Cardiac output estimation with a new Doppler device after off-pump coronary artery bypass surgery

Monitoring haemodynamic changes during transjugular portosystemic shunt insertion with electric cardiometry in sedated and spontaneous breathing patients. A diagnostic test accuracy study

Background and Aims

Transjugular intrahepatic portosystemic shunt (TIPS) allows a high blood volume into systemic circulation abruptly. The primary aim of the study was to investigate the effect of TIPS on systemic, portal hemodynamics, and electric cardiometry (EC) parameters in sedated and spontaneous breathing patients. Secondary aims??

Material and Methods

Adult consecutive hepatic patients scheduled for elective TIPS were included. Patients were sedated with bispectral index-guided propofol infusion + fentanyl boluses. EC parameters, i.e., cardiac output (CO) and systemic vascular resistance (SVR) were noted. Noninvasive blood pressure, heart rate, central venous pressure (CVP, cmH2O), and portal venous pressure (PVP, cmH2O) were measured pre- and post-TIPS.

Results

Thirty-six people were enrolled (n = 25 included) from Aug 2018 to Dec 2019. Data (expressed in median (IQ)) were: age 33 (27-40) years, body mass index 24 (22.0-27) kg/m2, child A 60%, B 36%, and C 4%. Post-TIPS, PVP decreased (from 40 [37-45] to 34 [27-37] mmHg, P < 0.001), whereas CVP increased (from 7 [4-10] to 16 [10.0-19.0] mmHg, P < 0.001). The CO increased (P = 0.03) and SVR reduced (P = 0.012).

Conclusion

The reduction in PVP following successful TIPS insertion elevated the CVP abruptly. EC was able to monitor an immediate increase in the CO and a reduction in SVR in association with the above PVP and CVP changes. The results of this unique study indicate that EC monitoring is promising; however, further evaluation in a larger population and in correlation with other gold-standard CO monitors is still indicated.

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.

Cardiac output monitoring: Technology and choice

The accurate quantification of cardiac output (CO) is given vital importance in modern medical practice, especially in high-risk surgical and critically ill patients. CO monitoring together with perioperative protocols to guide intravenous fluid therapy and inotropic support with the aim of improving CO and oxygen delivery has shown to improve perioperative outcomes in high-risk surgical patients. Understanding of the underlying principles of CO measuring devices helps in knowing the limitations of their use and allows more effective and safer utilization. At present, no single CO monitoring device can meet all the clinical requirements considering the limitations of diverse CO monitoring techniques. The evidence for the minimally invasive CO monitoring is conflicting; however, different CO monitoring devices may be used during the clinical course of patients as an integrated approach based on their invasiveness and the need for additional hemodynamic data. These devices add numerical trend information for anesthesiologists and intensivists to use in determining the most appropriate management of their patients and at present, do not completely prohibit but do increasingly limit the use of the pulmonary artery catheter.

[Meta-analyses on measurement precision of non-invasive hemodynamic monitoring technologies in adults]

An ideal non-invasive monitoring system should provide accurate and reproducible measurements of clinically relevant variables that enables clinicians to guide therapy accordingly. The monitor should be rapid, easy to use, readily available at the bedside, operator-independent, cost-effective and should have a minimal risk and side effect profile for patients. An example is the introduction of pulse oximetry, which has become established for non-invasive monitoring of oxygenation worldwide. A corresponding non-invasive monitoring of hemodynamics and perfusion could optimize the anesthesiological treatment to the needs in individual cases. In recent years several non-invasive technologies to monitor hemodynamics in the perioperative setting have been introduced: suprasternal Doppler ultrasound, modified windkessel function, pulse wave transit time, radial artery tonometry, thoracic bioimpedance, endotracheal bioimpedance, bioreactance, and partial CO₂ rebreathing have been tested for monitoring cardiac output or stroke volume. The photoelectric finger blood volume clamp technique and respiratory variation of the plethysmography curve have been assessed for monitoring fluid responsiveness. In this manuscript meta-analyses of non-invasive monitoring technologies were performed when non-invasive monitoring technology and reference technology were comparable. The primary evaluation criterion for all studies screened was a Bland-Altman analysis. Experimental and pediatric studies were excluded, as were all studies without a non-invasive monitoring technique or studies without evaluation of cardiac output/stroke volume or fluid responsiveness. Most studies found an acceptable bias with wide limits of agreement. Thus, most non-invasive hemodynamic monitoring technologies cannot be considered to be equivalent to the respective reference method. Studies testing the impact of non-invasive hemodynamic monitoring technologies as a trend evaluation on outcome, as well as studies evaluating alternatives to the finger for capturing the raw signals for hemodynamic assessment, and, finally, studies evaluating technologies based on a flow time measurement are current topics of clinical research.

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.

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.

Does stroke volume variation predict fluid responsiveness in children: A systematic review and meta-analysis

OBJECTIVE

Stroke volume variation (SVV) is a reliable predictor of fluid responsiveness in adult patients. However, the predictive value of SVV is uncertain in pediatric patients. We performed the first systematic meta-analysis to evaluate the diagnostic value of SVV in predicting fluid responsiveness in children.

