Noninvasive measurement of cardiac output in critically ill children

The role of Neonatologist Performed Echocardiography in the assessment and management of neonatal shock

One of the major challenges of neonatal intensive care is the early detection and management of circulatory failure. Routine clinical assessment of the hemodynamic status of newborn infants is subjective and inaccurate, emphasizing the need for objective monitoring tools. An overview will be provided about the use of neonatologist-performed echocardiography (NPE) to assess cardiovascular compromise and guide hemodynamic management. Different techniques of central blood flow measurement, such as left and right ventricular output, superior vena cava flow, and descending aortic flow are reviewed focusing on methodology, validation, and available reference values. Recommendations are provided for individualized hemodynamic management guided by NPE.

Centile Curves for Velocity-Time Integral Times Heart Rate as a Function of Ventricular Length: The Use of Minute Distance Is Advantageous to Enhance Clinical Reliability in Children

BACKGROUND

The generation of velocity-time integrals (VTIs) from Doppler signals is an essential component of standard echocardiographic investigations. The most effective algorithm to compensate for growth in children has, however, not yet been identified. This study was initiated to establish pediatric reference values for VTI and to enhance the interpretability of those values, considering technical and physiological factors.

METHODS

The echocardiographic data sets of healthy children and adolescents (N = 349; age range, 0-20 years) were recorded in a prospective approach and subsequently analyzed. In a pilot study, aortic and pulmonary VTIs were set in relation to the physiologic parameters of heart size as possible influencing parameters in a subgroup of children with comparable physical characteristics. The ratio with the smallest SD was taken as the base to generate centile curves using the LMS method. The clinical utility of the model was tested by examining patients (n = 80) with shunt lesions such as patent ductus arteriosus and atrial septal defect.

RESULTS

Feasibility was 94.6% for aortic VTI and 92.8% for pulmonary VTI. The pilot study identified ventricular length and heart rate as suitable parameters with the lowest relative SDs and high correlations with VTI. Gender differences were not relevant for children <7 years of age, and with increasing age, SD increased because of higher stroke volume variations. The detection of increased aortic VTI was possible with sensitivity of 73% for patients with patent ductus arteriosus with moderate or large hemodynamically significant ductus arteriosus. Patients with atrial septal defects with enlarged right ventricles could be identified as having increased pulmonary VTI with sensitivity of 84%.

CONCLUSIONS

These new reference values for VTI times heart rate as a function of ventricular length may be of specific clinical value to improve the assessment of cardiac function, therapeutic decision making, and follow-up in pediatric patients with heart disease.

Ultrasound dilution: an accurate means of determining cardiac output in children

BACKGROUND

Cardiac output is a useful measure of myocardial performance. Cardiac output monitoring is frequently performed in critically ill adults to guide physicians' treatment strategies. However, standard methods of determining cardiac output in children are not without risk and can be problematic secondary to their invasive nature and other technical problems. The COstatus system (Transonic Systems, NY), which is based on ultrasound dilution technology, works off in situ catheters and uses an innocuous indicator to allow for routine measurements of cardiac output and blood volumes in pediatric patients. The purpose of this study was to validate cardiac output measured by the COstatus system with those obtained by the clinical standard technique of pulmonary artery thermodilution.

METHODS

This was a prospective evaluation performed at a single institution. Any child with a structurally normal heart undergoing hemodynamic evaluation in the cardiac catheterization laboratory was included. A prograde right heart catheterization was performed, and cardiac output was first determined by using the pulmonary artery thermodilution technique. Thermodilution results were then compared with cardiac output measurements obtained using the COstatus system. The results were analyzed by standard correlation, Bland-Altman, and Critchley and Critchley analyses.

RESULTS

Twenty-eight patients were evaluated with a median age of 8 yrs and a median weight of 31 kg. The mean thermodilution cardiac index = 3.18 L/min (± 1.35 L/min), and the mean COstatus system cardiac index = 3.17 L/min (± 1.31 L/min). Standard Pearson correlation tests revealed an excellent correlation coefficient of 0.95 (p < .0001). Bland-Altman analysis revealed good clinical agreement with a mean difference of -0.004 L/min with a precision of 0.8 L/min at 2 SD. A percentage error of 25.4% was noticed in this study, which is less than the clinically acceptable limit.

CONCLUSION

The ultrasound dilution technique of determining cardiac output using the COstatus system provides a less invasive method than the traditional pulmonary artery thermodilution for accurately determining cardiac output in children. This is the first validation of the COstatus system in pediatric patients. Further studies are required to establish its accuracy in pediatric patients with cardiac shunts and other hemodynamically unstable conditions.

