Effectiveness of ultra-/very-high-frequency oscillations combined with helium-oxygen gas mixture in a rabbit model

High-frequency oscillatory ventilation (HFOV) at frequencies of approximately 15 Hz is associated with optimal CO₂ excretion. Higher frequencies using a nitrogen-oxygen gas mixture worsen CO₂ excretion. An in vitro experiment using HFOV and a helium-oxygen gas mixture showed a significant increase in CO₂ transport, which increased with increases in ventilation frequency. We hypothesised that in HFOV, the change in the arterial partial pressure of CO₂ (PaCO₂) would be greater at frequencies above 15 Hz when combined with helium-oxygen gas mixture administration. We tested this hypothesis in a hypoventilated healthy rabbit model by administering a helium-oxygen gas mixture at 15, 25, 35, and 45 Hz frequencies. One-way repeated measures ANOVA showed a significant decrease in PaCO₂ among the four ventilation frequency groups. Post-hoc analysis showed significant differences between 15 and 35 Hz frequencies and between 15 and 45 Hz frequencies. The mean (standard error) decrease of PaCO₂ was 10.8 (2.2), 14.1 (2.3), 21.3 (3.3), and 23.1 (2.5) mmHg at 15, 25, 35, and 45 Hz, respectively. Combination therapy of helium-oxygen gas mixture and high-frequency oscillation using ultra/very high frequencies (35-45 Hz) was associated with a greater PaCO₂ decrease than that using the standard frequency (15 Hz).