If the oxygen comes at 50 psi, since the area becomes bigger the pressure should be bigger... Does that mean the patient gets air at a higher pressure? I am confused.
Go back to Boyle's gas law. Temp is constant and increase space causes pressure to decrease. Also the O2 does not come from the flowmeter at 50 psi, it exits at a much lower pressure and is really dependent upon the flow. With the venturimask, look at flow and not pressure. This is using the Venturi principle of air entrainment.
Nice video but you got a bit confusing with the collar explanation... Clarify a little better next time also what is the difference with the high percentage vs low percentage with the air entrainment ports being open and closed a bit more?
The more the ports are open then the more entrainment occurs. This would be for the masks with multiple FiO2 and you twist. The multicolored ports have different sized internal ports/jets and potentially different size ports. As to the collar, some will use that to prevent sheets or other items from occluding the entrainment ports hence increasing the FiO2 due to less entrainment.
It truly depends on what FiO2 you are delivering. The total flow to the patient should be a minimum of 40 L/M. The lower the FiO2 the more room air is entrained thusly the lower the flow to reach the total flow. I have another video showing how to calculate this total flow. It involves the "Magic Box". Using the calculations with the magic box will tell you how at what flow to set the flow meter.