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.

Validation of cardiac output measurement by ultrasound dilution technique with pulmonary artery thermodilution in a pediatric animal model

Novel COstatus system (Transonic Systems, Inc., NY), based on ultrasound dilution (UD), works off in situ arterial and central venous catheters in pediatric patients to measure cardiac output (CO). The purpose of the present study was to validate CO measurement by UD (COUD) with pulmonary artery (PA) thermodilution (COTD) in a prospective animal study. Ten anesthetized pigs (16-45 kg) were instrumented with pediatric PA, central venous, and peripheral artery catheters. For COUD measurements, normothermic saline (0.5-1.0 ml/kg body weight, up to a maximum of 30 ml) was injected into the venous limb of an arteriovenous loop that was connected between in situ catheters. For COTD measurements, 5-10 ml cold saline was injected into the PA catheter. Sixty-four averaged sets were obtained for comparison. COTD mean was 2.98 ± 1.21 l/min (range 1.33-6.29), and COUD mean was 2.68 ± 1.16 l/min (range 1.33-5.85). This study yielded a correlation r = 0.96, COUD = 0.91*(COTD) - 0.04 l/min; bias was 0.3 l/min with limits of agreement as -0.39 to 0.99 l/min; and the percentage error was 23.73% between the methods. CO measurements by UD agreed well with thermodilution measurements in the pediatric swine model.

Clinical practice parameters for hemodynamic support of pediatric and neonatal septic shock: 2007 update from the American College of Critical Care Medicine

BACKGROUND

The Institute of Medicine calls for the use of clinical guidelines and practice parameters to promote "best practices" and to improve patient outcomes.

OBJECTIVE

2007 update of the 2002 American College of Critical Care Medicine Clinical Guidelines for Hemodynamic Support of Neonates and Children with Septic Shock.

PARTICIPANTS

Society of Critical Care Medicine members with special interest in neonatal and pediatric septic shock were identified from general solicitation at the Society of Critical Care Medicine Educational and Scientific Symposia (2001-2006).

METHODS

The Pubmed/MEDLINE literature database (1966-2006) was searched using the keywords and phrases: sepsis, septicemia, septic shock, endotoxemia, persistent pulmonary hypertension, nitric oxide, extracorporeal membrane oxygenation (ECMO), and American College of Critical Care Medicine guidelines. Best practice centers that reported best outcomes were identified and their practices examined as models of care. Using a modified Delphi method, 30 experts graded new literature. Over 30 additional experts then reviewed the updated recommendations. The document was subsequently modified until there was greater than 90% expert consensus.

RESULTS

The 2002 guidelines were widely disseminated, translated into Spanish and Portuguese, and incorporated into Society of Critical Care Medicine and AHA sanctioned recommendations. Centers that implemented the 2002 guidelines reported best practice outcomes (hospital mortality 1%-3% in previously healthy, and 7%-10% in chronically ill children). Early use of 2002 guidelines was associated with improved outcome in the community hospital emergency department (number needed to treat = 3.3) and tertiary pediatric intensive care setting (number needed to treat = 3.6); every hour that went by without guideline adherence was associated with a 1.4-fold increased mortality risk. The updated 2007 guidelines continue to recognize an increased likelihood that children with septic shock, compared with adults, require 1) proportionally larger quantities of fluid, 2) inotrope and vasodilator therapies, 3) hydrocortisone for absolute adrenal insufficiency, and 4) ECMO for refractory shock. The major new recommendation in the 2007 update is earlier use of inotrope support through peripheral access until central access is attained.

CONCLUSION

The 2007 update continues to emphasize early use of age-specific therapies to attain time-sensitive goals, specifically recommending 1) first hour fluid resuscitation and inotrope therapy directed to goals of threshold heart rates, normal blood pressure, and capillary refill 70% and cardiac index 3.3-6.0 L/min/m.

Continuous, non-invasive techniques to determine cardiac output in children after cardiac surgery: evaluation of transesophageal Doppler and electric velocimetry

BACKGROUND

Continuous and non-invasive measurement of cardiac output (CO) may contribute helpful information to the care and treatment of the critically ill pediatric patient. Different methods are available but their clinical verification is still a major problem.

AIM

Comparison of reliability and safety of two continuous non-invasive methods with transthoracic echocardiography (TTE) for CO measurement: electric velocimetry technique (EV, Aesculon) and transesophageal Doppler (TED, CardioQP). METHODS/MATERIAL: In 26 infants and children who had undergone corrective cardiac surgery at a median age of 3.5 (1-17) years CO and stroke volume (SV) were obtained by EV, TED and TTE. Each patient had five measurements on the first day after surgery, during mechanical ventilation and sedation.

