The Science Journal of the American Association for Respiratory Care
Background: Heliox has been utilized to reduce the work of breathing in pediatric patients with severe upper airway obstruction. We theorized that the high diffusion rate and the low specific gravity of Helium may result in a non-homogeneous Heliox mixture when a head hood is used as the delivery device. The clinical consequences being the potential to deliver FIO2 less than desired or measured at the inlet. Method: A 70/30 Heliox (HeO2) mixture was delivered into a Tenthouse hood (NOVA) at flowrates of 8, 16, and 24 lpm. The dimensions of the hood were 12
Results: The below table reflects the measured FiO2 at various heights in the hood at the specified liter flows.
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Conclusion: Variations of as much as 10.5% were observed when measuring FIO2 at different heights within the hood. FIO2 readings closer to that measured at the inlet were observed when flowrates of at least 16 lpm were used and the FIO2 was measured at a height of at least 8 inches. We do not recommend the use of a hood to deliver Heliox, however if necessary FIO2 should be measured at the height of the patient's mouth, flowrates may have to be adjusted upward and the patient should be monitored by an oximeter to alert the clinician to episodes of O2 desaturation.