Hemodynamic Precision in the Neonatal Intensive Care Unit using Targeted Neonatal Echocardiography

Published: January 27, 2023

doi:

Marjorie Makoni*¹, Trassanee Chatmethakul*^1,2, Regan Giesinger, Patrick J. McNamara

¹Department of Pediatrics, Division of Neonatal-Perinatal Medicine,University of Oklahoma Health Sciences Center, ²University of Iowa Department of Pediatrics, Division of Neonatology,University of Iowa

Summary

Presented here is a protocol to perform comprehensive neonatal echocardiography by trained neonatologists in the neonatal intensive care unit. The trained individuals provide longitudinal assessments of heart function, systemic and pulmonary hemodynamics in a consultative role. The manuscript also describes the requirements to become a fully trained neonatal hemodynamics specialist.

Abstract

Targeted neonatal echocardiography (TnECHO) refers to the use of comprehensive echocardiographic evaluation and physiologic data to obtain accurate, reliable, and real-time information on developmental hemodynamics in sick newborns. The comprehensive assessment is based on a multiparametric approach that overcomes the reliability issues of individual measurements, allows for earlier recognition of cardiovascular compromise and promotes enhanced diagnostic precision and timely management. TnECHO-driven research has led to an enhanced understanding of the mechanisms of illness and the development of predictive models to identify at-risk populations. This information may then be used to formulate a diagnostic impression and provide individualized guidance for the selection of cardiovascular therapies. TnECHO is based on the expert consultative model in which a neonatologist, with advanced training in neonatal hemodynamics, performs comprehensive and standardized TnECHO assessments. The distinction from point of care ultrasonography (POCUS), which provides limited and brief one-time assessments, is important. Neonatal hemodynamics training is a 1-year structured program designed to optimize image acquisition, measurement analysis, and hemodynamic knowledge (physiology, pharmacotherapy) to support cardiovascular decision-making. Neonatologists with hemodynamic expertise are trained to recognize deviations from normal anatomy and appropriately refer cases of possible structural abnormalities. We provide an outline of neonatal hemodynamics training, the standardized TnECHO imaging protocol, and an example of representative echo findings in a hemodynamically significant patent ductus arteriosus.

Introduction

Targeted neonatal echocardiography (TnECHO) refers to the bedside use of echocardiography to longitudinally assess myocardial function, systemic and pulmonary blood flow, and intracardiac and extracardiac shunts¹. When TnECHO is integrated with clinical findings, it can provide vital information in diagnosis, the guidance of therapeutic interventions, and the dynamic monitoring of response to treatments². TnECHO is frequently performed by trained neonatologists in response to a specific clinical question with the goal of acquiring hemodynamics information that can complement and provide physiologic insights into the clinical status of the patients, resulting in precise cardiovascular care³. Over the past 10-15 years, TnECHO services have been incorporated in multiple tertiary neonatal intensive care units (NICUs) in Australia, New Zealand, Europe, and North America, especially in the management of complex high-acuity cases⁴^,⁵^,⁶^,⁷^,⁸. To date, there are eight centers in the USA with trained practitioners providing TnECHO services and a growing number of centers involved in neonatal hemodynamics research. Furthermore, the establishment of the neonatal hemodynamics and TnECHO special interest group (SIG) at the American Society of Echocardiography (ASE) reinforces the academic collaboration with pediatric cardiology and creates a strong political platform for further growth in the field⁹.

Neonatal hemodynamics training is designed to ensure that individuals who have received the training can achieve high-level imaging and provide comprehensive cardiovascular decision-making. In 2011, training recommendations for TnECHO, endorsed by European and North American professional organizations, were published³. Currently, more than 50 North American neonatologists have completed formal training in TnECHO; of note, more than 50% of hemodynamic clinicians are considered emerging academic leaders in the field, which is an unanticipated but much-needed benefit of formal training. Figure 1 summarizes hemodynamics training and accreditation.

The essential elements of a TnECHO service include access to a dedicated echocardiography machine. This ensures immediate availability for image acquisition and allows longitudinal follow-up (Figure 2 and Figure 3). The database/image archive must include the ability to provide immediate playback without video degradation, standardized reports, and long-term storage as per the recommendations of the Intersocietal Commission for the Accreditation of Echocardiography Laboratories¹⁰. A standard TnECHO includes key measurements that allow comprehensive assessments of intricate cardiovascular physiology during the neonatal period. This includes left ventricular (LV) function, right ventricular (RV) function, intracardiac shunt (atrial-level shunt and ductal-level shunt), the hemodynamic effects of patent ductus arteriosus (PDA), right ventricular systolic pressure (RVSp)/pulmonary artery (PA) pressure, systemic and pulmonary blood flow, the presence of pericardial fluid, thrombus, and central line position. Table 1 shows the commonly used echocardiographic terms utilized to acquire some of the data for these measurements. The evaluation may be performed for both symptom- and disease-based indications. Supplementary File 1 and Table 2 outline the comprehensive neonatal echocardiography assessments with recommended measurements, interpretation, and reference ranges for term neonates in the first 7 postnatal days.

