Changes in transthoracic electrical impedance during endotoxemia in dogs

Our aim was to investigate the role of hematocrit (H) and respiration in transthoracic electrical impedance during endotoxemia. Transthoracic electrical impedance at end-expiratory apnea (Z0) and at end-inspiration (Zmax), H values, and extravascular lung water level (EVLW), estimated by means of gravimetric analysis and the impedance method, were measured in splenectomized and mechanically ventilated dogs. In endotoxemia, there were increases in Z0, Zmax, H and the respiratory frequency. In the splenectomized dogs, both impedances slightly increased without any significant change in H. In the ventilated dogs, Z0, and Zmax increased similarly, while H increased. In the splenectomized, ventilated dogs, no changes were found in the impedances or H. The EVLW values showed that there was no serious edema in the endotoxemic groups. The results suggest that Z0 increased mainly in association with the increase in H. We conclude that the noninvasive measurements of the changes in impedance can be used for continuous monitoring of the fluid and gas shifts in the thorax.