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. 2019 Mar 21;16(4):891–896. doi: 10.1111/iwj.13114

The smart negative pressure (SNaP) wound care system: A case series from Singapore

Ian J Y Wee 1, Manfred Mak 2, Gavin O'Donnell 2, Jerilyn Tan 2, Tze T Chong 3, Tjun Y Tang 3,✉
PMCID: PMC7948783  PMID: 30900370

Abstract

The Smart Negative Pressure (SNaP) wound care system is a novel device that is single‐patient use, ultra‐portable, and light weight and does not rely on battery or need recharging. A systematic search was performed on major databases to identify relevant articles including case reports, retrospective case series, and randomised controlled trials. Ten studies were identified, showing that the SNaP wound care system is an effective tool in treating small‐sized wounds and may serve as an alternative to current electrically powered modalities. Furthermore, the system's small size and convenience leads to greater patient satisfaction and improves quality of life. Finally, we report our initial positive experiences with two cases in our institution. Although the evidence thus far has been encouraging, and patient satisfaction is higher than other wound care systems, further evidence is required to determine its superiority over current systems in terms of wound‐healing outcomes.

Keywords: outcome, SNaP, vacuum‐assisted closure, wound

Key Messages.

  • the Smart Negative Pressure (SNaP) wound care system is a novel device that is single‐patient use, ultra-portable, and light weight and does not rely on battery or need recharging

  • the aim of the paper was to provide an appraisal of the current literature and report our initial positive experience with two cases in our institution

  • the SNaP wound care system is effective in treating smallsized wounds but not larger‐sized wounds; the system's small size and convenience brings greater patient satisfaction and improves quality of life

1. INTRODUCTION

Acute and chronic wounds continue to pose major public health problems globally, with a prevalence rate of about 2 per 1000 population.1, 2 Negative pressure wound therapy (NPWT) has traditionally been the cornerstone of treatment for wounds to be closed by secondary intention, with evidence demonstrating shorter healing time and improved granulation tissue formation.3, 4, 5 However, current systems, such as the KCI wound V.A.C system (KCI Licensing, Inc., San Antonio, Texas) and the Smith & Nephew RENASYS device (Smith & Nephew, Inc., St. Petersburg, Florida), do have their shortcomings. They are less suitable for smaller wounds, can be heavy and bulky, require longer dressing placement duration, electrical charging, and are mostly accessible only during inpatient hospitalisation.6

The Smart Negative Pressure (SNaP) wound care system (Spiracur, Inc., Sunnyvale, California) was later developed to address this unmet need. Some of its key novel features include its single use, ultra‐portability, light weight, and mechanically powered operation. Furthermore, it is fully disposable and silent throughout its use. As opposed to NPWT, it is also available “off‐the‐shelf,” averting the need for time‐consuming and costly rental procurements.

The SNaP system includes a 60 or 150 mL cartridge containing fluid that facilitates the removal of infectious materials from the wound bed. This is accompanied by the BIOLOCK technology that gels the exudate for improved containment, a one‐way valve to prevent exudate back‐flow into the wound, and a primary foam dressing that enables exudate removal and equal distribution of negative pressure at the wound site. In addition, the use of hydrocolloid paste can ensure adequate sealing on uneven surfaces and challenging anatomies, completing the cut‐to‐fit dressing (Figure 1).

Figure 1.

Figure 1

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Smart negative pressure (SNaP) wound care system components

Initial biochemical testing in animal wound healing models has reported similar characteristics between the SNaP system and the V.A.C system.7 These encouraging results have prompted the initiation of clinical studies examining this comparison. Preliminary data have now emerged from both randomised controlled trials (RCTs)8, 9 and retrospective studies,10, 11, 12 albeit with mixed conclusions, and predominantly from Western populations. Singapore General Hospital is the first hospital in Singapore to have gained access to this device.

The aims of this study are to evaluate the assemblage of literature assessing the efficacy of the SNaP wound care system and to describe our initial experience with this novel system in three cases.

