Heliox improves gas exchange during high-frequency ventilation in a pediatric model of acute lung injury

Because heliox has a lower density as compared with air, we postulated that heliox would improve gas exchange during high-frequency oscillatory ventil ation (HFOV) in a model of acute lung injury. In a prospective, cross-over trial, we studied I I piglets with acute lung injury created by saline lava ge. With initial conditions of permissive hypercapnia (Pa-CO2 55-80 mm Hg), each piglet underwent HFOV with a fixed mean airway pressure, pressure osc illation, and ventilatory frequency. The following gas mixtures were used: oxygen-enriched air (60% O-2/40% N-2) and heliox (60% O-2/ 40% He and 40% O -2/60% He). Compared with oxygen-enriched air, the 40% and 60% helium gas m ixtures reduced Pa-CO2 by an average of 10.5 and 20.3 mm Hg, respectively. A modest improvement in oxygenation was seen with the 40% helium mixture. W e conclude that heliox significantly improves carbon dioxide elimination an d modestly improves oxygenation during HFOV in a model of acute lung injury . On the basis of test lung data and plethysmography measurements, we also conclude that heliox improves carbon dioxide elimination primarily through increased tidal volume delivery. Although heliox improved gas exchange duri ng HFOV in our model, increased tidal volume delivery may limit clinical ap plicability.