Background: High-flow nasal cannula (HFNC) is an emerging therapy for respiratory failure but the extent of exhaled air dispersion during treatment is unknown. We examined exhaled air dispersion during HFNC therapy versus continuous positive airway pressure (CPAP) on a human patient simulator (HPS) in an isolation room with 16 air changes·h-1.
Methods: The HPS was programmed to represent different severity of lung injury. CPAP was delivered at 5-20 cmH2O via nasal pillows (Respironics Nuance Pro Gel or ResMed Swift FX) or an oronasal mask (ResMed Quattro Air). HFNC, humidified to 37°C, was delivered at 10-60 L·min-1 to the HPS. Exhaled airflow was marked with intrapulmonary smoke for visualisation and revealed by laser light-sheet. Normalised exhaled air concentration was estimated from the light scattered by the smoke particles. Significant exposure was defined when there was ≥20% normalised smoke concentration.
Results: In the normal lung condition, mean±sd exhaled air dispersion, along the sagittal plane, increased from 186±34 to 264±27 mm and from 207±11 to 332±34 mm when CPAP was increased from 5 to 20 cmH2O via Respironics and ResMed nasal pillows, respectively. Leakage from the oronasal mask was negligible. Mean±sd exhaled air distances increased from 65±15 to 172±33 mm when HFNC was increased from 10 to 60 L·min-1. Air leakage to 620 mm occurred laterally when HFNC and the interface tube became loose.
Conclusion: Exhaled air dispersion during HFNC and CPAP via different interfaces is limited provided there is good mask interface fitting.
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