肺内分流zuihou学习资料

肺内分流zuihou学习资料第1页/共145页111122223333444456肘静脉、下肢、上腔、右心房、右心室、肺动脉的静脉氧分压？静脉采血点的氧分压血压第2页/共145页Hypoxiaoccursmoreeasilythanhypercarbia.Why?PaO2的降低远多于PaCO2的升高第3页/共145页出着容易进着难浓度差、物理弥散化学解离性质，气体分压Pt=+++P1P2P3P4第4页/共145页气体分压PO2+PCO2=aconstantInthealveolus,themixtureofgassescontainsnitrogen,watervapor,tracegasses,oxygenandcarbondioxide.

Attheendofabreath,thepressureinthealveolus=atmosphericpressure.So..PB=PN2+PH2O+Ptracegasses+PO2+PCO2Or..PO2+PCO2=aconstant一个多了另一个就少了第5页/共145页Theburlyalveolus(highV/Q).Theweaklingalveolus(lowV/Q).第6页/共145页Afundamentalquestion:IntermsofarterialO2andCO2tensions,cantheburlyalveoluscompensatefortheweaklingalveolus?forPaO2.YesorNo？forPaCO2.YesorNo？Thisbasicfactexplainsalot.Knowitcold.第7页/共145页Theweaklingalveolus(shuntorV/Qmismatch)TheburlyalveolusCantheburlyalveoluscompensatefortheweaklingalveolus?Notforoxygen!Theburlyalveoluscan’tsaturatehemoglobinmorethan100%.SaO2ofequaladmixtureofburlyandweaklingalveolarblood=89%pO2=50mmHg

SaO2=75%pO2=50mmHgSaO2=80%SaO2=75%SaO2=98%pO2=130mmHg

pO2=40mmHgpO2=130mmHgpO2=40mmHg肌体的储备和动员第8页/共145页TheweaklingalveolusTheburlyalveolusCantheburlyalveoluscompensatefortheweaklingalveolus?Yes,forCO2!Theburlyalveolus,ifittriesrealhard,canblowoffextraCO2.PulmonaryvenousbloodpCO2andPaCO2=40mmHgpCO2=44mmHgpCO2=44mmHgpCO2=36mmHgpCO2=46mmHgpCO2=36mmHgpCO2=46mmHg第9页/共145页健壮的肺能排出更多的二氧化碳而吸进和运载储备更多的氧Shunt,or“weakling”(lowV/Q)alveolusSaO2=75%“Burly”(highV/Q)alveolusSaO2=99%NormalalveolusSaO2=96%Equaladmixtureof“weakling”and“burly”alveolarbloodhasSaO2=(75+99)/2=87%.第10页/共145页AveragealveolarPACO2=40mmHg.Hence,PaCO2=40mmHgForCO2,burlyalveolusCANcompensatefortheweaklingalveolus.WeaklingalveolusBurlyalveolusNormalalveolusAdmixtureofburlyandweaklingalveolarblood第11页/共145页第12页/共145页第13页/共145页二氧化碳的事好解决氧的事不好办面积时间溶解缓冲难受都有余地，有通气量就行。第14页/共145页PaO2isalwaysslightlylowerthanPAO2？第15页/共145页问题什么是肺内分流、肺外分流？正常肺内分流多少？分流的形式有哪些？分流增加的结果？分流量如何判断评估测算？怎么减少分流？第16页/共145页第17页/共145页第18页/共145页1.Gasexchange,2.Akeytolungdisorders,3.Unevendistributionoftidalvolumeandperfusion,4.Bloodgases,5.ThePO2-PCO2diagram,6.TheVA/Q-curve,7.Blood-R-curves,8.Deadspace,9.Anatomicvenous-to-arterialshunt,10.Fickslawofdiffusion,11.Single-breathdiffusingcapacity,12.CompensationofVA/Q-mismatch,13.Pulmonarybloodflow,14.Regionalventilation.……..第19页/共145页PulmonaryShunting第20页/共145页肺循环、体循环、冠脉循环

