rc.rcjournal.com/conten Blow-by Oxygen
Blow-by oxygen delivery is the simplest and least cumbersome form of available devices to provide oxygen therapy, but it is also the least reliable at delivering a specific FIO2. Blow-by oxygen can be achieved in numerous ways, but it is most commonly done by means of large bore or oxygen tubing connected to a face tent or a simple mask that is placed a relatively short distance from, and directed toward, the patient's face. This type of oxygen delivery is ideal for patients who cannot tolerate more cumbersome oxygen delivery devices and/or require a lower concentration of oxygen. There is limited evidence that suggests that blow-by therapy can deliver low concentrations of oxygen (0.3–0.4 at 10 L/min of flow) to an area large enough to provide some level of oxygen therapy, assuming adequate positioning of the device.83 Therefore, this type of therapy should be reserved for those who do not require high inspired oxygen concentrations but may require short-term or intermittent oxygen therapy.

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Note added at 1 hr (2024-01-06 01:26:19 GMT)
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links https://rc.rcjournal.com/content/62/6/645
https://en.wikipedia.org/wiki/Non-rebreather_mask

The non-rebreather mask is utilized for patients with physical trauma, chronic airway limitation, cluster headache, smoke inhalation, and carbon monoxide poisoning, or any other patients who require high-concentration oxygen, but do not require breathing assistance. Patients uncomfortable with having a mask on their face, such as those with claustrophobia, or patients with injuries to the mouth are more likely to benefit from a nasal cannula, or passive ***("blow-by") oxygen.***[4] Patients who are unable to breathe on their own would require invasive or noninvasive mechanical ventilation. [

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Note added at 1 hr (2024-01-06 01:41:26 GMT)
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https://onlinelibrary.wiley.com/doi/full/10.1111/pan.13515 Flow rate and distance from the face are important factors determining the performance of blow-by methods. Even flow rates of 10 L/min do not reliably maintain an FiO2 of more than 50% for many blow-by methods at 5 cm from the child's face. Flow rates of 3 L/min can only be used when the blow-by method is placed directly in contact with the patients face. Anesthetists should be aware of the limitations of these methods and use a blow-by method that will provide a sustainable FiO2 of 50% or more.