EVALUATION OF IMPEDANCE CARDIAC OUTPUT IN CHILDREN

In 20 children without shunts or valvular insufficiency, duplicate dye dilution and impedance cardiac outputs (ICO) were carried out. The duplicate dye dilutions had a standard deviation 0.259 L/min/m2, while duplicate ICO had a standard deviation 0.192 L/min/m2 (F = 1.82, p < 0.05). Of 53 sequential estimates, cardiac outputs measured by both indicator dye dilution and ICO had a 5.5% mean difference. In 21 subjects with left to right shunts, the ICO related well with pulmonary blood flow (r = 0.92) rather than systemic flow (r = 0.21). In 13 subjects with aortic insufficiency, sequential Fick and ICO had a 50% mean difference; the impedance measurement was found to be higher in every case. These data indicate that the impedance cardiograph can provide a noninvasive measure of cardiac output when there are no shunts or valvular insufficiencies. In subjects with left to right shunts the impedance cardiograph provides a measure of the pulmonary blood flow. When aortic insufficiency exists the impedance cardiograph is distorted such that it is consistently higher than Fick cardiac output.