Cardiac output measurement in children: comparison of the Ultrasound Cardiac Output Monitor with thermodilution cardiac output measurement

Hemodynamic evaluation in preterm infants using ultrasonic cardiac output monitor (USCOM)

We aimed to establish reference ranges for USCOM parameters in preterm infants, determine factors that affect cardiac output, and evaluate the measurement repeatability. This retro-prospective study was performed at Fondazione IRCCS San Gerardo dei Tintori, Monza, Italy. We included infants below 32 weeks of gestational age (GA) and/or 1500 g of birth weight (BW). We excluded infants with congenital heart diseases or hemodynamic instability. Measurements were performed at 3 ± 1, 7 ± 2, and 14 ± 2 postnatal days. We analyzed 204 measurements from 92 patients (median GA = 30.57 weeks, BW = 1360 g). The mean (SD) cardiac output (CO) was 278 (55) ml/min/kg, cardiac index (CI) was 3.1 (0.5) L/min/m2, and systemic vascular resistance (SVRI) was 1292 (294) d*s*cm-5/m2. CO presented a negative correlation with postmenstrual age (PMA), while SVRI presented a positive correlation with PMA. The repeatability coefficient was 31 ml/kg/min (12%).  Conclusion: This is the first study describing reference values for USCOM parameters in hemodynamically stable preterm infants and factors affecting their variability. Further studies to investigate the usefulness of USCOM for the longitudinal assessment of patients at risk for cardiovascular instability or monitoring the response to therapies are warranted. What is Known: • The ultrasonic cardiac output monitoring (USCOM) has been widely used on adult and pediatric patients and reference ranges for cardiac output (CO) by USCOM have been established in term infants. What is New: • We established reference values for USCOM parameters in very preterm and very-low-birth-weight infants; the reference ranges for CO by USCOM in the study population were 198-405 ml/kg/min. • CO normalized by body weight presented a significant negative correlation with postmenstrual age (PMA); systemic vascular resistance index presented a significant positive correlation with PMA.

Cardiac output monitoring in children: a review

Cardiac output monitoring enables physiology-directed management of critically ill children and aids in the early detection of clinical deterioration. Multiple invasive techniques have been developed and have demonstrated ability to improve clinical outcomes. However, all require invasive arterial or venous catheters, with associated risks of infection, thrombosis and vascular injury. Non-invasive monitoring of cardiac output and fluid responsiveness in infants and children is an active area of interest and several proven techniques are available. Novel non-invasive cardiac output monitors offer a promising alternative to echocardiography and have proven their ability to influence clinical practice. Assessment of perfusion remains a challenge; however, technologies such as near-infrared spectroscopy and photoplethysmography may prove valuable clinical adjuncts in the future.

Use of CO2-Derived Variables in Cardiac Intensive Care Unit: Pathophysiology and Clinical Implications

Shock is a life-threatening condition, and its timely recognition is essential for adequate management. Pediatric patients with congenital heart disease admitted to a cardiac intensive care unit (CICU) after surgical corrections are particularly at risk of low cardiac output syndrome (LCOS) and shock. Blood lactate levels and venous oxygen saturation (ScVO₂) are usually used as shock biomarkers to monitor the efficacy of resuscitation efforts, but they are plagued by some limitations. Carbon dioxide (CO₂)-derived parameters, namely veno-arterial CO₂ difference (ΔCCO₂) and the VCO₂/VO₂ ratio, may represent a potentially valuable addition as sensitive biomarkers to assess tissue perfusion and cellular oxygenation and may represent a valuable addition in shock monitoring. These variables have been mostly studied in the adult population, with a strong association between ΔCCO₂ or VCO₂/VO₂ ratio and mortality. In children, particularly in CICU, few studies looked at these parameters, while they reported promising results on the use of CO₂-derived indices for patients' management after cardiac surgeries. This review focuses on the physiological and pathophysiological determinants of ΔCCO₂ and VCO₂/VO₂ ratio while summarizing the actual state of knowledge on the use of CO₂-derived indices as hemodynamical markers in CICU.

Perioperative fluid management in children: an updated review

Background: Perioperative fluid management in children has been a major topic for debate. Objectives: Our aim is to review the current evidence on perioperative fluid management in children including: type of fluid, administration rates, preoperative fluid intake and monitoring techniques. Design: Narrative review. Method: Following the PRISMA-S guidelines we performed a search (2010-March 2022) in databases Medline (through PubMed) and Cochrane Library. 4297 citations were found and screened by two independent researchers. After screening, 64 articles were withheld for our review. Results: The perioperative administration of isotonic fluids is safer than hypotonic solutions, concerning the development of hyponatremia. A balanced isotonic solution with 1-2,5% glucose should be used as perioperative maintenance IV fluid in children (1 month to 18 years). Colloids can be used in children when inadequate effect in volume correction is achieved with crystalloids. The preferred synthetic colloid for children is a third generation HES in a balanced solution. To date, most clinicians use the “4-2-1 rule” for calculating fluid rate. This may not be the optimal fluid rate, as little research has been done. Preoperative fasting for clear fluids should be limited to 1 hour, children should even be encouraged to drink up until 1 hour before induction. Respiratory variation of aortic blood flow peak velocity (ΔVpeak) with echocardiography is currently the most reliable technique for evaluating fluid responsiveness in children.

Measurement of Cardiac Output Using an Ultrasonic Cardiac Output Monitor (USCOM) in Patients with Single-Ventricle Physiology

We evaluate the validity of cardiac index (CI) measurements utilizing the Ultrasonic Cardiac Output Monitor (USCOM), a non-invasive Doppler ultrasound device, by comparing measurements to cardiac catheterization-derived CI measurements in patients with single-ventricle physiology. USCOM measurements were repeated three times for each patient at the beginning of a cardiac catheterization procedure for twenty-six patients undergoing elective pre-Glenn or pre-Fontan catheterization. CI was measured by USCOM and was calculated from cardiac catheterization data using Fick's method. Bland-Altman analysis for CI showed bias of 0.95 L/min/m² with the 95% limits of agreement of - 1.85 and 3.75. Pearson's correlation coefficient was 0.89 (p < 0.001) indicating a strong positive relationship between USCOM and cardiac catheterization CI measurements. When excluding two patients with significant dilation of the neo-aortic valve (z-score >  + 5), the bias improved to 0.66 L/min/m² with the 95% limits of agreement of - 1.38 and 2.70. Percent error of limits of agreement was 34%. There was excellent intra-operator reproducibility of USCOM CI measurements with an intra-class coefficient of 0.96. We demonstrate the use of USCOM to measure CI in patients with single-ventricle physiology for the first time, showing acceptable agreement of the CI measurements between USCOM and cardiac catheterization with a high intra-operator reproducibility.

Characteristics of hemodynamic parameters after fluid resuscitation and vasoactive drugs administration in pediatric shock: A prospective observational study

Background

Prior studies have shown that septic shock survivors had a normal cardiac index (CI) and systemic vascular resistance index (SVRI). However, this feature seems to be questionable in other-caused shock, since several factors are associated with the hemodynamic profile. This study aims to describe hemodynamic profiles (preload, inotropy, afterload, stroke volume, and cardiac output) after fluid resuscitation and vasoactive therapy in children with shock.

