Closed incision negative pressure wound therapy versus standard dressings in obese women undergoing caesarean section: multicentre parallel group randomised controlled trial

Dear Editor

The above article seeks to answer an important question that has long escaped those concerned with wound healing. The use of negative pressure wound therapy (NPWT) on closed incisions is somewhat contentious, and poorly evidenced. (1)

This study is a welcome attempt to shed further light on the benefits of this treatment modality and its potential benefits to “at risk” wounds. The authors should be applauded for their careful patient selection, and the homogeneity of the cohort they have assembled.

However, there are a few significant concerns regarding this study that we wish to express:

Firstly; using NPWT on a closed wound is theoretically flawed: It is unlikely to confer any meaningful “splinting” of the wound edges in high BMI patients owing to the volume of tissue exerting deformational forces on the wound bed. Nor, given the size and depth of the surgical wound in caesarean section surgery, is an 80mmHg PICO dressing likely to provide any meaningful compressive force to eliminate dead space and prevent haematoma/seroma.

Conversely NPWT to an open wound, in which the sub-atmospheric pressure reduces the volume of a porous medium within the wound to promote granulation and tissue creep, would aid oedema reduction and removal of exudate whilst reducing overall wound size.(2) This would then facilitate a tension-free closure at a later date.

The authors rightly make the point that use of NPWT is not without risk, and identify a statistically significant increase in the risk of skin blistering. These new wounds present a potential site for future wound infection.

Of greatest concern is the phrase used in the results of this study: “close to statistical significance”

The correct phraseology is “not statistically significant”. It seems misleading to infer that there is a benefit of NPWT in these patients, when the data do not provide such evidence. Especially when the Cochrane review regarding NPWT in these circumstances identified no benefit.(1)

Indeed this is further compounded by a later suggestion “that prophylactic closed incision NPWT may be effective in reducing SSI rates”, when in fact the study fails to show significant benefit. This is in stark disagreement with BMJ’s own reporting standards, and indeed known statistical norms.(3)

Given the BMJ’s own push over the last few years to raise reporting standards in research, it is very surprising that this was allowed past editorial review.

It is our view that the decision to use NPWT in closed wounds is not always for the best reasons. If one is sufficiently concerned about the integrity of a wound closure, then perhaps the issue is the wound, and not the choice of dressings.

If one is concerned the closure is too tight, then would it not be better to leave the wound open with a NPWT device in place to reduce the wound size prior to closure, and thus alleviate the tension?

As the authors rightly point out, NPWT is not risk free, and should be considered as part of a balanced approach to wound closure, especially in high risk patients such as those described in this study.

1: Norman G, Goh EL, Dumville JC, Shi C, Liu Z, Chiverton L, Stankiewicz M, Reid A. Negative pressure wound therapy for surgical wounds healing by primary closure. Cochrane Database of Systematic Reviews 2020, Issue 6. Art. No.: CD009261. DOI: 10.1002/14651858.CD009261.pub6. Accessed 10 August 2021.
2: Lalezari S, Lee CJ, Borovikova AA, et al. Deconstructing negative pressure wound therapy. Int Wound J. 2017;14(4):649-657. doi:10.1111/iwj.12658
3: Wood J, Freemantle N, King M, Nazareth I. Trap of trends to statistical significance: likelihood of near significant P value becoming more significant with extra data. BMJ 2014; 348 doi: https://doi.org/10.1136/bmj.g2215 (Published 31 March 2014)