METHODS

PUBMED, EMBASE, and Cochrane Central Register of Controlled Trials were searched up to December 2016. Original studies assessing the diagnostic accuracy of SVV in predicting fluid responsiveness in children were considered to be eligible. A random-effects model was used to calculate pooled values of sensitivity, specificity and diagnostic odds ratio with 95% CI. The summary receiver operating characteristic curve was estimated and area under the curve was calculated. Quality of the studies was assessed with the QUADAS-2 tool.

RESULTS

Six studies with a total of 279 fluid boluses in 224 children were included. The analysis demonstrated a pooled sensitivity of 0.68 (95% CI,0.59-0.76), pooled specificity of 0.65 (95% CI, 0.57-0.73), pooled diagnostic odds ratio of 8.24 (95% CI, 2.58-26.30), and the summary area under the summary receiver operating characteristic curve of 0.81. However, significant inter-study heterogeneity was found (p<0.05, I2 = 61.3%), likely due to small sample size and diverse study characteristics.

CONCLUSIONS

Current evidence suggests that SVV was of diagnostic value in predicting fluid responsiveness in children under mechanical ventilation. Given the high heterogeneity of published data, further studies are needed to confirm the diagnostic accuracy of SVV in predicting fluid responsiveness in pediatric patients.

[Application of ultrasonic cardiac output monitor in evaluation of cardiac function in children with severe pneumonia]

OBJECTIVE

To study the clinical application of ultrasonic cardiac output monitor (USCOM) in evaluation of cardiac function in children with severe pneumonia.

METHODS

Twenty-nine children with severe pneumonia were enrolled in the observation group and forty-three children with common pneumonia were enrolled in the control group. The USCOM was used to measure the cardiac function indices in the two groups. The results were compared between the two groups. The changes in cardiac function indices after treatment were evaluated in the observation group.

ESULTS

The observation group had a significantly higher heart rate and significantly lower cardiac output, systolic volume, and aortic peak velocity than the control group (P<0.05). There were no significant differences in cardiac index or systemic vascular resistance between the two groups (P>0.05). In the observation group, the heart rate, cardiac output, systolic volume, aortic peak velocity, cardiac index, and systemic vascular resistance were significantly improved after treatment (P<0.05).

CONCLUSIONS

The USCOM is a fast, convenient, and accurate approach for dynamic measurement of cardiac function and overall circulation state in children with severe pneumonia. The USCOM can provide a basis for diagnosis, treatment, and evaluation of the disease, which is quite useful in clinical practice.

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.

In vitro evaluation of an ultrasonic cardiac output monitoring (USCOM) device

Non-invasive cardiac output monitoring techniques provide high yield, low risk mechanisms to identify and individually treat shock in the emergency setting. The non-invasive ultrasonic cardiac output monitoring (USCOM) device uses an ultrasound probe applied externally to the chest; however limitations exist with previous validation strategies. This study presents the in vitro validation of the USCOM device against calibrated flow sensors and compares user variability in simulated healthy and septic conditions. A validated mock circulation loop was used to simulate each condition with a range of cardiac outputs (2-10 l/min) and heart rates (50-95 bpm). Three users with varying degrees of experience using the USCOM device measured cardiac output and heart rate by placing the ultrasound probe on the mock aorta. Users were blinded to the condition, heart rate and cardiac output which were randomly generated. Results were reported as linear regression slope (β). All users estimated heart rate in both conditions with reasonable accuracy (β = 0.86-1.01), while cardiac output in the sepsis condition was estimated with great precision (β = 1.03-1.04). Users generally overestimated the cardiac output in the healthy simulation (β = 1.07-1.26) and reported greater difficulty estimating reduced cardiac output compared with higher values. Although there was some variability between users, particularly in the healthy condition (P < 0.01), all estimations were within a clinically acceptable range. In this study the USCOM provided a suitable measurement of cardiac output and heart rate when compared with our in vitro system. It is a promising technique to assist with the identification and treatment of shock.

Elevated positive end-expiratory pressure decreases cardiac index in a rhesus monkey model

RATIONALE

Clinicians are often concerned that higher positive end-expiratory pressure (PEEP) will decrease cardiac index (CI). PEEP affects CI through multiple inter-related mechanisms. The adult Rhesus monkey is an excellent model to study cardiopulmonary interaction due to similar pulmonary and chest wall compliances to human infants.

OBJECTIVE

Our goal was to examine the impact of increasing PEEP on CI in Rhesus monkeys as a model for critically ill children.

METHODS

Prospective, experimental animal study. Nine healthy anesthetized, intubated Rhesus monkeys were allowed to breathe spontaneously at a PEEP of 0, 5, 10, and 15 cm H2O while CI was measured with an ultrasonic Doppler (USCOM).

MEASUREMENTS AND MAIN RESULTS

Cardiac index decreased between PEEP levels of 5 and 15 cm H2O. The mean decrease in CI for the entire cohort of monkeys was 18% (p < 0.01) with a range of -11 to 49%. Stroke volume and oxygen delivery also decreased between PEEP levels of 5 and 15 cm H2O (p < 0.01).

CONCLUSION

Between PEEP levels of 5 and 15 cm H2O, there was a decrease in CI, stroke volume, and oxygen delivery in intubated Rhesus monkeys. A plausible mechanism is that over-distention of normally compliant lungs at increased PEEP resulted in decreased preload to the right ventricle, outweighing the potentially beneficial decrease in left ventricular afterload or pulmonary vascular resistance. Further investigation is warranted, particularly in children with lung injury, who have historically benefited from increased PEEP levels without over-distention.

