ABSTRACT
Topical Negative Pressure (TNP) has become an accepted intervention in wound healing with a growing body of scientific literature supporting the effectiveness of TNP across a wide variety of wound aetiologies. The range of TNP devices has also increased with perhaps the primary distinction being between those TNP devices that employ gauze or foam as a wound dressing. This study reports preliminary multi‐centre observations upon the use of a new gauze based TNP device in the treatment of wounds. Across 3 study centres twenty‐nine subjects were recruited to the study with 8 presenting with leg ulcers, 8 with pressure ulcers, 12 with acute or surgical wounds and 1 with a non‐healing burn injury. Wounds were then treated with the new TNP therapy for a maximum of 17 days (range 2–17 days). There appeared to be a trend for subjects with leg ulcers to be treated for longer (mean duration 12.9 days) compared to subjects with pressure ulcers (mean duration 6.5 days) or those with surgical wounds (mean duration 8.2 days). Given the relatively short duration of the TNP therapy no wound completely healed although 22/29 (75.9%) showed reductions in surface area per day of treatment with all but 1 pressure ulcer and 1 leg ulcer responding positively to treatment. While not an RCT, this and similar cohort studies may be central to the future selection of TNP devices given the increasing importance of the role of the user interface to reduce the likelihood of incorrect use and sub‐optimal outcomes.
Keywords: Topical negative pressure, TNP, Negative pressure wound therapy, NPWT, Wound management
INTRODUCTION
In an ideal world no intervention aimed at wound prevention or healing would be used until there was compelling evidence from a synthesis of robust randomised controlled trials (RCTs). However, there are multiple reasons why this ideal scenario is completely unrealistic—the complexity of controlled trials in wound healing is well recognised (1). There are many reasons for this, for example the rate of recruitment can be slow given the strict inclusion criteria, while exclusion criteria often serve to reject those patients for whom the treatment is, in practice, intended; such as those with chronic wounds and complex comorbidities. The challenges inherent in blinding staff, researchers and patients to the use of visible interventions such as beds and wound dressings are also very evident. In consequence, even where RCTs are available in wound healing, they are typically seen as being methodologically weak [e.g. (2)] with wound interventions rarely compared in sufficient numbers to facilitate synthesis across studies.
One exception to this general rule is the case of Topical Negative Pressure (TNP) also known as negative pressure wound therapy (NPWT). By October 2005, there were 36 RCTs or non randomised controlled studies available that explored the use of TNP in a variety of wound healing scenarios (3). While the quality of these older studies was reported to be poor (with eight either terminated prematurely or completed but not published), the trends consistently indicate that application of TNP therapy may improve wound healing with more recent investigations demonstrating both the clinical and economic benefits of TNP therapy. For example, (4) among 162 diabetic patients who experienced up to trans‐metatarsal amputations the average cost to heal these postamputation wounds using TNP therapy was $25 954, while the average cost to achieve healing using moist wound healing was $38 806. Given these broadly positive interpretations from the available data regarding efficacy, along with the specific challenges of conducting wound healing controlled trials, it is perhaps timely to consider different research designs. An open‐label case series is one approach which enables researchers to investigate aspects which, although highly relevant to patient outcomes, are typically under‐reported; such as the ease by which a device can be utilised in a less controlled naturalistic setting and the acceptability of the therapy from the patients’ perspective. These factors prevail outside the confines of a formal research protocol and, even when efficacy is a given, these more practical considerations may, in themselves, limit the clinical benefits to be gained through use of the intervention.
For example, the outcome may be influenced through the clinician knowing how to set up the device properly, use and troubleshoot the device during use as well as knowing the correct application for the type of wound. It is logical therefore to predict that the outcomes of a therapy such as TNP therapy are more likely to deviate from the optimum as the device becomes more complex to use, requires a greater level of training or is available in a number of different variants, which need to be changed depending on the clinical setting, for example on discharge from hospital. Typically these issues become apparent through the experience of early adopters of the new intervention. However, the present study is unusual in that it was designed to identify these issues prior to full commercial availability within a multi‐centre, open‐label, clinical outcome investigation (5) undertaken with four primary objectives:
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a)
To assess how easy the device was to use across three acute care hospitals with very different experiences of TNP therapy.
