Approaching volume status via electrical impedance tomography—an explorative study in healthy volunteers^*

<i>Objective.</i>Monitoring the volume status of patients remains a fundamentally unresolved issue in the perioperative setting but also in intensive care medicine. Electrical impedance tomography (EIT) enables noninvasive and radiation-free functional imaging of impedance changes of a cross-sectional plane of the thorax.<i>Approach.</i>We hypothesized that cardiac-induced impedance fluctuations in the EIT signal contain information about the global volume status. Therefore, we recorded EIT signals from 24 healthy volunteers before and up to 100 min after ingestion of 750 ml liquid following more than nine hours fluid restriction. We isolated a characteristic cardiac-induced impedance profile from the global impedance curve and compared its characteristics to measures of non-invasive hemodynamic monitoring and the diameter of the vena cava inferior (VCI) determined via ultrasonography.<i>Main results.</i>The diameter of the VCI, mean arterial pressure and stroke volume index, did not change systematically after liquid ingestion. Heart rate was increased 20 min after, and heart rate variability was increased immediately after liquid ingestion. The amplitude, the area under the curve and gradients of its rise and decline of the characteristic cardiac-induced impedance profile changed 60 min after liquid ingestion.<i>Significance.</i>Cardiac-induced pulsatile signals in EIT recordings changed characteristically after liquid ingestion, loosely corresponding with changes in heart rate and heart rate variability. These signals may contain valuable information about the general volume status and may be utilized for enhanced monitoring of a patient's volume status.