Less invasive methods of advanced hemodynamic monitoring: principles, devices, and their role in the perioperative hemodynamic optimization

The monitoring of the cardiac output (CO) and other hemodynamic parameters, traditionally performed with the thermodilution method via a pulmonary artery catheter (PAC), is now increasingly done with the aid of less invasive and much easier to use devices. When used within the context of a hemodynamic optimization protocol, they can positively influence the outcome in both surgical and non-surgical patient populations. While these monitoring tools have simplified the hemodynamic calculations, they are subject to limitations and can lead to erroneous results if not used properly. In this article we will review the commercially available minimally invasive CO monitoring devices, explore their technical characteristics and describe the limitations that should be taken into consideration when clinical decisions are made.

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.

Children's Discomfort during Noninvasive Cardiac Output Monitoring by Suprasternal Ultrasonographic Transducer

Objectives

To investigate the level of discomfort/pain in children receiving Ultrasonic Cardiac Output Monitoring (USCOM), as compared to blood pressure measurement.

Methods

Healthy children, aged 3-12 years old, were recruited from kindergartens and schools as a part of the “Healthy children's vital signs and USCOM values” project. Oscillometric blood pressure was measured, followed by USCOM measurement. The discomfort experienced by the child during each intervention was assessed using the Wong-Baker FACES pain rating scale. The pain scores (scale from 0-5) were compared using Wilcoxon signed rank test. A difference in score of one point was considered to be clinically relevant. Gender differences in pain score were analysed using Mann-Whitney-U test.

Results

A total of 254 subjects (131 boys, 123 girls) were included. Mean age was 7.9 years with standard deviation (SD) of 2.4 years. The median pain score for USCOM measurement was 1.0 (95% CI=1.0 to 2.0) with interquartile range 1.0 to 2.0. The median pain score for BP measurement was 1.0 (95% CI,=1.0 to 1.0) with interquartile range 0.0 to 2.0. Overall, the pain score associated with USCOM was significantly higher than that associated with BP measurement. However, the difference fails to reach the minimum clinically significant difference of one-point. No significant difference was shown between boys and girls.

Conclusion

USCOM appears to be tolerated well by healthy children. The discomfort reported during USCOM measurement is comparable to that associated with blood pressure measurements.

Accuracy of cardiac output measurements during off-pump coronary artery bypass grafting: according to the vessel anastomosis sites

Background

During beating heart surgery, the accuracy of cardiac output (CO) measurement techniques may be influenced by several factors. This study was conducted to analyze the clinical agreement among stat CO mode (SCO), continuous CO mode (CCO), arterial pressure waveform-based CO estimation (APCO), and transesophageal Doppler ultrasound technique (UCCO) according to the vessel anastomosis sites.

Methods

This study was prospectively performed in 25 patients who would be undergoing elective OPCAB. Hemodynamic variables were recorded at the following time points: during left anterior descending (LAD) anastomosis at 1 min and 5 min; during obtuse marginal (OM) anastomosis at 1 min and 5 min: and during right coronary artery (RCA) anastomosis at 1 min and 5 min. The variables measured including the SCO, CCO, APCO, and UCCO.

Results

CO measurement techniques showed different correlations according to vessel anastomosis site. However, the percent error observed was higher than the value of 30% postulated by the criteria of Critchley and Critchley during all study periods for all CO measurement techniques.

Conclusions

In the beating heart procedure, SCO, CCO and APCO showed different correlations according to the vessel anastomosis sites and did not agree with UCCO. CO values from the various measurement techniques should be interpreted with caution during OPCAB.

Pulmonary Artery Catheter (PAC) Accuracy and Efficacy Compared with Flow Probe and Transcutaneous Doppler (USCOM): An Ovine Cardiac Output Validation

Background. The pulmonary artery catheter (PAC) is an accepted clinical method of measuring cardiac output (CO) despite no prior validation. The ultrasonic cardiac output monitor (USCOM) is a noninvasive alternative to PAC using Doppler ultrasound (CW). We compared PAC and USCOM CO measurements against a gold standard, the aortic flow probe (FP), in sheep at varying outputs. Methods. Ten conscious sheep, with implanted FPs, had measurements of CO by FP, USCOM, and PAC, at rest and during intervention with inotropes and vasopressors. Results. CO measurements by FP, PAC, and USCOM were 4.0 ± 1.2 L/min, 4.8 ± 1.5 L/min, and 4.0 ± 1.4 L/min, respectively, (n = 280, range 1.9 L/min to 11.7 L/min). Percentage bias and precision between FP and PAC, and FP and USCOM was -17 and 47%, and 1 and 36%, respectively. PAC under-measured Dobutamine-induced CO changes by 20% (relative 66%) compared with FP, while USCOM measures varied from FP by 3% (relative 10%). PAC reliably detected -30% but not +40% CO changes, as measured by receiver operating characteristic area under the curve (AUC), while USCOM reliably detected ±5% changes in CO (AUC > 0.70). Conclusions. PAC demonstrated poor accuracy and sensitivity as a measure of CO. USCOM provided equivalent measurements to FP across a sixfold range of outputs, reliably detecting ±5% changes.

