GE CARESCAPE - The origin of the CO2 waveform; Dips in capnogram

CO2withCAPNOSTATMainstream,CapnoFlexLF,andDualCO2modules
TheoriginoftheCO
2
waveform
Thefollowingillustrationshowsanormalcapnogram.Inthisillustration,theletters
indicatethefollowing:
●A:Thegasrstexhaledisfromtheanatomicalandapparatusdead-space.It
containsnoCO
2
becauseithasnotbeeninthealveoliandnogasexchangehas
takenplace.
●B:Briey,theexhaledgasisamixtureofgasfromtheanatomicaldead-space
andgasfromthealveoli.
●C:Aplateauisreachedwhenthegasexhaledisentirelyfromthealveoli.The
end-tidalCO
2
(EtCO
2
)concentrationismeasuredattheendofthisplateau.
●D:Whenthenextinspirationstartsthecapnogramrapidlyfallstowardsthe
baseline.TheminimumlevelofCO
2
measuredduringtheinspiratoryphaseiscalled
theinspiredCO
2
concentration(normally0.0%).
●E:Withascale,theheightofthecapnogramtellsyoutheend-tidalCO
2
concentration.ThemonitorautomaticallycalculatesanddisplaytheEtCO
2
in
numbers.EtCO
2
approximatesthealveolarCO
2
concentrationbecauseitis
measuredwhenthepatientexhalesvirtuallypurealveolargas.
●1aand1d=inhalation
●1band1c=exhalation
EtCO
2
value%EtCO
2
valuemmHgIndicates
4.5%to5.5%34mmHgto41mmHg
normocapnia
<4%<30mmHg
hypocapnia
>6%
>45mmHg
hypercapnia
Dipsincapnogram
Thedipsseeninthecapnogramduringexpirationarerelatedtothesidestreamgas
sampling,thecontinuousgasowtotheY-piece,andpatient’scardiaccontractions,
whichcauseintra-thoracicpressurechangesandthereforeowvariations.
ThealterationsinexpiredCO
2
waveformarecardiogenicmovementsofexhaledand
circuitgasatthesidestreamgassamplingsite.Whentherespiratorygasowdrops
belowthegassamplingrate,avariablemixtureofCO
2
freefreshgasandexhaledCO
2
richgasissampled.ThiscausesvariationsinsampledCO
2
concentrations.
Intheillustrationbelow,CO
2
waveformistheoneontop,andowisthelower
waveform.
318CARESCAPEModularMonitors2062971-001