Performance of Unmodified Mechanical Ventilators With 2% Hydrogen Gas Mixtures

Background: Molecular hydrogen (H₂) is a breathable gas that has been shown to have anti-oxidative, anti-inflammatory, and anti-apoptotic properties that may positively impact ischemia-reperfusion injury. The provision of 2% H₂ through unmodified mechanical ventilators may facilitate the clinical translation of H₂ as a therapeutic in critical illness. The effect of 2% H₂ on ventilator performance is unknown. Methods: Unmodified Maquet Servo-i, Maquet Servo-u, Dräger Evita Infinity V500, and Dräger Evita Babylog VN500 ventilators from clinical stock were tested in an experimental closed system using certified, premixed air and O₂ containing 2% H₂ gas. Wall air and O₂ supply were used as control. Ventilator settings were varied across the spectrum of neonatal to adult settings. End points included (1) difference between set and delivered tidal volume (V_T) (Douglas method), (2) difference between set versus delivered O₂ concentration, (3) delivered H₂ concentration (gas chromatography), and (4) ventilator pre-use check malfunction. Correlation between set and measured end points were quantified by linear regression analysis and bias by Bland-Altman analysis. Results: During H₂ administration, the average bias in measured versus set V_T was within ± 10% for all ventilators except for the Babylog VN500, which exhibited an average bias of -89.2% (95% CI -107.0 to -71.3). The average bias in measured F_IO2 was within ± 10% of set for all ventilators. Except for the Babylog VN500, all ventilators passed the pre-use check. Conclusions: Unmodified Servo-i, Servo-u, and Evita V500 ventilators deliver 2% H₂ mixtures with acceptable accuracy in V_T and F_IO2. The Babylog VN500, which uses hot-wire anometry and a higher set operating temperature, exhibits unacceptably inaccurate delivery of V_T with H₂ mixtures.