Exhaled air leakage during application of high flow nasal cannula on a human patient simulator

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Background: High flow nasal cannula (HFNC) oxygen therapy has emerged as a treatment modality for hypoxemic respiratory failure but the exhaled air distances and directions are unknown. Aims and Objectives: We examined the exhaled air dispersion and direction during application of HFNC on a high fidelity human-patient-simulator (HPS) in a negative pressure isolation room with 16 air changes/hr. Methods: The HPS was placed at 45° and programmed to mimic different severity of lung injury. HFNC with air was delivered at 10, 30 and 60L/min respectively. Airflow was marked with intrapulmonary smoke for visualization. A leakage jet plume in the sagittal plane was revealed by a laser light-sheet and images captured by high definition video. Normalized exhaled air concentration in the plume was estimated from the light scattered by the smoke particles. Significant exposure was defined as where there was ≥20% of normalized smoke concentration. Results: When the HPS was programmed in normal lung condition (oxygen consumption 200ml/min, lung compliance 70ml/cm water, respiratory rate 12 breaths/min and tidal volume 700ml) and HFNC delivered at 10, 30 and 60L/min, the exhaled air distances along the sagittal plane above the nostrils were 128(19), 165(34) and 339(69)mm respectively. In severe lung injury, the corresponding exhaled air distances were 91(12), 110(21) and 145(30)mm respectively. Conclusion: Exhaled air dispersion from the patient’s nostrils was limited to 339mm along the sagittal plane when HFNC was delivered at 60L/min. More work is needed to assess exhaled air dispersion in the lateral directions. Acknowledgement: HMRF#15140282, Food & Health Bureau, HKSAR.

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