Some observations on negative pressure wound therapy in acute soft tissue trauma

Dear Editors

1.

We conducted a study of negative pressure wound therapy (NPWT) in 55 patients with a mean age 24 years (range 5‐72 years). All the patients presented with acute complex soft tissue wounds, and the aim of NPWT was to achieve wound closure with a split skin graft. The NWPT was repeated between 2 and 7 days and at each change, wound swabs were taken. However, the decision to perform the skin graft was made on clinical grounds, that is, that there was “healthy” bed of granulation tissue.

Prior to this study, a wound swab would be taken 48 hours before the scheduled skin graft. If there was >10⁵ bacteria or Streptococcus pyogenes the NPWT would again be continued until the wound was bacteriologically sterile. In this study, this was abandoned: prior to the performance of a skin graft, the patient had a wound swab taken and received 2 million units of intravenous penicillin (in case of Streptococcus). Graft take was assessed at 10 days using the grid method to assess percentage take.

The findings were as follows:

1. Split skin graft take was 90% and 30% of patients had 100% graft take. This occurred irrespective of the swabs.

2. Some bacteria which had been cultured during the time of granulation tissue formation, seemed to respond better to NPWT, for example, Proteus mirabilis and Enterococcus faecalis, in that their quantity decreased in response to continued NPWT‐as had been originally suggested by Argenta et al.1 However, some bacteria did not decrease in quantity, for example, Pseudomonas aeruginosa and Proteus vulgaris. These bacteria required additional measures to decrease or remove from the wound. Some bacteria responded in an erratic manner, sometimes decreasing in quality but in other patients there was no response to NPWT, for example, Staphylococcus aureus.

3. Where there was skin graft loss the bacteria were identified as “mixed growth ”.

Conclusion from the study

1. NPWT increases not only the quantity of granulation tissue but also the quality. Hence the graft bed is well prepared and can even accept a full thickness graft.2

2. The decision to perform a graft was made on clinical grounds i.e. on how the wound looked. Swabs were not taken 48 hours prior the grafting to assess the bacterial growth prior to grafting. Thus, it is suggested that the classic dictum3 of not skin grafting if there is a >10⁵ is not applicable in wounds prepared by NPWT.

3. When “mixed growth” was cultured, graft take was poor. Thus, may represent a biofilm.

4. Our experience show that NPWT has a variable effect on wound bacteria.