Methods

Children aged 1 month to 18 years old with shock conditions were included in this study. Fluid resuscitation was administered following the American College of Critical Care Medicine (ACCM) protocol. Hemodynamic profiles were assessed at 1 and 6 h from the start of fluid resuscitation. Grouping of the subjects was determined by the USCOM examination in 1st hour until the end of the study and we divided into 3 groups.

Results

At 1 h, group 1 (low CI) was 14% (CI:2.5[1.2–3.2]L/min/m²), group 2 (normal CI) was 66% (CI:4.2[3.4–5.8]L/min/m²), and group 3 (high CI) was 20% (CI:7.1[6.1–9.4]L/min/m²). SVRI was higher in groups 1 and 2 compared to group 3 (p < 0.05). Group 1 and 2 revealed fluid-refractory shock (SVV:25[12–34]% and 29(13–58)%, respectively), lower Smith-Madigan Inotropy Index (SMII) and higher Potential to Kinetic Ratio (PKR) compared to group 3 (p < 0.05). Group 3 revealed fluid-responsive shock (Stroke Volume Variation (SVV):32[18–158]%), higher SMII and lower PKR. At 6th hour, CI in all groups were normal (group 1:3.5[1.2–7.5]; group 2:4.0[1.7–6.1]; group 3:6.0[3.1–6.2]). However, 71.4% and 54.5% of subjects in groups 1 and 2, respectively, still revealed low inotropy. Group 3 revealed a significant increase in SVRI and PKR (p < 0.01).

Conclusions

Most pediatric shock patients were hypodynamic. Even when the CI was normal, the preload, inotropy, and afterload may still be abnormal. It represented the inotropy as a key to hemodynamic.

•

Describe the macrocirculation parameter (preload, inotropy, afterload) in children with shock.

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Most pediatric shock tend to be hypodynamic.

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Fluid and vasoactive agent therapy should be guided by combination of the hemodynamic parameters.

A novel, hands-free ultrasound patch for continuous monitoring of quantitative Doppler in the carotid artery

Quantitative Doppler ultrasound of the carotid artery has been proposed as an instantaneous surrogate for monitoring rapid changes in left ventricular output. Tracking immediate changes in the arterial Doppler spectrogram has value in acute care settings such as the emergency department, operating room and critical care units. We report a novel, hands-free, continuous-wave Doppler ultrasound patch that adheres to the neck and tracks Doppler blood flow metrics in the common carotid artery using an automated algorithm. String and blood-mimicking test objects demonstrated that changes in velocity were accurately measured using both manually and automatically traced Doppler velocity waveforms. In a small usability study with 22 volunteer users (17 clinical, 5 lay), all users were able to locate the carotid Doppler signal on a volunteer subject, and, in a subsequent survey, agreed that the device was easy to use. To illustrate potential clinical applications of the device, the Doppler ultrasound patch was used on a healthy volunteer undergoing a passive leg raise (PLR) as well as on a congestive heart failure patient at resting baseline. The wearable carotid Doppler patch holds promise because of its ease-of-use, velocity measurement accuracy, and ability to continuously record Doppler spectrograms over many cardiac and respiratory cycles.

Ultrasound Cardiac Output Monitor (USCOM™) Measurements Prove Unreliable Compared to Cardiac Magnetic Resonance Imaging in Adolescents with Cardiac Disease

The purpose of this stuy is to prospectively assess the reliability of the ultrasound cardiac output monitor (USCOM™) for measuring stroke volume index and predicting left ventricular outflow tract diameter in adolescents with heart disease. Sixty consecutive adolescents with heart disease attending a tertiary medical center underwent USCOM™ assessment immediately after cardiac magnetic resonance imaging. USCOM™ measured stroke volume index and predicted left ventricular outflow tract diameter were compared to cardiac magnetic resonance imaging-derived values using Bland-Altman analysis. Ten patients with an abnormal left ventricular outflow tract were excluded from the analysis. An adequate USCOM™ signal was obtained in 49/50 patients. Mean stroke volume index was 46.1 ml/m² by the USCOM™ (range 22-66.9 ml/m²) and 42.9 ml/m² by cardiac magnetic resonance imaging (range 24.7-59.9 ml/m²). The bias (mean difference) was 3.2 ml/m²; precision (± 2SD of differences), 17 ml/m²; and mean percentage error, 38%. The mean (± 2SD) left ventricular outflow tract diameter was 0.445 ± 0.536 cm smaller by the USCOM™ algorithm prediction than by cardiac magnetic resonance imaging. Attempted adjustment of USCOM™ stroke volume index using cardiac magnetic resonance imaging left ventricular outflow tract diameter failed to improve agreement between the two modalities (bias 28.4 ml/m², precision 44.1 ml/m², percentage error 77.3%). Our study raises concerns regarding the reliability of USCOM™ for stroke volume index measurement in adolescents with cardiac disease, which did not improve even after adjusting for its inaccurate left ventricular outflow tract diameter prediction.

Determining pediatric fluid responsiveness by stroke volume variation analysis using ICON® electrical cardiometry and ultrasonic cardiac output monitor: A cross-sectional study

Purpose:

The purpose is to determine the adequacy fluid responsiveness by the validity and cut off point of stroke volume variation (SVV) usingelectrical cardiometry, ICON® (Osypka Medical, Berlin, Germany) and ultrasonic cardiac output monitor (USCOM) and to recognize cut off point of tidal volume in shock children with mechanical ventilation.

Materials and Methods:

A cross-sectional study was conducted from March 2017 to September 2017 in a single center. The selection of subject through consecutive sampling. Measurements of SVV and stroke volume (SV) using USCOM and ICON were performed before and after fluid challenge. The tidal volume of individuals was measured and recorded.

Results:

Analysis was performed in 45 patients with median age of 14 months and 62.2% of male population. It showed that the sensitivity and specificity of ICON were 58% and 74%, respectively. The optimal cut off point of SVV using ICON was 16.5% and the area under the curve (AUC) value was 53% (95% confidence interval [CI] 35.9%–70%), P > 0.05 and cut off point of SVV using USCOM was 33.5% with the AUC value was 70% (95% CI 52.9%–87.7%), P < 0.05. The optimal cut off point of tidal volume to fluid responsivenes was 6.8 ml/kg BW and the AUC value was 44.6% (95% CI 27.4%–61.9%), P > 0.05.

Conclusion:

This study showed that electrical cardiometry (ICON) is unable to assess preload and the response of fluid resuscitation in children.

