A comparison of cardiac output by thoracic impedance and direct fick in children with congenital heart disease undergoing diagnostic cardiac catheterization

Cardiac Output Measurement in Neonates and Children Using Noninvasive Electrical Bioimpedance Compared With Standard Methods: A Systematic Review and Meta-Analysis

OBJECTIVE

To systematically review and meta-analyze the validity of electrical bioimpedance-based noninvasive cardiac output monitoring in pediatrics compared with standard methods such as thermodilution and echocardiography.

DATA SOURCES

Systematic searches were conducted in MEDLINE and EMBASE (2000-2019).

STUDY SELECTION

Method-comparison studies of transthoracic electrical velocimetry or whole body electrical bioimpedance versus standard cardiac output monitoring methods in children (0-18 yr old) were included.

DATA EXTRACTION

Two reviewers independently performed study selection, data extraction, and risk of bias assessment. Mean differences of cardiac output, stroke volume, or cardiac index measurements were pooled using a random-effects model (R Core Team, R Foundation for Statistical Computing, Vienna, Austria, 2019). Bland-Altman statistics assessing agreement between devices and author conclusions about inferiority/noninferiority were extracted.

DATA SYNTHESIS

Twenty-nine of 649 identified studies were included in the qualitative analysis, and 25 studies in the meta-analyses. No significant difference was found between means of cardiac output, stroke volume, and cardiac index measurements, except in exclusively neonatal/infant studies reporting stroke volume (mean difference, 1.00 mL; 95% CI, 0.23-1.77). Median percentage error in child/adolescent studies approached acceptability (percentage error less than or equal to 30%) for cardiac output in L/min (31%; range, 13-158%) and stroke volume in mL (26%; range, 14-27%), but not in neonatal/infant studies (45%; range, 29-53% and 45%; range, 28-70%, respectively). Twenty of 29 studies concluded that transthoracic electrical velocimetry/whole body electrical bioimpedance was noninferior. Transthoracic electrical velocimetry was considered inferior in six of nine studies with heterogeneous congenital heart disease populations.

CONCLUSIONS

The meta-analyses demonstrated no significant difference between means of compared devices (except in neonatal stroke volume studies). The wide range of percentage error reported may be due to heterogeneity of study designs, devices, and populations included. Transthoracic electrical velocimetry/whole body electrical bioimpedance may be acceptable for use in child/adolescent populations, but validity in neonates and congenital heart disease patients remains uncertain. Larger studies in specific clinical contexts with standardized methodologies are required.

Detection of Low Cardiac Index using a Polyvinylidene Fluoride-Based Wearable Ring and Convolutional Neural Networks

This study investigated the use of a wearable ring made of polyvinylidene fluoride film to identify a low cardiac index (≤2 L/min). The waveform generated by the ring contains patterns that may be indicative of low blood pressure and/or high vascular resistance, both of which are markers of a low cardiac index. In particular, the waveform contains reflection waves whose timing and amplitude are correlated with pulse travel time and vascular resistance, respectively. Hence, the pattern of the waveform is expected to vary in response to changes in blood pressure and vascular resistance. By analyzing the morphology of the waveform, our aim was to create a tool to identify patients with low cardiac index. This was done using a convolutional neural network which was trained on data from animal models. The model was then tested on waveforms that were collected from patients undergoing pulmonary artery catheterization. The results indicate high accuracy in classifying patients with a low cardiac index, achieving an area under the receiver operating characteristics and precision-recall curves of 0.88 and 0.71, respectively.

