Negative Pressure Wound Therapy With Instillation and Dwell Time Modifications for Lower Limb Wounds With the Waterfall Technique: A Case Series

Negative pressure wound therapy with instillation and dwell time (NPWTi-d) is an integrated system that incorporates an irrigation feature into conventional NPWT. The process comprises controlled delivery of a solution into the specialized foam dressing. The instilled fluid is allowed to dwell in the wound for a period of time, after which NPWT suction resumes, and the remaining fluid is removed. Negative pressure wound therapy with instillation and dwell time facilitates the removal of bioburden and cytotoxic molecules from the wound surface, helps maintain a moist wound environment, and promotes angiogenesis.^1,2

Previous studies have reported that NPWTi-d is an effective treatment for acute and chronic wounds.^3-10 It is commonly employed as an adjunct therapy to treat complex diabetic foot wounds and infections, including postsurgical diabetic foot wounds.^4,5 Studies have shown that the use of NPWTi-d results in a significant decrease of bioburden in wounds compared with the use of NPWT alone.⁸ In addition, NPWTi-d is associated with a reduction of repeat surgical debridements, hospital length of stay, and duration of treatment.¹¹

However, application of the V.A.C VERAT.R.A.C Pad (3M + KCI) to a diabetic foot wound site with a small entry point (eg, a second ray amputation wound located between the hallux and middle toes) poses certain challenges. To date, there are no reports in the literature that address the difficulties of NPWTi-d application to such wounds.

This study presents the use of a novel NPWTi-d application approach (the waterfall technique) in a case series of postsurgical diabetic foot wounds with small entry points. The authors also aimed to describe and evaluate the effectiveness of this application technique in comparison to methods presented in the literature.

Study population
This is a case series of patients who were admitted to Sengkang General Hospital, a tertiary health care institution in Singapore, from September 2019 to May 2020. All study participants had presented with an infected diabetic foot ulcer and underwent a surgical procedure, either ray amputation or wound debridement, to remove the infectious and devitalized tissue during their inpatient stay.¹² Negative pressure wound therapy with instillation and dwell time was employed as an adjunctive therapy to the postsurgical diabetic foot wounds. The waterfall technique was introduced to aid instillation, allowing the cleansing solution to reach wounds that were typically too small or narrow to allow application of the NPWTi-d tubing pad.

Relevant baseline patient information, wound characteristics, laboratory markers, NPWTi-d settings, and clinical outcomes were collected. All patients gave consent for their clinical photos to be taken. Ethics approval was obtained from the local institutional review board (reference number: 2020/2784).

The waterfall technique
For conventional NPWT, the local institutional practice is to create a “bridge” that extends the foam dressing proximally to either the dorsal or plantar surface of the foot. However, in the context of NPWTi-d, extending the foam proximal to the wound resulted in the cleansing solution flowing against gravity. As such, during the instillation phase of NPWTi-d, much of the instilled solution flowed into the suction tubing (following gravitational pull) instead of the wound. The authors subsequently attempted to increase the instillation volume to overcome this issue. However, this resulted in either a blockage in the NPWTi-d system or a leak due to excessive fluid in the tubing and/or the foam. Hence, the waterfall application technique was designed to address these issues faced in a diabetic foot wound with an unfavorable wound size and location.

V.A.C. VERAFLO dressing kit (3M + KCI) was used in this case series (Figure 1). The initial steps of NPWTi-d application followed the usual practice (Figure 2). First, the periwound skin was prepared using the Cavilon No Sting Barrier Film wipes (3M) available in the dressing kit. Next, the wound edges were lined with Duoderm Thin (ConvaTec) to prevent both excessive skin maceration and subsequent leakage. The wound then was packed with the specialized NPWTi-d foam dressings and secured with V.A.C. Advanced drape (3M + KCI). Finally, a 2-cm diameter hole was cut on the drape, usually to allow direct placement of the pad.

The waterfall technique refers to the unique application of a hanging bridging foam extension and placement of the pad in a dependency position to the wound location (Figure 2). The bridging extension was created using the foam and draped—one end of the bridging extension was secured over the cutout hole on the wound foam. A second hole was cut on the opposite end of the bridging extension for placement of the pad. With its attached tubings, the pad was arranged and placed in a dependent direction to allow gravity to aid the flow of cleansing solution to fill up the foam. The tubings were then connected to the machine and NPWTi-d initiated.

