Oxygen Bleed with CPAP

Many CPAP users also require supplemental oxygen. Oxygen is provided into the CPAP respiratory circuit using an "oxygen bleed adapter". Concentrated oxygen is generally delivered at pressures in excess of 15 psi, and is metered by Flow. CPAP air pressure is delivered at pressures less than 30 cm H2O. 1-PSI is 70 cm-H2O, so the oxygen concentrator flow is fully delivered to the CPAP circuit. A typical oxygen bleed circuit delivers between 1-liter/minute (L/min) to 3-L/min. The typical CPAP or Bilevel respiratory circuit flows 40 to 80 L/min of air volume in the absence of large leaks. (our example will assume 60 L/min)

What is the oxygen concentration in the diluted CPAP circuit?

(oxygen flow rate (litres) at 100% + air volume (litres) at 21% O2) / Total air volume = oxygen concentration % therefore, at 1 litres/minute oxygen addition and assuming a total CPAP flow of 60 L/min: (1L x 100) + (60L x 21) = 1360 /60 L/min = 22.% Oxygen. at 1 litre/minute oxygen (3L x 100) + (60L x 21) = 1560 / 60 L/min = 26% oxygen.

Any variable can be changed based on available data. If the flow rate is 40 L/min from the CPAP, the oxygen concentrations will be higher. If leaks are present or pressure results in a higher average vent-rate, the oxygen concentrations will be lower.

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