The evaluation of LV systolic function is a key component as it assists in the delineation of the etiology and management of hemodynamic instability in critically ill neonates. Quantitative assessment is recommended as qualitative assessment is prone to inter-observer and intra-observer variability¹¹. The calculation of the ejection fraction using a multi-plane method such as Simpson's biplane or the area-length method is superior to M-mode estimations, which may miss regional wall motion abnormalities and is inaccurate in the presence of septal flattening¹². LV diastolic dysfunction is an emerging concept in neonatal hemodynamics. However, the data remain limited¹³.

An assessment of RV function is crucial in neonatal life because the RV is the dominant ventricle in transitional circulation, and many neonatal diseases are associated with right heart pathology. For a similar reason, in the assessment of LV systolic function, subjective assessment should be avoided¹⁴. However, due to the RV's unusual shape, highly trabeculated surface, and position wrapped around the LV, the measurement of RV function is more difficult. Despite this, several reliable quantitative parameters have been studied, and normative data have been published¹⁵^,¹⁶. Fractional area change (FAC) and tricuspid annular plane systolic excursion (TAPSE) are two of the recommended quantitative measurements used¹⁷.

Intracardiac shunt (atrial and ductal level) is another important aspect of the comprehensive neonatal echocardiography assessment. In most situations, left atrial pressures are higher in comparison to right atrial (RA) pressures, resulting in a left-to-right shunt. However, in the neonatal period, a bidirectional shunt can still be normal. Elevated right-sided filling pressures, especially in association with pulmonary hypertension (PH), should be considered when there is right-to-left shunting at the atrial level, but this should not be used in isolation given that variation in ventricular compliance/pressure may also influence atrial pressure at various points during the cardiac cycle.

An assessment of patent ductus arteriosus (PDA) should include the determination of ductal shunt direction and the measurement of ductal pressure gradients, which are used to assist in treatment decisions. An arch-sidedness evaluation is also important, especially when there is consideration of surgical PDA ligation. PDA shunt direction is reflective of the difference between aortic and PA pressures, as well as the relative resistance of the pulmonary and systemic circulation. One factor used to adjudicate hemodynamic significance is the presence of holodiastolic retrograde flow in the descending thoracic or abdominal aorta¹⁸. Hemodynamic significance can be further assessed by quantifying the degree of volume overload by comprehensive measurements¹⁹. Scoring systems that assess the surrogate consequences of volume loading on the heart and the systemic hypoperfusion associated with PDA shunt, such as the Iowa PDA score, have been published (Table 3)¹⁹^,²⁰^,²¹ The Iowa PDA score has been adopted clinically at the University of Iowa to enhance objectivity in determining the hemodynamic significance of a PDA shunt. A score of more than 6 is suggestive of a hemodynamically significant patent ductus arteriosus (hsPDA)¹⁹.

In the assessment of pulmonary hemodynamics, the absolute value of RVSp is estimated by the measurement of the tricuspid regurgitant (TR) gradient. Continuous wave Doppler is used to measure the maximal tricuspid regurgitation velocity through the tricuspid valve, referred to as the tricuspid regurgitant peak velocity. An assumed RA pressure of 5 mmHg is typically used for the calculation. The RVSp is then calculated using the simplified Bernoulli equation²²:

RVSp = 4 × (tricuspid regurgitant peak velocity [m/s])² + RA pressure

Occasionally an alternative, the Doppler-derived pressure gradient across a PDA, is used for the calculation of PA (pulmonary artery) pressures²³. However, a TR jet is only present in approximately 50% of patients with chronic PH²⁴^,²⁵^,²⁶. In these situations, measurements such as the end-systolic eccentricity index (sEI), which is a measure of LV circularity, may indicate the relative pressure between the ventricles. This measurement should be interpreted with caution in patients with systemic hypertension as the mild disease may go undetected due to elevated LV end-diastolic pressure. Figure 4 gives an example of an algorithm and comprehensive neonatal echocardiography assessment guidelines for pulmonary hypertension.

For the assessment of LV stroke volume, a pulse Doppler tracing in an apical five-chamber view at the level of the aortic valve is measured to obtain the time-velocity integral (TVI). This is combined with a measurement of aortic annulus diameter in the parasternal long-axis view. A calculation with the following formula is used to estimate LV output²⁷:

LV output (mL/min/kg) = (TVI [cm] × π x [D/2]² [cm²] × heart rate)/weight.