2. METHODS

A systematic search was performed on Medline, EMBASE, and the Cochrane Library to identify relevant articles evaluating the use of the SNaP wound care system in patients with acute or chronic wounds. Animal and in‐vivo studies, as well as review articles, were excluded. A manual search was also performed on the reference lists of these studies to identify additional articles. The following search terms were used and combined using Boolean operators: (smart negative pressure wound care system OR SnAP system OR mechanically powered negative pressure wound device).

3. RESULTS

3.1. Literature review

Various randomised trials have been conducted to investigate the safety and efficacy of the SNaP system. The largest trial to date was reported by Armstrong et al, who randomised 115 patients to either V.A.C (n = 56) or SNaP (n = 59) therapies. Baseline characteristics were similar between both groups, except for the significantly larger wound size in the V.A.C group (9.95 ± 11.38 cm versus 5.37 ± 6.14 cm, P = 0.0093). Nevertheless, the authors demonstrated no significant differences in their primary endpoint of percentage decrease in wound area, when measured at 4, 8, 12, and 16 weeks. A corroborative trend was observed in the proportion of wounds healed, which were similar in both groups when measured at 0 to 4, 4 to 8, 8 to 12, and 12 to 16 weeks (P = 0.962). The risk of adverse events, including infection, maceration, allergic reaction, pain, and blistering, were again comparable between both groups. However, patients in the SNaP group reported greater satisfaction and better overall quality of life compared with the V.A.C group, which could in part be because of the shorter dressing application time and original size of the wound.8

A differing conclusion was, however, reported by Marston et al in the latest RCT to date. The authors recruited 40 patients with venous leg ulcers, who were either treated with the SNaP (n = 19) or V.A.C system (n = 21). Similar to Armstrong's RCT, the initial wound size was smaller in the SNaP group compared with the V.A.C group (4.85 ± 4.49 cm2 versus 11.60 ± 12.12 cm2. Despite the trend towards improved wound closure in the SNaP group, this was not significant (P = 0.47 after adjustment for baseline wound size). However, the SNaP group was 3.5 times more likely to have achieved the surrogate endpoint of 50% wound closure at 30 days compared with the V.A.C group (odds ratio [OR] 3.560, 95% CI 0.923‐13.699). When the analysis was extended to 90 days, the proportion of subjects in the SNaP group who achieved wound healing was 57.9% compared with 38.2% in the V.A.C group (OR 2.230, 95% CI 0.630‐7.930). Furthermore, the SNaP group showed a significantly greater percentage wound closure than the V.A.C group at 4, 8, 12, and 16 weeks (P‐value = 0.0039, 0.0086, 0.0002, and 0.0005, respectively). Although the rates of adverse events were comparable between both groups, there were trends towards reduced risks of allergic reaction, pain, and wound infection in the SNaP group, which is likely a result of the protective effect of hydrocolloid dressing.9

Aside from RCTs, the first comparative cohort study was published by Lerman et al, who examined 63 patients with difficult‐to‐treat lower extremity ulcers, of which 21 were treated with the SNaP system and 42 treated with modern wound care protocols comprising of Apligraf, Regranex, and skin grafting. The SNaP‐treated group yielded a 100% improvement in wound size, with 86% of subjects achieving a statistically significant healing trend. In contrast to the control group, Kaplan–Meier estimates showed that the SNaP group demonstrated a shorter healing duration time (mean 74.25 ± 20.1 days versus 148.73 ± 63.1 days, P < 0.0001), which also represents a 50% reduction in absolute healing time with the SNaP system. However, a notable 25% of subjects in the SNaP group experienced complications that resulted in treatment discontinuation. It was unclear what the specific complications were and whether they were directly related to the SNaP system.11

Huttons et al compared the SNaP system with modern dressings and NPWT in their retrospective analysis. They demonstrated that the SNaP system was superior to modern dressings but equivalent to NPWT in terms of wound‐healing rate (83.1% versus 35.7% versus 83.1% respectively), rate of amputations (3.7% versus 10.4% versus 3.7% respectively), and wound debridement (28.6% versus 44.7% versus 28.6% respectively).13 However, the study was lacking in detail regarding patient characteristics and complication rates.

