RESUMO
PURPOSE: High-flow nasal cannula (HFNO) reduces the need for invasive mechanical ventilation in COVID-19 patients with hypoxemic-respiratory failure. During HFNO entrainment of room air dilutes the delivered fractional inspiratory oxygen (FiO2), thereby preventing improvement in oxygenation. The placement of a mask over HFNO to improve oxygenation has provided conflicting results. We aimed to determine and compare the effect of placing various mask types over HFNO on oxygen saturation (SPO2). MATERIALS AND METHODS: In this prospective physiological study 40 patients with COVID-19-associated hypoxemic respiratory failure on HFNO with O2 concentration <92% were included. The effect of placing different masks over HFNO on oxygenation, respiratory rate, heart rate, blood pressure, patient comfort, and partial pressure of carbon dioxide level (pCO2) was recorded after a prespecified time interval. RESULTS: We observed a significantly higher mean SPO2 and lower mean respiratory rate on using various study masks over HFNO compared to HFNO alone. On comparing various mask types, the use of N95 masks and nonrebreather (NRB) masks with O2 showed a significant increase in O2 concentration and reduction in respiratory rate compared to surgical mask (SM) and NRB without O2. The proportion of patients who achieved SPO2 of >92% was higher with the use of N95 masks (47.5%) or NRB with O2 (45%) over HFNO compared to SM (35%) and NRB without O2 (35%). No significant change was observed in heart rate, blood pressure, and CO2 level with the use of any mask over HFNO. CONCLUSION: This study demonstrates improvement in oxygenation and reduction in respiratory rate with the use of various masks over HFNO in patients of COVID-19-related hypoxemic-respiratory-failure. Significantly greater benefit was achieved with the use of N95 or NRB with O2 compared to SM or NRB without O2.