[The physics of vacuum therapy].

Background: Vacuum therapy is a routine and successful method for wound treatment and for the temporary covering of soft-tissue defects. It is an occlusive method that can be used for treating acute, chronic and infected wounds. To date, no data are available regarding secretion transit times and pressure conditions in lesions treated with vacuum therapy. The present study had as its objectives to examine the mechanisms of vacuum therapy and determine the effects of physical forces on the wound surface with the purpose of formulating recommendations for pressure settings using the various available vacuum pumps.
Material and Methods: Using an appropriate model, we measured secretion transit times and pressures using two different vacuum therapy pads. We then conducted pressure measurements during dressing change in eight patients with wound surfaces greater than 20 cm(2).
Results: The secretion transit times remained unchanged with the polyvinyl alcohol (PVA) pad and a negative pressure of 40 kPa, but decreased by about 50 % when the black polyurethane (PU) pad was used. Pressure measurements showed that, at this negative pressure, there was only a slight positive external pressure of 31 mmHg on the wound surface.
Conclusion: When the PVA pad is used, negative pressures greater than 40 kPa should be applied in order to effect a maximum transit of wound secretion and prolongation of the use of the vacuum dressing. When the PU pad is used, the applied negative pressure can be lower due to the pad's larger pores, as recommended by Argenta and Morykwas. An excessive external pressure on the wound surface does not occur.