# Inhaled Gases as Therapies for Post-Cardiac Arrest Syndrome: A Narrative Review of Recent Developments.
> 心停止後症候群に対する吸入ガス療法の最近の動向：ナラティブレビュー


## Abstract

Post-cardiac arrest syndrome (PCAS) arises from whole-body ischemia and subsequent reperfusion, and neurologically intact survival rates remain low despite advances in resuscitation care. Multiple pathological processes contribute to neuronal injury in PCAS, including vasoconstriction, protein modification, mitochondrial respiratory dysfunction, cell death signaling cascades, inflammatory responses, and excessive oxidative stress. This narrative review examines recent basic and clinical research on three inhaled gases—nitric oxide (NO), molecular hydrogen (H2), and xenon (Xe)—each of which has demonstrated cytoprotective properties in the context of PCAS. Although all three gases appear capable of mitigating ischemia-reperfusion injury, their underlying mechanisms likely differ. The authors conclude that further preclinical and clinical investigations combining standard post-cardiac arrest care with inhaled gas administration are needed to clarify optimal strategies and improve patient outcomes.

### Mechanism

Inhaled H2, NO, and Xe are proposed to reduce ischemia-reperfusion injury following cardiac arrest through complementary but distinct mechanisms involving mitochondrial protection, suppression of oxidative stress, and modulation of inflammatory signaling pathways.

## Bibliographic

- **Authors**: Hayashida K, Miyara SJ, Shinozaki K, Takegawa R, Yin T, Rolston DM, et al.
- **Journal**: Front Med (Lausanne)
- **Year**: 2020
- **PMID**: [33585501](https://pubmed.ncbi.nlm.nih.gov/33585501/)
- **DOI**: [10.3389/fmed.2020.586229](https://doi.org/10.3389/fmed.2020.586229)
- **PMC**: [PMC7873953](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7873953/)
- **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 33585501. https://h2-papers.org/en/papers/33585501
> **Source**: PubMed PMID [33585501](https://pubmed.ncbi.nlm.nih.gov/33585501/)