肺內(nèi)分流zuihou學(xué)習(xí)資料

肺內(nèi)分流zuihou學(xué)習(xí)資料第1頁/共145頁111122223333444456肘靜脈、下肢、上腔、右心房、右心室、肺動(dòng)脈的靜脈氧分壓？靜脈采血點(diǎn)的氧分壓血壓第2頁/共145頁Hypoxiaoccursmoreeasilythanhypercarbia.Why?PaO2的降低遠(yuǎn)多于PaCO2的升高第3頁/共145頁出著容易進(jìn)著難濃度差、物理彌散化學(xué)解離性質(zhì)，氣體分壓Pt=+++P1P2P3P4第4頁/共145頁氣體分壓PO2+PCO2=aconstantInthealveolus,themixtureofgassescontainsnitrogen,watervapor,tracegasses,oxygenandcarbondioxide.

Attheendofabreath,thepressureinthealveolus=atmosphericpressure.So..PB=PN2+PH2O+Ptracegasses+PO2+PCO2Or..PO2+PCO2=aconstant一個(gè)多了另一個(gè)就少了第5頁/共145頁Theburlyalveolus(highV/Q).Theweaklingalveolus(lowV/Q).第6頁/共145頁Afundamentalquestion:IntermsofarterialO2andCO2tensions,cantheburlyalveoluscompensatefortheweaklingalveolus?forPaO2.YesorNo？forPaCO2.YesorNo？Thisbasicfactexplainsalot.Knowitcold.第7頁/共145頁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肌體的儲(chǔ)備和動(dòng)員第8頁/共145頁TheweaklingalveolusTheburlyalveolusCantheburlyalveoluscompensatefortheweaklingalveolus?Yes,forCO2!Theburlyalveolus,ifittriesrealhard,canblowoffextraCO2.PulmonaryvenousbloodpCO2andPaCO2=40mmHgpCO2=44mmHgpCO2=44mmHgpCO2=36mmHgpCO2=46mmHgpCO2=36mmHgpCO2=46mmHg第9頁/共145頁健壯的肺能排出更多的二氧化碳而吸進(jìn)和運(yùn)載儲(chǔ)備更多的氧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頁/共145頁AveragealveolarPACO2=40mmHg.Hence,PaCO2=40mmHgForCO2,burlyalveolusCANcompensatefortheweaklingalveolus.WeaklingalveolusBurlyalveolusNormalalveolusAdmixtureofburlyandweaklingalveolarblood第11頁/共145頁第12頁/共145頁第13頁/共145頁二氧化碳的事好解決氧的事不好辦面積時(shí)間溶解緩沖難受都有余地，有通氣量就行。第14頁/共145頁P(yáng)aO2isalwaysslightlylowerthanPAO2？第15頁/共145頁問題什么是肺內(nèi)分流、肺外分流？正常肺內(nèi)分流多少？分流的形式有哪些？分流增加的結(jié)果？分流量如何判斷評(píng)估測(cè)算？怎么減少分流？第16頁/共145頁第17頁/共145頁第18頁/共145頁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頁/共145頁P(yáng)ulmonaryShunting第20頁/共145頁肺循環(huán)、體循環(huán)、冠脈循環(huán)

第21頁/共145頁肺內(nèi)分流量（Qsp,Qs/Qt）概念每一次右心室搏出的血液均進(jìn)入肺循環(huán)，經(jīng)過氧合作用后流回左心。生理?xiàng)l件下，心排血量（Qt）只有很小部分未經(jīng)氧合直接回入左心，此部分血量稱為解剖分流。在沒有房、室間隔或其他心血管缺陷的前提下，生理性的解剖分流由支氣管動(dòng)脈的部分血液營養(yǎng)支氣管后，血中氧已被消耗，流回入肺靜脈，還有少量冠狀靜脈血流通過迷走靜脈（ThebesianVein）也直接回入左心所形成，一般在5%以下。在病理情況下，如因炎性滲出液或水腫液充滿肺泡腔或因肺不張肺泡完全萎陷時(shí)，吸入氣完全不能進(jìn)入該病變區(qū)肺泡內(nèi)，雖然血流仍經(jīng)過此區(qū)域但不能進(jìn)行氣體交換，含還原血紅蛋白的靜脈血直接回入左心，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總和稱為肺內(nèi)分流（Qs）。當(dāng)肺內(nèi)分流占心排血量成分過大時(shí)，將引起低氧血癥。此種低氧血癥與上述V/Q失調(diào)所引起的低氧血癥有所不同，它不伴有CO2分壓的升高，而PA-aO2顯著增加，而且不能因提高吸入氣氧濃度使之得到改善。第22頁/共145頁1.Theword“shunt”referstobloodthathasnotexchangedgasesthatmixeswithbloodthathasexchangedgases.2.Sourcesofshunt:Thebesiancirculationthatperfusestheleftventriclethendumpsintotheleftventricle.Bronchialcirculation