RESULTS

Values for CO and SV from TED and EV correlated well with those of TTE (r = 0.85 and r = 0.88), but mean values were significantly lower than the values of TTE for TED (P = 0.02) and EV (P = 0.001). According to Bland-Altman analysis, bias was 0.36 l/min with a precision of 1.67 l/min for TED vs. TTE and 0.87 l/min (bias) with a precision of 3.26 l/min for EV vs. TTE. No severe adverse events were observed and the handling of both systems was easy in the sedated child.

CONCLUSIONS

In pediatric patients non-invasive measurement of CO and SV with TED and EV is useful for continuous monitoring after heart surgery. Both new methods seem to underestimate cardiac output in terms of absolute values. However, TED shows tolerable bias and precision and may be helpful for continuous CO monitoring in a deeply sedated and ventilated pediatric patient, e.g. in the operating room or intensive care unit.

Echocardiographic assessment of blood flow volume in the superior vena cava and descending aorta in the newborn infant

BACKGROUND

Clinical methods of assessing adequacy of the circulation are poor predictors of volume of blood flow in the newborn preterm. Doppler echocardiography can be used to assess perfusion at various sites in the circulation.

OBJECTIVE

To assess repeatability of measurement of volume of superior vena caval (SVC) and descending aortic (DAo) flow.

DESIGN

SVC and DAo flow volume were assessed four times in the first 48 h of postnatal life in a cohort of preterm (<31 weeks) infants. Within-observer and between-observer repeatability was assessed in a subgroup of preterm infants. Normative values were derived from 14 preterm infants who required <48 h respiratory support and 13 healthy term infants.

RESULTS

Within-observer repeatability coefficient was 30 ml/kg/min for quantification of SVC flow, and 2.2 cm for DAo stroke distance. Measurement of DAo diameter had poor repeatability. Between-observer repeatability appeared poorer than within-observer repeatability. The fifth centile for volume of SVC flow in healthy preterm infants was 55 ml/kg/min and 4.5 cm for DAo stroke distance.

CONCLUSIONS

Echocardiographic assessments of volume of SVC flow and velocity of DAo flow have similar within-observer repeatability to other neonatal haemodynamic measurements. Between-observer repeatability for both measurements was poor, reflecting the difficulty of standardising these novel techniques. In this small cohort of preterm infants, SVC flow volume <55 ml/kg/min and DAo stroke distance <4.5 cm represented low or borderline systemic perfusion in the first 48 h of postnatal life.

Accuracy and repeatability of pediatric cardiac output measurement using Doppler: 20-year review of the literature

OBJECTIVE

Review of the accuracy and repeatability of Doppler cardiac output (CO) measurements in children.

DESIGN

Publications in the scientific literature retrieved using a computerized Medline search from 1982-2002 and a manual review of article bibliographies. Studies comparing Doppler flow measurements with thermodilution, Fick, or dye dilution methods in the pediatric critical care setting were identified to assess the bias, precision, and intra- and interobserver repeatability of Doppler CO measurement. Where results were not suitable for comparison and the original measurements available, data were re-analyzed using appropriate statistical methods and presented in comparative tables.

RESULTS

The precision of pediatric Doppler CO measurements compared to thermodilution, dye dilution, or Fick methods is around 30% and repeatability varies from less than 1% to 22%. Bias is generally less than 10% but varies considerably.

CONCLUSIONS

The bias, precision, and repeatability from study to study indicate that Doppler CO measurements are acceptably reproducible in children, with best results when used to track changes rather than absolute values, and using the transesophageal approach.

Critical care in cardiovascular medicine

The field of cardiac intensive care is rapidly evolving with nearly simultaneous advances in surgical techniques and adjunctive therapies, respiratory care, intensive care technology and monitoring, pharmacologic research and development, and computing and electronics. The focus of care has now shifted toward reducing morbidity and improving "quality of life" while the survival of infants and children with congenital heart defects, including those with univentricular hearts has dramatically improved during the last three decades. Despite these advances, there remains a predictable fall in cardiac output after cardiopulmonary bypass. This article focuses on early identification and aggressive treatment of the low cardiac output syndrome peculiar to these patients. The authors also briefly review the recent advances in the treatment of pulmonary hypertension, mechanical support, and neurologic surveillance after cardiac surgery.