Pressure at the Bowel Surface during Topical Negative Pressure Therapy of the Open Abdomen: An Experimental Study in a Porcine Model

Abstract

Topical negative pressure (TNP) therapy is increasingly used in open abdomen management. It is not known to what extent this pressure propagates through the dressing to the bowel surface, potentially increasing the risk of bowel fistula formation. The present study in a porcine model was designed to evaluate pressure propagation. A commercially available TNP therapy system (ABThera/VAC) was applied in six pigs after laparotomy. Pressure sensors were placed in predetermined positions in the dressing and in the abdominal cavity and the pressure was registered at TNP settings of -50, -75, -100, -125, and -150 mmHg. Next, after infusing 200 ml of saline into the abdomen through a catheter, the amount of fluid drained through the system during 10 min of TNP therapy was registered. Finally, pressure was measured above and below eight layers of paraffin gauzes during TNP therapy. Observed pressure within the outer two foams and the foam of the visceral protective layer correlated with preset TNP. The median pressure at the bowel surface was between -2 and -10 mmHg, regardless of preset TNP. Median fluid drainage was 95% of the infused fluid at -75 mmHg and 124% at -150 mmHg. Paraffin gauzes had a limited isolating effect, reducing the pressure by 13% in median. Negative pressure reaching the bowel surface during TNP therapy with the ABThera system is limited for all TNP levels. Reduced therapy pressure does not lead to reduced pressure at the bowel surface. The system drains the abdominal cavity completely of fluid. Paraffin gauzes are of limited value as a means of pressure isolation.