I am a new student and love your forum. What is the criteria that determines a device to be low flow or high flow? In school we just got a list of low flow and high flow to memorize, I'll understand better if I know the logic behind it.
Please help a student.
High flow---ALL the inspiratory flow demand is met by the device, whatever that may be. The device is set to 40% O2 and the patient is breathing at 20 L/M. If you could put an oxygen analyzer down in their trachea, and measure during inspiration, the O2 would be 40%. If the patient later kicked up their inspiratory flow demand to 100L/M the analyzer would still measure 40%.
Low Flow is everything else. Nasal cannulas, simple masks, NRB, venti masks. The patient can easily overtake the delivered flow and dilute with room air.
In reality not many (any?) of the high flow systems are really that when the patient really pulls in a lot of flow.
We used to attach a high flow flowmeter from a blender, run it through a cascade. The large bore tubing went to a face mask. The holes in the face mask were then fitted with a big loop of tubing (little holes at the end) so that (again in theory) the entire insp flow was the set FIO2 on the blender.
Just thought of something...
Gwendy, could you list the devices from the school, both labeled low and high flow?
Unless the patient is intubated, or affixed to a Bipap/CPAP run off a blender, most of the labeled high flow devices aren't that when the patient has a really large inspiratory flow demand.
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