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b)
To gather patient and clinician user satisfaction.
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c)
To allow clinician input to the final presentation of the device user interface, the dressing pack components and all user information/training packs (this practical objective is not addressed in this report).
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d)
To report clinical outcomes in patients with a range of complex and chronic wounds.
METHODS
This multi‐centre, open‐label, non‐comparative prospective, convenience sample study was undertaken across three acute care centres in Poland. Centre A, a tertiary referral centre for burns and plastic surgery within a 1100‐bed military hospital, was considered to have wide experience using TNP in wound healing and the principal investigator (WW) was based at this site. Centres B (600 beds) and C (700 beds), both regional specialist hospitals, had less experience with TNP; site B tended to use this intervention only in the healing of their perceived most difficult wounds (and even in these cases for short periods only because of cost restrictions) while centre C was aware of TNP but had no experience of using this intervention. All centres identified clinicians who would both recruit subjects and take responsibility for their treatment with TNP. All site investigators were trained in the use of the new TNP device (Figure 1) along with appropriate training in the collection of the required outcome data. Once the data collection commenced no interaction was had with the supplier of the device.
Figure 1.
The WoundASSIST ® TNP therapy system consists of an intuitive portable console, a semi‐opaque canister for the collection of wound exudate and a range of comprehensive wound packs. Both the console and disposables have been designed for use in a variety of care environments from hospital to community care.
The TNP device used in this study (WoundASSIST ® TNP Therapy System, Arjo‐Huntleigh, UK * ) comprised of three principle components: a therapy console, a semi‐opaque disposable canister for the collection of wound exudate and a gauze‐based wound dressing. The therapy console is compact (200mm × 230mm × 100mm ) and lightweight (1· 4 kg) and has been designed to provide both continuous and intermittent suction upon the wound bed at a default setting of −75 mmHg (operating range of −25 mmHg to −200 mmHg). Intuitive touch screen technology and a comprehensive ‘help’ screen function provide a user friendly system, that is both easy to learn and easy for clinicians to use across all health care settings. There was a 500‐ml semi‐opaque canister attached to the console that collected the wound exudate and facilitated visual inspection.
Dressing components were based upon the technique as described by Chariker and Jeter (6) and consisted of a non adherent wound liner, an antimicrobial gauze, a perforated flexible silicon wound drain and a transparent, semi‐permeable, adhesive film dressing.
Participants were considered for inclusion if they presented with acute, sub‐acute or chronic wounds where either healing might be expected or it was considered by the clinicians to be either problematic or slow if standard wound management techniques were used. To gain experience of use of the new TNP device across a range of wound aetiologies, the study planned to stratify data collection recruiting subject's with four different wound types:
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Pressure ulcers on different anatomical locations
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Venous or mixed aetiology leg ulcers
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Acute surgical or traumatic wounds
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Shallow but highly exuding wounds such as burns, graft sites
Other inclusion criteria included being 18 years or older, with a wound with a surface area of under 100 cm2, able to understand the purpose of the evaluation and was willing and able to give informed written consent.
Potential subjects were excluded where the target wound was greater than 100 cm2, where the wound presented covered with non viable eschar, the patient had untreated osteomyelitis, malignancy (excluding terminally ill patients where TNP might benefit quality of life issues), where the wound exposed arteries, veins or internal organs and finally patients with coagulopathies were excluded in line with the contraindications to the therapy. The study was approved for all three sites by the ethical committee for the lead site.
As a primary objective of this exploratory study was to gather patient opinion upon the new TNP device, subjects were requested to comment upon their comfort during TNP therapy and any pain during dressing changes. Comfort was rated from 1 ‘very comfortable’ to 4 ‘very uncomfortable’, while pain was rated from ‘completely painless’ (rated as 1) to ‘very painful’ (rated as 3). Finally, the subjects were asked to comment whether the size of the TNP console unit was compact enough to facilitate movement and also whether the sound made by the console disturbed them during treatment.
The clinicians were asked whether their clinical objectives for each subject were met, whether they encountered difficulty with the device or dressing and whether they would use the new TNP system again in their clinical practice.
