Experimental principles of the VAC®-therapy -: Pressure values in superficial soft ttissue and the applied foam

Object of the study: Measurement of the pressure during V.A.C.(R)-therapy in superficial parts of the affected soft tissue as well as at the soft tissue/foam-interface, measurement of pressure values along bigger distances in the foam and the comparison of pressure transfer between polyurethane and polyvinyl-alcohol foams. Material and Methods: A multi-channel electronic transducer-tipped catheter system based on the piezoresistive principle was used. Measurement was performed on a plain table surface, at a bovine muscle as well as in human tibial anterior muscle of a patient after fasciotomy. Applied pressure values by V.A.C.(R)-therapy-units were 50 to 200 mmHg (continuous suction modus). Results: 100% pressure transition through vacuum-therapy-foams to wound surface, almost 100% pressure transition even along 60 cm in very large polyurethan-foams using only one trac-pad connector. Pressure values >125 mm Hg using polyvinyl-alcohol-foams showed a reduction of up to 25% in distances >15 cm from trac-pad-connector. On the surface of the affected soft tissue there are negative and positive pressure values (25% quartile: -25 mm Hg; 75% quartile: + 15 mm Hg). Discussion: Pore walls of the foam can produce positive pressure conditions resulting in soft tissue compression and consecutively hypoperfusion or ischemia. V.A.C.(R)-therapy seems to produce an heterogeneity of pressure distribution at the wound ground leading to pressure gradients and facilitating drainage of interstitial fluid. This mechanism could explain the anti-edema effects of V.A.C.(R)-therapy resulting indirectly in an increased nutritive perfusion.