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?
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