An observational study conducted more recently, in 2015, by Bradbury et al examined 38 patients with venous (n = 15) and mixed aetiology leg ulcers (n = 13) and neuropathic ulcers (n = 9) who received SNaP therapy. However, four patients dropped out during treatment because of various reasons (one withdrew of their own accord; two were withdrawn by clinician because of referral to vascular surgery and maceration; one withdrew because of dressing allergy). Based on the intention‐to‐treat analysis, 37 were eventually included in the final analysis at 6 weeks of follow up. The mean decrease in wound area overall was 42.64%, with the largest decrease seen in patients with venous ulcers (63.75%) compared with those with mixed aetiology (9.60%) or neuropathic foot ulcers (55.14%). The neuropathic foot ulcer subgroup demonstrated the biggest mean percentage increase in granulation tissue, and the majority of subjects experienced either decreased or unchanged exudate levels after treatment. A substantial 15 patients experienced wound infection and underwent treatment suspension until the infection resolved. However, 46% of patients reported an improvement in the overall quality of life, and indicated that the SNaP system was user‐friendly and less burdensome than conventional NPWT.12

Encouraging results of the SNaP system have been reported in individual case studies by various authors. Awad et al reported a case of a type 2 diabetic male who developed an ulcer on the lateral border of the left foot. There was significant wound size reduction both during and after treatment with the SNaP system, and the wound eventually attained full closure. The patient further reported greater satisfaction with the device compared with prior NPWT systems.14 The same authors also reported a different case of a patient with a dehisced surgical breast wound, who was treated with the SNaP system for 6 weeks. The wound depth decreased substantially from 6 cm to less than 1.5 cm after treatment.15 Neiderer et al reported encouraging results of the SNaP system in an elderly male with a large venous leg ulcer after prior failure of treatment from prednisone and topical application of tacrolimus. After 12 weeks of treatment, the wound size decreased by over 50% and was completely epithelised by 16 weeks after the application of both APLIGRAF and the SNaP system.16

One of the earlier case series was conducted by Fong et al, who treated 12 consecutive patients with chronic neuropathic wounds and venous stasis ulcers with the SNaP system. The wound healing rate at 4 weeks was 41.7%. Of the subjects, 25% complained of mild or moderate pain; however, there were no direct severe adverse events.10

A similar observation was noted in another case series by Lerman et al, who described four patients with diabetic lower‐extremity wounds receiving therapy with the device. All patients attained complete wound closure after 4 to 8 weeks of treatment after application, with no reported adverse events.17

3.2. Case series

Here, we present two cases of patients who have undergone wound therapy with the SNaP system at our local institution for diabetic foot wounds and ulcers.

3.2.1. Case 1

This case was a 54‐year‐old male with a past medical history of type 2 diabetes mellitus, an episode of embolic stroke, heparin‐induced thrombocytopenia, chronic obstructive pulmonary disease, and abdominal aortic aneurysm. The patient suffered from an acute left anterior tibial artery (ATA) occlusion and underwent a left ATA embolectomy. This was accompanied by a left dorsalis pedis (DP) artery embolectomy and a short‐segment interposition vein graft. The patient required a limited anterior compartment fasciotomy to relieve compartment syndrome following revascularisation. The SNaP system was applied postoperatively on the left shin wound fasciotomy. The wound showed complete closure by 8 weeks, with no complications.

The patient expressed great satisfaction with the SNaP experience, reporting no pain during application and no interruption in his sleep at night (Figure 2).

Figure 2.

Figure 2

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Case 1: Smart negative pressure (SNaP) wound care system application, with wound status at weeks 3 and 8

3.2.2. Case 2

This case was a 63‐year‐old male with type 2 diabetes mellitus, stage 4 chronic kidney disease, coronary artery disease, peripheral vascular disease, hyperlipidaemia, ischaemic heart disease, and hypertension. He also had a previous left forefoot amputation. He underwent a ray amputation of the right third toe, and the SNaP system was applied 1 week postoperatively for a period of 2 months (Figures 3 and 4). The wound achieved full closure 4 weeks after the end of the application period, with no complications (Figure 5).

