Cerebral blood flow and energy metabolism in the newborn.

In normal newborn term and preterm infants CBF is relatively low corresponding to a low metabolic rate for oxygen, whereas cross-brain oxygen extraction is similar to that in adults. This provides for a considerable reserve capacity to deal with decreased CBF or decreased oxygen content in arterial blood. CBF reactivity to CO2 is normal, and the evidence is that pressure-flow autoregulation is present, even in very preterm infants. Absence of autoregulation and CBF-CO2 reactivity has been documented in severely asphyxiated infants, and in preterm infants who went on the develop severe intracranial hemorrhage. A number of methods are available to study CBF and brain metabolism in newborn infants. Several of them involve ionizing radiation, which has limited their use, even though it is unlikely that the associated risks are particularly high. Magnetic resonance spectroscopy has demonstrated a delayed disturbance of energy metabolism following severe asphyxia. Doppler ultrasound has rarely been helpful to obtain quantitative data. Near infrared spectrocopy has now been in use for more than 10 years. It has been slow to fulfill its promise as a continuous monitor of cerebral circulation and of oxygen sufficiency of neurons.