Objective: To correlate cardiac index in normal late thirdtrimester pregnancy using the thoracic electrical bioimpedance 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. (Obstet Gynecol 1994;83: 669-72)
(C) 1994 The American College of Obstetricians and Gynecologists