第21页/共145页肺内分流量（Qsp,Qs/Qt）概念每一次右心室搏出的血液均进入肺循环，经过氧合作用后流回左心。生理条件下，心排血量（Qt）只有很小部分未经氧合直接回入左心，此部分血量称为解剖分流。在没有房、室间隔或其他心血管缺陷的前提下，生理性的解剖分流由支气管动脉的部分血液营养支气管后，血中氧已被消耗，流回入肺静脉，还有少量冠状静脉血流通过迷走静脉（ThebesianVein）也直接回入左心所形成，一般在5%以下。在病理情况下，如因炎性渗出液或水肿液充满肺泡腔或因肺不张肺泡完全萎陷时，吸入气完全不能进入该病变区肺泡内，虽然血流仍经过此区域但不能进行气体交换，含还原血红蛋白的静脉血直接回入左心，宛如有右至左的分流存在。此部分因病理原因引起的分流和解剖分流的总和称为肺内分流（Qs）。当肺内分流占心排血量成分过大时，将引起低氧血症。此种低氧血症与上述V/Q失调所引起的低氧血症有所不同，它不伴有CO2分压的升高，而PA-aO2显著增加，而且不能因提高吸入气氧浓度使之得到改善。第22页/共145页1.Theword“shunt”referstobloodthathasnotexchangedgasesthatmixeswithbloodthathasexchangedgases.2.Sourcesofshunt:Thebesiancirculationthatperfusestheleftventriclethendumpsintotheleftventricle.Bronchialcirculation

thatperfuseslungtissueandemptiesintothepulmonaryvein.Innormalpeoplethisaccountsforabout2-4%oftotalbloodflow.Perfusingcollapsedalveoliorhavingaholeinthewalloftheatriaorventricleswillproducearighttoleftshunt.左冠状动脉主要供应左心室前部，右冠状动脉主要供应左心室后部和右心室。左冠状动脉的血液流经毛细血管和静脉后，主要经由冠状窦回流入右心房，而右冠状动脉的血液则主要经较细的心前静脉直接回流入右心房。还有一小部分冠脉血液可通过心最小静脉直接流入左、右心房和心室腔内。第23页/共145页PulmonaryShuntingPERFUSIONWITHOUTVENTILATIONPulmonaryshuntisthatportionofthecardiacoutputthatenterstheleftsideoftheheartwithoutcomingincontactwithanalveolus.“True”Shunt–Nocontact

Anatomicshunts(Thebesian,Pleural,Bronchial)Cardiacanomalies\intrapulmonaryfistula\vascularlungtumors“Shunt-Like”(Relative)Shunt–contactbutnotenough

Someventilation,butnotenoughtoallowforcompleteequilibrationbetweenalveolargasandperfusion.第24页/共145页TrueShuntAnatomicshunts+CapillaryShuntAlveolarcollapse(atelectasis)Alveolarfluidaccumulation(pulmonaryedema)Alveolarconsolidation(pneumonia)

TureShuntsarerefractorytooxygentherapy.oxygentherapywillNOThelp(atleasttotheexpecteddegree).第25页/共145页解剖分流生理情况下，肺内也存在解剖分流(anatomicshunt)，即有一小部分静脉血经支气管静脉和肺内动—静脉吻合支直接流入肺静脉，以及心内最小静脉直接流至左心，其分流量约占心输出量的2％~3％。这部分血液未经氧合即流入体循环动脉血中，称之为真性分流(真性静脉血掺杂，turevenousadmixture)。解剖分流增加的原因可见于：支气管扩张时伴有支气管血管扩张，和肺小血管栓塞时肺动脉压增高导致的肺内动—静脉短路开放；以及慢性阻塞性肺病时，支气管静脉与肺静脉之间形成的吻合支等，都使相当多的静脉血掺人动脉血中。

肺不张或肺实变时，病变肺泡完全无通气功能，但仍有血流，流经该处的血液完全未进行气体交换而掺入动脉血中，类似解剖分流。临床呼吸衰竭的发病机制中，单纯通气不足，单纯弥散障碍，单纯的肺内分流或死腔通气增加的情况较少，常常是几个因素共同或相继发生作用。如慢性阻塞性肺病发生呼吸衰竭的机制为：①支气管炎症、分泌物堵塞等引起气道狭窄或阻塞，而有明显的阻塞性肺通气障碍；②呼吸肌疲劳所致的呼吸动力减弱，肺组织的炎症、间质和肺的纤维化以及累及胸膜，引起肺和胸廓顺应性的降低，导致限制性肺通气障碍；③肺泡的纤维化、炎症等引起肺泡膜损伤，弥散面积减少和弥散距离增加，导致弥散障碍；④由于部分肺泡的通气减少或丧失，造成功能性分流增加。由于毛细血管床的破坏，血管的重建使部分肺泡的肺血流明显减少，造成死腔样通气增加，从而导致VA／Q失调；⑤由于动—静脉吻合支的开放等引起真性分流显著增多。由解剖分流增加引起的换气障碍，其血气变化也仅有PaO2降低。鉴别功能性与真性分流的一个有效方法是吸入纯氧，若吸入纯氧30min能提高PaO2，则为功能性分流；而对真性分流，则吸入纯氧无明显提高PaO2的作用。第26页/共145页Normalshunt–bronchialcirculationandThebesianveinsaortaPulmonaryveins第27页/共145页ShuntetiologiesNormalBronchialcirculationThebesianveinsIntracardiacTetralogyofFallot,VSD,etc.IntrapulmonaryBronchialintubationObesityCirrhosisOsler-Weber-Rendu第28页/共145页功能性分流肺内的、肺外的解剖分流第29页/共145页Shunt-LikeEffect

