Negative pressure wound therapy in cardiac surgery

University dissertation from Clinical Sciences, Lund University

Abstract: Negative pressure wound therapy in cardiac surgery Rainer Petzina, M.D. Clinical Sciences, Lund, Lund University Poststernotomy mediastinitis is a devastating complication for patients undergoing cardiac surgery. Conventional treatment includes surgical revision, continuous irrigation with drainage and wound closure with the use of the greater omentum and muscle flaps. Widespread adoption of negative pressure wound therapy (NPWT) has been driven through favorable clinical experience and excellent healing effects. The aims of the research in this thesis were: I. To quantify cardiac output and left ventricular chamber volumes after NPWT, using magnetic resonance imaging (MRI). II. To examine the effects of NPWT on peristernal soft tissue blood flow after internal mammary artery harvesting, using laser Doppler velocimetry. III. To study the effect of NPWT on blood and fluid content of the sternal wound edge and bone marrow, using MRI (T2-STIR). IV. To identify the effects of NPWT on the position of the heart in relation to the thoracic wall, using MRI. An uninfected porcine sternotomy wound model was used for all studies. The hemodynamic effects of NPWT in cardiac surgery are debated. MRI measurements show that NPWT results in an immediate decrease in cardiac output, although to a lesser extent than shown in previous studies. MRI is known to be the most accurate method for quantifying cardiac output. Patients with poor blood perfusion of the sternotomy wound edge tissue have a higher risk of developing post-sternotomy mediastinitis. We show that the peristernal wound edge microvascular blood flow is decreased when the left internal mammary artery is harvested. NPWT therapy stimulates blood flow in the in the wound edge both before and after the mammary artery is removed. Stimulating blood flow to the wound edge in patients with impaired microcirculation may be crucial to ensure healing. MRI measurements show that NPWT increases sternotomy wound edge tissue fluid and/or blood content. Presumably, NPWT creates a pressure gradient that draws fluid from the surrounding tissue into the sternal wound edge and into the vacuum source. This “endogenous drainage” may be one possible mechanism by which osteitis is resolved. Heart rupture is a devastating complication to NPWT of sternotomy wounds. MR imaging shows that NPWT causes the heart to be sucked up towards the thoracic wall and, in some cases, the right ventricular free wall to bulge into the space between the sternal edges and the sharp edges of the sternum to poke into and deform the anterior surface of the heart. These can be effectively hindered by the placement of a rigid barrier over the anterior portion of the heart. Taken together, the studies of the present thesis demonstrate the effects of NPWT on the thorax and intrathoracic organs. NPWT alters wound edge microvascular blood flow and fluid content and affects heart pumping and heart position in relation to the thoracic wall. Rainer Petzina, MD Lund, January 15, 2009