Cerebral Blood Flow Monitoring in High-Risk Fetal and Neonatal Populations

Abstract

Cerebrovascular pressure autoregulation promotes stable cerebral blood flow (CBF) across a range of arterial blood pressures. Cerebral autoregulation (CA) is a developmental process that reaches maturity around term gestation and can be monitored prenatally with both Doppler ultrasound and magnetic resonance imaging (MRI) techniques. Postnatally, there are key advantages and limitations to assessing CA with Doppler ultrasound, MRI, and near-infrared spectroscopy. Here we review these CBF monitoring techniques as well as their application to both fetal and neonatal populations at risk of perturbations in CBF. Specifically, we discuss CBF monitoring in fetuses with intrauterine growth restriction, anemia, congenital heart disease, neonates born preterm and those with hypoxic-ischemic encephalopathy. We conclude the review with insights into the future directions in this field with an emphasis on collaborative science and precision medicine approaches.

Keywords: cerebral autoregulation; cerebroplacental Doppler; congenital heart disease; fetal MRI; fetal brain; hypoxic ischemia encephalopathy (HIE); near-infrared spectroscopy; neonatal brain.

Figure 1

The key questions regarding cerebral autoregulation (CA) are unique to each neonatal pathophysiology. In the preterm neonate, due to immature mechanisms of cerebrovascular adaptation, there is a limited plateau of stable cerebral blood flow (CBF) and there is no strong evidence to guide the optimal lower limit of cerebral perfusion pressure (CPP) by gestational age. In the neonate with congenital heart disease (CHD), postnatal hypoxia and stabilization of CBF before, during, and after cardiac surgery are the prominent challenges. For neonates with hypoxic ischemic encephalopathy (HIE), avoidance of reperfusion injury plays a key role in limiting neurologic damage.

Figure 2

Wavelet transform coherence analysis can be used to characterize cross-correlations between mean arterial pressure and ScO₂ as a function of a wide range of both time and frequencies. The coherence depicted by color mapping represents the correlations across the time-frequency axis and can be translated into percent coherence from 0 (least coherent, blue) to 1 (most coherent, red). In-phase coherence indicates impaired cerebral autoregulation.