A comparison of Escherichia coli endotoxin single bolus injection with low-dose endotoxin infusion on pulmonary and systemic vascular changes.

The purpose of this study was to compare effects of single bolus endotoxin injection with sustained low-dose endotoxin infusion on systemic and pulmonary hemodynamics in anesthetized dogs. When administered as a bolus (.01 mg/kg), endotoxin induced systemic vascular changes whose evolution could be divided into two consecutive phases. In the early phase, marked hepatic venoconstriction caused a rise in portal pressure followed by abrupt decreases in both cardiac output and blood pressure. Mean pulmonary artery pressure remained unchanged. Because of lowered blood flow, both peripheral and pulmonary resistances increased. The rise in the latter was due to a prominent vasoconstriction of pulmonary arteries. Following a partial spontaneous recovery from shock, the late phase was characterized by a low-output state combined with high systemic vascular resistances. In contrast, when endotoxin was given at a slow infusion rate (250 ng/kg/min) over a 2-hour period of time, cardiovascular effects were basically different from the preceding ones, and they were measurable only after a certain period of time had elapsed from the start of endotoxin insult. First, blood pressure decreased gradually, while cardiac output remained almost unchanged. Therefore, peripheral resistance was decreased. Second, in the pulmonary circulation, the site of vasoconstriction was shifted from arteries to veins. We conclude that there is a fundamental difference in the response of the dog's systemic and pulmonary circulation as a function of endotoxin administration as either a bolus or slow infusion. This difference might be due to sudden elevated portal pressure responsible for an abrupt cardiovascular collapse in dogs subjected to bolus injection.