Electronic cardiometry (EC), using internal calibration, is a method for measuring SV and CO that considers the weight and length of newborns. In recent years, research efforts have been focused on examining the correlation, accuracy and precision of ultrasonic monitoring methods, bioimpedance methods, and nuclear magnetic resonance methods. Katheria et al. [19] have studied the feasibility of using EC in the first 5 minutes after delivery in 20 full-term babies with complete umbilical cord and have recorded the measurement results used for trend monitoring. Freidl et al. [20] have also used EC in the delivery room to monitor the first 15 minutes of the life of full-term infants. Studies show that EC can provide fast and accurate bedside monitoring.

Torigoe et al. [21] have applied EC in 28 infants with very low birth weight (VLBW) and low birth weight (LBW), implying that PDA and ventilator’s influence on this method. Grollmuss et al. [22] compared SV and HR of 228 premature infants with transthoracic echocardiography (TTE) (134 LBW, 94 VLBW) and EC (134 LBW, 94 VLBW) by bland-Altman diagram. The accuracy of the method was expressed by calculating coefficient of variation (CV). This study evaluated whether EC and TTE were interchangeable, even in LBW and VLBW infants, suggesting that EC was also suitable for LWB/VLBW infants, and it was a safe and easy method to perform. Song et al. [23] evaluate the practicability of EC monitoring by comparing the results of CO and system blood flow, measured by EC and echocardiography (ECHO). Through prospective observation, 40 premature infants received 108 pairs of EC and ECHO measurements, and analyzed the correlation between EC, left ventricular opacification (LVO), and right ventricular opacification (RVO), indicating that EC is expected to become the trend of CO monitoring for premature infants. EC is considered as a noninvasive method for continuous measurement of CO. Blohm et al. [24] showed that EC is comparable to the aortic flow-based TTE method for pediatric patients. Boet et al. [25, 26] showed that EC method is feasible, reproducible, fast, and it is a useful tool for continuous monitoring, and hemodynamic evaluation of neonates. EC is particularly meaningful for the clinical treatment of premature infants.

EC was once applied to monitor stroke and CO in 79 premature infants with hemodynamic stability (mean gestational age (GA): 31 $\pm$ 3.2 weeks), and the results were well correlated with echocardiographic monitoring results. Basic hemodynamic monitoring can be performed by ECG measurements, and ultrasound during both pediatric and neonatal transport. These two techniques demonstrate considerable reliability, and the accuracy of the results were not affected by transfer processes. Noori et al. [27] conducted 115 pairs of measurements in 20 premature infants with or without PDA, with no difference in accuracy and deviation of the measurement results. The study shows that EC is in good consistency with echocardiography monitoring results. The results of LVO (EC) and LVO (Echocardiography, (ECHO)) were similar (534 $\pm$ 105 vs 538 $\pm$ 105 mL/min, p = 0.7). The EC offset was –4 mL/min and the precision was 234 mL/min. The true accuracy of EC is shown to be similar to that of ECHO (31.6% and 30%, respectively). Grollmuss et al. [28] have found that EC and Doppler TTE have good consistency in estimating SV, and they are interchangeable. EC offers the advantage of being user-friendly, allowing to continuous measurements.

CO, a product of SV and HR, is particularly important for ensuring organ perfusion, especially in the NICU. Due to the risk of complications associated with invasive CO monitoring, noninvasive alternatives are required. Ren Xinrui et al. [29] selected 17 children with congenital heart disease using EC and TTE to examine SV, stroke volume variation (SVV) and distensibility index of the inferior vena cava (dIVC), and found that EC had good consistency with TTE monitoring results. Critchley et al. [30] conclude that when bias and accurate statistics are used, CO bias, consistent limit, and percentage error standards are proposed, acceptance of new technology should rely on a consistent limit of $\pm$30%. Sanders et al. [31] have found through meta-analysis that ECG cannot replace thermodilution and TTE to measure absolute CO. However, Suehiro et al. [32] conducted a series of prospective observational meta-analysis of more than 300 premature infants and more than 100 full-term infants, and they found that ECG measurement had a minimal deviation (–0.03 L min${}^{-1}$ and a smallest percentage error (23.6%). The EC method is considered to be the most accurate and precise technique for monitoring CO in children compared to noninvasive and invasive techniques. Most premature infants require respiratory support that includes both noninvasive and invasive ventilation techniques. The hemodynamic monitoring indexes of premature infants will be affected during high-frequency oscillation and PDA occurrence [21]. Hsu et al. [33] reported that a total of 280 neonates are studied and the results indicate that CO is positively correlated with gestational age, body weight and body surface area (r = 0.681, 0.822, 0.830; all p 0.001). The hemodynamic index of EC is significantly different in neonates with different maturity.

