Negative pressure wound therapy: manufacturer data provided later allow benefit conclusion

April 08, 2019

Negative pressure wound therapy (NPWT) has been used in hospitals for over 20 years; over 100 studies have been completed. However, conclusions on benefit and harm are in part uncertain because study initiators are withholding results. In the summer of 2018, the proportion of missing data was still so large for the area of application "secondary wound healing" that an assessment was not possible. After the manufacturer KCI (Acelity) eventually provided sufficient information, in its final report the German Institute for Quality and Efficiency in Health Care (IQWiG) now sees an indication of a greater benefit of NPWT compared with standard treatment. Regarding primary wound healing, for which the Institute now presents the preliminary assessment, the results are also in favour of NPWT; however, the differences are markedly smaller. IQWiG sees a hint of an advantage here. Comments on this preliminary report are possible until 29 April 2019.

In general, the Institute still regards the transparency regulations for clinical studies on medical devices to be insufficient and demands that the same requirements should apply that have long been the norm for drugs. Because for NPWT too, not all study results are on the table. Gaps now primarily exist for studies conducted by research institutions themselves.

Negative pressure is supposed to increase circulation

In NPWT, the wound is covered with an airtight bandage to which a pump is attached via a thin tube. This tube constantly sucks out wound fluid from the wound, thus creating negative pressure in the wound area. This is supposed to increase circulation in the wound. In addition, the wound stays wet, which is also supposed to promote healing.

NPWT is, among others, used for poorly healing or large wounds, for example, in patients with a decubitus ulcer (bed sore) or after surgery. In primary wound healing or healing by primary intention, the margins of the wound are aligned and can be sewn together, as is the case, for example, after surgery. In contrast, in secondary wound healing or healing by secondary intention, tissue has to be newly formed and the wound has to contract or skin has to be transplanted.

Data gap reduces certainty of conclusions

In the preliminary report on secondary wound healing published in the summer of 2018, data on more than half of the participants were still missing in the manufacturer-initiated trials. However, with a total of 40% of missing data, a large gap was also noticeable in investigator-initiated trials (IITs), i.e., studies initiated by researchers working at universities, for example. IQWiG had at that time repeatedly requested these data in vain from the responsible researchers.

While the manufacturer KCI subsequently provided a sufficiently large proportion of these data during the commenting procedure, the increase in the data basis was less pronounced for the IITs. An assessment of benefit and harm is now possible. However, as overall 24% of the data are still missing for secondary wound healing and 17% are missing for primary wound healing, IQWiG downgraded the certainty of conclusions of its assessments ("indication" instead of "proof"; "hint" instead of "indication"). This is because missing data can strongly bias the assessment result, meaning that the benefit or harm of an intervention appears to be bigger or smaller. This is referred to as publication bias.

Secondary wound healing: advantage for several outcomes

The final report on secondary wound healing acknowledges advantages of NPWT versus standard treatment that are relevant for patients: the Institute sees an indication of a greater benefit for the outcome of wound closure. The data show that wounds heal more often and the healing process is faster. In addition, the length of hospital stay is shortened.

In contrast, the data show no advantages or disadvantages for the outcomes of mortality, adverse events (side effects of treatment), frequency of amputations, pain, quality of life, and social functioning. No conclusions are possible on the outcomes "need of third-party help" or "need of long-term care", as IQWiG had no access to usable data.

Studies on primary wound healing: focus on risk factors

Usable data were available from a total of 39 randomized controlled trials for the area of application "primary wound healing", i.e., the use of NPWT after surgery. These studies, with a total of 5674 patients, investigated wounds after surgery, primarily after obstetrical, abdominal, vascular and heart surgery, as well as after endoprosthetic surgery (joint replacement). Poor wound healing was to be expected for the vast majority of patients, as they had at least one risk factor such as obesity or diabetes. Wound complications and treatment-related complications (adverse events) were the outcomes most commonly recorded in the studies.

At the same time, adverse events in the form of complications were the only outcome where the data showed at least one advantage: for instance, infections occurred less frequently if NPWT was used. IQWiG sees a "hint" of a greater benefit of NPWT here; this was not the case for any other patient-relevant outcome, including the overall rate of complications (adverse events).

The Institute requests written comments on this preliminary result of the benefit assessment, the preliminary report, by 29 April. These will be scrutinized and, if IQWiG has open questions, discussed in a public hearing with the persons submitting comments.

Medical devices: stricter transparency rules needed

An assessment of NPWT was only possible after the manufacturer KCI provided previously unpublished study results to IQWiG. In contrast, the increase in the data basis was less pronounced for the IITs.

Stefan Sauerland, Head of IQWiG's Non-Drug Interventions Department notes: "The fact that about a quarter of all data are still missing for secondary wound healing can particularly be ascribed to those responsible for IITs; for primary wound healing, nearly a sixth of the data are missing. NPWT again shows that we need to regulate publication obligations for medical devices or non-drug interventions just as strictly as we have done for drugs. For the latter, the data situation has considerably improved in the past 10 years due to various measures, including legal ones. The EU Medical Device Regulation (MDR) is overall a step in the right direction, but unfortunately only a small one with regard to publication obligations. Ethics committees or public funders such as the Ministry of Science could also put pressure on study initiators by linking approvals to publications. I suggest that any study initiator who has not published properly in the past receives no funding or no approval for the next study."

German studies also help close the evidence gap

IQWiG had already assessed NPWT in 2006 on behalf of the Federal Joint Committee (G-BA). The conclusion was that no superiority versus standard treatment could be determined. Data from meaningful studies were lacking. Several publicly funded studies were then started in Germany, also on the initiative of the G-BA.

Stefan Sauerland explains: "Instead of making decisions on an uncertain data basis, to generate meaningful evidence yourself seems to me like an effective and targeted approach. In particular the NPWT studies on diabetic foot wounds and superficial post-surgical wound infections, funded by statutory health insurance, were important for obtaining specific results on wound therapy in Germany."

Process of report production

The Institute had published the preliminary report on secondary wound healing in August 2018 and in the corresponding press release had criticized the study manufacturers and investigators who violate scientific and ethical standards if they do not publish study results. In the following commenting procedure, which also included an oral hearing in Cologne, KCI subsequently submitted study data. The written comments, as well as the verbatim minutes of the hearing, are also available on the Institute`s website.

Together with the final report, IQWiG published the preliminary report on NPWT for primary wound healing. Interested persons and institutions can submit written comments on these still preliminary assessment results up to 29 April 2019. The Institute will scrutinize these comments and invite persons submitting comments to an oral hearing if open questions in the written comments remain. The preliminary report will then be revised, sent as the final report to the commissioning agency G-BA, and published 8 weeks later on the IQWiG website.
More English-language information will be available soon (Sections 1 to 6 of the German final report as well as easily understandable information for patients and consumers on If you would like to be informed when these documents are available, please send an e-mail to

Institute for Quality and Efficiency in Health Care

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