Considering the wound outcomes, data was gathered upon patient age, gender, wound aetiology and anatomical location of the treated wound. The wound was photographed and the surface area of each wound was measured at the start, then at least weekly until the end of their participation in the study using Visitrak (Smith & Nephew Healthcare, Hull UK).
Visual inspection of the wound surface was undertaken at the beginning, at each dressing change and at the end of each patient's treatment with the new TNP device and recorded presence and consistency of any exudate, presence of odour, and obvious infection along with the proportion of the wound bed covered with granulation, epithelial tissue or non viable tissue such as slough. Obvious wound odour was also recorded. Each of these visual and olfactory inspections was repeated at dressing changes and at the end of each patient's treatment with the TNP device. Finally, the number of days the wound was treated with the TNP therapy was recorded along with the reason for discontinuation of the therapy.
RESULTS
Between April 2007 and August 2007, 29 subjects were recruited to the study. Of these, 12 (41· 4%) were recruited from centre A with 7 (24· 1%) and 10 (34· 5%) recruited from centres B and C, respectively. Subjects ranged in age from 18 to 79 years [mean (SD) age 55· 0±18· 0 years] with 19 (65· 5%) of the subjects being male.
Eight subjects presented with leg ulcers (venous or mixed aetiology), 8 with pressure ulcers, 12 with acute surgical or traumatic wounds and 1 with a shallow highly exuding wound (chronic non healing burn injury) (Table 1). Regardless of wound aetiology, TNP therapy was predominantly considered for use given the clinicians’ opinion that the wound was not progressing with its current therapy (n = 25/29; 86· 2%). The final four wounds were treated with the new TNP device primarily to prepare for future surgery (n = 1) traumatic wound or for surgical grafting (two pressure ulcers, one surgical wound).
Table 1.
Wound aetiology and baseline characteristics prior to treatment with a new Topical Negative Pressure (TNP) device
| Wound aetiology | ||||
|---|---|---|---|---|
| Leg ulcer(n = 8) | Pressure ulcer(n = 8) | Surgical or traumatic traumatic wound (n = 12) | Shallow highly exuding wound(n = 1) | |
| Centre A:B:C | 0:1:7 | 6:2:0 | 5:4:3 | 1:0:0 |
| Age (years), mean (SD); range | 71· 5 (8· 7); 56–79 | 46· 5 (17· 7); 23–72 | 50· 7 (18· 5); 18–79 | 47 |
| Gender M:F | 4:4 | 6:2 | 9:3 | 0:1 |
| Surface area (cm2) at baseline, mean (SD) range | 29· 86 (20· 32); 12· 8–71· 9 | 26· 09 (15· 77); 6· 6–56· 4 | 29· 91 (27· 31); 1· 9–76· 6 | 69· 0 |
| Exudate | Moderate 4, mild 4 | Heavy 6, mild 2 | Heavy 6, moderate 6 | Moderate |
| Composition of exudate | Seropurulent 1 | Purulent 4 | Purulent 7 | Seropurulent |
| Serous fluid 7 | Seropurulent 3 | Seropurulent 3 | ||
| Serous fluid 1 | Serous fluid 2 | |||
| Odour (Y:N) | 1:7 | 4:4 | 5:7 | 1:0 |
| Infection (Y:N) | 4:4 | 6:2 | 10:2 | 1:0 |
| Granulation tissue [% of wound base; mean (SD)] | 69· 4 (10· 1) | 41· 9 (39· 4) | 50· 2 (32· 2) | 20 |
| Epithelial tissue (%) | 8· 1 (7· 9) | 3· 7 (10· 6) | 3· 7 (8· 8) | 0 |
| Non viable tissue (%) | 3· 1 (2· 6) | 7· 3 (8· 2) | 5· 8 (6· 7) | 20 |
| Slough (%) | 16· 9 (9· 6) | 15· 4 (12· 1) | 23· 9 (21· 1) | 30 |
Wound dressings, in all except four cases, took less than 30 minutes to complete and were changed on average every 3· 5 days. The console was most commonly set to continuous mode (27/29) at −75 mmHg pressure. The second most common (n = 7) negative pressure setting was −125 mmHg (based on the clinician's past experience) with the remaining wounds treated at variable pressure ranging from −75 mmHg to −150 mmHg.