thatperfuseslungtissueandemptiesintothepulmonaryvein.Innormalpeoplethisaccountsforabout2-4%oftotalbloodflow.Perfusingcollapsedalveoliorhavingaholeinthewalloftheatriaorventricleswillproducearighttoleftshunt.左冠狀動(dòng)脈主要供應(yīng)左心室前部，右冠狀動(dòng)脈主要供應(yīng)左心室后部和右心室。左冠狀動(dòng)脈的血液流經(jīng)毛細(xì)血管和靜脈后，主要經(jīng)由冠狀竇回流入右心房，而右冠狀動(dòng)脈的血液則主要經(jīng)較細(xì)的心前靜脈直接回流入右心房。還有一小部分冠脈血液可通過心最小靜脈直接流入左、右心房和心室腔內(nèi)。第23頁/共145頁P(yáng)ulmonaryShuntingPERFUSIONWITHOUTVENTILATIONPulmonaryshuntisthatportionofthecardiacoutputthatenterstheleftsideoftheheartwithoutcomingincontactwithanalveolus.“True”Shunt–Nocontact

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

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

TureShuntsarerefractorytooxygentherapy.oxygentherapywillNOThelp(atleasttotheexpecteddegree).第25頁/共145頁解剖分流生理情況下，肺內(nèi)也存在解剖分流(anatomicshunt)，即有一小部分靜脈血經(jīng)支氣管靜脈和肺內(nèi)動(dòng)—靜脈吻合支直接流入肺靜脈，以及心內(nèi)最小靜脈直接流至左心，其分流量約占心輸出量的2％~3％。這部分血液未經(jīng)氧合即流入體循環(huán)動(dòng)脈血中，稱之為真性分流(真性靜脈血摻雜，turevenousadmixture)。解剖分流增加的原因可見于：支氣管擴(kuò)張時(shí)伴有支氣管血管擴(kuò)張，和肺小血管栓塞時(shí)肺動(dòng)脈壓增高導(dǎo)致的肺內(nèi)動(dòng)—靜脈短路開放；以及慢性阻塞性肺病時(shí)，支氣管靜脈與肺靜脈之間形成的吻合支等，都使相當(dāng)多的靜脈血摻人動(dòng)脈血中。

肺不張或肺實(shí)變時(shí)，病變肺泡完全無通氣功能，但仍有血流，流經(jīng)該處的血液完全未進(jìn)行氣體交換而摻入動(dòng)脈血中，類似解剖分流。臨床呼吸衰竭的發(fā)病機(jī)制中，單純通氣不足，單純彌散障礙，單純的肺內(nèi)分流或死腔通氣增加的情況較少，常常是幾個(gè)因素共同或相繼發(fā)生作用。如慢性阻塞性肺病發(fā)生呼吸衰竭的機(jī)制為：①支氣管炎癥、分泌物堵塞等引起氣道狹窄或阻塞，而有明顯的阻塞性肺通氣障礙；②呼吸肌疲勞所致的呼吸動(dòng)力減弱，肺組織的炎癥、間質(zhì)和肺的纖維化以及累及胸膜，引起肺和胸廓順應(yīng)性的降低，導(dǎo)致限制性肺通氣障礙；③肺泡的纖維化、炎癥等引起肺泡膜損傷，彌散面積減少和彌散距離增加，導(dǎo)致彌散障礙；④由于部分肺泡的通氣減少或喪失，造成功能性分流增加。由于毛細(xì)血管床的破壞，血管的重建使部分肺泡的肺血流明顯減少，造成死腔樣通氣增加，從而導(dǎo)致VA／Q失調(diào)；⑤由于動(dòng)—靜脈吻合支的開放等引起真性分流顯著增多。由解剖分流增加引起的換氣障礙，其血?dú)庾兓矁H有PaO2降低。鑒別功能性與真性分流的一個(gè)有效方法是吸入純氧，若吸入純氧30min能提高PaO2，則為功能性分流；而對(duì)真性分流，則吸入純氧無明顯提高PaO2的作用。第26頁/共145頁Normalshunt–bronchialcirculationandThebesianveinsaortaPulmonaryveins第27頁/共145頁ShuntetiologiesNormalBronchialcirculationThebesianveinsIntracardiacTetralogyofFallot,VSD,etc.IntrapulmonaryBronchialintubationObesityCirrhosisOsler-Weber-Rendu第28頁/共145頁功能性分流肺內(nèi)的、肺外的解剖分流第29頁/共145頁Shunt-LikeEffect

