Hemodynamic effects of vacuum-assisted closure therapy in cardiac surgery: Assessment using magnetic resonance imaging

Cross section of the thoracic cavity with an open sternotomy. The heart is covered with 4 layers of paraffin gauze dressing. A polyurethane foam dressing is placed between the sternal edges, and noncollapsible drainage tubes are inserted into the foam. The open wound is sealed with transparent adhesive drape, and drainage tubes are connected to a purpose-built vacuum source.

Cardiac output (A and D), stroke volume (B and E), and heart rate (C and F) were measured using the established technique for MRI flow quantification. Measurements were performed before the vacuum source was turned on (VAC off) and at a negative pressure of 75 mm Hg (white bars), 125 mm Hg (light gray bars), and 175 mm Hg (dark gray bars), and 0, 0.5, 1, 1.5, 2, 2.5 and 3 minutes after the vacuum source was turned on (VAC on). Measurements were undertaken both with (A, B, and C) and without (D, E, and F) 4 layers of paraffin gauze dressing covering the heart. The results are shown as means of 6 experiments. *P < .05, **P < .01, and ***P < .001. Note how cardiac output and stroke volume decrease over time.

Results from one experiment during the application of −175 mm Hg in a sternotomy wound without interface dressing. Real-time MRI flow quantification in the ascending aorta throughout 42 seconds of the application of VAC (top panel). VAC on denotes when the vacuum source was turned on, and sternal edges adapted denotes when the lateral movement of the sternal edges was completed, which presumably reflects the completion of VAC application. (Bottom panel) A magnification of the flow in the top panel during representative heart beats. The first 2 beats (duration = 1.5 seconds) show representative flow prior to the application of VAC. The second 2 beats (duration = 1.5 seconds) show representative flow after the completion of VAC application, showing a reduced area under the curve compared with the bottom left panel, indicating a reduced stroke volume. These data are the basis for the results presented in Figure 4.

Changes in cardiac output (top), stroke volume (middle), and heart rate (bottom) measured using real-time MRI flow quantification during the application of −175 mm Hg in a sternotomy wound without interface dressing. VAC on denotes when the vacuum source was turned on, and sternal edges adapted denotes when the lateral movement of the sternal edges was completed, which presumably reflects the completion of VAC application. Note how the cardiac output and stroke volume declined during the application of negative pressure and then seemed to stabilize. See Methods for further details.

End-diastolic volume (top) and end-systolic volume (bottom) were measured using MRI chamber volume quantification before VAC negative pressure was turned on (0 mm Hg) and approximately 1.5 minutes after the application of −75, −125, and −175 mm Hg. Measurements were undertaken both with and without a wound interface dressing covering the heart. The results are shown as means of 6 experiments. *P < .05, **P < .01, and ***P < .001.

The vacuum source was set to successively deliver negative pressures from 50 to 200 mm Hg at 25 mm Hg increments. Wound pressures were recorded with no interface dressing (under foam) and after the interposition of 4 layers of the paraffin gauze dressings (under interface dressing). Values are presented as means ± SEM from 6 experiments. **P < .01. Note how the pressure in the wound was lower in the presence of an interface dressing.