You are transporting your patient, who has emphysema, from
your unit to radiology for a CT scan. Without oxygen
at 6 L/min, your patient's O2 saturation on room air drops
to 75%. It will take you 10 minutes to get there and
back. The portable O2 tank you grabbed has 500 psi
left in it. Do you have enough oxygen left for the
trip? See the example below
At 500 psi with a flow rate of 6 liters per
min, there is 29 minutes of oxygen left. Yes, there
is enough for the trip.
Formula
The average service capacity for an e-cylinder
carrying oxygen is 1900 psi.
The average volume of oxygen in an e-cylinder
is 660 liters.
My text book uses the following formula:
capacity (in L) / service pressure (in psi) = remaining
contents (in L) / gauge pressure (in psi)
I find it easier to look at this formula this
way:
0.35
x psi on gauge L/min to be delivered
The 0.35 comes from dividing 660 by 1900.
In the example above:
0.35 x 500 psi 6 L/min
= 29 min
Information obtained from Nagelhout &
Zaglaniczy (2001).