Electrocardiometry Fluid Responsiveness in Pediatric Septic Shock

Hemodynamic monitoring and categorization of patients based on fluid responsiveness is the key to decisions prompting the use of fluids and vasoactive agents in septic shock. Distinguishing patients who are going to benefit from fluids from those who will not is of paramount importance as large amounts of fluids used conventionally based on surviving sepsis guidelines may be detrimental. Noninvasive monitoring techniques for the assessment of various cardiovascular parameters are increasingly accepted as the current medical practice. Electrical cardiometry (EC) is one such method for the determination of stroke volume, cardiac output (CO), and other hemodynamic parameters and is based on changes in electrical conductivity within the thorax. It has been validated against gold standard methods such as thermodilution [Malik V, Subramanian A, Chauhan S, et al. World J 2014;4(7):101-108] and is being used more often as a point-of-care noninvasive technique for hemodynamic monitoring. EC is Food and Drug Administration approved and validated for use in neonates, children, and adults. A meta-analysis in 2016, including 20 studies and 624 patients comparing the accuracy of CO measurement by using EC with other noninvasive technologies, demonstrated that EC was the device that offered the most correct measurements. The article in the current issue of IJCCM by Rao et al. (2020) has extended the use of EC to categorize pediatric patients with septic shock into vasodilated and vasoconstricted states based on systemic vascular resistance and correlate the categorization clinically. The authors also studied the changes in hemodynamic parameters after an isotonic fluid bolus of 20 mL/kg was administered. This is a pilot prospective observational study of 30 patients, which has given an insight into physiological rearrangements following fluid administration in patients with septic shock. How to cite this article: Gupta D, Dhingra. Electrocardiometry Fluid Responsiveness in Pediatric Septic Shock. Indian J Crit Care Med 2021;25(2):123-125.

A Novel Mechanism for Improved Exercise Performance in Pediatric Fontan Patients After Cardiac Rehabilitation

Patients with a Fontan circulation have impaired exercise capacity. Cardiac rehabilitation (CR) has shown promise in enhancing peak exercise parameters in this population, but an improvement in submaximal exercise has not been consistently demonstrated. We assessed the hypothesis that participation in CR will be associated with more efficient oxygen extraction and ventilation during submaximal exercise. In this prospective study, pediatric Fontans completed two 60 min CR sessions per week for 12 weeks. Cardiopulmonary exercise testing and stress echocardiography were performed at baseline and last CR session, and then compared with a paired sample t test. Ten pediatric Fontans completed the study. Five had tricuspid atresia and five had hypoplastic left heart syndrome. No serious adverse events occurred during CR sessions. Peak indexed oxygen consumption increased by a mean of 3.7 mL/kg/min (95% CI 1.5-5.9; p = 0.004), and peak oxygen pulse increased by a mean of 0.9 mL/beat (95% CI 0.4-1.4; p = 0.004). The peak respiratory exchange ratio did not change significantly. The significant difference in oxygen pulse became evident during submaximal exercise without a corresponding difference in echocardiographic stroke volume. Indexed oxygen consumption at ventilatory anaerobic threshold increased by a mean of 3.0 mL/kg/min (95% CI - 0.07 to 6.0; p = 0.055). The slope for the volume of expired ventilation to volume of carbon dioxide production improved by a mean of 4.5 (95% CI - 8.4 to - 0.6; p = 0.03). We observed significant improvements in both submaximal and peak exercise performance in pediatric Fontans undergoing CR with no serious adverse events. These changes appeared to be mediated, at least in part, by more efficient oxygen extraction and ventilation.

Understanding the Haemodynamics of Hypertension

PURPOSE OF REVIEW

This article introduces the haemodynamic principles that underpin the pathophysiology of hypertension and introduces a rational physiological approach to appropriate pharmacologic treatment.

RECENT FINDINGS

Outdated understanding of haemodynamics based on previous measurement systems can no longer be applied to our understanding of the circulation. We question the current view of hypertension as defined by a predominantly systolic blood pressure and introduce the concept of vasogenic, cardiogenic and mixed-origin hypertension. We postulate that failure to identify the individual's haemodynamic pattern may lead to the use of inappropriate medication, which in turn may be a major factor in patient non-compliance with therapeutic strategies. A population-based approach to treatment of hypertension may lead to suboptimal functional dynamics in the individual patient. Finally, we question the validity of current guidelines and published evidence relating morbidity and mortality to the future treatment of hypertension. The importance of individual haemodynamic profiles may be pivotal in the understanding, diagnosis and treatment of hypertension if optimal control with minimal adverse effects is to be achieved. Research based on individual haemodynamic patterns is overdue.

