Dear Editor:

  This is a letter to comment on the original article by McNulty et al published in the WOUNDS May 2010 issue—“The Consistent Delivery of Negative Pressure to Wounds Using Reticulated, Open Cell Foam and Regulated Pressure Feedback.”   Negative pressure wound therapy is usually applied using either foam or gauze. Wound healing may be optimized by selecting the wound filler that each specific wound benefits the most from.^1,2 McNulty et al have examined the effect on macrostrain by foam and gauze, and also the use of regulated pressure feedback (the T.R.A.C.™ technology) to consistently deliver the set negative pressure to the wound. In my view, the authors have jumped to conclusions when it comes to the first aim. The conclusions from the second aim are interesting but the clinical relevance may be questioned.
  The fact that the study was performed using an in-vitro surrogate wound model, where the wound fillers were either covered top and bottom with V.A.C.® drape or attached to Plexiglas sheets, concerns us. In real wounds, both systemic and local conditions affect the outcome while an in-vitro surrogate wound is static and the outcome depends largely on the construction of the model. McNulty et al came to the conclusion that foam under negative pressure induced macrostrain, while gauze did not. This is in direct contradiction to the result of previous in-vivo studies where both wound fillers induced macrostrain.2,3 It seems logical that the spongy features of foam allow macrostrain when the foam is completely covered top to bottom in adhesive drape (as in the McNulty study), whereas gauze induces macrostrain only if placed in real wounds with compliant wound edges. ^2,3 Furthermore, numerous studies demonstrate that the use of both gauze and foam result in granulation tissue formation.^1,2,4
  McNulty et al also emphasize the role of maintaining the set level of negative pressure, and the use of vacuum systems without regulated feedback systems is being questioned. The results show that when using the Versatile 1 pump (without the regulated pressure feedback feature) in gauze-filled surrogate wounds, there is a pressure drop from -125 mmHg to -96 mmHg. This is a significant pressure drop, but the clinical relevance may be questioned. There is strong evidence that these different levels of negative pressure have similar wound healing effects in both in-vivo experimental models^1–3,5,6 and also in the clinical treatment of patients.⁷

Malin Malmsjö¹ and Ola Borgquist^2
1Department of Ophthalmology, Lund University and ²Skåne University Hospital, Lund, Sweden

References

1. Borgquist O, Gustafsson L, Ingemansson R, et al. Tissue ingrowth into foam but not into gauze during negative pressure wound therapy. WOUNDS. 2009;21(11):302–309.

2. Borgquist O, Ingemansson R, Malmsjö M. Micro- and macromechanical effects on the wound bed by negative pressure wound therapy using gauze and foam. Ann Plast Surg. 2010;64(6):789–793.

3. Malmsjo M, Ingemansson R, Martin R, et al. Negative-pressure wound therapy using gauze or open-cell polyurethane foam: similar early effects on pressure transduction and tissue contraction in an experimental porcine wound model. Wound Repair Regen. 2009;17(2):200–205.

4. Paglinawan R, Colic M, Simon M. A comparative study of the influence of different pressure levels combined with various wound dressings on negative pressure wound therapy driven wound healing. European Tissue Repair Society; Malta: 2008.

5. Borgquist O, Ingemansson R, Malmsjo M. Wound edge microvascular blood flow during negative-pressure wound therapy: examining the effects of pressures
from -10 to -175 mmHg. Plast Reconstr Surg. 2010;125(2):502–509.

6.