Negative Pressure Wound Therapy - Effects on Sternotomy Wounds and the Intrathoracic Organs

Sammanfattning: Negative pressure wound therapy (NPWT) has been widely adopted for the treatment of deep sternal wound infections due to its excellent clinical outcome. However, the mechanisms of action and effects on hemodynamics have not been thoroughly elucidated. The aims of the work presented in this thesis were, therefore, to examine the effects of NPWT on sternotomy wounds and on the intrathoracic organs. An uninfected porcine sternotomy wound model was used in all studies. The studies showed that negative pressure is transmitted only to tissues that are in direct contact with the foam dressing and not to deeper parts of the wound or thoracic cavity. As NPWT was applied, a transient increase was seen in the plasma levels of norepinephrine and epinephrine, followed by an increase in the adrenergic co-transmitter neuropeptide Y, which may reflect the effect of NPWT on the intrathoracic organs. Increased levels of the sensory nerve transmitter substance P may result from shearing forces arising from the mechanical effects of the negative pressure. Magnetic resonance imaging showed that cardiac output increased while the cardiac pumping efficiency decreased following sternotomy, and then returned to presternotomy values when the negative pressure resealed the thorax. NPWT contracts the wound and causes macrodeformation of the wound edge tissue. This may contribute to the clinical benefits of NPWT over open-chest treatment, including the stabilizing effect and reduced need for mechanical ventilation. The results of the present work underline the importance of correct placement of the wound filler with regard to pressure transmission. The findings also reduce concerns that NPWT could impair cardiac output, and emphasize the beneficial effects of temporary closure provided by NPWT on restoring the intrathoracic anatomy.