Reliability of Peak Exercise Stroke Volume Assessment by Impedance Cardiography in Patients with Residual Right Outflow Tract Lesions After Congenital Heart Disease Repair

Global ventricular response to exercise may be useful in follow-up of patients with residual right outflow tract lesions after congenital heart disease repair. In this context, impedance cardiography is considered accurate for stroke volume (SV) measurement during exercise testing, however, to date, only partial assessment of its reliability has been reported. We retrospectively evaluated relative and absolute reliability of peak SV by impedance cardiography during exercise using intraclass correlation (ICC) and standard error of measurement (SEM) in this population. Peak SV was measured in 30 young patients (mean age 14.4 years ± 2.1) with right ventricular outflow tract reconstruction who underwent two cardiopulmonary exercise tests at a mean one-year interval. SV was measured using a signal morphology impedance cardiography analysis device (PhysioFlow^®) and was indexed to body surface area. ICC of peak indexed SV measurement was 0.80 and SEM was 10.5%. High heterogeneity was seen when comparing patients according to peak indexed SV; in patients with peak SV < 50 ml/m² (15 patients), ICC rose to 0.95 and SEM dropped to 2.7%, while in patients with a peak SV > 50 ml/m² relative and absolute reliability decreased (ICC = 0.45, SEM = 12.2%). Peak exercise SV assessment by a PhysioFlow^® device represents a highly reliable method in patients with residual right outflow tract lesions after congenital heart disease repair, especially in patients with peak SV < 50 ml/m². In this latter group, a peak SV decrease > 7.3% (corresponding to the minimum "true" difference) should be considered a clinically-relevant decrease in global ventricular performance and taken into account when deciding whether to perform residual lesion removal.

Cardiac Output Monitoring in Preterm Infants

Maintaining optimal circulatory status is a key component of preterm neonatal care. Low-cardiac output (CO) in the preterm neonate leads to inadequate perfusion of vital organs and has been linked to a variety of adverse outcomes with heightened acute morbidity and mortality and adverse neurodevelopmental outcomes. Having technology available to monitor CO allows us to detect low-output states and potentially intervene to mitigate the unwanted effects of reduced organ perfusion. There are many technologies available for the monitoring of CO in the preterm neonatal population and while many act as useful adjuncts to aid clinical decision-making no technique is perfect. In this review, we discuss the relative merits and limitations of various common methodologies available for monitoring CO in the preterm neonatal population. We will discuss the ongoing challenges in monitoring CO in the preterm neonate along with current gaps in our knowledge. We conclude by discussing emerging technologies and areas that warrant further study.

Stroke Volume Monitoring: Novel Continuous Wave Doppler Parameters, Algorithms and Advanced Noninvasive Haemodynamic Concepts

PURPOSE OF REVIEW

Adequate oxygen delivery is essential for life, with hypoxia resulting in dysfunction, and ultimately death, of the cells, organs and organism. Blood flow delivers the oxygen bound in the blood, while haemodynamics is the science of blood flow. Stroke volume (SV) is the fundamental unit of blood flow, and reflects the interdependent performance of the heart, the vessels and the autonomic nervous system. However, haemodynamic management remains generally poor and predominantly guided by simple blood pressure observations alone.

RECENT FINDINGS

Doppler ultrasound measures SV with unequalled clinical precision when operated by trained personnel. Combining SV with BP measurements allows calculation of flow-pressure based measures which better reflect cardiovascular performance and allows personalised physiologic and pathophysiologic modelling consistent with Frank's and Starling's observations.

SUMMARY

Doppler SV monitoring and novel flow-pressure parameters may improve our understanding of the cardiovascular system and lead to improved diagnosis and therapy. This review examines the physics and practice of Doppler SV monitoring and its application in advanced haemodynamics.

Impedance cardiography in healthy children and children with congenital heart disease: Improving stroke volume assessment

INTRODUCTION

Stroke volume (SV) and cardiac output are important measures in the clinical evaluation of cardiac patients and are also frequently used in research applications. This study was aimed to improve SV scoring derived from spot-electrode based impedance cardiography (ICG) in a pediatric population of healthy volunteers and patients with a corrected congenital heart defect.

METHODS

128 healthy volunteers and 66 patients participated. First, scoring methods for ambiguous ICG signals were optimized to improve agreement of B- and X-points with aortic valve opening/closure in simultaneously recorded transthoracic echocardiography (TTE). Building on the improved scoring of B- and X-points, the Kubicek equation for SV estimation was optimized by testing the agreement with the simultaneously recorded SV by TTE. Both steps were initially done in a subset of the sample of healthy children and then validated in the remaining subset of healthy children and in a sample of patients.

