therapy with Enhanced Functionality in Achieving Wound-related Treatment Goals: A Small Prospective Study

In the US, chronic wounds affect at least 8.6 million patients per year.¹ It has been estimated that around half of wounds will fail to heal within a 12-month period.² This failure to heal is a growing burden to society, both from a human and financial perspective.^1-3 It has been estimated that a wound will negatively affect the quality of life of approximately 2.5% of the US population, suggesting a huge human burden.³ In the US, annual Medicare expenditure on wound management exceeds $28 billion, a substantial financial burden.¹ The number of patients at risk for hard-to-heal or chronic wounds is growing rapidly due to an aging population and a sharp rise in the incidence of diabetes, obesity, and other risk factors in the US.^1,3

NPWT is a common treatment option for complex acute, chronic, and postsurgical wounds in both inpatient and outpatient settings. It has been shown clinically to reduce wound size and edema, promote granulation tissue formation, and remove exudate and infectious material.⁴ NPWT is most often used as a tool to promote closure of hard-to-heal wounds, but often is discontinued when the wound has progressed to a stage where a standard dressing can be used instead.

Several NPWT options are available, many of which offer different levels of functionality.⁵ In recent years, there has been a shift from the use of larger devices towards smaller, personal-use NPWT devices, especially to facilitate discharge so a patient can continue therapy for up to 3 years in their own home. Key advantages of personal-use NPWT devices include their small size and self-contained design that reduces restriction of patient mobility.⁶ One downside is that the adoption of these personal-use options may have been constrained by the limited functionality possible in earlier generations of such small devices. Examples of these constraints include the lack of alarms, strict limits of treatment duration, and limited exudate capacity.⁵ Until recently, health care professionals have faced a trade-off between enhanced mobility and ease of use versus enhanced functionality.

As this technology develops, new personal-use devices are becoming available that retain the small size and ease of use already seen but also offer additional functionality. For example, a new personal-use, ultraportable NPWT device has recently become available that has audible alarms, has good exudative capacity, does not limit duration of therapy, and ensures the maintenance of the selected pressure level at the wound bed via an electronically controlled feedback system.⁷ While the duration of therapy from other disposable NPWT devices is typically limited to 7 to 14 days, the novel NPWT personal-use system utilized in the current study has the benefit of enabling therapy durations up to 3 years. Other organizations have demonstrated that this electronic feedback system for pressure level maintenance may be particularly beneficial and may make the treatment safer for patients.⁶

The purpose of the current study was to evaluate how well this newly available personal-use NPWT system with enhanced functionality (including an electronically controlled feedback system) could be integrated into the standard of care and deliver clinically acceptable progress towards therapeutic goals of patients with a variety of wounds.

Study design

This study was a prospective, nonrandomized, interventional case series evaluating the use of a personal-use NPWT system and was registered on ClinicalTrials.gov (identifier: NCT03670225). Ethical approval for the study was obtained from the Central Institutional Review Board in August 2018.

The general study design comprised 2 phases: (1) the screening phase and (2) the study treatment phase. During the screening phase, potential subjects were screened against the prespecified inclusion and exclusion criteria, and informed consent was obtained before start of the study interventions. In the study treatment phase, use of the study intervention was initiated.

Patient selection

A total of 12 adult (≥18 years) patients with varying wound indications—including DFUs, PIs, surgical, acute/traumatic, or dehisced wounds—were evaluated to determine whether they were suitable candidates for treatment during a 4-week study period with a commercially available, US Food and Drug Administration–approved NPWT wound care system (Invia Motion Endure; Medela AG, Switzerland) in an advanced wound care clinic setting; patients would be discharged home to continue treatment. All patients, or their legally authorized representative, provided signed, informed consent before screening. All patient data were anonymized. Exclusion criteria included patients whose wounds contained necrotic tissue with eschar present, untreated osteomyelitis, nonenteric and unexplored fistulas, malignancy or exposed vasculature, nerves, anastomotic sites, or organs. Patients with concurrent conditions or comorbidities that in the opinion of the investigator may have compromised patient safety or study objectives were also excluded.

Materials

The NPWT system used in this study was a single-patient, portable, rechargeable, battery-powered, maintenance-free NPWT pump with a typical battery life of greater than 10 hours. Fluid management was facilitated via a canister with 150-mL capacity. Despite being a personal-use unit, this NPWT device had enhanced functionality; the device was able to deliver a range of negative pressure levels (from -50 to -150 mm Hg) at either continuous or intermittent delivery of negative pressure, modifiable according to clinical judgment in a manner similar to that of more traditional, larger NPWT pumps. The device also maintained target negative pressure at the wound bed through its double-lumen tubing, using an electronic feedback system to monitor and control pressure at the wound bed to ensure that set pressure was delivered. Any faults or deviations from set values triggered acoustic and optical signals. The NPWT system was used along with an appropriate wound filler; black polyurethane foam or gauze were available options and were chosen according to clinical judgment.

