Impact of Hypoxia-Ischemia on Neurogenesis and Structural and Functional Outcomes in a Mild-Moderate Neonatal Hypoxia-Ischemia Brain Injury Model.

Hypoxic-ischemic encephalopathy (HIE) is a common type of brain injury caused by a lack of oxygen and blood flow to the brain during the perinatal period. The incidence of HIE is approximately 2−3 cases per 1000 live births in high-income settings; while in low- and middle-income countries, the incidence is 3−10-fold higher. Therapeutic hypothermia (TH) is the current standard treatment for neonates affected by moderate−severe HIE. However, more than 50% of all infants with suspected HIE have mild encephalopathy, and these infants are not treated with TH because of their lower risk of adverse outcomes. Despite this, several analyses of pooled data provide increasing evidence that infants who initially have mild encephalopathy may present signs of more significant brain injury later in life. The purpose of this study was to expand our knowledge about the effect of mild−moderate hypoxia-ischemia (HI) at the cellular, structural, and functional levels. An established rat model of mild−moderate HI was used, where postnatal day (P) 7 rats were exposed to unilateral permanent occlusion of the left carotid artery and 90 min of 8% hypoxia, followed by TH or normothermia (NT) treatment. The extent of injury was assessed using histology (P14 and P42) and MRI (P11 and P32), as well as with short-term and long-term behavioral tests. Neurogenesis was assessed by BrdU staining. We showed that mild−moderate HI leads to a progressive loss of brain tissue, pathological changes in MRI scans, as well as an impairment of long-term motor function. At P14, the median area loss assessed by histology for HI animals was 20% (p < 0.05), corresponding to mild−moderate brain injury, increasing to 55% (p < 0.05) at P42. The data assessed by MRI corroborated our results. HI led to a decrease in neurogenesis, especially in the hippocampus and the lateral ventricle at early time points, with a delayed partial recovery. TH was not neuroprotective at early time points following mild−moderate HI, but prevented the increase in brain damage over time. Additionally, rats treated with TH showed better long-term motor function. Altogether, our results bring more light to the understanding of pathophysiology following mild-moderate HI. We showed that, in the context of mild-moderate HI, TH failed to be significantly neuroprotective. However, animals treated with TH showed a significant improvement in motor, but not cognitive long-term function. These results are in line with what is observed in some cases where neonates with mild HIE are at risk of neurodevelopmental deficits in infancy or childhood. Whether TH should be used as a preventive treatment to reduce adverse outcomes in mild-HIE remains of active interest, and more research has to be carried out in order to address this question.

Association Between Early EEG Background and Outcomes in Infants With Mild HIE Undergoing Therapeutic Hypothermia.

BACKGROUND: Hypoxic-ischemic encephalopathy (HIE) occurs in 1-4:1000 live births. Although neonates with moderate-severe HIE have been studied over several decades, newborns with mild HIE remain understudied, including seizure occurrence, electroencephalography (EEG) characteristics, and outcome. METHODS: We conducted a retrospective cohort study of neonates ≥35 weeks of gestation with mild HIE who underwent therapeutic hypothermia to correlate the early EEG background pattern with clinical course and outcomes. RESULTS: Of the included 29 neonates, 10 infants had a moderately to severely abnormal EEG background and 19 had either a normal or a mildly abnormal background. Those with moderately to severely abnormal background also had more multiorgan dysfunction (90% vs 42%, P = 0.02) and a higher incidence of subdural and intraventricular hemorrhages (80% vs 26%, P = 0.02). The overall seizure incidence was 20.7% and was significantly higher in newborns with more severely abnormal background compared to neonates with less abnormal background (50% vs 5%; P = 0.01; relative risk, 9.5; 95% confidence interval, 1.28-70.6). Seizure onset was between 11 and 63 hours of life. Regardless of the EEG background pattern, seizures were brief with an overall low seizure burden. None of the newborns with normal or mildly abnormal background had a new onset of seizures after 24 hours of recording or developed epilepsy during infancy. CONCLUSIONS: In neonates with mild HIE, early moderately to severely abnormal EEG background is common and strongly associated with an increased risk for seizures.

New Horizons in Mild Hypoxic-ischemic Encephalopathy: A Standardized Algorithm to Move past Conundrum of Care.

Hypoxic-ischemic encephalopathy (HIE) presents clinically with a neonatal encephalopathy (NE) whereby the mild spectrum is difficult to classify immediately after birth. For decades trials have focused exclusively on infants with moderate-severe HIE s, as these infants were easier to identify after birth and had the highest risk of adverse outcomes. Twenty years after those trials, the PRIME study finally solved the first part of the conundrum by providing a definition of mild HIE in the first 6 hours. There is strong biological plausibility and preclinical evidence supporting the efficacy of therapeutic hypothermia (TH) but there is a lack of comparative clinical data to establish the risk-benefit in mild HIE. The fundamental question of how best to manage mild HIE remains unanswered. This review will summarize (1) the evidence that neonates with mild HIE are at significant risk for adverse outcomes, (2) the gaps/controversies in management, and (3) an algorithm of care is proposed to ensure standardized management of mild HIE and the direction of future trials.