Intestinal bacterial translocation has been postulated as an important risk
factor for the development of multiple organ failure (in the absence of a
definite focus of infection). Research on this topic has been focused on
detection of bacteria and endotoxins in (portal) blood or mesenteric lymph nodes
(MLN's). Lymphatic translocation beyond the level of MLN's, i.e. the thoracic
duct, has not been studied, although this could be of significant importance
because it implicates bypass of the reticuloendothelial system of the liver and
direct discharge of bacteria and endotoxins into the systemic circulation.
Aim: To determine whether bacterial translocation occurs in a (clinically
relevant) model of severe non-bacterial tissue damage and to assess the various
routes of bacterial translocation.
Materials and Methods: In a porcine model of 2 hrs ischemia and 5 hrs
reperfusion of the liver, the thoracic duct and the portal and subclavian vein
were cannulated (n=5 pigs). Lymph was drained through siphoning and collected in
a plastic bag. During the ischemic period, a hemihepatectomy was performed. To
prevent venous congestion of the gut, a portocaval shunt was made prior to
hepatic ischemia. MLN's were cultured before and after ischemia and after 5 hrs
reperfusion. Lymph, portal blood and systemic blood were collected before and
after ischemia and after 1, 2, 4 and 5 hrs of reperfusion, and analyzed for the
presence of bacteria and endotoxins. In addition, TNF-alpha concentrations were
measured (ELISA) at different timepoints.
Results: Culture-positive MLN's were present in 2/5 pigs after 2 hrs of
ischemia and also in 2/5 pigs after 5 hrs reperfusion. Thoracic duct lymph
cultures were positive in 3/5 pigs after 2 hrs of ischemia; lymph cultures were
positive in 4/5 pigs 1 hr after reperfusion and in all pigs 2, 4 and 5 hrs after
reperfusion (p< 0.05 compared to the preischemic state). During the ischemic
and reperfusion period, the incidence of positive portal blood cultures did not
increase significantly in comparison to the preischemic state. The incidence of
positive systemic blood cultures was significantly increased 4 hrs after
reperfusion (4/5 pigs compared to 0/5 pigs at preischemia, p< 0.05). Median
endotoxin levels increased threefold in the thoracic duct lymph from 0.04
Endotoxin Units (EU)/mL (= 3.3 pg/mL) at preischemia to 0.136 EU/mL (= 11.3
pg/mL), 5 hrs after reperfusion (p<0.001, ANOVA). Portal and systemic blood
endotoxin levels did not increase significantly during the experiment. TNF-alpha
concentrations in lymph and portal and peripheral blood were not detectable (<
38.4 pg/mL) during the experiment except 1 hr after reperfusion in lymph, the
median TNF-alpha concentration peaked to 50.7 pg/ml.
Conclusion: This study shows that the thoracic duct is one of the routes for
bacterial translocation to the systemic circulation.
