# Hydrogen and therapeutic gases for neonatal hypoxic-ischemic encephalopathy: potential neuroprotective adjuncts in translational research.
> 新生児低酸素性虚血性脳症に対する水素および治療用ガスの神経保護的可能性：トランスレーショナルリサーチにおける補助的アプローチ


## Abstract

Neonatal hypoxic-ischemic encephalopathy (HIE) involves neuronal and nervous system cell damage driven largely by excessive oxidative stress. This review synthesizes evidence on the neuroprotective properties of molecular hydrogen and other therapeutic gases, drawing on translational research in adult conditions such as cerebral ischemia, traumatic brain injury, and neurodegenerative diseases including Alzheimer's disease. Animal and human studies have established the safety and feasibility of molecular hydrogen administration. In neonatal translational HIE models, hydrogen ventilation—used alone or combined with hypothermia—has demonstrated both short- and long-term neuroprotective outcomes. Despite robust adult-focused research, pediatric and neonatal applications remain underexplored. The review highlights the need to define optimal target severity levels for intervention to maximize clinical benefit, and identifies hydrogen as a candidate adjunct neuroprotective agent in the HIE setting.

### Mechanism

Molecular hydrogen exerts potent antioxidative effects that are thought to mitigate neuronal damage caused by excessive oxidative stress in HIE. Combination with hypothermia may produce additive neuroprotective effects in translational animal models.

## Bibliographic

- **Authors**: Htun Y, Nakamura S, Kusaka T
- **Journal**: Pediatr Res
- **Year**: 2021
- **PMID**: [32505123](https://pubmed.ncbi.nlm.nih.gov/32505123/)
- **DOI**: [10.1038/s41390-020-0998-z](https://doi.org/10.1038/s41390-020-0998-z)
- **Study type**: review
- **Delivery route**: inhalation
- **Effect reported**: not assessed

## Delivery context

For inhalation applications of molecular hydrogen, the lower flammability limit (LFL) deserves careful handling. The classical 4% figure applies to closed-system mixtures; the practical inhalation-environment threshold is 10%. Even pure-hydrogen output (the UFL 75% paradox) passes through the flammable range at the air–gas boundary. High-concentration (66% / 100%) inhalers are documented in the Japanese Consumer Affairs Agency accident-information database and are not recommended.

## Safety notes

For inhalation applications of molecular hydrogen, the lower flammability limit (LFL) deserves careful handling. The classical 4% figure applies to closed-system mixtures; the practical inhalation-environment threshold is 10%. Even pure-hydrogen output (the UFL 75% paradox) passes through the flammable range at the air–gas boundary. High-concentration (66% / 100%) inhalers are documented in the Japanese Consumer Affairs Agency accident-information database and are not recommended.

See also:
- [Inhalation concentration and LFL / UFL](https://h2-papers.org/en/safety-notes/inhalation-concentration)
- [Consumer Affairs Agency accident cases](https://h2-papers.org/en/safety-notes/accident-cases)
- [LFL / UFL terminology](https://h2-papers.org/en/safety-notes/lfl-ufl-explained)
- [Inhalation safety threshold lineage](https://h2-papers.org/en/safety-notes/lineage)

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> **Cite as**: H2 Papers — PMID 32505123. https://h2-papers.org/en/papers/32505123
> **Source**: PubMed PMID [32505123](https://pubmed.ncbi.nlm.nih.gov/32505123/)