BloodthatdoesexchangegaseswithalveolargasesbutdoesnotobtainaPO2thatequalsthatofanormalalveolusHypoventilation低通氣Unevendistributionofventilation分布不均

BronchospasmExcessivemucusinthetracheobronchialtreeAlveolar-capillarydiffusiondefects

彌散異常

PulmonaryfibrosisNotenoughtimefordiffusiontooccurReadilyimprovedbyoxygentherapy第30頁/共145頁地球上必然的第31頁/共145頁區(qū)別？真解剖分流（肺內(nèi)外）相對(duì)解剖（功能）性分流（肺內(nèi)）分流樣效應(yīng)（肺內(nèi)）第32頁/共145頁ventilation—perfusionbalanceorimbalance第33頁/共145頁肺泡與血液之間的氣體交換，不僅取決于足夠的肺泡通氣和有效的氣體彌散，還取決于肺泡通氣量與肺血流量的比例配合，即通氣血流比值。正常人平靜呼吸時(shí)平均肺泡通氣量（VA）為4L/min，平均肺血流量（Q）為5L/min，通氣血流（VA/Q）比值為0.8。由于受重力影響氣體和血流的分布在肺內(nèi)各部分并不均勻，直立體位時(shí)，肺通氣量和肺血流量自上而下都是遞增的，但以血流量的增幅更為明顯，因而VA/Q比值肺上部可高達(dá)3.0，而肺底部僅為0.6，但通過自身調(diào)節(jié)機(jī)制，使總的VA/Q保持在最合適的生理比值0.8

通氣血流匹配matching第34頁/共145頁VA/Q比例失調(diào)的基本形式

當(dāng)肺部病變時(shí)，由于部分肺泡的通氣量不足或血流量減少，使肺泡的通氣血流比例失調(diào)(ventilation-perfusionimbalance)，而引起氣體交換障礙，這是呼吸衰竭發(fā)生的最常見機(jī)制。VA／Q比例失調(diào)，表現(xiàn)為如下兩種基本形式：（1）部分肺泡通氣不足—VA/Q比值降低

