Transthoracic electrical impedance as an index of extracellular fluid volume in man.

Findings in 76 subjects without cardiac failure were analyzed to detect relationships between observed changes in transthoracic electrical impedance (TEI) and total body extracellular fluid volume (ECFV) during various manoeuvres and between absolute TEI and ECFV values. TEI was normalized to electrode distance (Z0/delta el) and ECFV to lean body mass (ECFV/LBM). A distinct relation was found between percent changes of TEI and ECFV (r = -0.76, p less than 0.0001) and between absolute Z0/delta el and ECFV/LBM values (r = -0.66, p less than 0.0001 for men; r = -0.61, p less than 0.0001 for women). It is concluded that in the same subject a change in TEI is possibly a sensitive index for a change in ECFV and that a single measurement of TEI, normalized to electrode distance, gives information about the state of hydration (ECFV) of patients without cardiac failure.