BloodthatdoesexchangegaseswithalveolargasesbutdoesnotobtainaPO2thatequalsthatofanormalalveolusHypoventilation低通气Unevendistributionofventilation分布不均

BronchospasmExcessivemucusinthetracheobronchialtreeAlveolar-capillarydiffusiondefects

弥散异常

PulmonaryfibrosisNotenoughtimefordiffusiontooccurReadilyimprovedbyoxygentherapy第30页/共145页地球上必然的第31页/共145页区别？真解剖分流（肺内外）相对解剖（功能）性分流（肺内）分流样效应（肺内）第32页/共145页ventilation—perfusionbalanceorimbalance第33页/共145页肺泡与血液之间的气体交换，不仅取决于足够的肺泡通气和有效的气体弥散，还取决于肺泡通气量与肺血流量的比例配合，即通气血流比值。正常人平静呼吸时平均肺泡通气量（VA）为4L/min，平均肺血流量（Q）为5L/min，通气血流（VA/Q）比值为0.8。由于受重力影响气体和血流的分布在肺内各部分并不均匀，直立体位时，肺通气量和肺血流量自上而下都是递增的，但以血流量的增幅更为明显，因而VA/Q比值肺上部可高达3.0，而肺底部仅为0.6，但通过自身调节机制，使总的VA/Q保持在最合适的生理比值0.8

通气血流匹配matching第34页/共145页VA/Q比例失调的基本形式

当肺部病变时，由于部分肺泡的通气量不足或血流量减少，使肺泡的通气血流比例失调(ventilation-perfusionimbalance)，而引起气体交换障碍，这是呼吸衰竭发生的最常见机制。VA／Q比例失调，表现为如下两种基本形式：（1）部分肺泡通气不足—VA/Q比值降低

部分肺泡因阻塞性或限制性通气障碍而引起严重通气不足，但血流量未相应减少，VA/Q比值下降，造成流经该部分肺泡的静脉血未经充分氧合便掺入动脉血中，称静脉血掺杂(venousadmixtrure)，因为如同动-静脉短路又称功能性分流(functionalshunt)。正常成人也存在功能性分流仅约占肺血流量的3%，严重的慢性阻塞性肺病时，可以增至肺血流量的30%~50%，从而严重地影响换气功能。第35页/共145页第36页/共145页（2）部分肺泡血流不足—VA/Q比值升高肺动脉分支栓塞、炎症，肺动脉收缩，肺毛细血管床大量破坏可使流经该部分肺泡的血液灌流量减少，而该部分肺泡的通气相对良好，使VA/Q比值明显升高。这使该部分肺泡内的气体未能与血液进行有效的气体交换，则使死腔气量增加。死腔气量包括解剖死腔（指不参与气体交换的气管及支气管管腔容积）和肺泡死腔（指有通气而无血流灌注的肺泡容量）。死腔样通气(deadspacelikeventilation)指的就是有通气的肺泡血流相对地减少，以致于这些肺泡内的气体，得不到充分的利用。正常人死腔气量与潮气量之比低于30%，严重肺疾患时可高达60%~70%。第37页/共145页VA／Q比例失调的血气变化肺泡通气与血流比例失调时的血气变化，无沦是部分肺泡通气不足引起的功能性分流增加，还是部分肺泡血流不足引起的死腔样通气，均主要引起PaO2降低，而PaCO2可正常、降低或升高，这主要由健全肺泡的代偿功能，以及氧与二氧化碳解离曲线的特性所决定。(1)当部分肺泡通气不足，流经该处的血液得不到充分的气体交换，使血液氧分压降低，二氧化碳分压升高。健全肺泡代偿性的增加通气量，使流经健全肺泡的血液氧分压升高。但由于氧解离曲线S型的特点，氧分压达100mmHg(13.3kPa)时，血氧饱和度已高达95％以上，已处于S型曲线上端的平坦段，此时，即使健全肺泡因通气加强进一步提高了氧分压，但血氧含量的增加也极少，因此无法代偿通气不足肺泡所造成的低氧血症。

