oxygen and carbondioxide cascade (1) (1)

7/23/2019 Oxygen and Carbondioxide Cascade (1) (1)

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.

SeniorResident

DeptofPulmonaryMedicine

OXYGENANDCARBONDIOXIDE

CASCADE


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Oxygen indispensableforlife

Nostoragesystem

ont nuoussupp yrequ re Carbondioxide majorbyproductofenergy

metabolism


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Convection(bulkflow)

Chemicalcombinationwithhemoglobin

30100foldincreaseinO2transport 1520foldincreaseinCO transport


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Uptakeinthelungs

Globaldeliveryfromlungstotissue

Regionaldistributionofoxygendelivery

Cellularuse

of

oxygen


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Uptakeinthelungs



Cellularuse

of

oxygen


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Dependsonrateofbreathingandtidal

T

Hyperbolicrelationshipbetweenalveolar

ven an A 2

Affectedbydisordersofrespiratorycentre

andrespiratorymuscles Highfrequencyventilationallowslowertidal


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Administrationofnitrousoxide

Largequantitiesofmoresolublegasreplacesmaller

uantitiesoflesssolublenitro en

Net transfer of inert as from alveoli into bod

2


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ca illaries

2 =


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ca illaries PAO2ismaindeterminantofPaO2

(Aa)gradientdescribestheoverallefficiency

Capillarybloodisfullyoxygenatedbefore

traversin distanceofalveolarca illar interface


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Trueshuntv/s

effectiveshunt

C inica

corre atesHighPEEPstrategy

BMJ1998;317:13026


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BMJ1998;317:13026


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Uptakeinthelungs



Cellularuseofoxygen


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2

2%inplasma

98%inhemoglobin


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ExtenttowhichtheHb

is combined with O

DependsonPO2ofthe

Phenomenonof

coopera v y

P50~28mmHg Rapidandreversible

reaction


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pH

(Oxyhemoglobin equilibriumcurve)

2

Temperature

2,3DPG PercentageoffetalHb

Chest2005;128:554S560S


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1911)

ec o CO2

on

Conceptofpermissive

hypercapnia


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,

FormedintheRapoportLuebering shuntof

DPGmutase activityincreasedathighpH

DecreasedDPG instoredblood

Increasedin anemia

highaltitude


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2

TotalamountofO2presentin100mlofblood

(1.34xHb xSaO2) +(0.003xPaO2)

a 2 =

vo

v 2=

vo

O2contentdecreasedin

Hypoxemia(lowPO ) Anemia(lowHb)

H ercarbia acidemia h erthermia lowSaO


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AnemiaHbO2

carryingcapacityofblood&O2content

CarbonMonoxide affinityforHb 250fold

2

CompeteswithO2binding

Lshift interferewithOunloadingattissues

Severetissuehypoxia


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Uptakeinthelungs



Cellularuseofoxygen


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2

QuantityofO2madeavailabletobodyinone

2

EqualtocardiacoutputXarterialoxygen

con en DO2isapproximately1000mL/min


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2

TotalamountofO2consumedbythetissues

Normalrestin O consum tion~250mL min

2 2 2

inadulthumans

OER=VO2/DO2


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2 2

Jindal SK,Agarwal R.OxygenTherapy.2nd Ed.pp78


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2 2

SlopeofmaximumOERis

lesssteep

Reducedextractionof

oxygenbytissues

Doesnotplateau(consumptionremainsu y v

atsupranormallevelsof DO CriticallevelofDO ran efrom

2.1to6.2mL/min/kg

BMJ1998;317:13026


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ox endeliver

Fallinhemoglobinconcentration

Failureofoxygenuptakeb blood


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RelativeeffectsofchangesinPaO2,Hb andCOonDO2inacriticallyill

