Investigation of the thoracic electrical impedance during endotoxemia in dogs

The purpose of our study was to examine the effect of sustained low-dose endotoxin infusion on changes in thoracic electrical impedances (Z0 at end-expiratory apnoea, Zmax at end-inspiration), Zmax-Z0, hematocrit (H) values, and extravascular lung water (EVLW) estimated with gravimetrical analysis (WW/DW) and the impedance method (dEVLWimp) in anesthetized dogs. To define the role of H in changes in the Z0 and Zmax, we applied splenectomy. To determine whether changes in respiration might be involved in changes in Z0 and Zmax, mechanically ventilated dogs were examined. During the infusion of endotoxin there was an increase in Z0, Zmax, H and the respiratory rate in the spontaneously breathing dogs. In splenectomized dogs both impedances slightly increased without any significant change in H. In the ventilated dogs Z0 and Zmax increased similarly, and H increased to a slightly lower level than in the spontaneously breathing dogs. In the ventilated-splenectomized dogs no changes were found in the impedances and in H. The EVLW values showed no serious edema in the endotoxemic groups. The results suggest that Z0 increased mainly in association with the increase in H. The Zmax-Z0 parameter proved to be a suitable parameter for demonstrating the changes in respiration.