Physiologic and Clinical Principles behind Noninvasive Resuscitation Techniques and Cardiac Output Monitoring

Clinical assessment and vital signs are poor predictors of the overall hemodynamic state. Optimal measurement of the response to fluid resuscitation and hemodynamics has previously required invasive measurement with radial and pulmonary artery catheterization. Newer noninvasive resuscitation technology offers the hope of more accurately and safely monitoring a broader range of critically ill patients while using fewer resources. Fluid responsiveness, the cardiac response to volume loading, represents a dynamic method of improving upon the assessment of preload when compared to static measures like central venous pressure. Multiple new hemodynamic monitors now exist that can noninvasively report cardiac output and oxygen delivery in a continuous manner. Proper assessment of the potential future role of these techniques in resuscitation requires understanding the underlying physiologic and clinical principles, reviewing the most recent literature examining their clinical validity, and evaluating their respective advantages and limitations.

The resuscitation package in sepsis

Sepsis and its attendant complications are commonly encountered in the intensive care unit. Early recognition of sepsis is critical because it allows for rapid deployment of a multifaceted resuscitation package. The cornerstones of sepsis management are antibiotic therapy, source control, and hemodynamic resuscitation. In select patients, ancillary therapies are indicated, such as activated protein C, corticosteroids, and glycemic control. Given the complexity of sepsis management, optimal care can be delivered as a bundle-a protocol encompassing the above interventions. The evidence behind the various components of sepsis management are reviewed here.

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.

Non-invasive stroke volume measurement and passive leg raising predict volume responsiveness in medical ICU patients: an observational cohort study

Introduction

The assessment of volume responsiveness and the decision to administer a fluid bolus is a common dilemma facing physicians caring for critically ill patients. Static markers of cardiac preload are poor predictors of volume responsiveness, and dynamic markers are often limited by the presence of spontaneous respirations or cardiac arrhythmias. Passive leg raising (PLR) represents an endogenous volume challenge that can be used to predict fluid responsiveness.

Methods

Medical intensive care unit (ICU) patients requiring volume expansion were eligible for enrollment. Non-invasive measurements of stroke volume (SV) were obtained before and during PLR using a transthoracic Doppler ultrasound device prior to volume expansion. Measurements were then repeated following volume challenge to classify patients as either volume responders or non-responders based on their hemodynamic response to volume expansion. The change in SV from baseline during PLR was then compared with the change in SV with volume expansion to determine the ability of PLR in conjunction with SV measurement to predict volume responsiveness.

Results

A total of 102 fluid challenges in 89 patients were evaluated. In 47 of the 102 fluid challenges (46.1%), SV increased by ≥15% after volume infusion (responders). A SV increase induced by PLR of ≥15% predicted volume responsiveness with a sensitivity of 81%, specificity of 93%, positive predictive value of 91% and negative predictive value of 85%.

Conclusions

Non-invasive SV measurement and PLR can predict fluid responsiveness in a broad population of medical ICU patients. Less than 50% of ICU patients given fluid boluses were volume responsive.

Assessment of portable continuous wave Doppler ultrasound (ultrasonic cardiac output monitor) for cardiac output measurements in neonates

BACKGROUND AND STUDY PURPOSE

The ultrasonic cardiac output monitoring (USCOM, USCOM Pty Ltd, Coffs Harbour, NSW, Australia) device provides a new method of non-invasively assessing cardiac output (CO). It has been successfully used in adults, but there have been few studies in neonates.

AIMS

To study the inter-operator reliability, and to compare the aortic (systemic) CO and pulmonary CO in a neonatal population.

PATIENT AND METHODS

In a study using the USCOM device, we have determined: (i) the inter-operator (rater) agreement for aortic (left ventricular output) and pulmonary (right ventricular output) CO; and (ii) by combining the measurements of aortic and pulmonary CO from each operator to obtain average aortic and pulmonary CO in neonates admitted to the neonatal unit during the first 8 days of life. Neonates with congenital heart disease were excluded from the study.

RESULTS

Twelve neonates were enrolled in the study, and their mean gestational age was 34.1 +/- 3.7 weeks, mean birth weight 2.268 +/- 0.872 kg with eight boys and four girls. There was no significant difference in CO measurements between the two operators (inter-rater correlation = 0.93 (0.86-0.97 (95% CI), P < 0.0001). However, the mean aortic CO was significantly lower than the mean pulmonary CO (228 mL/kg/min (202-254 (95% CI)) versus 282 mL/kg/min (256-309 (95% CI), P= 0.006).

CONCLUSIONS

Although there was a good correlation between operators, further investigations are required to study the discrepancy between aortic (systemic)/pulmonary CO in this population. Other than this discrepancy, the validity of this technique in neonates requires further detailed studies as it uses continuous wave Doppler for the measurements.

Nurse-determined assessment of cardiac output. Comparing a non-invasive cardiac output device and pulmonary artery catheter: a prospective observational study

BACKGROUND

The accurate measurement of Cardiac output (CO) is vital in guiding the treatment of critically ill patients. Invasive or minimally invasive measurement of CO is not without inherent risks to the patient. Skilled Intensive Care Unit (ICU) nursing staff are in an ideal position to assess changes in CO following therapeutic measures. The USCOM (Ultrasonic Cardiac Output Monitor) device is a non-invasive CO monitor whose clinical utility and ease of use requires testing.