However, in the presence of a PDA, the LV output measurement is not reflective of systemic blood flow secondary to the shunting at the PDA level³. The diastolic flow to peripheral organs by Doppler interrogation of the celiac artery, superior mesenteric artery, and middle cerebral artery can give an indication of a systemic steal by a PDA but may, alternately, reflect organ resistance, with low or absent diastolic flow seen in the setting of high resistance.

TnECHO can also be utilized to assist in detecting the presence of intracardiac thrombus, pericardial fluid, and its hemodynamic significance, guiding pericardiocentesis, as well as assisting in the placement of peripheral arterial lines, peripherally inserted central catheters, and umbilical venous catheters²⁸. Here, to show the comprehensive approach to obtaining TnECHO and the hemodynamics information, we describe the imaging protocol and the elements of a TnECHO service (Figure 3).

Protocol

This protocol was approved by the institution's human research ethics committee, and written consent was obtained from the patient before the procedure. 1. Preparation For image acquisition, use ultrasound systems that include two-dimensional (2D), M-mode, and full Doppler capabilities, as well as simultaneous electrocardiographic tracing display ability. Ensure that multi-frequency probes, 5-6 MHz (for infants >2 kg) and 8-12 MHz (for infants &#6…

Representative Results

The following representative results outline the evaluation of a hemodynamically significant patent ductus arteriosus (hsPDA) as an example of the use of TnECHO in clinical settings. As mentioned earlier, a comprehensive assessment with multiple measurements is performed to adjudicate hemodynamic significance. The Iowa PDA score (Table 3) is one of the scoring systems adopted into clinical use as it assists in quantifying the consequences of volume loading and systemic hypoperfusion associated with PDA s…

Discussion

TnECHO-guided care has been adopted in many neonatal intensive care units as an adjunct to the clinical assessment of hemodynamic instability in infants by neonatologists⁴. Accredited training programs have been developed in accordance with the 2011 ASE³ with a focus on a competence-based approach to training. The unique vulnerability of the immature cardiovascular system and the complexity of cardiovascular adaptation during the postnatal transition are key determinants of…

Offenlegungen

The authors have nothing to disclose.

Acknowledgements

The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. M.M. is supported by the National Institute on Minority Health and Health Disparities of the National Institutes of Health under Award Number R25MD011564.

Resources for the figures, reference values, and training recommendations were adapted from Ruoss et al.³⁰, the TnECHO teaching manual⁴⁷, the Neonatal Hemodynamics Research Center (NHRC)⁴⁸, and the Targeted neonatal echocardiography application⁴⁹.

Materials

DICOM VIEWER EP	GEHealthcare	H45581CC	DICOM Viewer on MediaThis option provides the ability to export DICOM images including a DICOM viewer to storage media (USB, DVD), for easy access to patient images on offline computers.
2D Strain	GEHealthcare	H45561WF	Automated 2D EF Measurement tool based upon 2D-Speckle tracking algorithm.
EchoPAC* Software Only v203	GEHealthcare	H8018PF
EchoPAC* Advanced Bundle Package	GEHealthcare	H8018PG	Advanced QScan provides dedicated parametric imaging applications for quantitative display of regional wall deformation.
Multi-Link 3-lead ECG Care cable neonatal DIN, AHA (3.6 m/12 feet)	GEHealthcare	H45571RD	Multi-Link 3-lead ECG Care cable neonatal DIN, AHA (3.6 m/12 feet) Used together with neonatal leads H45571RJ
Myocardial Work		H45591AG	Myocardial Work adjusts the AFI (strain) results using the systolic and diastolic blood pressure measured immediately prior to the echo exam. Using the Myocardial Work feature helps achieve a less load dependent strain/ pressure curve and work efficiency index
12S-D Phased Array Probe	GEHealthcare	H45021RT
6S-D Phased Array Probe	GEHealthcare	H45021RR
Sterile ultrasound gel	Parker labs	PM-010-0002D	sterile water solubel single packet ultrasound transmission gel
Ultrasound gel warmer	Parker Labs	SKU 83-20	ultrasound gel warmer for single gel package.
Wireless USB adapter		H45591HS	Wireless external G type USB adapter with extension cable and hardware for mounting on the rear panel.
Vivid* E90 v203 Console Package	GEHealthcare	H8018EB	Vivid E90 w/OLED monitor v203 Console

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Makoni, M., Chatmethakul, T., Giesinger, R., McNamara, P. J. Hemodynamic Precision in the Neonatal Intensive Care Unit using Targeted Neonatal Echocardiography. J. Vis. Exp. (191), e64257, doi:10.3791/64257 (2023).