機(jī)械通氣的呼吸力學(xué)基礎(chǔ)(修改)課件

1、機(jī)械通氣的呼吸力學(xué)基礎(chǔ) 空軍總醫(yī)院呼吸科 張 波主要內(nèi)容重要的呼吸力學(xué)指標(biāo)呼吸力學(xué)指標(biāo)測定的方法和意義呼吸力學(xué)曲線的分析新的通氣模式What are the New AdvancementsRespiratory Mechanics Compliance, Resistance & auto-PEEP”Under the instruction of respiratory mechanics to apply individualized ventilationLung protection strategy正壓通氣與負(fù)壓通氣的比較Volume Change Gas FlowPressure

2、 Difference 自 主 呼 吸重要的呼吸力學(xué)指標(biāo)壓力 阻力 容量 峰壓力 吸氣阻力 吸氣潮氣量平臺(tái)壓力 呼氣阻力 呼氣潮氣量 平均氣道壓力 彈性阻力 可壓縮氣量胸膜腔內(nèi)壓力 呼氣末肺容積 autoPEEP重要的呼吸力學(xué)指標(biāo)順應(yīng)性靜態(tài)順應(yīng)性動(dòng)態(tài)順應(yīng)性呼吸系統(tǒng)順應(yīng)性肺順應(yīng)性（C=V/ P，正常肺0.2-0.3L/cmH2O）胸壁順應(yīng)性（C= V/ Ppl，正常0.2 L/cmH2O）流速呼吸功 P-V曲線P0.1timePressurePEEPPIPPplatAlveolar Distending (recoil) Pressure difference (Pdis)Flow-Resist

3、ive Pressure difference (Pres) Pressure componentsdP = R x Flow + dV / C st不同通氣方式下在不同部位測得壓力的含義測壓部位和通氣方式 所克服的阻力 PV曲線的斜率自主呼吸時(shí)的食道內(nèi)壓 肺吸氣和呼氣阻力 肺順應(yīng)性機(jī)械通氣時(shí)的食道內(nèi)壓 胸壁的吸氣和呼氣阻力 胸壁順應(yīng)性自主呼吸時(shí)隆突上氣管 整個(gè)呼吸裝置（氣管插管、 整個(gè)呼吸設(shè)備的順應(yīng)性 插管內(nèi)壓力 呼吸管路、呼吸機(jī)）阻力機(jī)械通氣時(shí)隆突上氣管 肺和胸壁的吸氣和呼氣阻力 呼吸系統(tǒng)的順應(yīng)性 插管內(nèi)壓力自主呼吸時(shí)氣道開口處 呼吸管路和呼吸機(jī)的吸氣和 呼吸管路的順應(yīng)性 （Y型管接口處）

4、 呼氣阻力、機(jī)械通氣時(shí)氣道開口處 肺和胸壁阻力加氣管插管阻力 呼吸系統(tǒng)順應(yīng)性流速監(jiān)測部位肺（氣道）阻力與順應(yīng)性的改變都可導(dǎo)致氣道壓力的改變通過氣道壓力的改變可以推測病變的性質(zhì)和部位 Paw (cm H2O)NormalNormal PPlat(Normal Compliance)Increased PIPIncreased PTA(increased Airway Resistance)NormalPIPPPlatHigh RawPIPPPlatIncreased Airway Resistance DECREASED COMPLIANCETime (sec)Paw (cm H2O)Low C

5、ompliancePIPPPlatNormalPIPPPlatNormal PPlat(Normal Compliance)Increased PPlat(Decreased Compliance)NormalPIPRespiratory MechanicsAs pressure rises or decreases in patients on mechanical ventilation, it is important to know whyHigh pressure can result from either stiffness of the lung/thorax or resis

6、tance to flowCauses of stiffness or resistance to flow and therefore treatment are different Resistance氣道阻力的計(jì)算公式和意義RI=（PIPPpla）/吸氣末流速RE=（PplaPEEP）/最大呼氣流速 氣管插管產(chǎn)生的阻力在總的呼吸阻力中占很大比例，與管腔內(nèi)徑關(guān)系最大，流速和氣管插管長度也對阻力有一定的影響改變吸入氣體的性質(zhì)，如氦-氧混合氣也可減低吸氣阻力，減少呼吸功。在COPD和哮喘患者采用高壓力和高流速通氣時(shí)肺泡內(nèi)壓不會(huì)有很大的升高Airway Resistance Calculatio

7、nsResistance =PIP - PlateauPeak FlowResistance = 20 - 151 L / sec= 5 cmH20 / L / secPlateau Pressure 15 cmPIP 20 cmVTE 500 ccPeak Flow = 60 L/minStatic Mechanics ConceptsMeasurements are typically displayed as compliance and resistanceCompliance - measures the stiffness of the lungStaticNo flowdynam

