Estimation of Preload:
This is potentially one of the most valuable uses for functional echocardiography in the NNU, particularly to guide aggressiveness of fluid resuscitation in the collapsed neonate. However the measures have not currently been standardised, so assessments of filling volume are subjective.
Inferior Vena Caval Filling
To assess IVC filling place the ultrasound transducer in the midline, just below the xiphisternum, and in the sagittal plane. The probe marker should be pointing upward, so that the heart appears just visible on the right of the screen. The IVC can be seen coursing through the liver.
A normally filled IVC will have some pulsation with the cardiac cycle and respiratory motion. An under-filled IVC will be barely visible, or collapse entirely on inspiration:
An over-filled IVC will appear large, and minimally pulsatile. BUT BEWARE the child on the ventilator, especially high frequency oscillatory ventilation - high intrathoracic pressure can effectively tamponade venous return at the level of the IVC, making the IVC appear well-filled, when the cardiac chambers themselves are under-filled.
Therefore when assessing preload status always examine the intra-cardiac filling too.
This is often most easily accomplished from the sub-costal view, using the view used to interrogate the atria. This is convenient as it can follow directly on from the sagittal subcostal view used for IVC assessment.