Cerebral blood flow velocity in the human newborn: the value of its determination

An ultrasonic technique based on measurement of the Doppler frequency shift produced by the movement of red blood cells in an insonated vessel has been useful for measurement of cerebral blood flow velocity in the newborn. When the transducer is applied to the anterior fontanel, flow velocity in each anterior cerebral artery can be determined noninvasively. Reliable application ofthe technique requires utilization of both the audible and visible signals produced by the instrument. Experience and awareness of the anatomy are also important in interpretation. Serial measurements of cerebral blood flow velocity have provided useful information concerning changes in the cerebral circulation under important neonatal circumstances. Examples of the latter include PDA, pneumothorax, hydrocephalus, and hyperviscosity. Most of the changes in the cerebral circulation appear to reflect directly systemic hemodynamic changes. This relation between cerebral and systemic hemodynamic events is compatible with other observations, indicating that in the human newborn—particularly the infant most at risk for hypoxic-ischemic and/or hemorrhagic brain injury—the cerebral circulation is pressure passive. Indeed, the changes in the cerebral circulation observed so far with the Doppler technique may have important implications for the genesis of neonatal ischemic and hemorrhagic brain injury.