Study objectives

The primary objective of this study was to determine acceptable progress towards the goal of therapy for DFU and PI wounds when using the experimental NPWT system during the 4-week study duration. The goal of therapy was defined by the physician (at the screening visit) according to initial assessment; therefore, the endpoints were dependent on goal of therapy, namely, decrease in wound volume, decrease in size of the tunnelling area, decrease in size of undermining, decrease in amount of slough, and increase in granulation tissue. In addition, the physician decided on a case-by-case basis whether the wound bed was progressing acceptably towards a transition to another treatment modality, such as standard dressing, surgical closure, a flap, or graft.

The secondary objectives of the study were (1) to evaluate the novel system’s ease of use as reported by clinicians and (2) to evaluate the clinicians’ overall satisfaction with the experimental device. The tertiary objective was to determine whether the device provided adequate management of the exudate.

To enable an objective assessment of healing, wounds were assessed at a screening visit, at baseline (when NPWT was applied), at week 1, at week 2 or 3, and at week 4 (final assessment). Wound assessment included measurement of wound volume, the presence and extent of any undermining or tunnelling, assessment of the wound bed, wound edge assessment, drainage, presence of edema, presence of infection, and wound odor.

To assess the secondary study objectives, clinicians were given a 4-point categorical scale to evaluate the ease of use of the device. Briefly, clinicians were asked whether their level of satisfaction with various aspects of the single-patient personal-use NPWT device compared with the NPWT device typically used in their daily practice (ie, less satisfied, neutral, satisfied, more satisfied). The ability of the device to handle wound exudate was monitored by recording the number of canisters used. Any AEs or issues with the device or associated dressings were also logged.

Data analysis

No sample size calculation was carried out; results were considered observational. Differences in wound measurements between baseline and the end of the study were expressed as mean (± standard deviation) and median (IQR). Any missing data points (from time points after baseline) were imputed using last observation carried forward. All descriptive analyses were computed using R software for Mac (R Foundation for Statistical Computing; Vienna, Austria).

Patients were enrolled from October 2018, with the final follow-up visit in October 2019. A total of 12 patients were enrolled into the study; 2 were withdrawn. In 1 patient, culture results returned after enrollment revealed infection, leading to a clinical decision to withdraw the patient. In the second patient, concerns about their home environment led to the decision to withdraw the individual from this study. This left an evaluable population of 10 patients, described in Table 1.

Six patients were female, and mean age was 55.2 years (range, 39-70 years). Five patients were White, 4 were African American, and 1 was Hispanic. A wide variety of wounds was represented in the cohort, reflecting the broad inclusion criteria (Table 1). Neither tunnelling nor undermining were assessed in any of the wounds. The most common ultimate treatment goal selected by the attending clinicians was to “achieve wound closure” (chosen in 6 of 10 patients), with the most relevant endpoint being a reduction in wound volume and improved granulation tissue. NPWT was applied for a median of 19.5 days (range, 7-35 days); at the end of the 4-week evaluation period, acceptable progress towards the ultimate treatment goal had been met in all 10 patients (Table 1).

All wounds improved during the 4-week treatment period. Example case images are shown in Figure 1, showing a variety of wound types with different clinical needs.

A clear trend towards reduced wound size was observed; when wound volume at the final assessment was compared with baseline, a median reduction of 12.7 cm³ (IQR, 27.4-3.24 cm³) was observed (Table 2). Median wound volume at baseline was 24 cm³; this reduced to 1.76 cm³ by week 4, a median reduction of 84.70% (IQR, 53.12-96.42%).

There were no device-related deficiencies reported; 1 minor issue with the NPWT device battery was easily resolved when a new NPWT device was provided as a replacement, and there was no disruption to NPWT. Two AEs were reported: worsening bilateral lower limb edema in 1 patient and hypertension in a second patient that resolved by the following visit. Neither AE was deemed to be related to the device.

Clinicians were typically satisfied with the personal-use NPWT device compared with other NPWT devices that were more commonly used; 8 of 10 clinicians were satisfied with the overall performance of the device (Figure 2). No clinicians reported being less satisfied with the personal-use device than with their previously used NPWT device in any of the categories assessed. The personal-use device performed well in the categories of patient satisfaction and patient mobility; in these categories, 4 of 10 clinicians were more satisfied with the personal-use device than with other commonly used devices with which they were familiar (with the remainder of clinicians being satisfied or neutral). Clinician scores were generally seen to be improved at the end of the 4-week study period compared with baseline scores (not shown) in relation to ease of use and patient mobility.