(2)当部分肺泡血流不足时，流经该处的血液氧分压虽显著增高，同理血氧含量的增加也很少。而健全肺泡因血流量增加，使VA／Q比值小于正常，流经此处的血流量虽多却不能充分氧合，所以造成VA／Q比例失调时PaO2和氧含量都明显降低。由于二氧化碳解离曲线的特性，当PaCO2在37.5-60mmHg(5~8kPa)范围内，血液二氧化碳含量与PaCO2几乎呈直线关系，代偿性通气增强的肺泡，血中的二氧化碳可得以大量排出，使PaCO2保持在正常水平，甚至因代偿过度，而致PaCO2低于正常，只有在严重障碍和代偿不足时，PaCO2才会高于正常。第38页/共145页Intrapulmonaryshuntinobesity:WhenFRCisbelowclosingcapacity,perfusionofnon-ventilatedalveoli

isSHUNT.肥胖低氧的原因？第39页/共145页手术后病人低氧原因？麻醉体位手术吸纯氧容量分布第40页/共145页Thesameminuteventilationcancausemarkedlydifferentamountsofalveolarventilation,dependingontidalvolume.功能残气量下降时肺泡萎陷多分流增加第41页/共145页AuthorSamee,S;AltesT;PowersP;deLangeEE;Knight-ScottJ;RakesG

TitleImagingthelungsinasthmaticpatientsbyusinghyperpolarizedhelium-3magneticresonance:assessmentofresponsetomethacholineandexercisechallenge

JournalTitleJournalofAllergy&ClinicalImmunology

Volume111

Issue6

Date2003

Pages:1205-11

He3MRshowingventilationdefectsinanormalsubjectandinincreasinglysevereasthmatics.肺泡萎陷第42页/共145页BaselineMethacholineAlbuterolHe3MRscans–ventilationdefectsinasthmatics第43页/共145页肺泡萎陷第44页/共145页分流的结果是什么？Resuleofshunting

:VenousAdmixture血氧含量下降

第45页/共145页VenousAdmixture静脉血混杂Themixingofoxygenatedbloodwith“contaminated”deoxygenatedblood→

VenousAdmixture

Itresultsinareductionin:PaO2SaO2↓↓显著的静脉血混杂的部位？第46页/共145页混合静脉血混合静脉血指的是将上腔静脉、下腔静脉及冠状静脉血充份混合后的血液，可由肺动脉导管（pulmonaryarterycatheter）在右心室或肺动脉内取得以推算出CvO2。利用CaO2、CvO2及CcO2便可求得Qsp/Qt，此指数包含两部份，分别是流经肺部时得到充份氧合及没有得到氧合的血流量比，代表着中央静脉及全身动脉循环间的静脉混合（venousadmixture）。Qsp/Qt被视为临床评估肺部氧合功能的标准，它不会受氧气消耗量、血红素量或混合静脉氧血红素饱和度等因素所影响。第47页/共145页混合静脉血效应：动脉血氧分压下降供氧下降,引发循环呼吸功能的代偿反应第48页/共145页Componentsofvenousadmixture1.Anatomicalshunt(trueshunt,extra-pulmonaryshunt)Bloodwhichentersthearterialsystemwithoutpassingthroughventilatedareasofthelung.1.1.Physiological·CoronarybloodentersLVviathethebesianveins·SomebronchialarterybloodentersthepulmonaryveinsBloodfromthesesourcesisNOTmixedvenousbloodandthuswouldhavedifferentPO2fromPvO2.1.2.PathologicalThesebloodmaybeofmixedvenousbloods.·CongenitalheartdiseasewithR->Lshunt·Perfusionofnon-ventilatedalveoli(V/Q=0)(atelectasis,bronchialobstruction)·Pulmonaryarterio-venousshunts(haemangioma)2.RegionsoflowV/Q(lowerthanN=0.86)2.1.Physiological·NormalscatterofV/Qratios·Changeswithposture2.2.Pathological·AbnormalscatterofV/Qratios·Alveolar-capillaryblock第49页/共145页ShuntSubstitutesP(A-a)O2

PaO2

/

PAO2

PaO2

/

FIO2P(A-a)O2

/PaO2Shuntfraction血氧混合、下降的程度的几个指标第50页/共145页P(A-a)O2分流：氧瀑布的一个局部第51页/共145页P(A-a)O2第52页/共145页P(A-a)O2第53页/共145页正常空气21%氧第54页/共145页第55页/共145页各种吸入氧浓度下的吸入气氧分压+肺泡二氧化碳分压就可以得到肺泡氧分压肺泡氧分压PAO2第56页/共145页呼吸商(R)=

PACO2×VA．(PiO2-PAO2)

