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Towards more accurate assessment of preterm systemic blood flow
  1. Nick Evans
  1. Correspondence to A/Professor Nick Evans, Department of Newborn Care, Royal Prince Alfred Hospital and University of Sydney, Missenden Rd, Camperdown, Sydney, New South Wales 2111, Australia; nicholas.evans{at}sydney.edu.au

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Ficial et al1 describe a modification of the technique for measurement of superior vena cava (SVC) flow in preterm infants originally described by Martin Kluckow and myself. Why might one want to measure SVC flow?

Up to the 1990s, the field of preterm neonatal haemodynamics was based on maintaining mean blood pressure (BP) above a threshold. There was a seductive simplicity to this thinking but it was always built on a flawed assumption of universal pressure passivity of the cerebral circulation. However there was (and still is) little data linking low BP with worse neurodevelopmental outcome and none showing that maintaining BP above these thresholds improved outcomes. Further there was little understanding of the cardiovascular basis of low BP and how that was impacted by circulatory support measures. It was in this milieu that several neonatologists started to use cardiac Doppler ultrasound to study transitional haemodynamics in preterm infants.

The complexity of what we found was in stark contrast to the simplicity of the above thinking. Shunts through the ductus arteriosus were mostly left to right, even early after birth, and, although clinically silent, were larger and earlier after birth than had been appreciated.2 The foramen ovale was only considered as a site for right to left shunts. In fact, like the ductus, the dominant shunt direction was left to right and the interatrial shunts could be as large as the ductal shunts. With blood moving from the systemic to the …

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