OBJECTIVES

To compare cardiac output measurement using a non-invasive ultrasonic device (USCOM) operated by a non-echocardiograhically trained ICU Registered Nurse (RN), with the conventional pulmonary artery catheter (PAC) using both thermodilution and Fick methods.

DESIGN

Prospective observational study.

SETTING AND PARTICIPANTS

Between April 2006 and March 2007, we evaluated 30 spontaneously breathing patients requiring PAC for assessment of heart failure and/or pulmonary hypertension at a tertiary level cardiothoracic hospital.

METHODS

SCOM CO was compared with thermodilution measurements via PAC and CO estimated using a modified Fick equation. This catheter was inserted by a medical officer, and all USCOM measurements by a senior ICU nurse. Mean values, bias and precision, and mean percentage difference between measures were determined to compare methods. The Intra-Class Correlation statistic was also used to assess agreement. The USCOM time to measure was recorded to assess the learning curve for USCOM use performed by an ICU RN and a line of best fit demonstrated to describe the operator learning curve.

RESULTS

In 24 of 30 (80%) patients studied, CO measures were obtained. In 6 of 30 (20%) patients, an adequate USCOM signal was not achieved. The mean difference (+/-standard deviation) between USCOM and PAC, USCOM and Fick, and Fick and PAC CO were small, -0.34+/-0.52 L/min, -0.33+/-0.90 L/min and -0.25+/-0.63 L/min respectively across a range of outputs from 2.6L/min to 7.2L/min. The percent limits of agreement (LOA) for all measures were -34.6% to 17.8% for USCOM and PAC, -49.8% to 34.1% for USCOM and Fick and -36.4% to 23.7% for PAC and Fick. Signal acquisition time reduced on average by 0.6 min per measure to less than 10 min at the end of the study.

CONCLUSIONS

In 80% of our cohort, USCOM, PAC and Fick measures of CO all showed clinically acceptable agreement and the learning curve for operation of the non-invasive USCOM device by an ICU RN was found to be satisfactorily short. Further work is required in patients receiving positive pressure ventilation.

Ultrasonic cardiac output monitor provides accurate measurement of cardiac output in recipients after liver transplantation

BACKGROUND

The ultrasonic cardiac output monitor (USCOM; USCOM Pty. Ltd., Sydney, NSW, Australia) has been accepted as a noninvasive device for measuring cardiac function in various clinical conditions. The present study aimed at comparing the accuracy of this device with that of the thermodilution technique in recipients in the early postoperative period after liver transplantation.

METHODS

Fifteen mechanically ventilated patients were studied on the first postoperative day after liver transplantation. We compared the left-sided and right-sided cardiac output (CO) determined by USCOM with that obtained from the thermodilution technique with a pulmonary artery catheter every 8 hours in the intensive care unit. Each patient received a total of four paired measurements. Bland-Altman analysis was used for bias and precision testing. The CO measured by USCOM and the thermodilution method were considered interchangeable if the limits of agreement lay within +/- 1 L per minute or 20% of the mean CO.

RESULTS

Forty-eight paired left-sided CO measurements were obtained from 12 patients. Three patients were excluded due to unacceptable signals. Comparison of these two techniques revealed a bias of 0.13 L per minute and limits of agreement at -0.65 L and 0.92 L per minute. Fifty-six paired right-sided CO measurements were obtained from 14 patients with one patient excluded due to an unobtainable optimal signal. A bias of 0.11 L per minute with limits of agreement at -0.51 L and 0.72 L per minute were found for these two techniques.

CONCLUSION

This is the first study to evaluate the accuracy of USCOM in the post-liver transplant setting. This device is accurate in measuring CO in liver transplant recipients postoperatively. Possible risks of arrhythmia, infection and pulmonary artery rupture can be avoided because of its noninvasive nature. USCOM should be considered as an alternative in hemodynamic monitoring after liver transplantation.

Minimally invasive cardiac output monitoring in the perioperative setting

With advancing age and increased co-morbidities in patients, the need for monitoring devices during the perioperative period that allow clinicians to track physiologic variables, such as cardiac output (CO), fluid responsiveness and tissue perfusion, is increasing. Until recently, the only tool available to anesthesiologists to monitor CO was either a pulmonary artery catheter or transesophageal echocardiograph. These devices have their limitations and potential for morbidity. Several new devices (including esophageal Doppler monitors, pulse contour analysis, indicator dilution, thoracic bioimpedance and partial non-rebreathing systems) have recently been marketed which have the ability to monitor CO noninvasively and, in some cases, assess the patient's ability to respond to fluid challenges. In this review, we will describe these new devices including the technology, studies on their efficacy and the limitations of their use.

Noninvasive Doppler ultrasonography for assessing cardiac function: can it replace the Swan-Ganz catheter?

BACKGROUND

Cardiac function, including cardiac index (CI), traditionally has been measured by a pulmonary artery catheter (PAC). A noninvasive alternative for measuring cardiac function would offer obvious advantages.

METHODS

A prospective study of trauma and nontrauma patients was performed in a surgical intensive care unit over a 3-month period. CI was determined using both a standard PAC and a continuous-wave Doppler ultrasound (UTS). The study had 2 phases: phase I was nonblinded and phase II was blinded; the correlation between UTS- and PAC-derived CI was assessed.

