Improvement in aerosol delivery with helium-oxygen mixtures during mechanical ventilation

In mechanically ventilated patients with airway obstruction, helium-oxygen (He-O-2 mixtures reduce airway resistance and improve ventilation, but thei r influence on aerosol delivery is unknown. Accordingly, we determined the effect of various He-O-2 mixtures on albuterol delivery from metered-dose i nhalers (MDIs) and jet nebulizers in an in vitro model of mechanical ventil ation. Albuterol delivery from a MDI was increased when the ventilator circ uit contained 80% helium and 20% oxygen (He-O-2 80/20) versus O-2: 46.7 +/- 3.3 versus 30.2 +/- 1.3 (SE)% of the nominal dose (p < 0.001)-the differen ce was mainly due to decreased drug deposition in the spacer chamber, mean 39.2% and 55.2%, respectively (p < 0.001). Nebulizer efficiency at a flow r ate of 6 L/min was five times lower with He-O-2 80/20 than O-2, and the amo unt of nebulized drug was inversely correlated with gas density (r = 0.94, p < 0.0001). When the nebulizer was operated with O-2, greater albuterol de livery was achieved when the ventilator circuit contained He-O-2 rather tha n O-2. In summary, He-O-2 mixtures in the circuit increased aerosol deliver y for both MDIs and nebulizers in the mechanically ventilated model by as m uch as 50%. In conclusion, at appropriate flow rates and concentrations, He -O-2 in the ventilator circuit may improve aerosol delivery in mechanically ventilated patients with severe airway obstruction.