Background: Vacuum-assisted closure (VAC) therapy is a recently introduced method for the treatment of poststernotomy mediastinitis. The aim of this study was to examine the effects of negative pressure on peristernal soft tissue blood flow and metabolism because the mechanisms by which vacuum-assisted closure therapy promotes wound healing are not known in detail.
Methods: Microvascular blood flow was examined by laser Doppler velocimetry in an uninfected porcine sternotomy wound model. Microvascular blood flow was examined in the muscular and subcutaneous tissue, at different distances from the wound edge, after the application of -50 to -200 mm Hg. Wound fluid pH, partial pressures of oxygen and carbon dioxide, bicarbonate, and lactate were analyzed after 0, 30, and 60 minutes of continuous negative pressure.
Results: Vacuum-assisted closure therapy induced an increase in the microvascular blood flow a few centimeters from the wound edge. In muscular tissue, the distance from the wound edge to the position at which the blood flow was increased was shorter than that in subcutaneous tissue. Close to the wound edge, relative hypoperfusion was observed. The hypoperfused zone was larger at high negative pressures and was especially prominent in subcutaneous tissue. Wound fluid partial pressure of oxygen and lactate levels were increased after 60 minutes of vacuum-assisted closure therapy, which may be the result of changes in the microvascular blood flow.
Conclusions: Vacuum-assisted closure therapy induces a change in microvascular blood flow that is dependent on the pressure applied, the distance from the wound edge, and the tissue type. It may be beneficial to tailor the negative pressure used for vacuum-assisted closure therapy according to the wound tissue composition. Wound fluid partial pressure of oxygen and lactate levels increased during vacuum-assisted closure therapy. This combination is known to promote wound healing.