RESULTS

A total of 120 paired measurements of CI were observed in 31 patients. The UTS-derived CI measurements showed agreement with PAC measurements in both phase I and phase II of the study with a bias of .06 L/min/m(2) +/- .4 L/min/m(2). Paired measurements correlated well in both phase I (r = .97, R2 = .95, P < .0001) and phase II (r = .93, R2 = .86, P < .0001) of the study.

CONCLUSIONS

Doppler UTS correlates well with PAC measurements of CI. This noninvasive modality is an accurate and safe alternative to PAC.

Cardiac output monitoring: comparison of a new arterial pressure waveform analysis to the bolus thermodilution technique in patients undergoing off-pump coronary artery bypass surgery

OBJECTIVE

To analyze the clinical agreement between the conventional intermittent bolus thermodilution (TD) technique and a new arterial pressure waveform analysis (APCO) technique (FloTrac; Edward Lifesciences, Irvine, CA) for cardiac output (CO) estimation.

DESIGN

Prospective observational clinical study.

SETTING

Cardiac surgery operating room of a tertiary care cardiac center.

PARTICIPANTS

Twelve patients undergoing elective off-pump coronary artery bypass (OPCAB) surgery.

MEASUREMENTS AND MAIN RESULTS

CO was determined by 2 different methods: TD and APCO at 8 time points (preinduction, postinduction, poststernotomy, left internal mammary artery to left anterior descending artery anastomosis, left [obtuse marginal/diagonal] anastomosis, right [right coronary/posterior descending coronary artery] anastomosis, postprotamine administration, and poststernal closure) in 12 patients undergoing elective OPCAB surgery. The mean bias and limits of agreement (2 standard deviations) expressed in liters per minute at respective points of measurement were -0.54 +/- 1.12, -0.37 +/- 1.0, -0.42 +/- 1.50, -0.25 +/- 1.18, -0.31 + 1.28, +/-0.41 +/- 1.0, 0.06 +/- 1.50, and 0.09 +/- 1.40.

CONCLUSION

Good agreement was found between the CO values obtained by the APCO and TD techniques throughout the intraoperative period including the period of coronary artery graft surgery.

Distinct hemodynamic patterns of septic shock at presentation to pediatric intensive care

OBJECTIVE

Early aggressive resuscitation is accepted best practice for severe pediatric sepsis. Targeting of therapy to individual hemodynamic patterns is recommended, but assessment of patterns is difficult early in the disease process. New technologies enabling earlier hemodynamic assessment in shock may inform choices for vasoactive drugs in fluid-resistant cases.

METHODS

This was a prospective observational study of 30 children with suspected fluid-resistant septic shock (minimum: 40 mL/kg) admitted to the PICU of a tertiary care children's hospital between July 2004 and July 2005. Children were classified according to admission diagnosis (community-acquired sepsis or central venous catheter-associated infection) and assessed within 4 hours after the onset of shock with a noninvasive cardiac output device. Cardiac index and systemic vascular resistance index were measured for all patients. Central venous oxygen saturation was measured for patients with accessible central venous lines at the time of hemodynamic measurements (typically at the superior vena cava-right atrium junction).

RESULTS

Fluid-resistant septic shock secondary to central venous catheter-associated infection was typically "warm shock" (15 of 16 patients; 94%), with high cardiac index and low systemic vascular resistance index. In contrast, this pattern was rarely seen in community-acquired sepsis (2 of 14 patients; 14%), where a normal or low cardiac index was predominant.

CONCLUSIONS

The hemodynamic patterns of fluid-resistant septic shock by the time children present to the PICU are distinct, depending on cause, with little overlap. If these findings can be reproduced, then targeting the choice of first-line vasoactive infusions in fluid-resistant shock (vasopressors for central venous catheter-associated infections and inotropes for community-acquired sepsis) should be considered.

Association between Cardiac Index and Mortality in Patients Assessed on the Ward by a Nurse-Led Critical Care Outreach Team

Derangements in cardiac output are associated with mortality in various patient groups but the relationship between cardiac output and mortality in critically ill patients on standard hospital wards has not been investigated. In this single-centre observational study, cardiac output was measured using a non-invasive supra-sternal Doppler technique in patients referred to a critical care outreach team. Data were collected at baseline and four hours later in 113 patients, of whom 28 died (24.8%) and 37 were admitted to critical care (32.7%). During this period, there was a significant decrease in mean cardiac index (2.74 L/min/m2 [95% confidence intervals 1.78–4.35] to 2.18 L/min/m2 [95% CI 1.54–3.21]; p=0.049) and stroke volume index (24 mL/m2 [95% CI 16–36] to 20 mL/m2 [95% CI 15–31]; p=0.02) in non-survivors, whilst in survivors these variables remained unchanged. There were no changes in heart rate or mean arterial pressure in either survivors or non-survivors. For 216 patients in whom only baseline data were available, only age, heart rate, arterial pressure, respiratory rate and temperature were independently associated with mortality. In conclusion, in the four hours following assessment on the ward by a critical care outreach team, cardiac index and stroke volume index were maintained in survivors, but decreased significantly in non-survivors. At baseline, neither variable was associated with mortality.

