A significant increase in impedance was observed using the low frequency domain for the “Transthoracic” vector after thoracentesis. There was a moderate correlation between the amount of removed PE and the change in impedance using the “Foot to Hand” vector in the low frequency domain. Demonstrated feasibility of measuring fluid shifts by BIS in thoracentesis. Use as an adjunct diagnostic tool to evaluate PEs and monitor patients after thoracentesis. BIS measurement was safe, noninvasive, and easy to handle. Open access: Yes View