8、icflow and resistance肺順應(yīng)性監(jiān)測的意義靜態(tài)順應(yīng)性（Cs）反映肺和胸壁的彈性（彈性阻力）特征,排除了氣道阻力成分動(dòng)態(tài)順應(yīng)性（Cd）反映氣道的阻力（非彈性阻力）和呼吸系統(tǒng)彈性（彈性阻力）特征，氣道阻力可明顯影響Cd的水平順應(yīng)性的動(dòng)態(tài)變化趨勢更有意義Static Mechanics CalculationsCompliance = Volume Pressure orCompliance = ml cmH20Resistance = Pressure Flow orResistance = cmH20 / L / SEC 順應(yīng)性測定要求The gold standard for

9、 measuring compliance and resistance utilizes a volume breath delivered with a square wave flow and adequate plateau40PCIRCcmH2OINSPLminEXPPLOT SETUP302010 010-2080604020020-804060V.04812s2610UNFREEZECompliance Calculations 500 15-5= 50 ml/cmH20Compliance =VtePlateau - PEEPPlateau Pressure 15 cmPEEP

10、 5 cmVTE 500 ccPeak Flow = 60 L/minVTE 500 cc10 cmH20區(qū)分肺順應(yīng)性和胸壁順應(yīng)性的意義CRS=（CLCW）/（CL+CW）胸壁順應(yīng)性相對穩(wěn)定時(shí)，CRS的動(dòng)態(tài)變化可代表肺的順應(yīng)性改變評(píng)價(jià)PEEP對血流動(dòng)力 學(xué)的影響Crs = Vt / dPdist (aw)Ccw = Vt / dPdist (pl)CL = Vt / Pdist (aw - pl)機(jī)械通氣時(shí)氣體分布 機(jī)械通氣時(shí)氣體在肺內(nèi)分布特點(diǎn)自主呼吸時(shí)吸入氣體主要進(jìn)入肺的下垂區(qū)域和肺周邊胸膜下部位機(jī)械通氣時(shí)氣體主要分布在肺非下垂區(qū)和大氣道內(nèi)在ARDS時(shí)，病變分布以雙側(cè)肺下垂區(qū)域?yàn)橹?，機(jī)械通氣

11、時(shí)氣體主要進(jìn)入非下垂區(qū)域COPD和哮喘患者除存在肺內(nèi)氣體分布不勻外，還存在較嚴(yán)重的小氣道塌陷氣流的波形（方波和正弦、加速波和減速波）對氣體的分布無明顯影響 機(jī)械通氣時(shí)肺內(nèi)氣體分布MVexpinspSBexpinspFroese, Bryan 1974Pleural pressure-13 cm H2O+4 cm H2O-2 cm H2O-10 cm H2OMVSBRoussos et al 1976Relaxed diapragmTensed diapragm提倡應(yīng)用自主通氣模式壓力-容積曲線P-V曲線的測定方法大注射器法吸氣阻斷法持續(xù)氣流法準(zhǔn)靜態(tài)順應(yīng)性測定注意事項(xiàng)鎮(zhèn)靜、肌松近口端壓力和流速監(jiān)

12、測注意干擾因素（如明顯腹脹）大注射器法費(fèi)時(shí)、費(fèi)力需脫開呼吸機(jī)安全性差不易標(biāo)準(zhǔn)化很少應(yīng)用VolumePressure持續(xù)氣流法Slow (5-10 lpm) inspiratory flow with large Vt and ZEEP The inspiratory curve of the dynamic P-V loop closely approximates the static curve The flow-resistive pressure component could be subtractedEasy to perform, fast and relatively comf

13、ortablePressureVolumeLPIflexUPIflexinspirationStatic curveUpper And Lower Inflection Points02040602040-600.2LITERS0.40.6PawcmH2OVTUpper And Lower Inflection Points02040602040-600.2LITERS0.40.6PawcmH2OVTAlveolar overdisentionAlveolar collapsePTUpper And Lower Inflection Points02040602040-600.2LITERS0

14、.40.6PawcmH2OVTAlveolar collapsePTLower inflection points are thought to be a point of critical opening pressurePEEP對血流動(dòng)力 學(xué)的影響Ppl=PEEPCL/（CL+CW）正常人CLCW，故Ppl1/2（PEEP）相當(dāng)于大約一半的胸腔內(nèi)壓（PEEP 或PEEPi）傳遞到胸膜腔，引起胸內(nèi)壓增高。當(dāng)肺實(shí)變、肺順應(yīng)性減小時(shí)，傳遞比例減少。而胸壁順應(yīng)性減小時(shí)，氣道內(nèi)壓力向胸膜腔內(nèi)傳遞增加。ARDSPEEP水平在15cmH2O以下，可不必考慮對PCWP讀數(shù)的影響。肺順應(yīng)性增大（肺氣腫）或胸