Cardiac output measurements via echocardiography versus thermodilution: A systematic review and meta-analysis

Echocardiography, as a noninvasive hemodynamic evaluation technique, is frequently used in critically ill patients. Different opinions exist regarding whether it can be interchanged with traditional invasive means, such as the pulmonary artery catheter thermodilution (TD) technique. This systematic review aimed to analyze the consistency and interchangeability of cardiac output measurements by ultrasound (US) and TD. Five electronic databases were searched for studies including clinical trials conducted up to June 2019 in which patients’ cardiac output was measured by ultrasound techniques (echocardiography) and TD. The methodological quality of the included studies was evaluated by two independent reviewers who used the Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2), which was tailored according to our systematic review in Review Manager 5.3. A total of 68 studies with 1996 patients were identified as eligible. Meta-analysis and subgroup analysis were used to compare the cardiac output (CO) measured using the different types of echocardiography and different sites of Doppler use with TD. No significant differences were found between US and TD (random effects model: mean difference [MD], -0.14; 95% confidence interval, -0.30 to 0.02; P = 0.08). No significant differences were observed in the subgroup analyses using different types of echocardiography and different sites except for ascending aorta (AA) (random effects model: mean difference [MD], -0.37; 95% confidence interval, -0.74 to -0.01; P = 0.05) of Doppler use. The median of bias and limits of agreement were -0.12 and ±0.94 L/min, respectively; the median of correlation coefficient was 0.827 (range, 0.140–0.998). Although the difference in CO between echocardiography by different types or sites and TD was not entirely consistent, the overall effect of meta-analysis showed that no significant differences were observed between US and TD. The techniques may be interchangeable under certain conditions.

Fluid responsiveness in the pediatric population

It is challenging to predict fluid responsiveness, that is, whether the cardiac index or stroke volume index would be increased by fluid administration, in the pediatric population. Previous studies on fluid responsiveness have assessed several variables derived from pressure wave measurements, plethysmography (pulse oximeter plethysmograph amplitude variation), ultrasonography, bioreactance data, and various combined methods. However, only the respiratory variation of aortic blood flow peak velocity has consistently shown a predictive ability in pediatric patients. For the prediction of fluid responsiveness in children, flow- or volume-dependent, noninvasive variables are more promising than pressure-dependent, invasive variables. This article reviews various potential variables for the prediction of fluid responsiveness in the pediatric population. Differences in anatomic and physiologic characteristics between the pediatric and adult populations are covered. In addition, some important considerations are discussed for future studies on fluid responsiveness in the pediatric population.

Cardiac Output Measurement Using the Ultrasonic Cardiac Output Monitor: A Validation Study in Newborn Infants

OBJECTIVES

We aimed to determine the accuracy and validity of the Ultrasonic Cardiac Output Monitor (USCOM) measurements of cardiac output (CO) compared to echocardiography in newborn infants, and the inter-rater agreement of USCOM measurements.

METHODS

In a single-center study we prospectively evaluated neonates undergoing an echocardiographic evaluation. USCOM measurements of CO were obtained at the pulmonary and aortic valve by 2 physicians blinded to the echocardiographic results. All echocardiographic measurements were performed blinded to USCOM measurements. We first enrolled an ascertainment cohort which was subsequently validated in an independent new cohort. Agreement between echocardiography and USCOM methods was assessed by Bland-Altman analysis. Intra-class correlation coefficients (ICC) assessed the agreement between the 2 operators. The ascertainment cohort correction factors were applied in a second validation cohort and agreement of the calibrated measures evaluated with repeat Bland-Altman comparisons.

RESULTS

A total of 50 infants were enrolled in the initial cohort and 15 in the validation cohort. There was a high degree of correlation between the USCOM operators (ICC = 0.975). USCOM measurements of CO were significantly higher compared to echocardiography (left ventricular output bias 95 ± 52 mL/kg/min and right ventricular output bias 64 ± 30 mL/kg/min). There was no difference in the subgroup of infants with and without a ductus arteriosus. After the correction was applied to the validation cohort, there was no longer a significant difference between the measures.

CONCLUSIONS

CO measured by USCOM consistently overestimated the results obtained from echocardiography. USCOM is not adequate to provide absolute estimates of CO. However, it may allow longitudinal hemodynamic assessment of sick neonates.

Noninvasive hemodynamic monitoring of septic shock in children

Septic shock in children is associated with high mortality and morbidity. Its management is time-sensitive and must be aggressive and target oriented. The use of clinical assessment alone to differentiate between cold and warm shock and to select the appropriate inotropic and vasoactive medications is fraught with errors. Semi-quantitative and quantitative assessment of the preload, contractility and afterload using non-invasive tools has been suggested, in conjunction with clinical and laboratory assessment, to direct shock management and select between vasopressors, vasodilators and inotropes or a combination of these drugs. This review aims to describe non-invasive tools to assess the hemodynamic status in septic shock including echocardiography, trans-thoracic/trans-esophageal Doppler and electrical cardiometry. As septic shock is a dynamic condition that changes markedly overtime, frequent or continuous measurement of the cardiac output (CO), systemic vascular resistance (SVR) and other hemodynamic parameters using the above-mentioned tools is essential to personalize the treatment and adapt it over time. The different combinations of blood pressure, CO and SVR serve as a pathophysiological framework to manage fluid therapy and titrate inotropic and vasoactive drugs. Near infrared spectroscopy is introduced as a non-invasive method to measure end organ perfusion and assess the response to treatment.

Comparison of three non-invasive hemodynamic monitoring methods in critically ill children

Introduction

Hemodynamic parameters measurements were widely conducted using pulmonary artery catheter (PAC) with thermodilution as a reference standard. Due to its technical difficulties in children, transthoracic echocardiography (TTE) has been widely employed instead. Nonetheless, TTE requires expertise and is time-consuming. Noninvasive cardiac output monitoring such as ultrasonic cardiac output monitor (USCOM) and electrical velocimetry (EV) can be performed rapidly with less expertise requirement. Presently, there are inconsistent evidences, variable precision, and reproducibility of EV, USCOM and TTE measurements. Our objective was to compare USCOM, EV and TTE in hemodynamic measurements in critically ill children.

Materials and methods

This was a single center, prospective observational study in critically ill children. Children with congenital heart diseases and unstable hemodynamics were excluded. Simultaneous measurements of hemodynamic parameters were conducted using USCOM, EV, and TTE. Inter-rater reliability was determined. Bland-Altman plots were used to analyse agreement of assessed parameters.

Results

Analysis was performed in 121 patients with mean age of 4.9 years old and 56.2% of male population. Interrater reliability showed acceptable agreement in all measured parameters (stroke volume (SV), cardiac output (CO), velocity time integral (VTI), inotropy (INO), flow time corrected (FTC), aortic valve diameter (AV), systemic vascular resistance (SVR), and stroke volume variation (SVV); (Cronbach’s alpha 0.76–0.98). Percentages of error in all parameters were acceptable by Bland-Altman analysis (9.2–28.8%) except SVR (30.8%) and SVV (257.1%).

Conclusion

Three noninvasive methods might be used interchangeably in pediatric critical care settings with stable hemodynamics. Interpretation of SVV and SVR measurements must be done with prudence.

