The flow rates of air and oxygen for a patient can be calculated once the percent oxygen to deliver and the oxygen flow rate are known.
Parameters:
(1) percent oxygen (as a number between 21 and 100)
(2) oxygen flow rate in liters per second
air-to-oxygen ratio =
= (100 - (percent oxygen to deliver)) / ((percent oxygen to deliver) - 21)
total ratio parts =
= (air-to-oxygen ratio) + 1
total output flow in L per minute =
= (oxygen flow in L per minute) * (total ratio parts)
air flow in L per minute =
= (total output flow in L per minute) - (oxygen flow in L per minute)
where:
• This can be derived by rearranging the equation in the previous section for percent oxygen in a gas mixture. This gives:
air flow in L/min =
= (1.00 - (percent oxygen to deliver)) / ((percent oxygen to deliver) - 0.21) * (oxygen flow)
total flow = (air flow) + (oxygen flow) =
= ((1.00 - (percent oxygen to deliver)) / ((percent oxygen to deliver) - 0.21) + 1) * (oxygen flow)
