The Effects of Flow Settings During High Flow Nasal Cannula for Adult Hypoxemia Patients

High flow nasal cannula (HFNC) delivers oxygen at a flow which exceeds the patient's inspiratory flow demand in order to improve oxygenation. Numerous randomized control trials and meta-analyses have shown that HFNC improves oxygenation and helps avoid intubation in hypoxemic patients, as well as reduce work of breathing, improve ventilation, and decrease hypercapnia in COPD patients. Flow settings play a critical role when using HFNC, as increased flow can reduce inspiratory effort, improve ventilation, and dynamic lung compliance. However, flow rates used in many studies vary widely. The clinical effects of different HFNC flow setting, specifically to match or over than a patients' own inspiratory flow, is still unknown.

High flow nasal cannula (HFNC) delivers oxygen at a flow which exceeds the patient's inspiratory flow demand in order to improve oxygenation. Numerous randomized control trials and meta-analyses have shown that HFNC improves oxygenation and helps avoid intubation in hypoxemic patients, as well as reduce work of breathing, improve ventilation, and decrease hypercapnia in COPD patients. Flow settings play a critical role when using HFNC, as increased flow can reduce inspiratory effort, improve ventilation, and dynamic lung compliance. However, flow rates used in many studies vary widely, from 20-40 LPM in COPD patients and 30-60 LPM in hypoxemic patients. The clinical effects of different HFNC flow setting, specifically to match or over than a patients' own inspiratory flow, is still unknown.

Adult patients with hypoxemia will be recruited, their own breathing profiles (inspiratory flow, respiratory rates and tidal volume) will be measured. Then patients will be placed on high flow nasal cannula (HFNC), HFNC flow will be titrated based on the hospital's policy or protocol and patient's comfort, patient's clinical effects on oxygenation will be monitored and recorded during the titration process.

Adult healthy volunteers will be recruited, their own breathing profiles (inspiratory flow, respiratory rates and tidal volume) will be measured. Then they will be placed on HFNC, HFNC flow will be increased sequentially by research protocol and their comfort, subjects' lung expansion effects in different flow will be quantified by Electrical impedance tomography (EIT), a noninvasive assessment tool. Their comfort will also be assessed using a visual scale.

HFNC flow will be titrated based on the hospital's policy or protocol for hypoxemic patients and research protocol for healthy volunteers

SpO2/FIO2 at the optimal/maximum /tolerable/ HFNC flow setting compared to the SpO2/FIO2 at HFNC flow matching patient's inspiratory flow or 30 L/min for hypoxemic patients

Respiratory rates at the optimal/maximum /tolerable/ HFNC flow setting compared to the SpO2/FIO2 at HFNC flow matching patient's inspiratory flow or 30 L/min for hypoxemic patients

comfort will be self-evaluation using a visual analog scale with measured score of 0 is the worst and 10 is the best

Inclusion Criteria: Adult patients (Age > 18yrs and < 90yrs) who need nasal cannula oxygen flow ≥ 5 L/min to maintain SpO2 at 90-97%. Exclusion Criteria (Common): - Unable to use resuscitation mask, such as facial trauma, claustrophobia Inability to verbally communicate; Pregnant Inability to breathe via nose, such as nasosinusitis, stuffy nose or nasal obstruction, etc. Ordered SpO2 goal is above 97% FIO2 needs ≤ 0.4 Using inhaled pulmonary vasodilator via HFNC

Individual participant data after deidentification that underlie the reports reported in this article can be obtained by contacting the corresponding author. Data will be available immediately following publication and ending in 5 years.

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