Maternal hemodynamics in normal pregnancy: reference ranges and role of maternal characteristics

OBJECTIVES

The main aim of this study was to construct reference ranges of maternal central hemodynamic parameters during pregnancy. The second aim was to determine the maternal and pregnancy characteristics that influence these hemodynamic parameters.

METHODS

This was a prospective cohort study of low-risk pregnant women attending for routine antenatal care at St George's Hospital, London, UK. Exclusion criteria included any medical disorder present at the time of study recruitment, or development of hypertension or intrauterine fetal growth restriction following study recruitment. Stroke volume (SV), cardiac output (CO) and systemic vascular resistance (SVR) were obtained using non-invasive cardiac output monitoring (USCOM-1A®). USCOM-1A utilizes a non-imaging probe in the suprasternal notch to obtain velocity-time integrals of transaortic blood flow at the left ventricular outflow tract. Once the distribution of the data with respect to gestational age had been determined, maternal characteristics were added to the model to test whether they provided a significant improvement in the prediction of the median value.

RESULTS

The study included 627 women with a singleton pregnancy. The estimated median CO was constant for a maternal age above 32 years, but was around 0.5 L/min higher for women aged ≤ 25 years (P < 0.001). Maternal weight (P < 0.001) and height (P < 0.001) significantly affected CO values and there was a significant interaction (P = 0.002) between them. In women with a height of less than 1.60 m, there was no association between median CO and weight; however, in those with a height exceeding 1.60 m, an increase in weight was associated with an increase in CO. SV was primarily associated with height (P < 0.001), although some positive association with weight (P < 0.001) could also be observed within the normal body-mass-index range. Greater height (P < 0.001) was associated with lower median values of SVR, with an estimated difference of around 120 dynes × s/cm⁵ between 1.60 m and 1.80 m. Advancing maternal age was associated with higher median SVR, with an estimated difference of around 50 dynes × s/cm⁵ between 25 and 35 years. Smokers had a lower SVR by 73.5 (95% CI, 8.6-138.4) dynes × s/cm⁵ .

CONCLUSION

Maternal hemodynamics are influenced significantly by maternal age, height and weight. We provide USCOM-1A-specific reference ranges and a calculator for SV, CO and SVR in uncomplicated pregnancies that correct for maternal age, height and weight. This should enable clinical application and comparison in both uncomplicated and pathological pregnancies. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Effect of a nitric oxide donor on maternal hemodynamics in fetal growth restriction

OBJECTIVE

To evaluate the effect on maternal cardiovascular parameters of treatment with a nitric oxide (NO) donor and plasma volume expansion in pregnancies complicated by fetal growth restriction (FGR).

METHODS

Twenty-six pregnant women with a diagnosis of FGR were treated with transdermal patches of a NO donor and plasma volume expansion by co-administration of oral fluids. We compared the treated group to a historical control group of untreated FGR patients. Hemodynamic indices were obtained using the UltraSonic Cardiac Output Monitor system.

RESULTS

At diagnosis, the two groups were similar in terms of maternal and hemodynamic characteristics. In the treated group, we found a significant increase in maternal cardiac output and stroke volume and a decrease in systemic vascular resistance after 2 weeks of therapy. No significant differences were found 2 weeks after diagnosis in the untreated group. The treated group delivered infants with higher birth-weight centile than did the untreated control group.

CONCLUSIONS

The combined therapeutic approach of NO donor administration and plasma volume expansion in FGR apparently improves significantly maternal hemodynamic indices. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

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.

Cardiac output assessment in pregnancy: comparison of two automated monitors with echocardiography

OBJECTIVE

To compare non-invasive hemodynamic measurements obtained in pregnant and postpartum women using two automated cardiac output monitors against those obtained by two-dimensional (2D) transthoracic echocardiography (TTE).

METHODS

This was a cross-comparison study into which we recruited 114 healthy women, either with normal singleton pregnancy (across all three trimesters) or within 72 hours following delivery. Cardiac output estimations were obtained non-invasively using two different monitors, Ultrasound Cardiac Output Monitor (USCOM®, which uses continuous-wave Doppler analysis of transaortic blood flow) and Non-Invasive Cardiac Output Monitor (NICOM®, which uses thoracic bioreactance), and 2D-TTE. The performance of each monitor was assessed relative to that of TTE by calculating bias, precision, 95% limits of agreement and mean percentage difference (MPD). Intraobserver repeatability was assessed for both monitors and interobserver reproducibility was assessed for USCOM, NICOM being operator-independent.

RESULTS

Following exclusions due to poor-quality results of a monitor or TTE, or for medical reasons, our analysis included 98 women (29 in the first trimester, 25 in the second and 21 in the third, and 23 postpartum). For cardiac output estimation, when compared with TTE, USCOM had a bias ranging from 0.4 to 0.9 L/min. The MPD of USCOM was 29% in the third-trimester cohort. NICOM had a bias ranging from -1.0 to 0.6 L/min, with a MPD of 32% in the third-trimester group. There was limited agreement between the cardiac output monitors and TTE in the first and second trimesters, with a MPD of 38% for USCOM in both first and second trimesters, and 71% and 61% for NICOM in first and second trimesters, respectively. For cardiac output estimation using USCOM, we found excellent intraobserver repeatability (intraclass correlation coefficient (ICC), 0.97; 95% CI, 0.95-0.98) and interobserver reproducibility (ICC, 0.90; 95% CI, 0.81-0.94), and the repeatability for NICOM was comparable (ICC, 0.95; 95% CI, 0.93-0.97).

CONCLUSIONS

We found good agreement of both USCOM and NICOM when compared with 2D-TTE, specifically in the third trimester of pregnancy. Both devices had good intraobserver repeatability and either had good interobserver reproducibility or were operator-independent. Future studies should take into account the significant differences in the precise maternal hemodynamic values obtained by these devices, and consider developing device-specific reference ranges in pregnancy and the postpartum period. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

Usefulness of the maximum rate of pressure rise in the central and peripheral arteries after weaning from cardiopulmonary bypass in pediatric congenital heart surgery: A retrospective analysis

The maximum rate of pressure rise (dP/dtmax) in radial artery has been proposed as a noninvasive surrogate of aortic dp/dtmax, reflecting left ventricular (LV) contractility in children. The aim of this study was to investigate relationship between aortic and radial dp/dtmax at weaning from cardiopulmonary bypass (CPB) and usefulness of these indices for estimating postoperative outcomes in pediatric congenital heart surgery.Aortic and radial arterial pressure waveforms were analyzed simultaneously during weaning from CPB in 29 congenital heart surgery. The maximum first derivatives of aortic and radial arterial waveforms were calculated and averaged from 3 consecutive respiratory cycles. We obtained the maximum vasoactive inotropic score during the first 36 postoperative hours, LV ejection fraction, and fractional shortening on transthoracic echocardiography performed within postoperative day 7.A significant difference between aortic and radial dP/dtmax was observed (mean difference 356 mm Hg/s, 44% of averages), and radial dP/dtmax was weakly correlated with aortic dP/dtmax (r =0.373, P = 0.047). Aortic dP/dtmax was significantly associated with the maximum vasoactive inotropic score (P < 0.001), postoperative LV ejection fraction (P = 0.018), and fractional shortening (P = 0.015); however, radial dP/dtmax was not. On Receiver operating characteristic analysis, aortic dP/dtmax had a greater area under the curve than radial dP/dtmax in predicting higher vasoactive inotropic score (0.827 vs 0.673).Immediately after CPB in pediatric congenital heart surgery, radial dP/dtmax may not replace aortic dP/dtmax because of a discrepancy between central and peripheral arterial waveforms. In this critical period, aortic dP/dtmax can be useful to estimate postoperative ventricular function rather than peripherally derived dP/dtmax.

