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Table 4 Primary and Secondary Indicators of Noninvasive Respiratory (NIRS) failure

From: Noninvasive respiratory support for COVID-19 patients: when, for whom, and how?

Primary Indicators of Noninvasive Respiratory Support Failure
1) PaO2/FiO2 < 150 or inability to improve PaO2/FiO2 after 1 h of NIV [39, 50, 55]
2) Worsening/unimproved dyspnea or tachypnea > 25 after 1 h of NIV [24, 39, 53, 56]
3) Failure to maintain PaO2 of 60 on FiO2 of 0.6 [39, 53]
4) SpO2/FiO2 < 196 [35]
5) Tidal volume of > 9 ml/kg predicted body weight [21, 43, 54]
6) ROX value less than 2.85 at 2 h, less than 3.47 at 6 h, or less than 3.85 at 12 h predict HFNC failure [57]
7) pH < 7.25 or PaCO2 > 75 after 2 h of NIV [42]
Secondary Indicators of Noninvasive Respiratory Support Failure
1) SAPS II > 35, APACHE II > 17, or rising SOFA score [39, 51, 52, 55]
2) High peak pressure requirement [39, 53]
3) Worsening bronchorrhea [39, 53]
4) Intolerance of mask [39, 53]