Huang et al. [34] reported that the use of EC to guide the intraoperative treatment of target fluid in patients undergoing surgery for congenital heart disease significantly reduce the dose of artificial colloid during surgery, and the tissue perfusion and oxygen supply are sufficient, thus reducing the postoperative tracheal catheter removal time.

Chen Bailang et al. [35] report that EC is used to monitor fluid management and treatment for early resuscitation of patients with septic shock, so as to guide fluid resuscitation and accurate fluid replenishing, which is conducive to disease recovery and reduced complications caused by blind fluid replenishing.

Yuan et al. [36] used EC to monitor newborn children with congenital heart disease, and they found that the differences in cardiac index (CI), left ventricular ejection fraction (LVEF), N-terminal pro-brain natriuretic peptide (NT-probNP) and pulmonary arterial pressure (PAP) among groups with heart failure were statistically significant. CI to some extent reflects the degree of heart failure and holds significant clinical applicability in assessing heart failure in newborns with congenital heart disease.

Zhang et al. [37] have indicated that patients with sepsis used EC to dynamically and continuously monitor the changes of CI, integrated cardiopulmonary operating network (ICON) and other indicators of cardiac function, so as to evaluate the changes of patients’ early cardiac function and guide clinical decision-making. Liu et al. [38] report 62 cases of neonatal meconium aspiration syndrome with pulmonary hypertension who are treated with mechanical ventilation using electronic cardiac hemodynamics measurement, implying that electronic cardiac measurement is a noninvasive, a highly sensitive, and a highly accurate monitoring tool.

Wu et al. [39] used EC and ECHO to detect the change of CO in 20 children with moderate and severe HIE during rewarming. CO measured by EC and ECHO during rewarming increased from 153 $\pm$ 43 mL/kg/min to 197 $\pm$ 42 mL/kg/min and 149 $\pm$ 35 mL/kg/min to 179 $\pm$ 34 mL/kg/min, respectively. It is found that the CO change during mild hypothermia is not related to stroke output, which remained unchanged, but is related however to the obvious change of cardiac rate during mild hypothermia. Studies show that the increase of the central rate leads to CO increase in neonates with HIE during the whole rewarming process of mild hypothermia treatment. During the rewarming period, systemic vascular resistance and mean arterial blood pressure decreased, but did not reach the gestational age threshold of intervention. Further studies are necessary to investigate whether the significant effect of mild hypothermia on HR and CO is a response to the reduction of basal metabolic rate, or the initiation of a self-protection mechanism. Noninvasive CO monitoring during mild hypothermia is feasible.

Neonatal Acute Respiratory Distress Syndrome (NARDS) is a common respiratory system disorder in neonatal care units, often leading to critical conditions. It typically occurs shortly after birth (24 hours) or during birth. The most severe cases occur within 48 hours after delivery, characterized by progressive respiratory distress, cyanosis, and even respiratory failure. Chest digital radiography (DR) examination is recommended for a comprehensive diagnosis, looking for indicators such as reduced lung translucency or “white lung”. Severe cases of NARDS often require the use of surfactant replacement therapy and mechanical ventilation. The use of EC to monitor hemodynamic changes in NARDS can timely detect unstable blood flow during the disease process, facilitating clinical decision-making. Paviotti et al. [40] include 96 neonates with gestational age of 37.9 $\pm$ 2.6 weeks in the study. Thoracic fluid content (TFC) is recorded within 3 h after birth (TFC1) and 24 h after birth (TFC2) by the bioimpedance method. It is found that TFC measured by electrical bioimpedance is independently associated with respiratory distress at birth and 24 h after birth in late preterm and term neonates.