Inter-rater reliability for noninvasive measurement of cardiac function in children

INTRODUCTION

A transcutaneous ultrasound monitor has recently been developed which noninvasively and quickly measures cardiac output. Validity and reliability testing has been reported in adults. No reliability testing has been undertaken in the pediatric population.

OBJECTIVE

Our objective was to evaluate the inter-rater reliability of a transcutaneous Doppler ultrasound technique to measure cardiac index (CI) and stroke volume index (SVI) in pediatric emergency department patients.

METHODS

An 8-month prospective observational study was conducted on a convenience sample of emergency department patients younger than 18 years old. Five raters were trained to use an ultrasound cardiac output monitoring device. Two raters, blinded to each other's results, obtained independent measurements from the same patient within 15 minutes of each other. Inter-rater agreement was measured with the Pearson product correlation coefficient. Bland-Altman analysis demonstrated the extent of deviation from a line of agreement between raters.

RESULTS

Ninety-seven patients were enrolled. Major diagnostic categories included infection, trauma, and gastrointestinal disorders. There was significant inter-rater correlation for CI (r = 0.76; 95% confidence interval, 0.66Y0.83; P G 0.0001) and SVI (r = 0.79; 95% confidence interval, 0.70Y0.86; P G 0.0001). Bland-Altman analysis of CI measurements between 2 raters showed bias of 0.06, SD of bias 1.00, and 95% limits of agreement j1.91 to 2.02 L/min/m2. Stroke volume index showed bias of j0.5, SD of bias 11.01, and 95% limits of agreement j22.08 to 21.08 mL/m2.

CONCLUSIONS

Transcutaneous Doppler ultrasound technique demonstrates acceptable inter-rater agreement for measuring CI and SVI in children.

Comparison of the USCOM ultrasound cardiac output monitor with pulmonary artery catheter thermodilution in patients undergoing liver transplantation

The aim of the study was to compare the standard technique of cardiac output determination by pulmonary artery catheter thermodilution (PAC-TD) with a noninvasive ultrasound Doppler monitor (USCOM Pty., Ltd., Coffs Harbour, Australia) in surgery for liver transplantation. We wished to determine if the degree of accuracy would allow the ultrasound cardiac output monitor (USCOM) to be used as an alternative monitor in a clinical setting in which wide fluctuations in cardiac output could be expected. This was a prospective method comparison study, with 71 paired measurements obtained in 12 patients undergoing liver transplantation in a university teaching hospital. Bland-Altman analysis of the 2 techniques showed a bias of 0.39 L/minute, with the USCOM cardiac output lower compared with that of PAC-TD. The bias was small and did not vary with the magnitude of the cardiac output. The 95% limits of agreement were -1.47 and 2.25 L/minute. There was good repeatability for USCOM measurements, with a repeatability coefficient of 0.43 for USCOM versus 0.77 for PAC-TD. We conclude that USCOM is acceptable for the clinical determination of noninvasive cardiac output, particularly in situations in which tracking changes over time is more important than knowing the precise value. However, the utility of USCOM is limited by its inability to measure pulmonary artery pressure.

Reliability of a new ultrasonic cardiac output monitor in recipients of living donor liver transplantation

The ultrasonic cardiac output monitor (USCOM) is a new Doppler device for noninvasive hemodynamic monitoring. The aim of this prospective nonrandomized study was to test the feasibility, perioperative reliability, and clinical applicability of using USCOM as an alternative to pulmonary artery catheterization in recipients of living donor liver transplantation. Thirteen patients scheduled to receive living donor liver transplants were initially recruited. Three were subsequently excluded prior to the commencement of surgery because of technical difficulties in obtaining diagnostic-quality images with USCOM. Ten patients proceeded to be studied. Cardiac output measurements by thermodilution and USCOM were compared at 30-minute intervals throughout the procedure and at 10 specific procedural reference points during the surgery when hemodynamic changes were most likely to be observed. The data were analyzed with Lin's concordance coefficient and Bland-Altman analysis. Two hundred ninety paired cardiac output values were obtained from the 10 patients. The concordance between both methods was excellent in 8 patients and satisfactory in 2. Bland-Altman analysis of all data produced a mean bias of - 0.02 L/minute for USCOM, and the 95% limits of agreement were -1.06 to +1.10 L/minute. Further analysis of the 10 reference time points showed minimal bias and high levels of agreement between the methods. We conclude that USCOM provides an accurate and noninvasive method for cardiac output measurement during liver transplantation. It may therefore represent an alternative to pulmonary artery catheter placement with consequent reduction in patient's risk and morbidity associated with catheterization. Liver Transpl 14:1029-1037, 2008. (c) 2008 AASLD.

Does patient position influence Doppler signal quality from the USCOM ultrasonic cardiac output monitor?

BACKGROUND

The USCOM1A continuous wave cardiac output monitor (USCOM Pty Ltd., Sydney, NSW, Australia) is a novel Doppler-based device used to measure cardiac output noninvasively. The proper alignment of the transducer, and hence the ultrasound beam to the aortic or pulmonary outflow tracts, is essential to acquire accurate measurements and often much time is spent on transducer and/or patient positioning. In this prospective, observational, crossover study, we investigated the effect of patient positioning on the acquisition of cardiac output measurement with USCOM1A.