Thorax2002;57:170177


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2

Duringexercise

O re uirementma be20times Bloodremainsincapillaryblood


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Uptakeinthelungs



Cellularuseofoxygen


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consum tion

Perfusionpressureisanimportantdeterminant


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Uptakeinthelungs



Cellularuseofoxygen


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Importantforaerobicmetabolism

Krebscycle

Canbe

inhibited

by

cellular

metabolic

poisons

Exogenous(e.g.cyanide)or

Endogenous(e.g.endotoxins insepticshock)


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Dyspnea

Alteredmentalstate Tachypnea orhypoventilation

Arrh thmias

Peripheralvasodilatation

S stemich otension

Coma

C anosis(unreliable) Nausea,vomiting,andgastrointestinal

disturbance


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Disorderedregionaldistributionofbloodflow

Lossofautoregulation

seo vasopressors

Capillarymicrothrombosis afterendothelial

damage


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DecreasedO2carryingcapacityofblood

Hemorrhagesecondarytotrauma/surgery

n ammat on

Nutritionaldeficiencies

Decreasederythropoietinproduction

Altereddissociation rofileofOEC Acidosis,fever

,


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CardiacdysfunctioninICUpatients

InsufficientDO2tothecoronarycirculation,

Subendocardial ischemiafromLVH

Compromise myocar ia contracti ity romt e

effectsofinflammatorycytokines

Inappropriateintravascularfluidstatus


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CARBONDIOXIDE CASCADE


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2

2

CO2istwentyfoldmoresolublethanO2inplasma

CO2contentreflectsthesumofCO2inthebloodinallthreeforms

CaCO =48vol% CvCO =52vol%

Eachtimebloodcirculatesthrou hthebod 4vol%

ofCO2isremovedfromthetissuesanddeliveredtothelungstobeexhaled


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2

Only5%oftotalarterialcontentispresentin

2

0.3mlofCO2/100mlinabsoluteterms

Duringheavyexercisemayincreaseuptosevenfold


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KeyenzymeinCO2transport

fold)

Notpresentinplasma 7isoz mes

CAIIinRBCsandCAIVmembranebound

Inhibitedbythiazides andacetazolamide


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Hamburgerin1918

3

membrane

ass veprocess

Mediatedbymembraneboundproteinband3

Band3anchoringsiteforankyrin andspectrin


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2

CO2reactsdirectlywithHb

Dependson

O2satn

ofHb and2,3DPG(bindingtoHb) H+ concn (bothHb &plasmaproteins)

However, Hb desat and inH+ concn work


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JBSHaldane[18921964]

ChristiansenJ,DouglasCG,HaldaneJS.JPhysiol 1914;48:24471


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ReducedHb isbetterthan

oxygenatedHb incombiningwith

1.H+ ions

2.CO2

toformcarbamino

compounds

inturnassistingbloodtoload

more 2 romt et ssues


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BindingofO2withhemoglobintendsto

2

LeadstouptakeofCO2inthetissuesandreleaseofCO2 inthelungs

2

releasedfromthebloodinthelungsandthat

p c e up n e ssues


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eri heraltissues

NEngJMed1998;338:23947


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2

Carbonicacidbicarbonatebuffersystem

IfH+ concentrationsinbloodbegintorise,excess+ 3

IfH+ concentrationsbegintodrop,carbonicacid+,


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Signsofventilatory failure:

Acidemia

Increasedpulsus paradoxus

Hyperinflation

Somnolence/Decreasedmentalstatus

H i Eti l i


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H erca nia Etiolo ies

VVCOCO22P CO RR(VRR(VTT VVDD))

VCO H ermetabolism VFever

Seizures

Skeletalmuscleweakness

Impairedneuromusculartransmission

Sepsis

Hyperalimentation

Lung/chestwallcompliance

Airwayobstruction

RR Centralh oventilation

Asthma

Obstructiveslee a neaDrugs

Brainstemlesions VD

Obesityhypoventilationsyndrome ExcessivePEEP

oxygen and carbondioxide cascade (1) (1)

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