Bohanon et al. [41] have found that HR variability analysis is more sensitive than routine vital signs in the diagnosis of neonatal sepsis, being the largest preventable disease of neonatal death in the world. Heart rate (HR) variability (HRV) analysis and noninvasive CO shown in many patients with sepsis are a useful auxiliary recognition, unconventional vital signs than traditional vital signs (HRV and CO) and mean arterial pressure are more sensitive to the confirmation of VLBW neonates with sepsis, which helps early recognition of sepsis.

The survey of Katheria et al. [42] show that an increase in LV output and a decrease in average blood pressure, indicating the necessary management of clinically significant PDA. Rodríguez et al. [43] used EC to detect hemodynamic changes in neonates undergoing surgical ligation or drug closure of PDA, and found that CI, stroke volume index (SVI), and ICON decreased in children with closed ductus arteriosus.

Eriksen et al. [44] have found that normal neonatal CO is stable within 0.5~6 hours after birth, and infants with perinatal asphyxia have lower CO before and during treatment. The lower rate of lactic acid loss is found to be less likely to be related to CO but more likely to be an indicator of organ damage due to asphyxia.

Literature reported that three small cohort studies compared the effect of infant position on CO and the presence of differences between prone, left decubitus, and supine positions [45, 46]. Ma et al. [45] found that neonatal EC detection in different positions resulted in reduced CO and stroke output in prone position compared with supine position. Wu et al. [46] used EC (Electrocardiogram) and ECHO (Echocardiography) techniques to confirm that in healthy full-term infants, the decrease in cardiac output (CO) in the prone position is due to a reduction in stroke volume (SV) rather than heart rate (HR) decrease. The cardiac output recovers when in the supine position. These results investigate the changes in systemic and cerebral haemodynamics between supine and prone sleep in healthy term infants, which may have important implications for clinical use, especially as many premature babies tend to be prone to feeding. Paviotti et al. [47] used the EC technique to compare left and supine positions, indicating that SV and CO were reduced.

Invasive mechanical ventilation is reported to affect hemodynamics by changing intrathoracic pressure and venous return volume. Studies are reported that positive end-expiratory pressure (PEEP) have little influence on hemodynamics in the range of 1–10 cm, and high-frequency ventilation affects hemodynamics changes.

Hsu et al. [48] report that PDA may affect EC measurement of CO in 79 premature infants with pulmonary PDA by comparing EC measurement with transthoracic echocardiography. Artery catheter refers to the fetal period significantly connected to the pulmonary artery; the aorta artery catheter function closes shortly after childbirth. However, for various reasons, it leads to the increase of pulmonary vascular resistance, ductus delay shut down and continue to exist. A large number of aorta shunt blood flow to the pulmonary artery, resulting in a large amount of blood flow from left to right shunt, and circulatory blood volume reduction. Increased blood flow in the pulmonary circulatory system leads to abnormal hemodynamic indicators.

The principle of ECG electromechanical measurement is based on the electrical conductivity of blood, and the content of red blood cells in the catheter affects the conduction of electrical signals. In the early stage, our research group conducted a study on two groups of premature infants with gestational age of 32~33 weeks, measured CO at 0.28 L/min in the non-transfusion group and 0.17 L/min in the transfusion group. This indicates that measurements of CO in children with anemia requiring transfusion are lower than those in the non-transfusion group.

A number of studies reported that CO decreases in all infants during mild hypothermia treatment, and the reason after analysis mainly lies in the reduction of HR and the constant output per wave [49, 50]. Study has found that lactic acid clearance rate has nothing to do with CO in HIE children [51].

Walther et al. [52] found that left ventricular output and stroke output of preterm infants significantly increased from day 1 to day 7 after caffeine treatment. Caffeine increased left ventricular output of preterm infants through the combination of positive inotropic and chronotropic effects, and such inotropic effects were accompanied by pressure-boosting effects.