Comparison between pressure-recording analytical method (PRAM) and femoral arterial thermodilution method (FATD) cardiac output monitoring in an infant animal model of cardiac arrest

Background

The pressure-recording analytical method is a new semi-invasive method for cardiac output measurement (PRAM). There are no studies comparing this technique with femoral artery thermodilution (FATD) in an infant animal model.

Methods

A prospective study was performed using 25 immature Maryland pigs weighing 9.5 kg. Fifty-eight simultaneous measurements of cardiac index (CI) were made by FATD and PRAM at baseline and after return of spontaneous circulation. Differences, correlation, and concordance between both methods were analyzed. The ability of PRAM to track changes in CI was explored with a polar plot.

Results

Mean CI measurements were 4.5 L/min/m² (95 % CI, 4.2–4.8 L/min/m²; coefficient of variation, 27 %) by FATD and 4.0 L/min/m² (95 % CI, 3.6–4.3 L/min/m²; coefficient for variation, 37 %) by PRAM (difference, 0.5 L/min/m²; 95 % CI for the difference, 0.1–1.0 L/min/m²; p = 0.003; n = 58). No correlation between both methods was observed (r = 0.170, p = 0.20). Limits of agreement were −2.9 to 4.0 L/min/m² (−69.9 to 84.9 %). Percentage error was 80.6 %. Only 26.1 % of data points lied within an absolute deviation of ±30° from the polar axis.

Conclusions

No correlation nor concordance between both methods was observed. Limits of agreement and percentage of error were high and clinically not acceptable. No concurrence between both methods in CI changes was observed. PRAM is not a useful method for measurement of the CI in this pediatric model of cardiac arrest.

Validation of an Ultrasound Cardiac Output Monitor as a Bedside Tool for Pediatric Patients

The aim of our study was to determine the validity of cardiac output (CO) measurements taken with the ultrasonic cardiac output monitor (USCOM) by comparing to CO measured by pulmonary arterial catheter (PAC) thermodilution during cardiac catheterization. We enrolled thirty-one children (<18 years) undergoing cardiac catheterization in this double-blinded, prospective, observational study. The median CO measured by USCOM was 4.37 L/min (IQR 3.73, 5.60 L/min) compared to 4.28 L/min (IQR 3.52, 5.26 L/min) by PAC thermodilution. The bias (mean difference) between the two methods was 0.2 L/min, and the 95% limits of agreement were -1.2 to 1.6 L/min. The mean percentage error of CO between USCOM and PAC thermodilution was 11%. When excluding a sole outlier, the bias between the two measures decreased to 0.1 L/min (95% limits of agreement -0.6 to 0.9 L/min), and the percentage error was reduced to 8%. The median SVRI measured by USCOM was 22.0 Wood Units (IQR 17.0, 26.8 Wood Units) compared to 22.1 Wood Units (IQR 17.6, 27.4 Wood Units) by PAC thermodilution. Bias (mean difference) between the two methods was -0.6 Wood Units, and the 95% limits of agreement were -8.2 to 6.9 Wood Units. We found that the estimation of CO and by extension SVRI with USCOM is reliable against pulmonary artery catheter thermodilution in children with normal cardiac anatomy. Given the noninvasive nature of USCOM, speed of measurement, and relative ease of use, it may be useful as a bedside tool for pediatric patients.

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.

Impedance cardiography (electrical velocimetry) and transthoracic echocardiography for non-invasive cardiac output monitoring in pediatric intensive care patients: a prospective single-center observational study

Introduction

Electrical velocimetry (EV) is a type of impedance cardiography, and is a non-invasive and continuously applicable method of cardiac output monitoring. Transthoracic echocardiography (TTE) is non-invasive but discontinuous.

Methods

We compared EV with TTE in pediatric intensive care patients in a prospective single-center observational study. Simultaneous, coupled, left ventricular stroke volume measurements were performed by EV using an Aesculon® monitor and TTE (either via trans-aortic valve flow velocity time integral [EVVTI], or via M-mode [EVMM]). H₀: bias was less than 10% and the mean percentage error (MPE) was less than 30% in Bland–Altman analysis between EV and TTE. If appropriate, data were logarithmically transformed prior to Bland–Altman analysis.

Results

A total of 72 patients (age: 2 days to 17 years; weight: 0.8 to 86 kg) were analyzed. Patients were divided into subgroups: organ transplantation (OTX, n =28), sepsis or organ failure (SEPSIS, n =16), neurological patients (NEURO, n =9), and preterm infants (PREM, n =26); Bias/MPE for EVVTI was 7.81%/26.16%. In the EVVTI subgroup analysis for OTX, NEURO, and SEPSIS, bias and MPE were within the limits of H₀, whereas the PREM subgroup had a bias/MPE of 39.00%/46.27%. Bias/MPE for EVMM was 8.07%/37.26% where the OTX and NEURO subgroups were within the range of H₀, but the PREM and SEPSIS subgroups were outside the range. Mechanical ventilation, non-invasive continuous positive airway pressure ventilation, body weight, and secondary abdominal closure were factors that significantly affected comparison of the methods.

Conclusions

This study shows that EV is comparable with aortic flow-based TTE for pediatric patients.

Impact of positive end-expiratory pressure on cardiac index measured by ultrasound cardiac output monitor*

OBJECTIVES

To evaluate the impact of different levels of positive end-expiratory pressure on cardiac index in children receiving mechanical ventilation. To explore the effect of lung recruitment on the relationship between positive end-expiratory pressure and cardiac output.

DESIGN

Prospective, single center, and interventional.

SETTING

PICU in a tertiary care children's hospital.

PATIENTS

Fifty mechanically ventilated, hemodynamically stable children between 1 month and 20 years old.

INTERVENTIONS

Positive end-expiratory pressure was altered to levels of 0, 4, 8, and 12 cm H2O in random order. Cardiac output was measured at different levels of positive end-expiratory pressure by continuous wave Doppler ultrasound (ultrasound cardiac output monitor). Baseline vital signs were recorded, as well as cardiac index and dynamic compliance of the respiratory system at each positive end-expiratory pressure level.