×VA．PACO2肺泡气二氧化碳分压；PiO2吸入气氧分压;PAO2肺泡气氧分压呼吸商第57页/共145页肺泡气CO2分压

0.863Vco2

PaCO2=PACO2=——————

VA

PACO2

：肺泡气CO2分压Vco2：每分钟CO2

产量

VA

：肺泡通气量PaCO2：动脉血CO2分压二氧化碳就是透第58页/共145页公式转换呼吸商(R)=

PACO2×VA．(PiO2-PAO2)

×VA．PiO2-PAO2=PACO2RPAO2=PiO2-PACO2R第59页/共145页肺泡气O2分压

PACO2PAO2=PiO2——————

RPAO2

：肺泡气O2分压PiO2：吸入气O2分压PACO2

：肺泡气CO2分压R：呼吸商第60页/共145页

GaseousEnvironmentAtmosphere:NitrogenandOxygen,negligibleCarbonDioxide.

ClinicalRelevanceofEnvironmentAltitude:PO2dependsonPB低于21%Suffocation:PO2dependsonfractionalO2Oxygentherapy:PO2dependsonfractionalO2第61页/共145页EvaluatingFIO2流量表刻度高吸入氧浓度就高吗？HighflowdevicesmaynotbedeliveringtheFIO2thatissetIfthepatient’stotalflowrateisexceedingtheflowfromtheoxygendeliverydevice,theFIO2willdecreaseWaterintheaerosoltubingwillincreaseFIO2Highflowoxygendeliverysystemsshouldbeanalyzed

管道流量吸入氧浓度常不精确在呼吸机上比较准确浓度、流量；压力第62页/共145页IdealAlveolarGasEquation.ClinicallyUsefulForm:CompleteForm:第63页/共145页PAO2PAO2=[(PBARO-PH2O)xFIO2]–(PaCO2/0.8)OnFIO2oflessthan60%PAO2=[(PBARO-PH2O)xFIO2]–PaCO2OnFIO2

greaterthan60%NormalValues:RoomAir:100–104mmHg100%Oxygen:600

第64页/共145页ComparePAO2

toPaO2Healthypeople:PAO2=PaO2Inanideallung,PaO2andPaCO2=PAO2andPACO2.Innormalhealthy,thesevaluesareclosebutnotidentical.Indiseaseconditions,thenumberscanvarygreatly.TwoApproachestoComparison(PAO2

—PaO2)difference

减法：差PaO2

/PAO2

ratio

除法：比第65页/共145页第66页/共145页A-aDifferencePAO2-PaO2Normally5-20mmHg

Valuesincreasewithincreasingageandthesupineposition.BecauseofnormalanatomicalshuntVentilation/PerfusionmismatchingA-adifferenceincreaseswithpulmonarydiseaseProblem:

Normalrangechangeson100%O2A：理想状态的一腔（肺泡）模型第67页/共145页Inahealthyyoungperson,thePAO2–PaO2isnormally<15mmHg;thisvalueincreaseswithageandmaybe30mmHginelderlypatients.PaO2(Upright)=104.2-0.27xage(Yrs)A-agradient=2.5+0.21xageinyears年龄、体位与A-agradient

第68页/共145页P(A-a)O2差Normalvaluesisaround10mmHgonroomair（21%）.Normalvalues25-65mmHgon100%.DifficulttousewhenFIO2variesfrom21or100%NormalvaluesdifferforeachFIO2Limitedvaluewhenusingsupplementaloxygen.第69页/共145页P(A-a)O2onRoomAirNormalA-agradienton21%isseenwith:PurehypoventilationHighaltitudeDiffusiondefect(patientatrest)AbnormalA-agradienton21%isseenwithRelativeshuntAbsoluteshunt5-20mmHg

﹥20mmHg

NormalA-agradient=(Age+10)/4

A-aincreases5to7mmHgforevery10%

increaseinFiO2第70页/共145页UsingP(A-a)O2toEstimateShuntNormalShuntis5%Add5%tothenormal5%shuntforevery100mmHggradient;Example:100mmHg–10%200mmHg–15%300mmHg–20%第71页/共145页UsingP(A-a)O2toEstimateShuntOn100%FIO2,a1%shuntisestimatedforevery10–15mmHgP(A-a)O2Example:A-agradientis140mmHg140=9.3%140=14.0%15 10第72页/共145页DiagnosisofTrueShuntBreathing100%oxygenwillnotabolishhypoxemiaduetoshuntREASON:shuntedbloodneverexposedtothehighalveolarPO2第73页/共145页P(A-a)O2on100%RelativeShuntwillimproveA-agradientlessthan300mmHgAbsoluteShuntwillnotimproveA-agradientisgreaterthan300mmHg0第74页/共145页IncreasedA-agradientcanbecausedby1pulmonarycollapse/consolidation2neoplasm3infection4alveolardestruction5drugs