NPWTi-d settings and wound reviews
Three types of irrigation solutions were used in this case series: normal saline 0.9% w/v, Prontosan Wound Irrigation Solution (B. Braun), and 0.6% povidone-iodine solution. The choice of irrigation solution was clinically correlated with the wound condition and results of the intraoperative culture. Normal saline was used for clinically clean wounds, irrigation solution for wounds that appear sloughy, and diluted povidone-iodine solution for wounds that were still infected. Irrigation volume varied and was estimated according to the wound size, as decided by podiatrists during assessment. Sufficient volume of fluid was instilled to adequately fill the foam dressing without causing leakage. Depending on the degree of wound bioburden during visual wound inspection, the duration of NPWTi-d cycles ranged from 1 to 3.5 hours. Dwell time and NPWT settings were standardized at 10 minutes and -125 mm Hg low intensity and were kept constant for all 9 patients. Regular wound inspections were performed by a multidisciplinary team, including orthopaedics surgeons and podiatrists, every 72 to 96 hours. Negative pressure wound therapy with instillation and dwell time dressing changes were administered by podiatrists and continued until the wounds were deemed suitable for stepping down of dressing.

Patient demographics and clinical details are reported in Table 1. The study population consisted of 6 males and 3 females, with a median age of 56 years (range, 45–67 years). Six patients had poorly controlled diabetes mellitus with a median HbA_1c of 8.8% (range, 5.2%–13.3%). Two patients had underlying peripheral vascular disease and had undergone angioplasty prior to the study, with satisfactory results to ensure adequate blood flow for optimum wound healing. Patients also had a history of cardiovascular risk factors such as hypertension (66.7%), hyperlipidemia (55.6%), and ischemic heart disease (22.2%). On admission, all patients displayed elevated inflammatory markers, which largely normalized following surgical debridement and NPWTi-d, suggesting eradication of the initial infection.

All patients underwent a surgical procedure to remove the source of infection (Table 2). This included 7 minor ray amputations and 2 wound debridement surgeries. In 6 patients (66.7%), intraoperative cultures were positive; among these, 50% were methicillin-sensitive Staphylococcus aureus.

The median duration from surgery to initiation of NPWTi-d was 2 days (range, 1–22 days). All wounds were inspected by the team of orthopaedic surgeons and podiatrists before the decision to initiate NPWTi-d was made. Factors that precluded use of NPWTi-d included bleeding, presence of purulent discharge or collection, need for further surgical debridement or amputation, heavy periwound maceration, or necrotic edges. In case 8, clinical suspicion of deep tissue infection resulted in the delay of NPWTi-d implementation until postoperative day (POD) 22. In case 9, wound inspection on POD 2 showed evidence of necrotic wound edges due to underlying peripheral vascular disease, thus NPWTi-d was only initiated on POD 5 after a bedside debridement and no further necrosis was observed.

Table 2 shows the relevant settings and duration of NPWTi-d treatment for each case. None of the cases had any incidents of blockage of the NPWTi-d system. Only 1 case reported a small leak in the NPWTi-d, which was resolved with minor adjustment without replacing the dressing in its entirety. Subsequent wound recovery was otherwise uneventful with no adverse events.

Figure 3 shows the wound recovery progress for case 5. None of the 9 patients required repeat surgical debridement or further amputation during the index hospitalization stay. Of note, 1 patient (case 2) required readmission for surgical debridement following a secondary wound infection. Full epithelialization was achieved in the 8 patients (88.9%).

This study describes the novel use of the waterfall technique for application of NPWTi-d on diabetic foot wounds with a small entry point following either surgical debridement or ray amputation. No patients required repeat surgical debridement, and full epithelization was achieved in 8 patients (88.9%). The authors found the waterfall technique to be effective in achieving good outcomes of promoting granulation and reducing the need for repeat debridements. Other benefits include relative ease of adoption with only a few additional steps required, and absence of added cost of treatment as no additional materials outside of the NPWTi-d kit necessary. There were no troubleshooting incidents except for 1 case requiring minor adjustment for a small leak of irrigation fluid, and no adverse events were noted.

The efficacy and use of NPWTi-d has been widely addressed in the literature. Successful outcomes using this approach are largely attributed to bioburden reduction. Instillation of wound cleansing solutions facilitates solubilization and removal of nonviable tissue.^1,2,8 Theoretically, this process is successful only when the cleansing solution covers the entire wound bed throughout the dwell time, aided by the reduced hydrophobic properties of the foam dressings used in NPWTi-d compared with conventional NPWT dressings.⁷ However, the application of NPWTi-d is not without challenges that could limit the therapeutic potential of this modality, particularly on diabetic foot wounds.