MEASUREMENTS AND MAIN RESULTS

Median cardiac index decreased marginally as positive end-expiratory pressure increased, with a median change in cardiac index of 0.4 (< 10%) between positive end-expiratory pressure of 0 and 12 cm H2O (p < 0.001). There was no difference in heart rate or blood pressure as positive end-expiratory pressure increased (p > 0.5). For a subset of 29 patients (58%) in whom the highest dynamic compliance was at a positive end-expiratory pressure of 4 or 8 cm H2O, there was no difference in cardiac index between positive end-expiratory pressure 4 below versus positive end-expiratory pressure at highest dynamic compliance, or cardiac index between positive end-expiratory pressure 4 above versus positive end-expiratory pressure at highest dynamic compliance (p > 0.2). Regardless of optimal dynamic compliance, cardiac index decreased as positive end-expiratory pressure increased (p = 0.02).

CONCLUSIONS

In hemodynamically stable mechanically ventilated children, although there is a statistically significant decrease in cardiac output as positive end-expiratory pressure is increased between 0 and 12 cm H2O, the mean change is less than 10%, and this is likely not clinically significant. In the presence of lung disease, intensive care physicians should feel less reluctant in their use of positive end-expiratory pressure for hemodynamically stable patients.

Effects of red cell transfusion on cardiac output and perfusion index in preterm infants

OBJECTIVE/AIM

The present investigation was designed to study the effect of blood transfusion on cardiac output and perfusion index. The aim was to demonstrate a relationship between hematocrit, lactate, cardiac output and perfusion index in anemic preterm infants and to investigate significant changes in these parameters induced by RBC transfusion.

METHODS

Anemic infants who were under 35 weeks of gestational age (GA) and were in a stable clinical condition without respiratory or cardiac problems, signs of sepsis, or renal disease at the time of investigation were enrolled in the study. Enrolled infants received 15 ml/kg pure red blood cells over 4 h. Hematocrit and lactate levels were studied before and after transfusion. Cardiac output was measured by an ultrasound device (USCOM 1A) and perfusion index was monitored by pulse oximeter (MasimoRad7).

RESULTS

Cardiac output decreased by 9% (p < 0.05), due to decrease in heart rate by 10% (p < 0.05) and stroke volume significantly by 5% (p < 0.05) both in left and right sided cardiac measurements. Perfusion index significantly increased and lactate levels significantly decreased after transfusion (p < 0.05). Htc was inversely correlated with lactate levels, HR, CI and CO (r = -0.33, p = 0.01; r = -0.53, p = 0; r = -0.37, p = 0.004, r = -0.28, p = 0.03). PI was not significantly correlated with Htc levels before and after transfusion (r = 0.07, p = 0.7 and r = 0.007, p =0.97).

CONCLUSION

Our data support that heart rate, CO and CI and lactate levels increased as a response to anemia in preterm infants and RBC transfusion improved perfusion index suggesting better tissue oxygenation.

Urgent ultrasound guided hemodynamic assessments by a pediatric medical emergency team: a pilot study

Purpose

To determine the feasibility of using the Ultrasound Cardiac Output Monitor (USCOM) as an adjunct during hemodynamic assessments by a pediatric medical emergency team (PMET).

Methods

Pediatric in-patients at McMaster Children’s Hospital aged under 18 years requiring urgent PMET consultation, were eligible. Patients with known cardiac outflow valve defects, Pediatric Critical Care Unit in-patients, and those in cardiorespiratory arrest, were excluded. The primary outcome was feasibility, and the ease of USCOM transport and application as assessed by a self-administered user questionnaire. Secondary outcomes included the quality of USCOM measurements, and agreement in clinical versus USCOM-derived assessments.

Results

Forty-one patients from 85 eligible PMET consultations were enrolled between March and August 2011. A total of 55 USCOM assessments were performed on 36 of 41 (87.8%) participants. USCOM could not be completed in 5 (12.2%) participants due to patient agitation (n = 4) and emergent care (n = 1). USCOM was reported as easy to transport and apply by 97.4% and 94.7% of respondents respectively, not obstructive to patient care by 94.7%, and yielded timely measurements by 84.2% respondents. USCOM tracings were of good quality in 41 (75.9%) assessments. Agreement between clinical and USCOM-derived hemodynamic assessments by two independent raters was poor (Rater 1: κ = 0.094; Rater 2: κ = 0.146).

Conclusion

USCOM can be applied by a PMET during urgent hemodynamic assessments in children. While USCOM has been validated in stable children, its role in guiding hemodynamic resuscitation and informing therapeutic goals in a hemodynamically unstable pediatric population requires further investigation.

Noninvasive transcutaneous Doppler ultrasound-derived hemodynamic reference ranges in Chinese adolescents

OBJECTIVES

The ultrasonic cardiac output monitor is a noninvasive, quantitative method for measuring and monitoring cardiovascular hemodynamic parameters in patients. The aims of this study were first to establish reference ranges for cardiovascular indices measured by the ultrasonic cardiac output monitor in Chinese children aged 12-18 yr, second to assess the interobserver reliability of the method, and third to compare these ranges with a Caucasian group from Australia.

DESIGN, SETTING, AND SUBJECTS

This was a population-based cross-sectional cohort study of Chinese adolescents 12-18 years old, performed in secondary schools in Hong Kong.

INTERVENTIONS

Ultrasonic cardiac output monitor scans were performed on each subject to measure stroke volume, cardiac output, and systemic vascular resistance together with standard oscillometric measurement of blood pressure and heart rate. Ultrasonic cardiac output monitor parameters were also standardized by deriving body surface area referenced indices. Normal ranges were defined as lying within two standard deviations on either side of the mean. To assess interobserver variability, a second, blinded operator repeated 17% of scans.

MEASUREMENTS AND MAIN RESULTS

A total of 590 Chinese adolescents (49% boys) were scanned. Normal ranges for cardiac output, cardiac index, stroke volume, stroke volume index, stroke volume resistance, and systemic vascular resistance index are presented. Males had a significantly higher mean stroke volume, cardiac output, and systemic vascular resistance index compared with females (p < 0.05), but no significant differences were found for the indexed values. When compared with a group of 31 Australian Caucasian adolescents (71% boys), Chinese adolescents have a significantly lower cardiac output and stroke volume (p <0.05), but these differences disappeared when adjusted for body surface area (i.e., stroke volume index, cardiac index, and systemic vascular resistance index). Interobserver variability of ultrasonic cardiac output monitor-derived stroke volume showed a coefficient of variation of 10.2%, a correlation coefficient of 0.90 (95% confidence interval 0.85-0.93), while Bland-Altman analysis showed a mean bias of 1.5% (95% limits of agreement were -19.9% to 23.0%).

CONCLUSIONS

This study presents normal values for cardiovascular indices in Chinese adolescents using the ultrasonic cardiac output monitor. When referenced to body surface area, the differences between Caucasians and Chinese were insignificant.

A minimally invasive monitoring system of cardiac output using aortic flow velocity and peripheral arterial pressure profile

BACKGROUND

In managing patients with unstable hemodynamics, monitoring cardiac output (CO) can provide critical diagnostic data. However, conventional CO measurements are invasive, intermittent, and/or inaccurate. The purpose of this study was to validate our newly developed CO monitoring system.

