• S L Clark, J Southwick, J M Pivarnik, D B Cotton, G D Hankins, and J P Phelan.
• Department of Obstetrics and Gynecology, University of Utah School of Medicine, Intermountain Health Care Perinatal Centers, Salt Lake City.
• Obstet Gynecol. 1994 May 1; 83 (5 Pt 1): 669-72.

ObjectiveTo correlate cardiac index in normal late third-trimester pregnancy using the thoracic electrical bio-impedance technique with that obtained from the oxygen extraction technique.MethodsEight 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.ResultsThe 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.ConclusionsThoracic 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.

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