Hemodynamic consequences of endotoxemia in sheep.

Sheep which have been previously prepared for cardiopulmonary studies and collection of lung lymph were given 0.75 micrograms/kg of E coli endotoxin iv. This induced sepsis produced a triphasic response. Phase 1 occurs during the first hour after endotoxin administration and is characterized by a decreased cardiac output, lymph to plasma protein ratio, neutrophil count, and an increased hematocrit, total plasma protein concentration, lymph flow, and pulmonary artery pressure. During phase 2 these variables tend to return toward their baseline values. Phase 3 begins 2.5 hr after the administration of endotoxin and shows many of the same changes that were observed in phase 1. Also during the late phase, the plasma protein concentration and lymphocyte count were reduced and the lymph to plasa protein ratio was increased. It is concluded that (1) An early fall in cardiac output occurs as a consequence of hypovolemia. The decreased volume is the result of fluid movement from the vascular compartment to the interstitial space consequent to a microvascular pressure increase. Since the changes occur coincidentally with a drop in neutrophil count, these cells may bear some causal relationship to the response. (2) The late fall in cardiac output in phase 3, also the result of a diminished vascular volume, occurs secondarily to extravasular fluid movement as a consequence of both an elevated microvascular pressure and an increased permeability to protein. The latter may be causally related to a fall in lymphocytes.