METHODS

This system automatically determines peak velocity of the ascending aortic flow using continuous-wave Doppler transthoracic echocardiography and estimates cardiac ejection time and aortic cross-sectional area using the pulse contour of the radial arterial pressure. These parameters are continuously processed to estimate CO (CO(est)). In 10 anesthetized closed-chest dogs instrumented with an aortic flowprobe to measure reference CO (CO(ref)), hemodynamic conditions were varied over wide ranges by infusing cardiovascular drugs or by random atrial pacing. Under each condition, CO(ref) and CO(est) were determined. Absolute changes of CO(ref) (ΔCOref) and CO(est) (ΔCO(est)), and relative changes of CO(ref) (%ΔCO(ref)) and CO(est) (%ΔCO(est)) from the corresponding baseline values were determined in each animal. We calibrated CO(est) against CO(ref) to obtain proportionally scaled CO(est) (CO(est)(N)).

RESULTS

A total of 1335 datasets of CO(ref) and CO(est) were obtained, in which CO(ref) ranged from 0.17 to 5.34 L/min. Bland-Altman analysis between CO(ref) and CO(est) indicated that the limits of agreement (the bias ± 1.96 × SD of the difference) and the percentage error (1.96 × [SD of the difference]/[mean CO] × 100) were from -1.01 to 1.13 L/min (95% confidence interval, -1.76 to 1.88 L/min) and 43%, respectively. The agreement between CO(ref) and CO(est)(N) was improved, with limits of agreement from -0.53 to 0.49 L/min (95% confidence interval, -0.62 to 0.59 L/min) and the percentage error of 20%. Polar plot analysis between ΔCO(ref) and ΔCO(est) indicated that mean ± 1.96 × SD of polar angle was -2° ± 22°. Four quadrant plot analysis indicated that %ΔCO(est) correlated tightly with %ΔCO(ref) (R(2) = 0.93). The %ΔCO(est) and %ΔCO(ref) changed in the same direction in 95% of the datasets. Reliability of this system was well preserved under conditions of random atrial pacing and also in a continuous manner.

CONCLUSION

Over a wide range of hemodynamic conditions, irrespective of cardiac beat irregularity, this system may allow minimally invasive monitoring of CO with a good trending ability. The present results warrant further research and development of this system for future clinical application.

Cardiac Output Measurements in Septic Patients: Comparing the Accuracy of USCOM to PiCCO

USCOM is an ultrasound-based method which has been accepted for noninvasive hemodynamic monitoring in various clinical conditions (USCOM, Ultrasonic cardiac output monitoring). The present study aimed at comparing the accuracy of the USCOM device with that of the thermodilution technique in patients with septicemia. We conducted a prospective observational study in a medical but noncardiological ICU of a university hospital. Septic adult patients (median age 55 years, median SAPS-II-Score 43 points) on mechanical ventilation and catecholamine support were monitored with USCOM and PiCCO (n = 70). Seventy paired left-sided CO measurements (transaortic access = CO_US-A) were obtained. The mean CO_US-A were 6.55 l/min (±2.19) versus CO_PiCCO 6.5 l/min (±2.18). The correlation coefficient was r = 0.89. Comparison by Bland-Altman analysis revealed a bias of −0.36 l/min (±0.99 l/min) leading to a mean percentage error of 29%. USCOM is a feasible and rapid method to evaluate CO in septic patients. USCOM does reliably represent CO values as compared to the reference technique based on thermodilution (PiCCO). It seems to be appropriate in situations where CO measurements are most pertinent to patient management.

Intra- and inter-observer reliability using a noninvasive ultrasound cardiac output monitor in healthy anesthetized children

BACKGROUND

Accurate and reliable evaluation of cardiac index (CI) in critically ill pediatric patients can optimize their management. Although validated, noninvasive ultrasound measurement techniques have been previously shown to be unreliable because of observer variability.

OBJECTIVE

To confirm intra- and inter-observer reliability when using the noninvasive USCOM(®) in healthy anesthetized children.

METHODS

Prospective observational study at the Children's Hospital of Eastern Ontario, Ottawa, included newborns to 12 years of age undergoing elective surgery or magnetic resonance imaging. The USCOM(®) was used to assess CI via aortic flow with a trans-sternal approach. Two trained observers were responsible for taking two measurements of CI each at steady state in randomized succession after stable depth of anesthesia was achieved.

RESULTS

Fifty-nine patients were included. Forty-seven (80%) were between 3 and 7 years old, with 57% male. The mean difference ± sd for repeat CI measurements by each of two observers was 0.11 ± 0.47 and 0.05 ± 0.65 l·min(-1) ·m(-2) , respectively. Intra-observer reliability for these repeat measurements by each observer determined by Lin's concordance correlation coefficient was 0.92 and 0.85, respectively. The mean difference ± sd between observers was 0.16 ± 0.59 l·min(-1) ·m(-2) , and Lin's concordance correlation coefficient was 0.87. The two observers subjectively rated measurements as 'Difficult' or 'Very difficult' only 14% (16/118) and 3% (4/118) of the time, respectively. No adverse events were reported.

CONCLUSION

This study confirms that the USCOM(®) is relatively easy to use and reliable in healthy children when operated by trained users.

Continuous arterial pressure waveform monitoring in pediatric cardiac transplant, cardiomyopathy and pulmonary hypertension patients

PURPOSE

A continuous cardiac output monitor based on arterial pressure waveform (FloTrac/Vigileo; Edwards Lifesciences, Irvine, CA) is now approved for use in adults but not in children. This device is minimally invasive, calculates cardiac output continuously and in real time, and is easy to use. Our study sought to validate the FloTrac with the pulmonary artery catheter (PAC) intermittent thermodilution technique in pediatric cardiac patients.

METHODS

This was a prospective pilot study comparing cardiac output measurements obtained via the FloTrac and arterial pressure waveform analysis with intermittent thermodilution. Subjects carried the diagnosis of pulmonary hypertension or cardiomyopathy, or were in the postoperative course after orthotopic heart transplantation.

RESULTS

Enrolled in the study were 31 subjects, and 136 data points were obtained. The age range was 8 months to 16 years. The mean body surface area (BSA) was 1.1 m(2). Bland-Altman plots for the mean cardiac outputs of all subjects with a BSA ≥ 1 m(2) showed limits of agreement of -2.7 to 8.0 l/min (± 5.4 l/min). Patients with a BSA ≤ 1 m(2) demonstrated even wider limits of agreement (± 8.5 l/min). The intraclass correlation for the PAC was 0.929 and 0.992 for the FloTrac.

CONCLUSION

There was poor agreement between the PAC and FloTrac in measuring cardiac output in a population of children with pulmonary hypertension or cardiomyopathy, or after cardiac transplantation. This is in contrast to adult studies published thus far. This suggests that the utility of the FloTrac and measurements obtained from arterial pulse wave analysis in children is uncertain at this time.

