NeonatalEchoSkills

Why is Neonatal Echocardiography important?

Preterm neonates are at risk

While the overall care provided to sick newborn infants has improved dramatically in recent decades, the most prematurely born infants remain at high risk of death and disability[1]. The impact of preterm birth on the population is vast – with an estimated annual socioeconomic burden of greater than £3 billion in the UK,[2] and greater than $26 billion in the USA[3].

As high quality research has improved preterm respiratory care, an increasing proportion of deaths occur due to episodes of sepsis or necrotizing enterocolitis[4]. In these systemic inflammatory disorders the release of pro-inflammatory cytokines may directly impair myocardial function[5], making circulatory failure the final mechanism of death.

Circulatory failure is a major cause of prem neonatal mortality

Circulatory factors are also linked to key morbidity. Failing cardiac function has been shown to cause cerebral hypoperfusion[6], and episodes of low cerebral blood flow are central to the pathophysiology of preterm brain injury which causes long term disability[7].

Clinical approaches to circulatory management in the neonatal unit vary significantly. The North American ELGAN study has demonstrated that the rate of vasopressor use in infants of less than 28 weeks gestation varies between 6% and 64% in different centres[8], and that this range is not due to differences in illness severity between populations. Similar variability is seen in rates of intervention to close a patent ductus arteriosus[9].

Circulatory managment varies wildly across neonatal units

It is clear that clinicians are limited either in their understanding of circulatory failure, their ability to detect it, or in their ability to make informed choices on optimal management. However, whatever the cause of the uncertainty, each year, thousands of preterm infants are either being exposed to unnecessary, potentially harmful treatments or are being deprived of potentially beneficial ones.

Lack of standardised care indicates a lack of evidence based treatment

Improving circulatory management is therefore a research priority in preterm infants[10]. However, understanding of the pathophysiology and optimal treatment of circulatory failure is hampered by the limited tools available to monitor circulatory function[11]. In particular, monitoring of circulatory status in the neonatal unit still relies heavily on arterial blood pressure. However, systemic arterial blood pressure is the product of systemic blood flow and systemic vascular resistance, and cannot itself distinguish between the two. While clinicians presumably feel that monitoring systemic blood pressure is a screening tool for low systemic perfusion, in fact blood pressure is at best weakly predictive of volume of blood flow[12], and some studies have suggested no[13] or even an inverse[14] relation between BP and flow in newborn preterm infants. Other clinical assessments, such as capillary refill time, volume of urine output, etc also have limited value in indicating circulatory health[12].

Some measures currently used to assess for circulatory failure like arterial blood pressure, capillary refilll time and urine output are unreliable

Even with its limitations echocardiography is the best method of assessment for neonate circulatory failure we currently have 

A number of research tools, including near infra-red spectroscopy have produced important advances in the understanding of circulatory physiology, but echocardiography certainly has the clearest role in the assessment of circulatory status at the cot-side. Echocardiography is cheap, safe, non-invasive and provides instant results with minimal or no post-processing of images.

However, the technique is not without its limitations. Critically, of course, there is scope for missed diagnosis or failed diagnosis of structural lesions. While some reports suggest this may be commonplace[15], other reports suggest that non-cardiologists may perform echo with a high degree of diagnostic accuracy in the newborn[16].

International guidelines have now been produced to guide the use of echocardiography in the neonatal setting (http://www.asecho.org/files/NICU.pdf). The aim of this website is not to teach individuals to perform echocardiography - we believe that this cannot be done without significant supervised scanning. We aim instead to provide a central resource to facilitate the use of echo on the neonatal unit which has significant scope to improve the care of newborn infants[17-19].

References

1.             Marlow N, Wolke D, Bracewell MA, and Samara M. Neurologic and developmental disability at six years of age after extremely preterm birth. N Engl J Med 2005; 352: 9-19.

2.             Mangham LJ, Petrou S, Doyle LW, Draper ES, and Marlow N. The cost of preterm birth throughout childhood in England and Wales. Pediatrics 2009; 123: e312-27.

3.             Behrman R and Stith Butler A, Preterm birth: causes, consequences, and prevention / Committee on Understanding Premature Birth and Assuring Healthy Outcomes, Board on Health Sciences Policy. 2007, Washington: The National Academies Press.

4.             Doyle LW, Gultom E, Chuang SL, et al. Changing mortality and causes of death in infants 23-27 weeks' gestational age. J Paediatr Child Health 1999; 35: 255-9.

5.             Ng PC, Li K, Wong RP, et al. Proinflammatory and anti-inflammatory cytokine responses in preterm infants with systemic infections. Arch Dis Child Fetal Neonatal Ed 2003; 88: F209-13.

6.             Kusaka T, Okubo K, Nagano K, Isobe K, and Itoh S. Cerebral distribution of cardiac output in newborn infants. Arch Dis Child Fetal Neonatal Ed 2005; 90: F77-8.

7.             Volpe JJ. Neurobiology of periventricular leukomalacia in the premature infant. Pediatr Res 2001; 50: 553-62.

8.             Laughon M, Bose C, Allred E, et al. Factors associated with treatment for hypotension in extremely low gestational age newborns during the first postnatal week. Pediatrics 2007; 119: 273-80.

9.             Laughon M, Bose C, and Clark R. Treatment strategies to prevent or close a patent ductus arteriosus in preterm infants and outcomes. J Perinatol 2007; 27: 164-70.

10.          Jobe AH. The cardiopulmonary system: research and training opportunities. J Perinatol 2006; 26 Suppl 2: S5-7.

11.          Kluckow M. Low systemic blood flow and pathophysiology of the preterm transitional circulation. Early Hum Dev 2005; 81: 429-37.

12.          Osborn DA, Evans N, and Kluckow M. Clinical detection of low upper body blood flow in very premature infants using blood pressure, capillary refill time, and central-peripheral temperature difference. Arch Dis Child Fetal Neonatal Ed 2004; 89: F168-73.

13.          Tyszczuk L, Meek J, Elwell C, and Wyatt JS. Cerebral blood flow is independent of mean arterial blood pressure in preterm infants undergoing intensive care. Pediatrics 1998; 102: 337-41.

14.          Groves AM, Kuschel CA, Knight DB, and Skinner J. The relationship between blood pressure and blood flow in newborn preterm infants. Arch Dis Child Fetal Neonatal Ed 2008; 93: F29-32.

15.          Ward CJ and Purdie J. Diagnostic accuracy of paediatric echocardiograms interpreted by individuals other than paediatric cardiologists. J Paediatr Child Health 2001; 37: 331-6.

16.          Moss S, Kitchiner DJ, Yoxall CW, and Subhedar NV. Evaluation of echocardiography on the neonatal unit. Arch Dis Child Fetal Neonatal Ed 2003; 88: F287-9; discussion F290-1.

17.          Sehgal A and McNamara PJ. Does echocardiography facilitate determination of hemodynamic significance attributable to the ductus arteriosus? Eur J Pediatr 2009; 168: 907-14.

18.          Sehgal A and McNamara PJ. Does point-of-care functional echocardiography enhance cardiovascular care in the NICU? J Perinatol 2008; 28: 729-35.

19.          Kluckow M, Seri I, and Evans N. Functional echocardiography: an emerging clinical tool for the neonatologist. J Pediatr 2007; 150: 125-30.