Figure 3.

Figure 3

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Case 2: Ray amputation of third right toe

Figure 4.

Figure 4

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Case 2: Smart negative pressure (SNaP) wound care system application after amputation

Figure 5.

Figure 5

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Case 2: Wound status at weeks 3 and 5 after smart negative pressure (SNaP) application

4. DISCUSSION

Our initial experience with the SNaP wound care system has been positive thus far, although it remains premature to establish any superiority over conventional treatment modalities given the lack of head‐to‐head comparative data in our own institution. To date, we have used the SNaP system in six patients, all of whom have reported high satisfaction with the device's convenience. In summary, this system offers a multitude of advantages, including accessibility during both inpatient and outpatient settings, silent use, user‐friendliness, ultra‐portable, light weight, and mechanically powered operations.

The SNaP wound care system may serve as an adjunctive treatment for acute or chronic wounds, improving granulation tissue formation and facilitating exudative management. Furthermore, it may replace traditional foams, gauze, or Gamgee and can be used in conjunction with other dressings, including collagen or silver dressings. Lerman et al, for instance, reported their successful use of the SNaP system for wound preparation prior to Apligraft application.11 However, further work needs conducted to establish if it enhances the use of advanced modalities such as Apligraf. Nevertheless, the SNaP system also provides dressing customisation, with three foam sizes to choose from, trim‐to‐size dressing, and cut‐to‐length tubing. Furthermore, subject to market availability and depending on the indication, various therapy cartridges of different pressure settings and fluid capacities can be used.

SNaP generally should not be placed over a weight‐bearing surface (eg, the plantar surface of the foot) as it may interfere with the patient's gait. In our experience, for ease of application, the practitioner should change to a new pair of gloves after applying the SecurRing to the wound, right before applying the hydrocolloid dressing. This is because the secure ring is very sticky. Hence, by using the same gloves that you used for the secure ring to manoeuvre the hydrocolloid paste onto the wound, it might stick to it and risks having to redo the whole application.

In our practice, we implemented strict patient selection criteria when deciding to use the SNaP system. In terms of disease factors, patients ideally should have adequate vascular supply and shallow cavity wounds of roughly 3 cm in depth, with a relatively clean base. Furthermore, it should be reserved for patients with smaller wound sizes of less than 10 cm by 10 cm and moderate level of exudate of about 80 mL in 3 days. Aside from the limitation of current dressing sizes, larger and deeper wounds may instead be better treated with electrically powered devices that can provide better exudate management.8, 17 Patient education is also crucial to achieving successful outcomes. For instance, they should be encouraged to ambulate during the period of application and be taught how to perform system troubleshooting and self‐monitoring.

Cost is also an important consideration that is currently understudied and should be an outcome of interest in future trials. In the only cost analysis study by Hutton et al, they showed that the SNaP system saves USD $2.8 K for private payers and $2.3 K in Medicare payments per treated wound compared with conventional wound care.13

Nevertheless, the overall quality of the current evidence remains poor, comprising of sporadic case series, retrospective studies, and only two RCTs8, 9, 10, 11, 12, 14, 15, 16, 17 with inconsistent conclusions. Whilst no firm conclusion can be made regarding its superiority over current NPWT systems in terms of wound‐healing outcomes, there are clear benefits from the shorter device application time, improved patient satisfaction, and quality of life.8

5. CONCLUSION

The SNaP wound care system is an effective tool in treating small‐sized wounds and may serve as an alternative to current electrically powered modalities. Furthermore, the system's small size and convenience may heighten its appeal amongst patients and clinicians. However, the paucity of high‐quality evidence precludes a firm recommendation as a first‐line VAC therapy. We recommend that clinicians adopt a judicious approach in selecting the right patients with the appropriate wound type to ensure clinical success.

CONFLICT OF INTERESTS

All authors have no conflict of interest to report.

Wee IJY, Mak M, O'Donnell G, Tan J, Chong TT, Tang TY. The smart negative pressure (SNaP) wound care system: A case series from Singapore. Int Wound J. 2019;16:891–896. 10.1111/iwj.13114

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