部分肺泡因阻塞性或限制性通氣障礙而引起嚴(yán)重通氣不足，但血流量未相應(yīng)減少，VA/Q比值下降，造成流經(jīng)該部分肺泡的靜脈血未經(jīng)充分氧合便摻入動(dòng)脈血中，稱靜脈血摻雜(venousadmixtrure)，因?yàn)槿缤瑒?dòng)-靜脈短路又稱功能性分流(functionalshunt)。正常成人也存在功能性分流僅約占肺血流量的3%，嚴(yán)重的慢性阻塞性肺病時(shí)，可以增至肺血流量的30%~50%，從而嚴(yán)重地影響換氣功能。第35頁/共145頁第36頁/共145頁（2）部分肺泡血流不足—VA/Q比值升高肺動(dòng)脈分支栓塞、炎癥，肺動(dòng)脈收縮，肺毛細(xì)血管床大量破壞可使流經(jīng)該部分肺泡的血液灌流量減少，而該部分肺泡的通氣相對(duì)良好，使VA/Q比值明顯升高。這使該部分肺泡內(nèi)的氣體未能與血液進(jìn)行有效的氣體交換，則使死腔氣量增加。死腔氣量包括解剖死腔（指不參與氣體交換的氣管及支氣管管腔容積）和肺泡死腔（指有通氣而無血流灌注的肺泡容量）。死腔樣通氣(deadspacelikeventilation)指的就是有通氣的肺泡血流相對(duì)地減少，以致于這些肺泡內(nèi)的氣體，得不到充分的利用。正常人死腔氣量與潮氣量之比低于30%，嚴(yán)重肺疾患時(shí)可高達(dá)60%~70%。第37頁/共145頁VA／Q比例失調(diào)的血?dú)庾兓闻萃馀c血流比例失調(diào)時(shí)的血?dú)庾兓?，無淪是部分肺泡通氣不足引起的功能性分流增加，還是部分肺泡血流不足引起的死腔樣通氣，均主要引起PaO2降低，而PaCO2可正常、降低或升高，這主要由健全肺泡的代償功能，以及氧與二氧化碳解離曲線的特性所決定。(1)當(dāng)部分肺泡通氣不足，流經(jīng)該處的血液得不到充分的氣體交換，使血液氧分壓降低，二氧化碳分壓升高。健全肺泡代償性的增加通氣量，使流經(jīng)健全肺泡的血液氧分壓升高。但由于氧解離曲線S型的特點(diǎn)，氧分壓達(dá)100mmHg(13.3kPa)時(shí)，血氧飽和度已高達(dá)95％以上，已處于S型曲線上端的平坦段，此時(shí)，即使健全肺泡因通氣加強(qiáng)進(jìn)一步提高了氧分壓，但血氧含量的增加也極少，因此無法代償通氣不足肺泡所造成的低氧血癥。

(2)當(dāng)部分肺泡血流不足時(shí)，流經(jīng)該處的血液氧分壓雖顯著增高，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，流經(jīng)此處的血流量雖多卻不能充分氧合，所以造成VA／Q比例失調(diào)時(shí)PaO2和氧含量都明顯降低。由于二氧化碳解離曲線的特性，當(dāng)PaCO2在37.5-60mmHg(5~8kPa)范圍內(nèi)，血液二氧化碳含量與PaCO2幾乎呈直線關(guān)系，代償性通氣增強(qiáng)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，甚至因代償過度，而致PaCO2低于正常，只有在嚴(yán)重障礙和代償不足時(shí)，PaCO2才會(huì)高于正常。第38頁/共145頁Intrapulmonaryshuntinobesity:WhenFRCisbelowclosingcapacity,perfusionofnon-ventilatedalveoli

isSHUNT.肥胖低氧的原因？第39頁/共145頁手術(shù)后病人低氧原因？麻醉體位手術(shù)吸純氧容量分布第40頁/共145頁Thesameminuteventilationcancausemarkedlydifferentamountsofalveolarventilation,dependingontidalvolume.功能殘氣量下降時(shí)肺泡萎陷多分流增加第41頁/共145頁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頁/共145頁BaselineMethacholineAlbuterolHe3MRscans–ventilationdefectsinasthmatics第43頁/共145頁肺泡萎陷第44頁/共145頁分流的結(jié)果是什么？Resuleofshunting

:VenousAdmixture血氧含量下降

第45頁/共145頁VenousAdmixture靜脈血混雜Themixingofoxygenatedbloodwith“contaminated”deoxygenatedblood→

VenousAdmixture

Itresultsinareductionin:PaO2SaO2↓↓顯著的靜脈血混雜的部位？第46頁/共145頁混合靜脈血混合靜脈血指的是將上腔靜脈、下腔靜脈及冠狀靜脈血充份混合后的血液，可由肺動(dòng)脈導(dǎo)管（pulmonaryarterycatheter）在右心室或肺動(dòng)脈內(nèi)取得以推算出CvO2。利用CaO2、CvO2及CcO2便可求得Qsp/Qt，此指數(shù)包含兩部份，分別是流經(jīng)肺部時(shí)得到充份氧合及沒有得到氧合的血流量比，代表著中央靜脈及全身動(dòng)脈循環(huán)間的靜脈混合（venousadmixture）。Qsp/Qt被視為臨床評(píng)估肺部氧合功能的標(biāo)準(zhǔn)，它不會(huì)受氧氣消耗量、血紅素量或混合靜脈氧血紅素飽和度等因素所影響。第47頁/共145頁混合靜脈血效應(yīng)：動(dòng)脈血氧分壓下降供氧下降,引發(fā)循環(huán)呼吸功能的代償反應(yīng)第48頁/共145頁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頁/共145頁ShuntSubstitutesP(A-a)O2

