Estimation of non-cardiogenic pulmonary oedema using dual-frequency electrical impedance.
The study investigates the effects of non-cardiogenic oedema, especially the accumulation of protein in extracellular fluid, on thoracic impedance and proposes a new method of oedema measurement based on an impedance ratio from a dual-frequency measurement. In vitro measurements in a cell containing an albumin-in-saline solution yield a resistance increase when the albumin concentration increases. Subsequently, 13 patients having acute respiratory failure are measured. The single-frequency Z0 measurements and the proposed impedance ratio are compared with extravascular lung water (EVLW) determined by the double indicator dilution method. The single-frequency measurement correlates poorly with EVLW (r = -0.24, p = 0.56). In some patients, a total thoracic impedance increase is found with increasing EVLW. The correlation between the impedance ratio and EVLW is r = -0.79 (p < 0.0005). The ratio decreases as EVLW increases. Thus, when oedema is measured using bio-impedance, cardiogenic and non-cardiogenic oedema yield different results. It is well recognised that cardiogenic oedema decreases total thoracic impedance. In non-cardiogenic oedema, however, protein accumulation causes an impedance increase. The decrease in the impedance ratio as EVLW increases can be explained by the accumulation of albumin in the extracellular compartment.
Raaijmakers
E
E
Department of Medical Physics & Informatics, University Hospital Vrije Universiteit, Amsterdam, The Netherlands.
Faes
T J
TJ
Meijer
J M
JM
Kunst
P W
PW
Bakker
J
J
Goovaerts
H G
HG
Heethaar
R M
RM
D000328:Adult; D000368:Aged; D017097:Electric Impedance; D004568:Electrodiagnosis / Q000379:methods*; D005260:Female; D006331:Heart Diseases / Q000150:complications; D006801:Humans; D008297:Male; D008875:Middle Aged; D011654:Pulmonary Edema / Q000175:diagnosis* / Q000209:etiology; D018805:Sepsis / Q000150:complications