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Analysis of the fraction of delivered oxygen by noninvasive ventilation devices working as invasive ventilators in pandemic times


 Purpose: In the context of the COVID-19 pandemic, mandatory ventilation with noninvasive ventilation (NIV) devices is a valid option when intensive care/anesthesia ventilators are unavailable. The fraction of delivered oxygen (FDO2) by NIV devices in intubated patients is unknown.Method: We simulated intubated patients with normal and sick lungs. NIV was used in pressure control mode with protective lung ventilatory settings. O2 flow was added into the NIV circuit in incremental steps of 1 L/min (from 1 to 15 L). The FDO2 in breathing gases was measured by a paramagnetic O2 sensor placed behind the endotracheal tube. Three NIV circuit options were analyzed: 1) leak at HME filter close to the patient, 2) anesthesia Bain circuit with leak distal to the patient, and 3) leak throughout a non-rebreathing valve near the patient.Results: FDO2 increased proportional to the supplemental O2 flow in all NIV options and in both kinds of patients. The range of FDO2 came from 0.25 to 0.98 in both, healthy and sick lungs. At 5 L/min, FDO2 was 0.53±0.04 and 0.47±0.02 in option 1 and 0.53±0.04 and 0.47±0.02 in option 2 for healthy and sick lungs, respectively. In option 3, 5 L/min of O2 reached 0.84±0.08 in healthy and 0.74±0.09 in sick lungs. Conclusions: In all setups, FDO2 was proportional to the administered O2 flow and it covered the range of FDO2 values commonly observed in ventilated patients.