Electrical velocimetry as a tool for measuring cardiac output in small infants after heart surgery

Purpose: Cardiac output (CO), the product of stroke volume (SV) and heart rate, is essential to guarantee organ perfusion, especially in the intensive care setting. As invasive measurement of CO bears the risk of complications there is a need for non-invasive alternatives. We investigated if electrical velocimetry (EV) and transthoracic Doppler (Doppler-TTE) are interchangeable for the non-invasive measurement of SV and able to reflect the post-surgical SV/CO trend. Methods: Comparison of SV measurements by EV and Doppler-TTE was performed in 24 newborns after switch operation (n = 240 measurements). Three subgroups of measurements (=periods) were created according to the patients' status in the course of post-surgical CO recovery. Results: Bland-Altman analysis found acceptable bias and limits of agreement for the interchangeability of the two methods. Mean overall SV was 3.7 ml with a mean overall bias of 0.28 ml (=7.6 %). The mean percentage error of 29 % was acceptable according to the method of Critchley and Critchley. Overall precision expressed by the coefficient of variation (CV) was 6.6 % for SV _TTE and 4.4 % for SV _EV. SV _TTE and SV _EV medians in the three periods were significantly different and documented the post-surgical CO trend. Conclusions: EV and Doppler-TTE are interchangeable for estimating SV. EV has the advantages of easy handling and allows continuous measurement.