Oxygen FAQ

Up to date, expert answers to frequently asked questions (FAQ) about oxygen supply systems, respiratory care and pulse oximetry written by OCC & collaborators.

High flow nasal cannula

  • Most are not considered reusable per manufacturer specifications 
  • Check with the manufacturer specification and clinical guidelines to determine if reuse is safe
  • Steps for disinfection must be closely adhered to and may be manufacturer specific 
  • Some reusable devices (e.g. some ventilator circuits) may have a finite lifespan (e.g. a predefined number of sterilizing cycles)
  • Reusability of respiratory care devices is often debated and may vary based on local/national practice guidelines and regulations   

Click here to review WHO tips for cleaning and disinfection of respiratory equipment 

Additional resources:


Any time the patient can cough or sneeze into the room – the  risk of infection is increased.  It is not clear that adding high flow nasal oxygen makes this worse.  However, at a flow of 40-60 lpm if the patient coughs, model studies have shown some additional movement of particles in the room.

Healthcare worker infection from nosocomial transmission of SARS CoV-1was associated with lack of adequate infection control precautions especially in the presence of  aerosol generating procedures. By definition this would also include HFNC. However, the risk of health care worker infection from HFNC was reported to be substantially less (8%) compared to intubation (35%) and NIPPV (38%) (Raboud et al. Plos One 2010). Moreover, placement surgical masks over a HFNC reduces the emission and dispersion of coronavirus bioaerosols (Leung et al. Nat Med 2020)

This is somewhat controversial. 

For short periods of time (hours), NIPPV may be tolerated without humidity, but for longer periods of time (days) humidity is essential, especially at high FIO2 (100% oxygen from a tank or other high pressure source is ~anhydrous). Leaks with NIPPV (around a mask seal) create issues with humidification and is one reason HMEs don’t work well with NIPPV. 

For HFNC, most people find >6LPM NC intolerable without humidification, but with humidification most people don’t notice flow until it exceeds 15LPM and will tolerate >40LPM. With HFNC (and nasal CPAP) gas flow is unidirectional (in the nose and out the mouth) and thus there is no possibility for reclaiming moisture from the exhaled breath. Without heat and humidification most patients will find this intolerable.  

Here is a comparison table by ECRI

(Please reference the manufacturers’ manuals as the accuracy of this table is not guaranteed).

Estimated Fraction of Inspired Oxygen (FiO2)

Oxygen Device
O2 Flow (L/min)

Nasal Cannula















Simple Facemask



Non-Rebreather Mask with Reservoir

(reservoir must be fully inflated)


Approx 0.6-0.8

At RR ~20 & Tidal Volume ~500

20 LPM flow = ~60% FiO2

30 LPM flow = ~70% FiO2

40 LPM flow = ~80% FiO2 (Farias et al).

The values represent estimates of FiO2. Actual FdO2 (delivered O2 concentration) is dependent on multiple factors including oxygen supply quality, patient’s minute ventilation and inspiratory flow rate. One general estimation rule is using oxygen flow rate: FiO2 =0.21 + 0.03 x oxygen flow rate in L/min (Frat et al).

Moisture present in patients’ lungs is rapidly lost at high breathing rates.

When breathing dry air, cilia stop functioning properly (in a matter of hours – Hirsch et al J Appl Physio 1975). When the moisture level becomes low, mucous in the patient’s lungs can become thick and hard, and quickly block the patient’s airways, or the endotracheal tube, stopping airflow. 

Additionally, heat is rapidly lost to non-humidified air.

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