REPEATABILITY IN MEASUREMENT OF CARDIAC-OUTPUT BY THORACIC ELECTRICALBIOIMPEDANCE IN NORMAL-PREGNANCY

Measurements of stroke volume and cardiac output (CO) are important pa rameters in the management of pregnant women who have or develop serio us cardiorespiratory or renal complications. Measurement by thermodilu tion utilising a pulmonary artery flotation catheter has numerous limi tations. This study evaluates the measurement of CO in normal pregnant women by non-invasive, thoracic electrical bio-impedance. The study d esign was cross-sectional, involving all trimesters of pregnancy and t he postpartum period. One hundred and one normal pregnant women were s tudied. The procedure for measurement of CO entailed 15 minutes of res t followed by 3 measurements at 5-minute intervals. The results demons trate a coefficient of repeatability of 22% for CO measurement as defi ned by the protocol in this study. The cross-sectional CO data analysi s was not able to detect the expected trend in CO changes during norma l pregnancy. The limitations of CO measurement by thoracic electrical bio-impedance and thermodilution method are discussed, and refinements in methods are suggested to achieve acceptable repeatability of these measurements.