19
The duration of any given gas cylinder depends on the size & pressure of the cylinder, and the rate at
which gas is being used to support the patient. The formula to calculate the operating duration of any
cylinder (based on the Ideal Gas Law) is given below. An example is worked out for a typical large
cylinder. It is recommended that the gas cylinder pressure not be allowed to fall below 300 psi.
V
start
= 9540 liter at 1 atm/ 70
o
F (21
o
C) : from label on cylinder
P
start
= 2640 psig : from label on cylinder
P
present in cylinder
= 300 psig : from pressure gauge on cylinder
V
present in cylinder
= volume remaining in cylinder = (P
present
/ P
start
) V
start
= 1084 liter at 1 atm/ 70
o
F (21
o
C)
V
delivered
= 9540 – 1084 = 8456 liter at 1 atm/ 70
o
F (21
o
C)
For a typical ventilator setting (20 BPM, Vt = 500 ml, FIO
2
=100%, I time = 1 sec, I:E = 1:2.0), the gas
consumption is 10 liter/min.
NOTE:
Whenever external high-pressure O
2
is used, the EMV+ automatically determines the O
2
usage and
displays it in the FIO
2
parameter window. (See O
2
Use under FIO
2
in Description of Controls and Display.
Total duration of the gas cylinder in above example = V
delivered
/ (10 liter/min) = 8456/10 min = ~14
hours
F
RESH GAS
/
EMERGENCY AIR INTAKE
:
F
IGURE
4
WARNING!
Never block the FRESH GAS/EMERGENCY AIR INTAKE. A free flow of air is required during
compressor operation or in the event of a device failure to allow spontaneous breathing. The FRESH
GAS/EMERGENCY AIR INTAKE also acts as an anti-asphyxia port in the event of a ventilator failure.
