The "optimal" pressure level using NPWT - Some technological aspects

The objective of this study was to analyse pressure conditions in the foam-tissue interface zone during application of vacuum therapy. We also focused on the question of whether the applied suction is undiminished over a longer distance as would be required when foams of larger area-size are used and whether there are important differences between the two currently available foam materials, polyurethane (PU) and polyvinyl alcohol (PVA).

Methods

Pressure measurements were performed using a multichannel computer-guided pressure measurement system (ARGUS®, MIPM GmbH) that uses a piezoresistive principle for pressure registration. The measurement method is based on changes in specific resistance in certain semiconductors in response to pressure.

Results

The results of the study show that suction is distributed almost undiminished through the foam to the wound surface. This is possible in the suction range of 50-200 mmHg even at distances of over 50 cm using only one port/connector. When a PVA foam is used, there is a relevant reduction in suction strength at suction levels of > 150 mmHg that increases in proportion to the distance from the port/connector. It was also shown that positive pressures reaching >50 mmHg may develop the uppermost tissue layers. The shape of the wound (whether convex or concave) has a significant effect on the developing pressure conditions.

Conclusions

The currently recommended suction strength of 125 mmHg was based on an animal experiment by Morykwas et al. And Isago et al. compared suction strengths of 0, 25, 50, 75 and 125 mmHg in terms of associated wound healing success. They found that there were no significant differences between respective speeds of wound healing achieved at suction strengths of 50, 75 and 125 mmHg. Hence, it appears that suction strengths falling in the range of 50 to 125 mmHg are essentially equivalent in terms of suitability for vacuum therapy. Based on these findings, it appears that suction pressure should be selected so as to create nonhomogeneous pressure conditions in the tissue yet not high as to cause extensive ischemia near the wound surface. The applied suction pressure should not, therefore, be standardized to 125 mmHg.

Christian Willy
Department of Traumatology / Orthopaedic Surgery, Septic and Reconstructive Surgery, Bundeswehr Hospital Berlin

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