Considering subject and clinician response to the new TNP device, all wounds have been grouped together with the majority of subjects reporting therapy to be either very comfortable (n = 12) or comfortable (n = 13). Four patients reported some discomfort; two with leg ulcers, one with a pressure ulcer and one surgical wound. All subjects reported dressing changes to be either painless (n = 13) or tolerable (n = 16). Where subjects reported the therapy to be uncomfortable (n = 4), there appeared to be no clear association between their discomfort and pain at dressing change with two reporting painless dressing changes and two noting tolerable pain at dressing change. Twenty‐six (89· 7%) subjects considered the TNP console to be reasonably compact and, as such, it did not impede their activity; the views of the final three subjects were unreported. Most (n = 21; 72· 4%) were aware of sound from the console during therapy from the TNP console but this noise did not concern them, while five found the noise to be distracting. In each case, the clinicians reported they would be willing to use the new TNP device in the treatment of similar wounds in the future.
Table 1 highlights the baseline characteristics of the 29 wounds treated in this study by wound aetiology. Given the exploratory nature of this uncontrolled study, no inferential statistical tests have been performed with apparent trends within the data reported. Subjects with leg ulcers tended to be older than the other subjects recruited and to have been treated within centre C where no prior experience of TNP existed. In contrast, subjects with pressure ulcers were mainly drawn from centre A where TNP therapy had previously been routinely used. Leg ulcer subjects also showed an equal distribution between genders whereas male subjects were more common among the pressure ulcer and surgical groups. Excluding the single shallow exuding wound, the mean surface area of the leg ulcers, pressure ulcers and surgical wounds recruited to this study were similar with all wounds producing at least mild exudate. Relatively more pressure ulcers and surgical wounds were infected compared to the cohort of leg ulcers with higher percentages of epithelial and granulation tissue seen in the leg ulcers at baseline.
Wounds were then treated with the new TNP therapy for a maximum of 17 days (range 2–17 days). There appeared to be a trend for subjects with leg ulcers to be treated for longer (mean duration 12· 9 days) compared to subjects with pressure ulcers (mean duration 6· 5 days) or those with surgical wounds (mean duration 8· 2 days). Given the relatively short duration of the TNP therapy no wound completely healed although 22/29 (75· 9%) showed reductions in surface area per day of treatment (Table 2) with all but one pressure ulcer and one leg ulcer responding positively to treatment. Where wounds were reported to increase in size the rate of change per day of treatment was under 1 cm2 (except in the single case of the single shallow exuding burn wound) and these apparent increases may simply reflect the challenge of measuring wound size accurately. The changes in surface area were mirrored by visible changes in the appearance of the wound bed with all but one surgical wound (remained unchanged) showing visible improvement during the course of therapy. These visible improvements resulted in an increase in both granulation and epithelial tissue and a decrease in non viable tissue or slough within the wound bed. For example, the treated pressure ulcers presented with a mean cover of 41· 9% granulation tissue and 3· 7% epithelial tissue at baseline rising to 64· 2% and 7· 7%, respectively, at the end of treatment. A reciprocal trend was seen, with the mean quantity of non viable tissue falling from 7· 3% to 0· 6% and slough falling from 15· 4% to 5· 1%. Wound improvement after therapy was also seen in the proportion of wounds visibly infected and where obvious odour was present. At baseline 21/29 wounds were considered infected this fell to 15 following treatment with a similar decline in the number of wounds with obvious odour −11 at baseline and 8 following therapy with the new TNP device.
Table 2.