PaO2

/

PAO2

PaO2

/

FIO2P(A-a)O2

/PaO2Shuntfraction血氧混合、下降的程度的幾個(gè)指標(biāo)第50頁/共145頁P(yáng)(A-a)O2分流：氧瀑布的一個(gè)局部第51頁/共145頁P(yáng)(A-a)O2第52頁/共145頁P(yáng)(A-a)O2第53頁/共145頁正?？諝?1%氧第54頁/共145頁第55頁/共145頁各種吸入氧濃度下的吸入氣氧分壓+肺泡二氧化碳分壓就可以得到肺泡氧分壓肺泡氧分壓PAO2第56頁/共145頁呼吸商(R)=

PACO2×VA．(PiO2-PAO2)

×VA．PACO2肺泡氣二氧化碳分壓；PiO2吸入氣氧分壓;PAO2肺泡氣氧分壓呼吸商第57頁/共145頁肺泡氣CO2分壓

0.863Vco2

PaCO2=PACO2=——————

VA

PACO2

：肺泡氣CO2分壓Vco2：每分鐘CO2

產(chǎn)量

VA

：肺泡通氣量PaCO2：動(dòng)脈血CO2分壓二氧化碳就是透第58頁/共145頁公式轉(zhuǎn)換呼吸商(R)=

PACO2×VA．(PiO2-PAO2)

×VA．PiO2-PAO2=PACO2RPAO2=PiO2-PACO2R第59頁/共145頁肺泡氣O2分壓

PACO2PAO2=PiO2——————

RPAO2

：肺泡氣O2分壓PiO2：吸入氣O2分壓PACO2

：肺泡氣CO2分壓R：呼吸商第60頁/共145頁

GaseousEnvironmentAtmosphere:NitrogenandOxygen,negligibleCarbonDioxide.

ClinicalRelevanceofEnvironmentAltitude:PO2dependsonPB低于21%Suffocation:PO2dependsonfractionalO2Oxygentherapy:PO2dependsonfractionalO2第61頁/共145頁EvaluatingFIO2流量表刻度高吸入氧濃度就高嗎？HighflowdevicesmaynotbedeliveringtheFIO2thatissetIfthepatient’stotalflowrateisexceedingtheflowfromtheoxygendeliverydevice,theFIO2willdecreaseWaterintheaerosoltubingwillincreaseFIO2Highflowoxygendeliverysystemsshouldbeanalyzed

管道流量吸入氧濃度常不精確在呼吸機(jī)上比較準(zhǔn)確濃度、流量；壓力第62頁/共145頁IdealAlveolarGasEquation.ClinicallyUsefulForm:CompleteForm:第63頁/共145頁P(yáng)AO2PAO2=[(PBARO-PH2O)xFIO2]–(PaCO2/0.8)OnFIO2oflessthan60%PAO2=[(PBARO-PH2O)xFIO2]–PaCO2OnFIO2

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

第64頁/共145頁ComparePAO2

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

—PaO2)difference

減法：差PaO2

/PAO2

ratio

除法：比第65頁/共145頁第66頁/共145頁A-aDifferencePAO2-PaO2Normally5-20mmHg

Valuesincreasewithincreasingageandthesupineposition.BecauseofnormalanatomicalshuntVentilation/PerfusionmismatchingA-adifferenceincreaseswithpulmonarydiseaseProblem:

Normalrangechangeson100%O2A：理想狀態(tài)的一腔（肺泡）模型第67頁/共145頁Inahealthyyoungperson,thePAO2–PaO2isnormally<15mmHg;thisvalueincreaseswithageandmaybe30mmHginelderlypatients.PaO2(Upright)=104.2-0.27xage(Yrs)A-agradient=2.5+0.21xageinyears年齡、體位與A-agradient