Rationale of the waterfall technique
The rationale for the waterfall technique is to address the problems with difficult topography, which may result in instillation of irrigation fluid against gravity, leading to blockage or leakages.

All 9 cases reported in this study were postsurgical foot wounds that resulted either from one or more ray amputations or surgical debridements. The location and anatomy of these foot wounds posed challenges during the application of NPWTi-d, because there needs to be a sufficient wound surface area for the placement of the pad. In addition, it may be difficult for the instillation solution to flow to the base of the foot wound and cover the entire wound base when the patient receives treatment in a supine position.

Benefits of the waterfall technique
The creation of a foam extension distally to the wounds guarantees a dependent position that can be adapted to any location on the foot. By allowing gravity to aid the flow of the cleansing solution, the NPWTi-d foam is filled fully and efficiently. The use of the waterfall technique also circumvents the need to instill higher amounts of solution to flow against gravity, thereby minimizing the risk of blockage and leakage. In the present study, only 1 episode of leakage was observed throughout all applications. Furthermore, reducing the risk of leakage or blockage not only avoids delays in therapy but also minimizes the need for constant monitoring  and lowers the treatment costs incurred by the patient, as leakages often require replacement with a new NPWTi-d dressing.

Challenges of the waterfall technique
Although the method is relatively uncomplicated, the additional steps required in the waterfall technique may be challenging to clinicians who first adopt this application technique. This method requires the clinician to join 2 separate pieces of NPWTi-d foam using the drape provided in the dressing kit. Of note, a common site of leakage is at the joint of the extension; hence, particular attention should be paid to application of the drape across this joint. Although this study did not compare the time required to apply the waterfall technique against conventional methods, the authors' anecdotal experience suggests that it should not exceed 10 additional minutes.

Wound healing and limb salvage rates
In terms of wound healing outcomes, results from this study are promising. None of the wounds required a repeated surgical debridement or a further amputation during the first period of admission. Only 1 patient (case 2) was re-admitted for surgical debridement following a secondary wound infection after discharge.

As shown in Figure 3, the amount of granulation tissue increased over time, while the amount of nonviable tissue gradually decreased. This suggests that the waterfall technique was effective in overcoming the challenge of ensuring a homogenous distribution of cleansing solution across the wound bed. All wounds became fully granulating and went on to full epithelialization.

It is of interest to note that various surgeons offered one patient (case 8), who had left cuboid and metatarsal base osteomyelitis, below-knee amputation as the definitive treatment. The waterfall technique allowed for an effective irrigation of the wound that augmented the effectiveness of surgical wound debridement and systemic antibiotics, resulting in eventual limb salvage. This highlights the potential of NPWTi-d in reducing bioburden and controlling infections when used with antimicrobial solutions, as long as the cleansing solution adequately covers the entire wound bed during instillation

The number of patients (9) included in this case series was small; as such, the findings may not be generalizable. Also, this is a descriptive study without a comparison group. Hence, further studies with a larger cohort or randomized controlled trials will be required to evaluate the study technique.

The waterfall technique is a modification of the usual bridging technique that can be adapted to any wound location on the foot. This novel application technique ensures the placement of the pad in a dependent position and utilizes gravity to aid in the flow of irrigation fluid to fill the foam efficiently. This minimizes the risk of leakage and/or blockage when employing NPWTi-d in the treatment of postsurgical diabetic foot wounds.

Authors: Kimberley Leow, BSc(Podiatry)¹; Jackie Tey, BSc(Podiatry)¹; Aprine Tan, MBBS, MRCS, MSc²; Kimberly Tan, BSc(Podiatry)¹; and Keng Lin Wong, MCI, FRCS (Orth), FAMS (Ortho)^2,3,4

Affiliations: ¹Department of Podiatry, Sengkang General Hospital, Sengkang, Singapore; ²Department of Orthopaedic Surgery, Sengkang General Hospital; ³Department of Orthopaedic Surgery, Yong Loo Lin School of Medicine, National University of Singapore, Kent Ridge, Singapore; ⁴Musculoskeletal Sciences Academic Clinical Programme, Duke-NUS Medical School, Singapore

Correspondence: Jackie Tey, Bsc(Hons), Sengkang General Hospital, Podiatry, 110 Sengkang East Way, Singapore, Singapore 544886; jackietey1991@gmail.com

Disclosure: Keng Lim Wong receives honorarium as a speaker for 3M-KCI MEDICAL ASIA PTE LTD. The rest of the authors disclose no financial or other conflicts of interest.