RESULTS

SV assessment by ICG in healthy children strongly improved (intra class correlation increased from 0.26 to 0.72) after replacing baseline thorax impedance (Z₀) in the Kubicek equation by an equation (7.337-6.208∗dZ/dt_max), where dZ/dt_max is the amplitude of the ICG signal at the C-point. Reliable SV assessment remained more difficult in patients compared to healthy controls.

CONCLUSIONS

After proper adjustment of the Kubicek equation, SV assessed by the use of spot-electrode based ICG is comparable to that obtained from TTE. This approach is highly feasible in a pediatric population and can be used in an ambulatory setting.

Clinical comparative analysis of histidine-tryptophan-ketoglutarate solution and St. Thomas crystalloid cardioplegia: A 12-year study from a single institution

Cardioplegic reperfusion during a long-term ischemic period interrupts cardiac surgery and increases cellular edema due to repeated administration. The present clinical study compared the protective effects of histidine-ketoglutarate-tryptophan (HTK) solution and St. Thomas crystalloid cardioplegia. Clinical experiences of the myocardial protection induced by one single perfusion with HTK were reviewed in high-risk patients with severe pulmonary arterial hypertension associated with complex congenital heart disease. This retrospective study included 88 high-risk patients (aortic cross-clamp time, >120 min) between March 2001 and July 2012. The cohort was divided into two groups according to the technique used. Either myocardial protection was performed with one single perfusion with HTK solution (HTK group) or with conventional St. Thomas crystalloid cardioplegia (St group). The duration of cardiopulmonary bypass did not differ between the two groups. The mortality, morbidity, intensive care unit (ICU) stay, postoperative hospitalization, and transfusions of HTK group are significantly lower than those of the St group (P<0.05). Univariate and multivariate analysis demonstrated that HTK is a statistically significant independent predictor of decreased early mortality and morbidity (P<0.05). In conclusion, the present findings suggested that HTK solution decreases mortality, morbidity, ICU stay, postoperative hospitalization, and transfusions in high-risk patients with severe pulmonary arterial hypertension associated with complex congenital heart disease.

Evaluation of Impedance Cardiography for Measurement of Stroke Volume in Congenital Heart Disease

Noninvasive measurement of cardiac output (CO) and particularly stroke volume (SV) remain difficult but potentially valuable. These variables can be particularly challenging to measure in children with congenital heart disease (CHD). Impedance cardiography (IC) is a technique shown to be accurate in measuring SV in adults and in children with structurally normal hearts. The ease of use and rapidity of SV measurement using IC makes it potentially attractive for young patients with CHD. Advances in IC technology have led to more sophisticated signal-morphology IC (SMIC) devices that may further improve accuracy. We tested the accuracy of SMIC to measure SV in 21 subjects with CHD by comparing measurements with those from cardiac magnetic resonance (CMR) imaging. There was good agreement between SMIC and CMR in measurement of SV: mean difference = 1.7 ml (p = 0.47); r = 0.89. The agreement and correlation persisted when controlling for the differences in blood pressure and heart rate during the two testing methods. We conclude that SMIC is accurate at measuring SV and thus CO when compared to CMR in a variety of forms of CHD.

Effect of patent ductus arteriosus and patent foramen ovale on left ventricular stroke volume measurement by electrical velocimetry in comparison to transthoracic echocardiography in neonates