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

﹥20mmHg

NormalA-agradient=(Age+10)/4

A-aincreases5to7mmHgforevery10%

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

-vasodilators

-volatileanaesthetics6hormones

-pregnancyandprogesterone

-hepaticfailure7extrapulmonaryshuntingIncreasedA-agradientisthemostcommoncauseofarterialhypoxemia第75頁/共145頁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頁/共145頁P(yáng)aO2/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頁/共145頁(A-a)Differencevs.a/ARatio

哪個(gè)相關(guān)分流更好？NormalNormal(A-a)PO2Difference(mmHg)a/APO2ratioSickSick第78頁/共145頁P(yáng)aO2/FIO2ratio氧合指數(shù)Normalvalueis400–500

Example:100mmHg/.21=476Valuebetween200–300=ALIValuelessthan200=ARDSValueslessthan200correlatewithashuntofgreaterthan20%肺泡-動(dòng)脈氧氣壓力差動(dòng)脈-肺泡氧氣分率氧合指數(shù)（Oxygenationindex）C(a-v)O2：動(dòng)脈-靜脈氧氣含量差第79頁/共145頁P(yáng)(A-a)O2/PaO2呼吸指數(shù)（Respiratoryindex）PaO2/FIO2于1974年由Dr.Horovitz提出，因?yàn)橛?jì)算容易，且與肺內(nèi)分流（Qsp/Qt）的相關(guān)性不錯(cuò)，所以臨床應(yīng)用甚廣。P(A-a)O2因加入了吸入氧氣分率及動(dòng)脈二氧化碳?jí)毫芍笖?shù)，可以分辨出因通氣量過低導(dǎo)至二氧化碳累積而造成的氧合不良，但影響P(A-a)O2的因素很多，包括吸入氧氣分率、通氣血流灌注比不配合、肺內(nèi)分流及右向左的心內(nèi)分流，其中肺內(nèi)分流又隨著各種肺疾狀況、病患年齡及不同的體位而改變，此外P(A-a)O2也受混合靜脈氧氣含量的相關(guān)因素影響，如組織氧氣消耗量、心搏出量及血紅素量。一般P(A-a)O2對(duì)呼吸常態(tài)空氣的病患有無氧合障礙相當(dāng)敏感，但由于它與肺內(nèi)分流間的相關(guān)性不佳且受太多非肺因素影響，所以在重癥病患并不實(shí)用。PaO2/PAO2及P(A-a)O2/PaO2分別由Dr.Gilbert與Dr.Goldfarb提出。與肺內(nèi)分流作相關(guān)性分析，PaO2/FIO2、PaO2/PAO2與P(A-a)O2/PaO2三者較近似（r=0.72~0.74），P(A-a)O2則稍差（r=0.62）。第80頁/共145頁RuleOfThumb“50/50Rule”AlthoughV/Qimbalancesarethemostcommoncauseofhypoxemiainpatientswithrespiratorydiseases,physiologicshuntingalsocanoccurcommonly,hecriticallyill.IftheFi02is>50%&thePa02is<50mmHg,significantshuntingispresent.OtherwisethehypoxemiaismainlycausedbyasimpleV/Qimbalance.第81頁/共145頁Theaffinityofhemoglobinforoxygenincreaseswitheachoxygenmoleculeattached理解血紅蛋白的氧合：AllorNothing第82頁/共145頁理解血氧飽和度不是所有的血紅蛋白都結(jié)合攜帶氧第83頁/共145頁QuantityofOxygenBoundtoHemoglobinNotallhemoglobinmoleculesareboundwithoxygen.NormalsaturationArterial(SaO2)–97%Venous(SO2)–75%Some“desaturated”hemoglobinexistsbecauseofnormalphysiologicshunts:MixingofpoorlysaturatedvenousbloodwitharterialbloodThebesian,bronchial,andpleuralveinsIntrapulmonaryshunts(perfusedalveolithatarenotventilated)Hemoglobinnotboundwithoxygeniscalledreducedhemoglobin.第84頁/共145頁MixedVenousOxygenationRequiresapulmonaryarterycatheter.Assessmentofoxygensupplyvs.demandSO2:Continuousvs.SpotCheckNormal75%if↓why?if↑why?DecreasedwithincreasedO2,decreasedSaO2,decreasedHbordecreasedCO.PO2:

