Formulas, Formulas Everywhere!
Air:Oxygen Entrainment Ratio
100-x
x-20*
x=FiO2
*use 21, if FiO2 <35%
What is the air:oxygen entrainment ratio, if the patient is on 60%?
Total Flow Determination
(Total parts of Air and Oxygen) x Flowmeter setting = Flow to Patient

Calculate the total flow to the patient if the patient is on a 40% cool aerosol with
the flowmeter set at 10 lpm.

The patient is on a 60% aerosol trach mask. The patient requires at least 28 lpm
total flow. What is the minimum flowmeter setting to be used?
Oxygen Cylinder Duration
Tank Factor x Pressure in tank = Minutes of Duration = Hours
Liter Flow
60

How many e cylinders must be taken on a 6 hour transport if the patient is being
manually bagged at 15 lpm?

How long will the H-cylinder last running at a rate of 8 lpm if there is 1000 psi in
the tank?
Liquid Oxygen Duration
Weight in pounds x 860 =
2.5

liters = minutes = hours
flow
60
How long will your portable liquid unit weighing 5 pounds running at 3 L/min
last?
Minute Volume
Tidal Volume x Respiratory Rate = Minute Volume

Your patient has a tidal volume of 450 ml and a respiratory rate of 18. What is
their minute volume?
Estimate Total Inspiratory Flow needs
Minute Volume (in liters) x 3

What is the patient’s inspiratory flow demand if they have a minute volume of 12
l/min?

If the patient has a tidal volume of 600ml and a respiratory rate of 20, what is
their total inspiratory flow demand?

If the patient’s tidal volume is 600 cc and the rate is 12, what is his expected
inspiratory flow rate?
If this patient is on a 40% venti-mask set at 8 l/min, will it meet his need? Why or
why not?
Nasal Cannula approximate percentage
(x times 4) + 20 = approximate NC %

The patient is on a 4 lpm nasal cannula, what is the approximate percentage?

If your patient is on a 40% VM, what nasal cannula setting will be approximately
the same percentage?
Heliox Therapy
Conversion factors:
80/20 mixture: use 1.8
70/30 mixture: use 1.6
Determine Actual flow from the flowmeter
Factor x flowmeter setting= Actual Flow

If your patient is receiving a 70/30 heliox mixture and the flowmeter is set
at 10lpm, what is the actual flow to the patient?
Determine flowmeter setting for a desired flowrate
Desired flow to patient = flowmeter setting
Factor

You want to deliver 8L/min of an 80/20 heliox mixture to your patient,
what should you set the flowmeter on?