METHODS

We measured cardiac output using USCOM1A in 30 healthy adult volunteers, each in five different positions: sitting, supine, Trendelenburg (20 degrees), left lateral tilt (20 degrees), and right lateral tilt (20 degrees) and compared the time required to obtain acceptable measurements. We also compared the quality of the Doppler signal obtained in these positions using a scoring system designed for this study.

RESULTS

There was a higher rate of failed measurement, the mean time to obtain the first acceptable measurement was prolonged and the optimal measurement obtained within a 5-min period was of a lower quality in the sitting position compared with the other four positions.

CONCLUSIONS

Our results suggested the sitting position is the least suitable and least reliable position in which to perform cardiac output measurements using USCOM1A compared with the supine, Trendelenburg (20 degrees), left lateral tilt (20 degrees), and right lateral tilt (20 degrees) positions.

Review article: Non-invasive assessment of cardiac output with portable continuous-wave Doppler ultrasound

Cardiac output is considered an important parameter when assessing the cardiovascular status of a critically ill patient. Both non-invasive (e.g. bioimpedance, echocardiography) and invasive methods (Swan Ganz catheter) have been used to measure cardiac output. The ultrasonic cardiac output monitoring device provides a new method of non-invasively assessing cardiac output in various clinical settings. The ultrasonic cardiac output monitoring device was introduced clinically in 2001, and appears to be a promising adjunct in the assessment of the cardiovascular state in a variety of patient cohorts. In this short review article, we will introduce this new technique, discuss the required skills and compare it with methods already in use. In particular, a critical comparison with the 'gold standard', the invasive measurement of cardiac output with the pulmonary artery catheter, will be given.

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

OBJECTIVE

To compare the assessment of cardiac output (CO) in children using the noninvasive Ultrasound Cardiac Output Monitor (USCOM) with the invasive pulmonary artery catheter (PAC) thermodilution cardiac output measurement.

DESIGN AND SETTING

Prospective observational study in a tertiary center for pediatric cardiology of a university children's hospital.

PATIENTS

Twenty-four pediatric patients with congenital heart disease without shunt undergoing cardiac catheterization under general anesthesia.

MEASUREMENTS AND RESULTS

CO was measured by USCOM using a suprasternal CO Doppler probe in children undergoing cardiac catheterization. USCOM data were compared to CO simultaneously measured by PAC thermodilution technique. Measurements were repeated three times within 5 min in each patient. A mean percentage error not exceeding 30% was defined as indicating clinical useful reliability of the USCOM. CO values measured by PAC ranged from 1.3 to 5.3 l/min (median 3.6 l/min). Bias and precision were -0.13 and 1.34 l/min, respectively. The mean percentage error of CO measurement by the USCOM compared to PAC thermodilution technique was 36.4% for USCOM.

CONCLUSIONS

Our preliminary data demonstrate that cardiac output measurement in children using the USCOM does not reliably represent absolute CO values as compared to PAC thermodilution. Further studies must evaluate the impact of incorporating effective aortic valve diameters on CO measurement using the USCOM.

Cardiac output estimation after off-pump coronary artery bypass: a comparison of two different techniques

The present study compares the cardiac output (CO) estimated by a new, non-invsive continuous Doppler device (Ultrasonic cardiac output monitor-USCOM) with that by bolus thermodilution technique (TD). Thirty post off-pump coronary artery bypass graft surgery patients were studied in this prospective nonrandomized study. Right heart CO estimation by USCOM and TD was performed and measured in quadruplet. A total of 120 paired observations were made. The mean CO was 4.63 and 4.76 Llmin as estimated by TD and USCOM respectively. For TD and USCOM, the CO had a mean bias (tendency of one technique to differ from other) of -0.13 L/min and limits of agreement (mean bias +/- 2SD) at -0.86 and 0.59 L/min. The study reveals very good agreement between the values of CO estimated by USCOM and TD.

Cardiac output measurement using a modified carbon dioxide Fick method: a validation study in ventilated lambs

Cardiac output can be measured using a modified carbon dioxide Fick (mCO2F) method. A validation study was performed comparing mCO2F method-derived cardiac output (Q(mCO2F)) with invasively measured pulmonary blood flow. In seven randomly bred ventilated newborn lambs, cardiac output was manipulated by creating hemorrhagic hypotension. When steady state was reached, Q(mCO2F) was measured. Gas analysis was performed in simultaneously obtained arterial and venous blood samples (right atrium [RA], superior vena cava [SVC], and inferior vena cava [IVC]). Carbon dioxide exchange and pulmonary blood flow was measured continuously using a CO2SMO Plus monitor and a pulmonary ultrasonic flow probe (Q), respectively. Mean bias, defined as Q(mCO2F) - Q(ufp), was small (respectively, -0.082 L.min, -0.085 Lx min(-1) and -0.183 Lxmin(-1) for venous sampling from RA, SVC, and IVC). The limits of agreement were -0.328 to 0.164 Lxmin(-1) (RA), -0.335 to 0.165 Lxmin(-1) (SVC), and 0.415 to 0.049 Lxmin(-1) (IVC). In conclusion, measurement of cardiac output with the mCO2F method is reliable and easily applicable in ventilated newborn lambs. For clinical use, the site of venous blood sampling is of minor importance.