Blood flow response in small intestinal loops at different depths during negative pressure wound therapy of the open abdomen.

High closure rates of the open abdomen have been reported following negative pressure wound therapy (NPWT). However, the method has occasionally been associated with increased development of intestinal fistulae. We have previously shown that the application of NPWT to the open abdomen causes a decrease in microvascular blood flow in the small intestinal loop and the omentum adjacent to the visceral protective layer of the dressing. In this study we investigate whether the negative pressure affects only small intestinal loops lying directly below the dressing or if it also affects small intestinal loops that are not in direct contact with the dressing. Six pigs underwent midline incision and application of NPWT to the open abdomen. The microvascular blood flow was measured in four intestinal loops at different depths from the visceral protective layer, at two different locations: beneath the dressing and at the anterior abdominal wall, before and after the application of NPWT of -50, -70, -100, -120, -150 and -170 mmHg, using laser Doppler velocimetry. Negative pressures between -50 and -170 mmHg caused a significant decrease in the microvascular blood flow in the intestinal loops in direct contact with the visceral protective layer. A slight, but significant, decrease in blood flow was also seen in the intestinal loops lying beneath these loops. The decrease in microvascular blood flow increased with the amount of negative pressure applied. No difference in blood flow was seen in the intestinal loops lying deeper in the abdominal cavity. A decrease in blood flow was seen in the upper two intestinal loops located apically and anteriorly, but not in the lower two, indicating that this is a local effect and that pressure decreases with distance from the source. A long-term decrease in blood flow in the intestinal wall may induce ischaemia and secondary necrosis in the intestinal wall, which could promote the development of intestinal fistulae. We believe that NPWT of the open abdomen is a very effective treatment, but that it could be improved by gaining more knowledge on the mechanisms involved.