Editors' ChoiceCRITICAL CARE

Inhaling H(2)ope

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Science Translational Medicine  19 Nov 2014:
Vol. 6, Issue 263, pp. 263ec198
DOI: 10.1126/scitranslmed.aaa2060

Cardiac arrest is a precarious state between life and death that has many diverse causes. Despite increased public awareness, rapid administration of cardiopulmonary resuscitation (CPR), and improved access to automated external defibrillators (AEDs), only a fraction of individuals survive longer than one month (5 to 15%) after cardiac arrest, with an even smaller portion returning to normal neurological function (~2%). Lack of blood flow and oxygen (ischemia) induce global brain injury, yet rapid reperfusion can exacerbate tissue damage by driving inflammation, free radical production, and oxidative stress. Recently, inhaled hydrogen (H2) was shown to have antioxidant properties,quenching harmful free radicals, without affecting the other reactive oxygen species critical to normal function.

Leveraging these properties of H2, Hayashida et al. demonstrated the potential of inhaled H2 therapy in improving survival and neurological outcomes in a rat model of cardiac arrest. Six minutes after inducing arrest through ventricular fibrillation, CPR was initiated for three minutes followed by defibrillation. Surviving rats were divided into four test groups receiving: (i) standard ventilation with 26% oxygen (O2), (ii) ventilation with a 1.3%/26% inhaled H2/O2 mixture, (iii) standard ventilation and therapeutic hypothermia (an established method of improving outcomes following arrest), or (iv) the combination of H2 inhalation and hypothermia. Compared with controls, 7-day survival doubled in animals receiving H2 and/or hypothermic treatments. Neurological function, motor activity, and spatial memory also improved markedly with either H2 or therapeutic hypothermia compared with standard treatment, with additional functional improvement in the group receiving both therapies.

Distinctions between rats and humans aside, these results offer a promising approach to mitigate ischemia/reperfusion injury following cardiac arrest. For patients and their families looking for hope after experiencing one of the most complex and acute of medical conditions, it is somewhat poetic that they may find it in H2, the simplest and most abundant molecule in the universe.

K. Hayashida et al., Hydrogen inhalation during normoxic resuscitation improves neurological outcome in a rat model of cardiac arrest, independent of targeted temperature management. Circulation 10.1161/CIRCULATIONAHA.114.011848 (2014). [Abstract]

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