Low bias flow oscillation with heliox in oleic acid-induced lung injury

Objective: To evaluate C_O2 clearance in oleic acid-induced lung injury in rabbits receiving high-frequency oscillatory ventilation with helium-oxygen mixtures through a low bias flow oscillation system designed to conserve expensive gases. Design: A prospective, controlled, interventional, in vivo animal laboratory study. Setting: Research laboratory of a health sciences university. Subjects: Eight New Zealand White Rabbits. Interventions: Lung injury (Pa_O2/F_IO2 of <250) was induced by intravenous infusion of oleic acid. Low bias flow oscillation was performed with a modified high-frequency oscillatory ventilation circuit that uses low bias flow (100 mL/kg/min) and a soda lime canister to clear C_O2. Low bias flow oscillation-heliox trials were performed with 40%, 50%, 60%, and 70% helium (balanced with oxygen) for 20 mins. Each heliox trial was preceded by a 20-min paired control trial with 40% oxygen/60% nitrogen. Measurements and Main Results: Helium concentrations of 40%, 50%, 60%, and 70% decreased Pa _CO2 by 13% (47 ± 7 to 41 ± 8 torr), 17% (50 ±7 to 41 ± 6 torr), 22% (49 ± 5 to 38 ± 7 torr), and 26% (48 ± 7 to 35 ± 9 torr), respectively. The gradient between partial pressure of alveolar oxygen and Pa_O2 was not affected by 60% helium; however, absolute Pa_O2 increased by 15%. Fluid and inotropic requirements were similar in both control and heliox low bias flow oscillation trials. Conclusion: Helium concentrations greater than 40% increase C _O2 clearance from oleic acid-injured lungs of rabbits during low bias flow oscillation. The low bias flow oscillation system makes this possible using 1% of the gas volume required during high-frequency oscillatory ventilation.