Introduction: Helium is known to reduce airway resistance and improve ventilatory physiology. Helium also has a high CO2 diffusion coefficient. Thus, CO2 diffusion occurs faster in a helium gas mixture than in air or oxygen. Helium-oxygen mixture has been used with mechanical ventilator settings such as conventional mechanical ventilation (CMV) or high-frequency oscillatory ventilation (HFOV). Although helium-oxygen mixture was shown to promote CO2 excretion in combination with either CMV or HFOV, it has not been examined which ventilatory mode is more effective in promoting CO2 excretion when used with helium-oxygen mixture. This study aimed to compare the changes of arterial partial pressure of CO2 (PaCO2) by using helium-oxygen mixture between CMV and HFOV.Methods: Six Japanese white rabbits were used, and following tracheostomy, they were connected to the ventilator. A control PaCO2 between 40 and 70 mmHg was maintained before administration of helium-oxygen mixture, and blood gas analysis was performed during and after administration of helium-oxygen mixture. The 2-way type repeated measures analysis of variance was used for comparison of PaCO2, and it was followed by post hoc tests. Simple pairwise comparisons were performed for oxygenation at each time points between under CMV and HFOV.Results: There was a statistical significance for the differences of time points (P-value＜0.000001) as well as for the interaction term (P-value＜0.001). According to the post hoc tests, under HFOV, PaCO2 during administration of helium-oxygen mixture was significantly lower compared to both before and after administration. In intergroup comparison, PaCO2 during helium-oxygen inhalation under HFOV was significantly lower than that under CMV. Arterial partial pressure of oxygen/fraction of inspiratory oxygen ratio during administration under HFOV was significantly higher than that under CMV.Conclusions: This study demonstrated that ventilatory management of healthy lung rabbits with helium-oxygen mixture results in more efficient ventilation and better oxygenation with piston-driven HFOV than with CMV.