Bedfont NoxBox - Noxbox Effect on Ventilator Circuit

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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ow.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
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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
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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
 ow;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modiedslightlybytheneteffectoftheNOxBOX
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addingandremovinggasesfromtheventilatorcircuit.Thismayrequiresomemodications
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