Continuous non-invasive cardiac output measurements in the neonate by electrical velocimetry: a comparison with echocardiography.

OBJECTIVE Electrical velocimetry (EV) is a non-invasive method of continuous left cardiac output monitoring based on measurement of thoracic electrical bioimpedance. The objective was to validate EV by investigating the agreement in cardiac output measurements performed by EV and echocardiography. DESIGN In this prospective observational study, left ventricular output (LVO) was simultaneously measured by EV (LVO(ev)) using Aesculon and by echocardiography (LVO(echo)) in healthy term neonates during the first 2 postnatal days. To determine the agreement between the two methods, we calculated the bias (mean difference) and precision (1.96×SD of the difference). As LVO(echo) has its own limitations, the authors also calculated the 'true precision' of EV adjusted for echocardiography as the reference method. RESULTS The authors performed 115 paired measurements in 20 neonates. LVO(ev) and LVO(echo) were similar (534±105 vs 538±105 ml/min, p=0.7). The bias and precision of EV were -4 and 234 ml/min, respectively. The authors found the true precision of EV to be similar to the precision of echocardiography (31.6% vs 30%, respectively). There was no difference in bias and precision between the measurements obtained in patients with or without a haemodynamically significant patent ductus arteriosus. CONCLUSIONS EV is as accurate in measuring LVO as echocardiography and the variation in the agreement between EV and echocardiography among the individual subjects reflects the limitations of both techniques.