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/gDel) and ECFV to lean body mass (ECFV/LBM). A distircet relation was found between percent changes of TEI and ECFV (r=-0.76, p<0.0001) and between absolute Z₀/el and ECFV/LBM values (r=-0.66, p<0.0001 for men; r=-0.61, p<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.