Wound aetiology and characteristics after treatment with a new Topical Negative Pressure (TNP) device
| Wound aetiology | ||||
|---|---|---|---|---|
| Leg ulcer(n = 8) | Pressure ulcer(n = 8) | Surgical or traumatic wound (n = 12) | Shallow highly exuding wound (n = 1) | |
| Number of days treatment [mean (SD); range] | 12· 9 (2· 3); 11–17 | 6· 5 (4· 7); 2–14 | 7· 7 (5· 1); 2–16 | 5 |
| Reason for termination of therapy | Partial closure 5 | Partial closure 5 | Partial closure 8 | Partial closure |
| Drainage reduced 2 | Discharge 2 | Drainage reduced 1 | ||
| Other 1 | Subject request 1 | Discharge/transfer 2 | ||
| Other 1 | ||||
| Surface area (cm2) at end, mean (SD) range | 23· 11 (17· 95); 8· 2–62· 2 | 18· 29 (11· 71); 3· 3–42· 0 | 22· 01 (19· 34); 0· 7–51· 1 | 87· 7 |
| Exudate | Mild 8 | Mild 4 | None 1 | Mild |
| Moderate 3 | Mild 5 | |||
| Heavy 1 | Moderate 6 | |||
| Composition of exudate | Serous fluid 7 | Purulent 2 | Purulent 2 | Seropurulent |
| Clear 1 | Seropurulent 5 | Seropurulent 4 | ||
| Serous fluid 1 | Serous fluid 4 | |||
| Clear 1 | ||||
| None 1 | ||||
| Odour (Y:N) | 0:8 | 4:4 | 3:9 | 1:0 |
| Infection (Y:N) | 2:6 | 5:3 | 7:5 | 1:0 |
| Granulation tissue [% of wound base; mean (SD)] | 52· 5 (22· 4) | 64· 2 (33· 9) | 73· 5 (19· 4) | 80 |
| Epithelial tissue (%) | 29· 4 (12· 7) | 7· 7 (14· 4) | 12· 1 (16· 2) | 0 |
| Non viable tissue (%) | 0 | 0· 6 (1· 8) | 1· 7 (2· 5) | 5 |
| Slough (%) | 0 | 5· 1 (7· 5) | 7· 2 (5· 5) | 10 |
| Improvement in wound bed (Y:N) | 8:0 | 8:0 | 11:1 | 1:0 |
| Wounds reduced in surface area (Y:N) | 7:1 | 7:1 | 8:4 | 0:1 |
| Surface area reduction per day (cm2); range (negative values denote wounds becoming smaller) | –1· 67 to +0· 27 | −7· 2 to +0· 2 | −15· 3 to +0· 83 | 3· 74 |
DISCUSSION
This uncontrolled cohort study aimed to recruit a mixture of patients with pressure ulcers, leg ulcers, surgical or traumatic wounds and a final cohort with shallow highly exuding wounds. Given that the information gathered was intended to further guide the final adjustments to the utility of this new TNP device, data collection was scheduled to terminate prior to the commercial availability of the product. At this point, 29 subjects had been recruited and included 12 surgical or traumatic wounds, 8 pressure ulcers and 8 leg ulcers. The final cohort (shallow highly exuding wounds) was represented by a single subject suggests that, at least across the three data collection centres included in this study, recruitment of shallow but highly exuding wounds may be slower than would be inclusion of patients with other forms of chronic or acute wound. Given the exploratory nature of this study no inferential statistics were performed and all trends observed within the data can only be assessed descriptively. Considering patient and clinician opinion of the new TNP device, views were almost universally positive with the device being seen as quiet, compact with a high level of patient acceptability and, in most cases, painless dressing changes. As a result of this study, further adjustments were made to the sound emitted from the console to further reduce impact on the small group of subjects who had been disturbed by the device. There did not appear to be any significant problems associated with the use of the new TNP device.
In this simple study therapy durations were relatively short, ranging from 2 to 17 days and given the treatment objectives, such as pre‐surgery wound bed preparation, wound closure was not expected in many cases. Despite this, wounds showed consistent reductions in surface area in addition to other improvements; such as reduced exudate and exudate management, less infection, less odour and an overall improvement in the conditions within the wound bed and wound margin. These findings would appear to be consistent with other studies that have reported wound outcomes following use of TNP [e.g. (7)]. While the conclusions of uncontrolled studies can be challenging to interpret (8) and may mask a placebo effect, the results of this exploratory study indicate that the new TNP device was acceptable to clinicians and patients and appeared to offer clinical benefits similar to those reported previously after use of TNP.