Averageend-capillarydrivingpressure.Usefulnessdependsondistributionofcardiacoutput.Decreasesareassociatedwithdecreasedsupplyorincreaseddemands.Increasesareassociatedwithreducedutilization

(NOTALWAYSAGOODTHING!)第85頁/共145頁氧含量：OxygenContentThetotalamountofoxygenin100mLofbloodisthesumofthedissolvedoxygen&theoxygenboundtohemoglobin.ArterialContentCaO2=(Hbx1.34xSaO2)+(PaO2x.003)VenousContentCvO2=(Hbx1.34xSvO2)+(PvO2x.003)CapillaryContentC?O2=(Hbx1.34xS?O2)+(P?O2x.003)S?O2=IdealSaturation=100%P?O2=IdealPartialPressure=PAO2第86頁/共145頁Arterial-VenousOxygenContentDifferenceC(a-v)O2CaO2–CvO2

Thevenousbloodis“mixedvenous”bloodobtainedfromthepulmonaryarteryviaapulmonaryarterycatheter.NormalCaO2:20vol%NormalCvO2:15vol%NormalCaO2–CvO2:5vol%↓Decreasedwith:IncreasedCOCertainPoisonsHypothermia第87頁/共145頁ShuntEquationClassicShuntEquation“GoldStandard”ClinicalShuntEquationAshuntgreaterthanor=15%issignificantIncreasedshuntswillcorrelatewith“Whiteoutonx-rayunlessitscardiacinorigin.Atelectasis,pneumonia,pulmonaryedema,ARDS血?dú)夥治龀鰜砹?，多算一算。?8頁/共145頁ShuntEquationSojusthowmuchbloodisshunted?

WhereC?O2=(Hbx1.34xFio2)+(PAO2*.003)YouwillneedPBARO–BarometricPressurePaO2–ArterialPartialPressureofOxygen

PaCO2–ArterialPartialPressureofCarbonDioxide

PvO2–VenousPartialPressureofOxygen

Hb–HemoglobinconcentrationPAO2–AlveolarPartialPressureofOxygen

FIO2–FractionalConcentrationofInspiredOxygen%CaO2CvO2AavAav第89頁/共145頁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頁/共145頁ClassicShuntEquationWhere:C?O2=(1.34xHbx1.0)+(PAO2x.003)Assumes100%saturationintheidealalveolusRequiresaPulmonaryArterialCatheter(BTFDC)formixedvenousblood

（V）

第91頁/共145頁第92頁/共145頁ClinicalShuntEquationRequiresaPulmonaryArterialCatheter(BTFDC)OnlyaccurateatlowerFIO2

第93頁/共145頁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頁/共145頁CvO2QTCc'O2QSCaO2QTQT

Cc'O2

-CvO2QS

Cc'O2

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

=>reducedPaO2

=>compensatoryhyperventilation

=>morethanenoughtooffsetthesmallincreaseinPaCO2

=>PaCO2oftenreducedratherthanincreasedIncreasesinPaCO2areseldomcausedbyvenousadmixture.第96頁/共145頁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頁/共145頁?Iso-shunt”diagramNunnJF.Appl.RespPhysiol.,1993

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

和Pao2

與shunt%第101頁/共145頁deadspaceAnareawithnoventilation(andthusaV/Qofzero)istermed"shunt."

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

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

NeedsPAO2,CcO2,CvO2,CaO2PaO2/FIO2(<200inARDS)Noneofthesegiveusetiologyorphysiology(shuntvs.V/Qmismatch).第103頁/共145頁AssessmentofHypoxemiaDefinitionof“Hypoxemia”.Severity?CausesofHypoxemiaDifferentialDiagnosisofHypoxemiaAbnormalityPaO2PaCO2RAP(A-a)O2100%O2P(A-a)O2Hypoventilationˉ-NNAbsoluteShuntˉNorˉ--RelativeShuntˉN,-,ˉ-NDiffusionDefectNatRest,ˉw/exerciseNorˉNatrest,-withexerciseN第104頁/共145頁HypoxemiaAnalysisStep1-3IsPACO2>40mmHg

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

Shunt

DiffusionAbnormality

V/QMismatchingNo