Background Low-molecular-weight gases such as helium are more likely to form laminar flows. Using helium-oxygen mixtures instead of nitrogen-oxygen mixtures during mechanical ventilation has been shown to accelerate carbon dioxide (CO2) excretion. Helium-oxygen mixtures have been used with mechanical ventilator settings such as high-frequency oscillatory ventilation (HFOV) and conventional mechanical ventilation (CMV). However, to the best of our knowledge, studies have not been conducted to determine the optimal ventilator setting for the promotion of CO2 excretion when helium is administered. This study aimed to compare the efficacy of using helium-oxygen gas mixtures between pressure-controlled CMV and piston-driven HFOV in rabbit models. CO2 transition was evaluated using blood gas analysis performed during and after helium administration. Experimental data were analyzed using parametric statistical methods. A repeated measures analysis of variance was used to compare CO2 excretion between HFOV and CMV. Results There was no statistically significant difference in the partial pressure of CO2 (PaCO2) or oxygen (PaO2) values before or after helium administration. Compared with pre-helium administration, PaCO2 values during helium administration were decreased under both CMV and piston-driven HFOV. Moreover, the PaCO2 transition during helium administration while using piston-driven HFOV was shown to be statistically significantly different (P < 0.001). Conclusions This study demonstrated that helium enhances CO2 elimination more significantly during piston-driven HFOV compared with that in CMV in rabbit models with normal lungs. With further study and clinical trials, these results imply that the use of HFOV while using a helium-oxygen mixture may improve CO2 excretion.

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Background The success rate of sedation with triclofos sodium and midazolam for pediatric magnetic resonance imaging (MRI) has been reported. However, there are no reports of an association of adverse events and examination success rates with patient medical backgrounds using a combination of these sedatives. We performed this study to investigate these points. Methods We investigated 191 pediatric patients who were sedated for MRI with triclofos sodium and midazolam at Matsudo City Hospital between November 2013 and October 2015. We surveyed the patients' characteristics, including age, sex, body weight, allergies, medication, neuromuscular, gastrointestinal, respiratory, and cardiac disorders, airway obstruction factors, and developmental disorders. Outcomes were sedation success and adverse events, including oxygen desaturation. We reviewed the relationship between patient backgrounds and each adverse event or success rate of sedation. Results Among all cases, the success rate was 92.7%. Older age (odds ratio [OR] = 0.984), developmental disorders (OR = 0.215), and respiratory disorders (OR = 0.353) were factors for lower success rates. Adding midazolam was associated with a higher success rate (OR = 5.971), but the higher total dose of midazolam was associated with sedation failure (OR = 0.003). The only adverse event was oxygen desaturation (11.5%). Older age affected oxygen desaturation with multiple analysis. However, by stepwise analysis, no patient medical background nor sedative dose was associated with oxygen desaturation. Conclusions Older age, developmental disorders, and respiratory disorders were associated with sedation failure. Increasing midazolam did not increase the success rate, and there might be an optimal dose of midazolam.