One observation deserving of closer follow‐up in a controlled study was that the positive clinical benefits seen in this study appeared to be unrelated to each data collection centre's prior experience of TNP—leg ulcers were mainly recruited from a centre with no prior experience of TNP, however, signs of wound healing were observed within this cohort suggesting that the new TNP device and the gauze‐based wound dressing were reasonably easy to use given clinician inexperience with the technique.
While the available efficacy studies may be methodologically weak and the economic studies limited, the trends such as those reported here support the assertion that using TNP to heal complex or problematic wounds may be associated with better outcomes and potentially lower health care costs. Studies such as these provide valuable data for clinicians who search for solutions based upon evidence. However, it is generally recognised that studies of healing in complex wounds can be logistically challenging with multiple comorbidities and the ethical issues that surround often very ill patient recruitment and retention in a controlled study limiting recruitment and the homogeneity of the subject population. These issues can be managed, to an extent, through appropriately sized multi‐centre studies and it may be that future studies of TNP therapy will require many more than three centres to achieve realistic recruitment rates.
As for all wound care applications there is a clear need for careful evaluation of the wide range of new TNP devices, often based upon gauze rather than foam within the wound cavity. Such evaluations should ideally conform to current ‘gold standards’ in the design, execution and reporting of RCTs and need to be adequately powered to detect differences should they exist between the efficacy of new TNP devices and the pre‐existing foam‐ based TNP device. It may be that such trials will be demanding in terms of the numbers of patients requiring to be recruited leading to multi‐centre, probably multi‐national studies. Such trials may be prohibitively expensive and alternative investigations may be required that rigorously address operational ease‐of‐use of the device among cohorts of new and experienced TNP users. While not an RCT, this and similar cohort studies may be central to the future selection of TNP devices given the increasing importance of the role of the user interface to reduce the likelihood of incorrect use and sub‐optimal outcomes.
Footnotes
WoundASSIST ® is a trademark of Huntleigh Technology Ltd. ArjoHuntleigh is a UK registered branch of Arjo Ltd Med AB.
REFERENCES
- 1. Clark M. Can we evaluate the effectiveness of pressure sore treatment without randomized controlled trials? In: Leaper DL, Cherry GW, Dealey C, Lawrence JC, Turner TD, editors. Proceedings of the 6th European conference on advances in wound management. London: Macmillan Magazines Ltd, 1996;124–126. [Google Scholar]
- 2. Ubbink DT, Westerbos SJ, Evans D, Land L, Vermeulen H. Topical negative pressure for treating chronic wounds. Cochrane Database Syst Rev 2001;(1):CD001898. DOI: 10.1002/14651858. CD001898. [DOI] [PubMed] [Google Scholar]
- 3. Gregor S, Maegele M, Sauerland S, Krahn JF, Peinemann F, Lange S. Negative pressure wound therapy. A vacuum of evidence? Arch Surg 2008;143(2):189–196. [DOI] [PubMed] [Google Scholar]
- 4. Apelqvist J, Armstrong DG, Lavery LA, Boulton AJM. Resource utilization and economic costs of care based on a randomized trial of vacuum‐assisted closure therapy in the treatment of diabetic foot wounds. Am J Surg 2008;195(6):782–8. [DOI] [PubMed] [Google Scholar]
- 5. Witkowski W. A prospective clinical evaluation of a topical negative pressure (TNP) wound therapy system in the management and resolution of complex wounds. 18th Conference of the European Wound Management Association (EWMA), Lisbon, Portugal, 14‐16th May 2008;[EWMA Journal Suppl2008;8(2):47].
- 6. Chariker ME, Jeter KF, Tintle TE. Effective management of incisional and cutaneous fistulae with closed suction wound drainage. Contemp Surg 1989;34: 59–63. [Google Scholar]
- 7. Mendonca D, Papini R, Price PE. Negative‐pressure wound therapy: a snapshot of the evidence. Int Wound J 2006;3: 261–271. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 8. Fernie GR, Dornan J. The problem with clinical trials with new systems for preventing or healing decubiti. In: Kenedi RM, Cowden JM, Scales JT, editors. Bedsore biomechanics. London: Macmillan Press, 1976. [Google Scholar]