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

OBJECTIVE: To evaluate Co(2) 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 (Pao(2)/Fio(2) 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 CO(2). 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 Paco(2) 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 Pao(2) was not affected by 60% helium; however, absolute Pao(2) 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 Co(2) 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.