This prospective single-center observational study compared impedance cardiography [electrical velocimetry (EV)] with transthoracic echocardiography (TTE, based on trans-aortic flow) and analyzed the influence of physiological shunts, such as patent ductus arteriosus (PDA) or patent foramen ovale (PFO), on measurement accuracy. Two hundred and ninety-one triplicate simultaneous paired left ventricular stroke volume (LVSV) measurements by EV (LVSV_EV) and TTE (LVSV_TTE) in 99 spontaneously breathing neonates (mean weight 3270 g; range 1227-4600 g) were included. For the whole cohort, the mean absolute LVSV_EV was 5.5 mL, mean LVSV_TTE was 4.9 mL, resulting in an absolute Bland-Altman bias of -0.7 mL (limits of agreement LOA -3.0 to 1.7 mL), relative bias -12.8 %; mean percentage error MPE 44.9 %; true precision TP_EV 33.4 % (n = 99 aggregated data points). In neonates without shunts (n = 32): mean LVSV_EV 5.0 mL, mean LVSV_TTE 4.6 mL, Bland-Altman bias -0.4 mL (LOA -2.8 to 2.0 mL), relative bias -8.2 %; MPE 50.7 %; TP_EV 40.9 %. In neonates with shunts (PDA and/or PFO; n = 67): mean LVSV_EV 5.8 mL, mean LVSV_TTE 5.0 mL, bias -0.8 mL (LOA -3.1 to 1.5 mL), relative bias -14.8 %, MPE 41.9 %, TP_EV 29.3 %. Accuracy was affected by PDA and/or PFO, with a significant increase in the relative difference in LVSV_EV versus LVSV_TTE: Subjects without shunts -2.9 % (n = 91), PFO alone -9.6 % (n = 125), PDA alone -14.0 % (n = 12), and PDA and PFO -18.5 % (n = 63). Physiological shunts (PDA and/or PFO) in neonates affect measurement accuracy and cause overestimation of LVSV_EV compared with LVSV_TTE.

Accuracy and precision of minimally-invasive cardiac output monitoring in children: a systematic review and meta-analysis

Several minimally-invasive technologies are available for cardiac output (CO) measurement in children, but the accuracy and precision of these devices have not yet been evaluated in a systematic review and meta-analysis. We conducted a comprehensive search of the medical literature in PubMed, Cochrane Library of Clinical Trials, Scopus, and Web of Science from its inception to June 2014 assessing the accuracy and precision of all minimally-invasive CO monitoring systems used in children when compared with CO monitoring reference methods. Pooled mean bias, standard deviation, and mean percentage error of included studies were calculated using a random-effects model. The inter-study heterogeneity was also assessed using an I(2) statistic. A total of 20 studies (624 patients) were included. The overall random-effects pooled bias, and mean percentage error were 0.13 ± 0.44 l min(-1) and 29.1 %, respectively. Significant inter-study heterogeneity was detected (P < 0.0001, I(2) = 98.3 %). In the sub-analysis regarding the device, electrical cardiometry showed the smallest bias (-0.03 l min(-1)) and lowest percentage error (23.6 %). Significant residual heterogeneity remained after conducting sensitivity and subgroup analyses based on the various study characteristics. By meta-regression analysis, we found no independent effects of study characteristics on weighted mean difference between reference and tested methods. Although the pooled bias was small, the mean pooled percentage error was in the gray zone of clinical applicability. In the sub-group analysis, electrical cardiometry was the device that provided the most accurate measurement. However, a high heterogeneity between studies was found, likely due to a wide range of study characteristics.

Continuous noninvasive cardiac output in children: is this the next generation of operating room monitors? Initial experience in 402 pediatric patients

BACKGROUND

Electrical Cardiometry(™) (EC) estimates cardiac parameters by measuring changes in thoracic electrical bioimpedance during the cardiac cycle. The ICON(®), using four electrocardiogram electrodes (EKG), estimates the maximum rate of change of impedance to peak aortic blood acceleration (based on the premise that red blood cells change from random orientation during diastole (high impedance) to an aligned state during systole (low impedance)).

OBJECTIVE

To determine whether continuous cardiac output (CO) data provide additional information to current anesthesia monitors that is useful to practitioners.

METHODS

After IRB approval and verbal consent, 402 children were enrolled. Data were uploaded to our anesthesia record at one-minute intervals. Ten-second measurements (averaged over the previous 20 heart beats) were downloaded to separate files for later comparison with routine OR monitors.

RESULTS

Data from 374 were in the final cohort (loss of signal or improper lead placement); 292,012 measurements during 58,049 min of anesthesia were made in these children (1 day to 19 years and 1 to 107 kg). Four events had a ≥25% reduction in cardiac index at least 1 min before a clinically important change in other monitored parameters; 18 events in 14 children confirmed manifestations of other hemodynamic measures; eight events may have represented artifacts because the observed measurements did not seem to fit the clinical parameters of the other monitors; three other events documented decreased stroke index with extreme tachycardia.

