Effectiveness of open-circuit and oxyhood delivery of helium-oxygen.

The combination of helium with oxygen is less dense than air and as such has been beneficial to patients with airflow obstruction within the large airways. The purpose of this study was to evaluate the effectiveness of delivering He-O2 by open-circuit systems by measuring DD50 in five adult volunteers. The mean (+/- SD) DD50 with a nonrebreathing mask was 1.32 +/- 0.89, with a simple mask was 1.21 +/- 0.87, and with a nasal cannula was 1.00 +/- 0.13; the DD50 with the nonrebreathing mask and the simple mask was statistically greater than with the cannula (p less than 0.05). Two infant oxygen hoods were assessed by measuring the nitrogen concentration at different locations in the hoods. The N2 concentration increased progressively from top to bottom, indicating that the helium was concentrated at the top. We conclude that the nonrebreathing mask and simple masks are probably satisfactory He-O2 delivery systems, that the infant oxyhood may be suboptimal, and that the nasal cannula is ineffective.