Lung sections with mechanical ventilation with high tidal volume (30 mL/kg), stained with hematoxylin and eosin. (a) Alveolar septal thickening and inflammatory cell infiltration were observed in the lung with ventilator-induced lung injury (VILI) (2% N2). Hydrogen administration markedly reduced these histopathological changes. Magnification = 400 ×. Representative images are shown. N = 6 animals for each experimental group. (b) Wet-to-dry (W/D) ratio of the lungs with mechanical ventilation with high tidal volume (30 mL/kg). VILI for 2 hours was accompanied with an increase of W/D ratio; ventilation with 2% hydrogen still induced lung edema but to a lesser extent compared with mechanical ventilation with 2% nitrogen in air. N = 6 for each group. (c) Tissue malondialdehyde (MDA) levels. Mechanical ventilation with high tidal volume (30 mg/kg) with 2% nitrogen in air increased tissue MDA levels. The supplementation of hydrogen significantly lowered levels of tissue MDA, a marker of lipid peroxidation. N = 6 for each group. *P < 0.05 versus sham/N2 and sham/H2; #P < 0.05 versus VILI/N2.