CONCLUSIONS

Electrical cardiometry provides real-time cardiovascular information regarding developing hemodynamic events and successfully tracked the rapid response to interventions in children of all sizes. Intervention decisions must be based on the combined data from all monitors and the clinical situation. Our experience suggests that this type of monitor may be an important addition to real-time hemodynamic monitoring.

The PhysioFlow thoracic impedancemeter is not valid for the measurements of cardiac hemodynamic parameters in chronic anemic patients

The aim of the present study was to test the validity of the transthoracic electrical bioimpedance method PhysioFlow® to measure stroke volume in patients with chronic anemia. Stroke volume index (SVI), as well as cardiac index (CI) obtained by transthoracic electrical bioimpedance method and doppler echocardiography were compared in healthy subjects (n = 25) and patients with chronic anemia (i.e. mainly with sickle cell anemia; n = 32), at rest. While doppler echocardiography was able to detect difference in SVI between the two populations, the Physioflow® failed to detect any difference. Bland & Altman analyses have demonstrated no interchangeability between the two methods to assess CI and SVI in anemic patients and healthy subjects. While doppler echocardiography displayed a good concordance for SVI results with those obtained in the literature for anemic patients, the Physioflow® did not. Finally, in contrast to doppler echocardiography: 1) the CI obtained with the Physioflow® was not correlated with the hemoglobin level and 2) the stroke volume determined by the Physioflow® was highly influenced by body surface area. In conclusion, our findings indicate that the Physioflow® device is inaccurate for the measurement of SVI and CI in patients with chronic anemia and has a poor accuracy for the measurement of these parameters in African healthy subjects.

Cardiac parameters in children recovered from acute illness as measured by electrical cardiometry and comparisons to the literature

Electrical cardiometry (EC) is a non-invasive cardiac output method that can assess cardiac index (CI) and stroke index (SI) but there are no reference values for children per se. The primary aim of this study was to develop reference values for clinical application. The secondary aim was to compare the EC measurements to published values. We performed a prospective observational study in patients (<21 years of age) without structural heart disease who had recovered from an acute illness. EC recordings in children that had normal heart rate and mean arterial blood pressure at discharge were eligible for analysis. The relationship of CI or SI and age in children was performed by regression analysis. Similar analysis was performed comparing measurements by EC to cardiac parameters values compiled from reference sources to assess bias in EC. Eighty-three children (2 weeks-21 years of age) were studied. There was a significant curvilinear relationship between CI or SI and age by EC (F-test, p < 0.05). Regression curves of cardiac parameters reported in the literature using 6 Fick's method, thermodilution, echocardiography and cardiac MRI were the same or higher than (0-19.6 %) values obtained with EC, with higher values being statistically significant (p < 0.05 all). There is a curvilinear relationship of CI or SI and age by EC in normal children. Cardiac parameters reported in the literature using alternative methods are different from those obtained with EC but are within acceptable ranges, with EC biased to underestimate CI. Adjustment of target value is required for EC goal-directed therapies.

New technologies in pediatric anesthesia

This article reviews potential pediatric applications of 3 new technologies. (1) Pulse oximetry-based hemoglobin determination: Hemoglobin determination using spectrophotometric methods recently has been introduced in adults with varied success. This non-invasive and continuous technology may avoid venipuncture and unnecessary transfusion in children undergoing surgery with major blood loss, premature infants undergoing unexpected and complicated emergency surgery, and children with chronic illness. (2) Continuous cardiac output monitoring: In adults, advanced hemodynamic monitoring such as continuous cardiac output monitoring has been associated with better surgical outcomes. Although it remains unknown whether similar results are applicable to children, current technology enables the monitoring of cardiac output non-invasively and continuously in pediatric patients. It may be important to integrate the data about cardiac output with other information to facilitate therapeutic interventions. (3) Anesthesia information management systems: Although perioperative electronic anesthesia information management systems are gaining popularity in operating rooms, their potential functions may not be fully appreciated. With advances in information technology, anesthesia information management systems may facilitate bedside clinical decisions, administrative needs, and research in the perioperative setting.