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A comparison of cardiac index in normal term pregnancy using thoracic electrical bio-impedance and oxygen extraction
S L Clark1, J Southwick, J M Pivarnik
1Department of Obstetrics and Gynecology, University of Utah School of Medicine, Intermountain Health Care Perinatal Centers, Salt Lake City.
Objective:
To correlate cardiac index in normal late third-trimester pregnancy using the thoracic electrical bio-impedance technique with that obtained from the oxygen extraction technique.
Methods:
Eight carefully screened normal pregnant women underwent assessment of cardiac index using both the thoracic electrical bio-impedance technique and the oxygen extraction technique. Measurements were obtained in various positions.
Results:
The correlation was good between the thoracic electrical bio-impedance and oxygen extraction techniques in the left lateral (r = 0.915) and right lateral (r = 0.863) positions, and the intercepts at the midpoints of the oxygen extraction data in these positions suggested good absolute correlation as well. Correlation between thoracic electrical bio-impedance and the Fick cardiac index was poor in all other positions.
Conclusions:
Thoracic electrical bio-impedance cardiac index assessment is influenced by maternal position and must be used with caution in clinical research protocols. This technique appears to be inappropriate for general clinical use during pregnancy.