This study reported the clinical efficacy and acceptability of a personal-use NPWT system with enhanced functionality in a series of patients with open, hard-to-heal wounds. Personal-use NPWT has been used extensively on closed wound incisions, and a series of meta-analyses have found it to improve outcomes.^8-10 Such devices also have great potential for use on open wounds, such as the range of chronic, traumatic, and postsurgical wounds reported here. Use of personal-use NPWT devices in open wounds benefits from the well-established success of traditional NPWT in the management of these wounds; meta-analyses based on randomized controlled trials have widely demonstrated faster reduction in wound volume and wound healing with traditional NPWT compared with advanced wound dressings.^11,12 In the current study, positive clinical outcomes were seen in all patients; acceptable progress towards the goal of therapy was met, wound volume was reduced by a median of 85% over a 4-week treatment period, and granulation tissue was enhanced in all wounds. These outcomes were similar to those reported in previously published clinical cases using the same⁷ and other^13-15 personal-use NPWT systems.

Some previously published studies have shown that personal-use NPWT may even improve outcomes over those seen with traditional (larger, multi-user) NPWT devices, including faster progression towards healing¹⁶ and reduced overall treatment costs.¹⁷ A randomized, controlled trial comparing single-use NPWT with traditional NPWT in DFU and venous leg ulcers reported an 88% reduction in wound volume over 12 weeks; this was significantly greater than that found with traditional NPWT (59% reduction over the same period).¹⁶ In another retrospective comparative study, single-use NPWT was found to result in a 50% reduction in the time to healing compared with matched historic controls treated with an advanced wound management protocol.¹⁸

Clinical practice is currently experiencing a paradigm shift in the way that NPWT is used, moving away from inpatient care to outpatient protocols, facilitated by small, portable, personal-use NPWT devices.^6,19 In this context, a number of features of personal-use devices become of heightened importance. First, health care professionals must be confident in the devices to accurately deliver the set level of pressure. Second, patient safety must be ensured. Third, devices must be easy to use by the community health care providers involved in outpatient care, and they must be very patient-friendly.⁶ The personal-use NPWT device assessed in this study was designed to maximize its utility in all care settings, including outpatient settings, and as a means of facilitating early mobilization and earlier discharge.¹⁹ Its dual lumen tubing and electronically controlled feedback mechanism ensured accurate delivery of set negative pressure at the wound site throughout therapy, which is needed to maximize perfusion of the wound bed, wound edge contraction (macrodeformation) and granulation tissue formation (microdeformation); all these features are important aspects of the mode of action of NPWT.⁴

An investigation utilizing a simulated wound model compared the ability of a novel NPWT system and a common NPWT system to deliver set levels of NPWT and manage fluid volume.²⁰ The results from the published presentation concluded that when subjected to a rapid introduction of 150 mL of fluid, the novel NPWT system cleared fluid more rapidly (range, 10-25 minutes) than a common NPWT system (range, 80-170 minutes). The novel NPWT system efficiently cleared the fluid volume due to the active-dynamic ability to adjust the rate of air-flow cycles in response to changing levels of exudate. The common NPWT system’s air-flow cycle was static and unresponsive to changing exudate levels in this evaluation. Compared with the common NPWT system, the novel NPWT system provided dynamic exudate removal, allowing for faster and more efficient removal of large fluid volumes while maintaining set pressure at the wound bed.²⁰

In terms of patient safety, the electronically controlled feedback system of the device evaluated in the present study demonstrated efficient exudate removal, and thereby aided in preventing potential blockages, which can be a source of risk to the condition of the patient’s wound. The ease of use of the device was demonstrated by the good satisfaction scores reported, particularly those relating to patient satisfaction and mobility, upholding the notion that the device was found to be easy to use. In an advanced wound care clinic where a great number of patients are seen per day, the device’s easy application, easy transition to home use, versatility, and applicability across care settings are desirable in treating patients efficiently.

This study has some limitations. First, only a small number of patients were enrolled; larger clinical studies are warranted. Second, some of the observations reported in this study were observational and based on clinical judgment rather than objective measurement; this is a potential risk of bias. The positive results observed following treatment with a personal-use NPWT device with enhanced functionality are comparable to those in the growing body of clinical evidence collected with other personal-use NPWT systems.   

In the past, personal-use NPWT pumps had limited functionality; however, the personal-use NPWT system used to treat patients in this case series offered greater ability to modify pressure settings, enhanced safety features, and an electronically controlled feedback system that automatically ensured delivery of set pressure to the wound bed. In this case series, acceptable progress towards therapy goals was reached for all 10 patients evaluated, including a clinically meaningful reduction in wound volume within a 4-week treatment period. Clinicians were satisfied with the ease of use of the device (in particular, patient mobility and patient satisfaction), and the device functioned well in an advanced wound clinic in which patients were transitioned to an outpatient setting.