Mild hypotension and body burns synergistically increase bacterial translocation in rats consistent with a "two-hit phenomenon".

Wistar rats were burned over 15% of their total body surface area and suffered hemorrhagic hypotension (mean blood pressure 80 mm Hg) 72 hours after the thermal injury (burn + hypotension group). Rats in other groups were treated in the same way except sham hypotension in burn group, sham burn in hypotension group, and sham hypotension and sham burn in control group. At the end of the study period, the mesenteric lymph nodes (MLN), liver, and spleen were cultured for translocated bacteria. The cecal bacterial burden was not affected by the insults. The number of bacteria translocated to the MLN after the thermal injury was much greater in the burn + hypotension group (156.19 +/- 42.29 colony-forming units [CFUs]/gm tissue) rather than in the other groups (5.24 +/- 8.34, 9.86 +/- 16.56, 40.21 +/- 45.8 in the control, hypotension, and burn groups, respectively). This indicates that bacterial translocation (BT) is the result of a two-hit phenomenon. The gut-MLN BT ratio, obtained by dividing the bacterial CFUs in the MLN by those in the cecum, was higher in the burn + hypotension group than in the other groups (p < 0.01). This ratio allows standardized measurements of BT to the MLN despite differences in the absolute bacterial load in the gut, and the elevated gut mesenteric lymph nodes BT ratio of the burn + hypotension group suggests that the two-hit phenomenon of BT may be the result of alterations in the gut mucosal barrier function.