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. The impact of preterm birth on the population is vast – with an estimated annual socioeconomic burden of greater than £3 billion in the UK, and greater than $26 billion in the USA.
As high quality research has improved preterm respiratory care, an increasing proportion of deaths occur due to episodes of sepsis or necrotizing enterocolitis. In these systemic inflammatory disorders the release of pro-inflammatory cytokines may directly impair myocardial function, making circulatory failure the final mechanism of death.
Circulatory factors are also linked to key morbidity. Failing cardiac function has been shown to cause cerebral hypoperfusion, and episodes of low cerebral blood flow are central to the pathophysiology of preterm brain injury which causes long term disability.
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, 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.
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.
Improving circulatory management is therefore a research priority in preterm infants. However, understanding of the pathophysiology and optimal treatment of circulatory failure is hampered by the limited tools available to monitor circulatory function. 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, and some studies have suggested no or even an inverse 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.
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, other reports suggest that non-cardiologists may perform echo with a high degree of diagnostic accuracy in the newborn.
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].