Purpose or Case Report: MRS is the best prognostic indicator for hypoxic-ischemic encephalopathy (HIE) but is difficult to obtain early after injury. We investigated whether cerebral blood flow measures of resistive indices (RI) and time average maximum velocities (TAMx) shortly after birth would relate to later degree of neural injury by MRI in hypothermic HIE newborns. We predicted that abnormally high/low blood flow would be associated with poor outcomes.
Methods & Materials: We retrospectively investigated 81 infants born between 2012 and 2018, ≥34 weeks gestation, treated with hypothermia, who received a transcranial Doppler ultrasound within 24 hours after birth, and MRI at 3-10 days. Cerebral blood flow measures (RI, TAMx) in anterior cerebral (ACA), middle cerebral (MCA) and basilar (BA) arteries were correlated with MRS ratios of neuronal health (N-acetylaspartate, NAA) in the basal ganglia (BG) and frontal white matter (WM). As both high and low RI and TAMx are abnormal, we divided our data into quartiles (Q) to find linear correlations between blood flow and NAA.
Results: As resistance in MCA increased above normal (Q3), NAA ratios in WM decreased (r² = -0.574, p=0.02), reflecting a decrease in neuronal integrity. Also, as blood flow velocity in BA (Q4) increased above normal, NAA ratios decreased in BG (r² = -0.550, p =0.012). Conversely, as velocity in the BA approached normal (Q2), NAA ratios increased in WM (r² = +0.618, p=0.011) indicating greater preservation of axons.
Conclusions: In this largest reported sample of cerebral blood flow in hypothermic HIE neonates, increased resistive index in the MCA and cerebral blood flow velocity in BA in the first 24h after HIE birth are associated with more injury, and worse NAA ratios. Transcranial doppler US can be performed at bedside shortly after birth and might prove useful for earlier prognosis in neonates with HIE.