-vasodilators

-volatileanaesthetics6hormones

-pregnancyandprogesterone

-hepaticfailure7extrapulmonaryshuntingIncreasedA-agradientisthemostcommoncauseofarterialhypoxemia第75页/共145页FactorsinfluencingA-agradient1Magnitudeofvenousadmixture

=>withsmallshunts,themagnitudeofvenousadmixtureisproportionaltoA-agradient

=>withlargershunts,therelationshipislost.2V/Qscatter3ActualalveolarPO2(PAO2)

=>duetothenon-linearshapeoftheoxygendissociationcurve,witheverythingelsebeingequal

=>thegreaterthePAO2,thegreatertheA-agradient4Cardiacoutput

=>cardiacoutputisinverselyproportionaltoalveolar/arterialO2contentdifference,giventhesamevenousadmixtureBUT,venousadmixturealsodecreasewithreducedCO

=>PaO2isrelativelyunchanged

5Hbconcentration

=>[Hb]doesnotinfluencepulmonaryend-capillary/arterialoxgencontentdifference

Butincreasein[Hb]wouldcausesmalldecreaseinthetensiondifference6Alveolarventilation

=>increasedventilationincreasebothPAO2andA-agradient.Whenvenousadmixture<3%,PaO2willalwaysincrease.Whenvenousadmixture>3%ANDventilation>1.5L/min,thehighertheshunt/ventilation,

=>lowerPCO2

=>lowerCO

=>greateralveolar/arterialO2contentdifference

=>A-agradientisgreaterthantheincreaseinPAO2

=>PaO2canactuallydecreasewithhigherventilation第76页/共145页PaO2/PAO2

a/Aratio比率Normallyaveragesjustover0.8

a/Aratiofallswithpulmonarydisease.Lowerlimitnormal:young(roomair): 0.74older

(roomair): 0.78Bothgroups(100%O2): 0.82Normalvalueisgreaterthan75%onanyFIO2Example:100/104=96%96%ofoxygenisdiffusingacrosstheA-Cmembrane第77页/共145页(A-a)Differencevs.a/ARatio

哪个相关分流更好？NormalNormal(A-a)PO2Difference(mmHg)a/APO2ratioSickSick第78页/共145页PaO2/FIO2ratio氧合指数Normalvalueis400–500

Example:100mmHg/.21=476Valuebetween200–300=ALIValuelessthan200=ARDSValueslessthan200correlatewithashuntofgreaterthan20%肺泡-动脉氧气压力差动脉-肺泡氧气分率氧合指数（Oxygenationindex）C(a-v)O2：动脉-静脉氧气含量差第79页/共145页P(A-a)O2/PaO2呼吸指数（Respiratoryindex）PaO2/FIO2于1974年由Dr.Horovitz提出，因为计算容易，且与肺内分流（Qsp/Qt）的相关性不错，所以临床应用甚广。P(A-a)O2因加入了吸入氧气分率及动脉二氧化碳压力两指数，可以分辨出因通气量过低导至二氧化碳累积而造成的氧合不良，但影响P(A-a)O2的因素很多，包括吸入氧气分率、通气血流灌注比不配合、肺内分流及右向左的心内分流，其中肺内分流又随着各种肺疾状况、病患年龄及不同的体位而改变，此外P(A-a)O2也受混合静脉氧气含量的相关因素影响，如组织氧气消耗量、心搏出量及血红素量。一般P(A-a)O2对呼吸常态空气的病患有无氧合障碍相当敏感，但由于它与肺内分流间的相关性不佳且受太多非肺因素影响，所以在重症病患并不实用。PaO2/PAO2及P(A-a)O2/PaO2分别由Dr.Gilbert与Dr.Goldfarb提出。与肺内分流作相关性分析，PaO2/FIO2、PaO2/PAO2与P(A-a)O2/PaO2三者较近似（r=0.72~0.74），P(A-a)O2则稍差（r=0.62）。第80页/共145页RuleOfThumb“50/50Rule”AlthoughV/Qimbalancesarethemostcommoncauseofhypoxemiainpatientswithrespiratorydiseases,physiologicshuntingalsocanoccurcommonly,hecriticallyill.IftheFi02is>50%&thePa02is<50mmHg,significantshuntingispresent.OtherwisethehypoxemiaismainlycausedbyasimpleV/Qimbalance.第81页/共145页Theaffinityofhemoglobinforoxygenincreaseswitheachoxygenmoleculeattached理解血红蛋白的氧合：AllorNothing第82页/共145页理解血氧饱和度不是所有的血红蛋白都结合携带氧第83页/共145页QuantityofOxygenBoundtoHemoglobinNotallhemoglobinmoleculesareboundwithoxygen.NormalsaturationArterial(SaO2)–97%Venous(SO2)–75%Some“desaturated”hemoglobinexistsbecauseofnormalphysiologicshunts:MixingofpoorlysaturatedvenousbloodwitharterialbloodThebesian,bronchial,andpleuralveinsIntrapulmonaryshunts(perfusedalveolithatarenotventilated)Hemoglobinnotboundwithoxygeniscalledreducedhemoglobin.第84页/共145页MixedVenousOxygenationRequiresapulmonaryarterycatheter.Assessmentofoxygensupplyvs.demandSO2:Continuousvs.SpotCheckNormal75%if↓why?if↑why?DecreasedwithincreasedO2,decreasedSaO2,decreasedHbordecreasedCO.PO2:

Averageend-capillarydrivingpressure.Usefulnessdependsondistributionofcardiacoutput.Decreasesareassociatedwithdecreasedsupplyorincreaseddemands.Increasesareassociatedwithreducedutilization

(NOTALWAYSAGOODTHING!)第85页/共145页氧含量：OxygenContentThetotalamountofoxygenin100mLofbloodisthesumofthedissolvedoxygen&theoxygenboundtohemoglobin.ArterialContentCaO2=(Hbx1.34xSaO2)+(PaO2x.003)VenousContentCvO2=(Hbx1.34xSvO2)+(PvO2x.003)CapillaryContentCćO2=(Hbx1.34xSćO2)+(PćO2x.003)SćO2=IdealSaturation=100%PćO2=IdealPartialPressure=PAO2第86页/共145页Arterial-VenousOxygenContentDifferenceC(a-v)O2CaO2–CvO2

Thevenousbloodis“mixedvenous”bloodobtainedfromthepulmonaryarteryviaapulmonaryarterycatheter.NormalCaO2:20vol%NormalCvO2:15vol%NormalCaO2–CvO2:5vol%↓Decreasedwith:IncreasedCOCertainPoisonsHypothermia第87页/共145页ShuntEquationClassicShuntEquation“GoldStandard”ClinicalShuntEquationAshuntgreaterthanor=15%issignificantIncreasedshuntswillcorrelatewith“Whiteoutonx-rayunlessitscardiacinorigin.Atelectasis,pneumonia,pulmonaryedema,ARDS血气分析出来了，多算一算。第88页/共145页ShuntEquationSojusthowmuchbloodisshunted?

WhereCćO2=(Hbx1.34xFio2)+(PAO2*.003)YouwillneedPBARO–BarometricPressurePaO2–ArterialPartialPressureofOxygen

PaCO2–ArterialPartialPressureofCarbonDioxide

PvO2–VenousPartialPressureofOxygen

Hb–HemoglobinconcentrationPAO2–AlveolarPartialPressureofOxygen

FIO2–FractionalConcentrationofInspiredOxygen%CaO2CvO2AavAav第89页/共145页MeasurementofvenousadmixtureQTxCaO2=(QT-QS)xCc'O2+QSxCvO2=>QSx(Cc'O2-CvO2)=QTx(Cc'O2-CaO2)=>QS/QT=(Cc'O2-CaO2)/(Cc'O2-CvO2)QS=bloodflowthroughtheshuntQT=totalbloodflowCaO2=concentrationofO2inarterialbloodCc'O2=concentrationofO2inpulmonaryend-capillarybloodCvO2=mixedvenousbloodShuntEquation:QS/QT=(Cc'O2-CaO2)/(Cc'O2-CvO2)·NormallycardiacoutputisusedforQT.

=>QS/QT=2-3%·CaO2-measuredbyABG·Cc'O2-derivedfromthe"ideal"alveolarPAO2(usingthealveloargasequation)(assumingPc'O2=idealPAO2)·CvO2-measuredfromRVorpulmonaryartery

NB.IVCandSVCPO2aredifferent,andatRAthesebloodremainseparate.第90页/共145页ClassicShuntEquationWhere:CćO2=(1.34xHbx1.0)+(PAO2x.003)Assumes100%saturationintheidealalveolusRequiresaPulmonaryArterialCatheter(BTFDC)formixedvenousblood

（V）

第91页/共145页第92页/共145页ClinicalShuntEquationRequiresaPulmonaryArterialCatheter(BTFDC)OnlyaccurateatlowerFIO2

