20
3.5 NOxBOX
i
Effect on Ventilator Circuit
The NOxBOX
i
has two main connections to the patient ventilator circuit. These produce the
following effects:
1.
At the NOxFlow: NO/N
2
concentrated gas is delivered into the inspiratory limb
of the ventilator circuit in direct proportion to the ventilator air flow. The proportion of
gas added is adjusted depending on desired patient dose and the concentration of
the NO gas supply. For example, to achieve a 20 ppm dose from a 400 ppm cylinder
supply, the NOxBOXi is adding 5% more gas to the air volume being delivered by the
ventilator.
2.
At the Sample Line: The NOxBOX
i
samples a side-stream from the ventilator
gases at a nominal rate of 225 ml/min (0.225 L/min).
3.5.1 Oxygen Dilution
Adding the NO/N
2
gas to the circuit has the effect of proportionally diluting the delivered
oxygen concentration. The NOxBOX
i
monitors the oxygen level being delivered to the
patient to assist the user in monitoring this effect. Oxygen dilution is directly related to the
proportion of NO gas that is added to the circuit.
Worked example:
For a 20 ppm dose from a 400 ppm cylinder: 5% NO/N
2
gas is added to the ventilator air
flow; the O
2
is therefore diluted by 5% of its original value.
If the O
2
was originally 50% v/v, the O
2
concentration after the NO is introduced will be
approximately 47.5% v/v
3.5.2 Measured Minute Volume
The measured volume ventilation may be modified slightly by the net effect of the NOxBOX
i
adding and removing gases from the ventilator circuit. This may require some modifications
to ventilator settings to compensate.
Added minute volume of NO gas can be calculated using:
NO Dose x Minute Volume
Cylinder Concentration - NO Dose
= Added minute volume
Worked Example:
Minute volume = 10 L/min
Dose = 10 ppm
Cylinder concentration = 400 ppm
Then the added minute volume may be calculated:
(10 x 10)/(400 – 10) = 0.26 L/min
To calculate the net change, subtract the NOxBOXi sampling rate from the added minute
volume:
0.26 – 0.225 = 0.035 L/min
Summary of Contents for NOxBOX mobile
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