Objective assessment of cardiac output in infants after cardiac surgery

An accurate measurement of cardiac performance in infants after cardiopulmonary bypass has long been considered to be an important part of postoperative management. To be useful in clinical decision making, such measurements should ideally be reproducible, non invasive and accurately reflect tissue perfusion and oxygen delivery. Historically, we have relied on intermittent measurements of cardiac output using indicator dilution methods; and more recently, technologies that use pulse contour analysis, bio-impedance, or Doppler methodology. These all have the same shortcoming, that they provide a number that the information as to whether it provides adequate tissue perfusion. There is increasing emphasis being placed on the measurement of oxygen delivery either by mixed venous oxygen saturation and serum lactate, which are important markers of the adequacy of organ perfusion; and relating this to outcome, the development of organ dysfunction and length of ICU stay.

The normal ranges of cardiovascular parameters in children measured using the Ultrasonic Cardiac Output Monitor

OBJECTIVE

The Ultrasonic Cardiac Output Monitor is a noninvasive method of hemodynamic assessment and monitoring in critically ill patients. There are no published reference ranges for normal values in children for this device. This study aimed to establish normal ranges for cardiovascular indices measured using Ultrasonic Cardiac Output Monitor in children aged 0-12 yrs old and to assess interobserver reliability.

DESIGN

This was a population-based cross-sectional observational study.

SETTING

Schools and kindergartens in Hong Kong.

SUBJECTS

Chinese children aged up to 12 yrs old.

INTERVENTIONS

Two operators performed Ultrasonic Cardiac Output Monitor scans on each child together with standard oscillometric measurement of blood pressure and heart rate. Software intrinsic to the Ultrasonic Cardiac Output Monitor device produces values for stroke volume, cardiac output, and systemic vascular resistance. For each parameter, normal ranges were defined as lying between the 2.5th and 97.5th percentiles. Interobserver reliability was assessed with Bland-Altman plots, coefficients of variation, and intraclass correlation.

MEASUREMENTS AND MAIN RESULTS

A total of 1,197 Chinese children (55% boys) were scanned. Normal ranges of values for cardiac output, stroke volume, and systemic vascular resistance indices are presented. Interobserver reliability for Ultrasonic Cardiac Output Monitor was superior to that for standard blood pressure and heart rate measurement.

CONCLUSIONS

This large study presents normal values for cardiovascular indices in children using the Ultrasonic Cardiac Output Monitor with good interobserver reliability.

A novel noninvasive ultrasonic cardiac output monitor: comparison with cardiac magnetic resonance

BACKGROUND

USCOM, a novel continuous wave Doppler (CWD) device, has been introduced for noninvasive determination of cardiac output (CO). The present study aimed to compare the accuracy and reproducibility of the new device, using cardiovascular magnetic resonance imaging (CMR) as the noninvasive gold standard.

METHODS AND RESULTS

The CO of 56 consecutive patients was prospectively determined by CWD either before or after CMR imaging. The CWD probe was placed in the suprasternal or supraclavicular notch aiming at the aortic valve. Valid CWD signals could be obtained in 45 patients yielding a CO of 5.3+/-1.1 L/min (range, 3.0-7.5 L/min) by CMR and 4.7+/-1.1 L/min by CWD (2.5-8.0 L/min, P = .004), respectively. CWD measurements showed an acceptable agreement with CMR (bias: 0.6+/-1.1 L/min) and a high reproducibility (bias: 0.1+/-0.4 L/min). Higher CO and body mass index (BMI) were identified as sources of inaccuracy in univariate analysis. By multivariate analysis, only CO(CMR) was found to be independently associated with larger variation. Estimated diameters of the left ventricular outflow tract (LVOT), a prerequisite for CO measurement by CWD, correlated only weakly with those measured by CMR.

CONCLUSIONS

Continuous wave Doppler is a feasible technique for measuring cardiac function. Although the overall agreement with CMR was acceptable, CWD showed a trend to underestimate CO. The estimated LVOT diameter by CWD is likely to be an important source of error. Nevertheless, the CWD device could be of clinical use especially for detection of intraindividual hemodynamic changes since a high reproducibility could be demonstrated.

Use of echocardiography and modalities of patient monitoring of trauma patients

PURPOSE OF REVIEW

Trauma patients require evaluation of the anatomic structure as well as the hemodynamic profile of the heart to improve effectiveness of resuscitation. They are prone to hemodynamic instability and must be monitored with various modalities to detect deterioration early. Newer, less invasive ultrasound technologies are replacing familiar 'gold standard' modalities of the past. This article reviews the indications, roles, imaging approaches, and limitations of modern echocardiography. A brief review of other ICU monitoring modalities is also presented.

RECENT FINDINGS

Echocardiography has emerged as a first-line diagnostic tool for assessment of trauma patients, especially those with hemodynamic compromise. It yields crucial information about structural damage as well as the hemodynamic profile and can be performed through either the transesophageal or transthoracic route. Quick and systematic use of echocardiography for diagnosis and management of critically injured patients may lead to improved outcomes.

SUMMARY

Echocardiography plays an important role in the trauma bay for diagnosis of thoracic injury and at the bedside in the ICU for evaluation of the hemodynamic profile.

Cardiac index measurements by transcutaneous Doppler ultrasound and transthoracic echocardiography in adult and pediatric emergency patients

INTRODUCTION

Non-invasive hemodynamic monitoring may facilitate resuscitation in critically ill patients. Validation studies examining a transcutaneous Doppler ultrasound technology, USCOM-1A, using pulmonary artery catheter as the reference standard showed varying results. In this study, we compared non-invasive cardiac index (CI) measurements by USCOM-1A with transthoracic echocardiography (TTE).

METHODS

This study was a prospective, observational cohort study at a university tertiary-care emergency department, enrolling a convenience sample of adult and pediatric patients. Paired measures of CI, stroke volume index (SVI), aortic outflow tract diameter (OTD), velocity time integral (VTI) were obtained using USCOM-1A and TTE. Pearson's correlation and Bland-Altman analyses were performed.

RESULTS

One-hundred and sixteen subjects were enrolled, with obtainable USCOM-1A CI measurements for 99 subjects (55 adults age 50 +/- 20 years and 44 children age 11 +/- 4 years) in the final analysis. Cardiac, gastrointestinal and infectious illnesses were the most common presenting diagnostic categories. The reference standard TTE measurements of CI, SVI, OTD, and VTI in all subjects were 3.08 +/- 1.18 L/min/m(2), 37.10 +/- 10.91 mL/m(2), 1.92 +/- 0.36 cm, and 20.36 +/- 4.53 cm, respectively. Intra-operator reliability of USCOM-1A CI measurements showed a correlation coefficient of r = 0.79, with 11 +/- 22% difference between repeated measures. The bias and limits of agreement of USCOM-1A compared to TTE CI were 0.58 (-1.48 to 2.63) L/min/m(2). The percent difference in CI measurements with USCOM-1A was 31 +/- 28% relative to TTE measurements.

CONCLUSIONS

The USCOM-1A hemodynamic monitoring technology showed poor correlation and agreement to standard transthoracic echocardiography measures of cardiac function. The utility of USCOM-1A in the management of critically ill patients remains to be determined.