第93页/共145页DeterminationofShuntFractionShuntEquation:Qs/Qt=(CcO2-CaO2)/(CcO2-CvO2)Ifalveolarcapillarycontentis20vol%,arterialcontentis18vol%andmixedvenouscontentis13vol%,whatpercentageofbloodisshuntedpastthelung?Approximately29%.Thereisasimpleclinicallyusefulwaytoestimatetheshuntfraction.Givethepatient100%O2tobreathe(FIO2=1),thenmeasurearterialPO2.Thereisapproximatelya1%shuntforevery20mmHgdifferencebetweenarterialandalveolarPO2.AtsealevelPAO2=760-47-40=673

whenFIO2=1.Inthisexample,ifarterialPO2=470mmHg,thereisanapproximate10%shunt.第94页/共145页CvO2QTCc'O2QSCaO2QTQT

Cc'O2

-CvO2QS

Cc'O2

-CaO2%SatO2canbeusedinplaceofCIfbreathing100%O2,theshuntfractioncanbeapproximatedas1%ofthecardiacoutputforevery20mmHgPAO2-PaO2difference.ScO2ScO2-ScO2ScO2-QTQS第95页/共145页EffectsofvenousadmixtureonarterialPaO2andPaCO2VenousadmixturereducesthearterialO2contentandincreasesthearterialCO2content.BecausePaO2isusuallyontheflatpartofthehaemoglobindissociationcurve=>smallreductioninO2contentleadstolargedropinPaO2=>increasedA-agradientBecauseCO2dissociationcurveisusuallysteepandmorelinear,=>increasesinCO2contentdon'tleadtolargeincreaseinPaCO2Inclinicalsettings,venousadmixture

=>reducedPaO2

=>compensatoryhyperventilation

=>morethanenoughtooffsetthesmallincreaseinPaCO2

=>PaCO2oftenreducedratherthanincreasedIncreasesinPaCO2areseldomcausedbyvenousadmixture.第96页/共145页DistinctionbetweeneffectsofshuntandeffectsofV/QinequalityItusuallyisimpossibletosaytowhatextentthecalculatedvenousadmixtureisduetoatrueshuntortoperfusionofalveoliwithlowV/Q.IfFIO2isincreased,theeffectonPaO2dependsonthecauseofthevenousadmixture.Ifoxygenationisimpairedbytrueshunt,increasesinFIO2willleadtoincreasesinthePaO2asperiso-shuntdiagram.·10%shuntrequiresFIO230%torestorenormalPaO2·20%shuntrequiresFIO257%torestorenormalPaO2·30%shuntrequiresFIO297%torestorenormalPaO2·40%shunt-normalPaO2cannotberestored·50%shunt-increasingFIO2hasalmostnoeffectonPaO2IfoxygenationisimpairedbyV/Qscatter,increasesinFIO2willcausethePaO2toapproachthenormalPaO2value

forthatparticularFIO2.AtFIO2of100%,V/QscatterhasalmostnoeffectonPaO2.QuantificationofV/Qscattercanbemeasuredbythealveolar-arterialPN2difference.<=becausePN2differenceisnotaffectbyshuntatall.ShuntexcludesblooddraininganyalveoliwithaV/Qratio>0.V/Qinequalityexcludesshunts.第97页/共145页„Iso-shunt”diagramNunnJF.Appl.RespPhysiol.,1993

DegreeofvenousadmixtureMolnár‘99100200300400PaO2Hgmm05%10%15%20%25%30%50%FiO20,20,61,0第98页/共145页第99页/共145页第100页/共145页Fio2

和Pao2

与shunt%第101页/共145页deadspaceAnareawithnoventilation(andthusaV/Qofzero)istermed"shunt."

Anareawithnoperfusion(andthusaV/Qofinfinity)istermed“deadspace”第102页/共145页Measuringseverity

ofoxygenationproblem:A-agradient(fromalveolargasequation).Calculates“PAO2”NeedsFIO2,PB,PaCO2,PaO2Shuntfractionequation

NeedsPAO2,CcO2,CvO2,CaO2PaO2/FIO2(<200inARDS)Noneofthesegiveusetiologyorphysiology(shuntvs.V/Qmismatch).第103页/共145页AssessmentofHypoxemiaDefinitionof“Hypoxemia”.Severity?CausesofHypoxemiaDifferentialDiagnosisofHypoxemiaAbnormalityPaO2PaCO2RAP(A-a)O2100%O2P(A-a)O2Hypoventilation¯­NNAbsoluteShunt¯Nor¯­­RelativeShunt¯N,­,¯­NDiffusionDefectNatRest,¯w/exerciseNor¯Natrest,­withexerciseN第104页/共145页HypoxemiaAnalysisStep1-3IsPACO2>40mmHg

ANDa/A>0.74or(A-a)<20mmHgPureHypoventilationyesChoosebetween:

Shunt

DiffusionAbnormality

V/QMismatchingNo