15、壁順應(yīng)性減小時(shí)較低水平的PEEP就可能干擾肺毛細(xì)血管楔壓的判斷，測定值高于實(shí)際水平。PEEP對血流動(dòng)力 學(xué)的影響Compensation of the PCWP for PEEP:Compliant lungs corrected PCWP = PCWP - PEEP (mm Hg)Noncompliant lungs corrected PCWP = PCWP - 1/4 PEEP (mm Hg)PEEP (cm H2O) /1.36 = PEEP (mm Hg)Auto-PEEP檢查方法呼氣末阻斷氣流法當(dāng)存在嚴(yán)重氣道狹窄及氣體陷閉時(shí)不能反映真實(shí)的肺泡壓力，用平臺(tái)壓更準(zhǔn)確吸氣末肺容積（VEI

16、）食道內(nèi)壓測定Auto-PEEP ManeuverPress Exp Pause key to schedule automatic expiratory pause maneuverDuring the next exhalation, the inspiratory and expiratory valves will close and pressure will equilibrate between the circuit and the patient PTEnd Exp Holdauto PEEP臨床跡象不能解釋的心動(dòng)過速、低血壓，特別是機(jī)械通氣治療剛開始時(shí)（由人工通氣過度為機(jī)械

17、通氣時(shí)）患者觸發(fā)每次呼吸非常費(fèi)力患者的吸氣努力并非每次都能觸發(fā)呼吸下一次吸氣開始時(shí)呼氣（喘鳴音）仍在進(jìn)行壓力流速圖形顯示異常Air TrappingInspirationExpirationNormalPatientTime (sec)Flow (L/min)Air TrappingAuto-PEEPauto PEEP監(jiān)測auto PEEP的處理改變呼吸機(jī)參數(shù)增加呼氣時(shí)間，減少通氣頻率，減少潮氣量降低病人的通氣需要減少碳水化合物的攝取，減少死腔通氣，治療焦慮、寒戰(zhàn)、疼痛、發(fā)熱減低呼吸道阻力（用大口徑的氣管插管，經(jīng)常吸痰避免分泌物潴留，應(yīng)用支氣管擴(kuò)張劑）加用適當(dāng)?shù)耐庠葱訮EEP，一般為PEEPi

18、的75%左右死腔通氣問題解剖死腔正常人100-150ml機(jī)械通氣時(shí)可明顯增大（延長管、濕化器）肺泡死腔肺栓塞時(shí)VD/VT可顯著增大（0.6）COPD、Asthma時(shí)V/Q比例失衡， VD/VT增大VD/VT增大將導(dǎo)致分鐘通氣量顯著增大呼吸力學(xué)測定的質(zhì)量控制No significant leaksCompliance should subtract out circuit compliance, especially in pediatricsManual calculations often contribute to errorsRespiratory Mechanics Requireme

19、nts For AccuracyThe patient must be at rest during peak and plateau pressure measurementsAdding plateau should not restrict exhalation and create auto-PEEPPlateau time must not be too short or too long Patient Effort During Inspiratory Plateau PTDiaphragm EffortsPlateau Pressure = ?Plateau Time Too

20、Short 500 20-5= 33 ml / cmH20 500 15 - 5= 50 ml / cmH20Results in falsely low compliance values !Displayed Plateau Pressure 20 cmPEEP 5 cmActual Plateau Pressure 15 cm VTE 500 ccPTInsufficient Exhalation Time(Auto-PEEP) 500 20-10= 50 ml / cmH20 500 20 - 5= 33 ml / cmH20Results in falsely low complia

21、nce values !VTE 500 ccPTPlateau = 20PEEP = 5Lung PEEP = 10Static Compliance Leaks and/or Too Long a Plateau 500 15-5= 50 ml / cmH20 500 10 - 5= 100 ml / cmH20Results in falsely high compliance values !Displayed Plateau Pressure 10 cmPEEP 5 cmActual Plateau Pressure 15 cm VTE 500 ccPTAir LeakVolume (

22、ml)Time (sec)Air LeakAir LeakVolume (ml)Pressure (cm H2O)Air LeakAir LeakInspirationExpirationVolume (ml)Flow (L/min)Air Leak in mLNormalAbnormalResponse to BronchodilatorBeforeTime (sec)Flow (L/min)PEFRAfterLong TEHigher PEFRShorter TEInadequate Inspiratory Flow Adequate FlowTime (sec)Inadequate Fl

23、owPaw (cm H2O)Inadequate Inspiratory FlowFlow (L/min)Time (sec)NormalAbnormalActive Inspiration or AsynchronyPatients effortFlow versus TimeACCELERATINGDECELERATINGSINESQUARELung Compliance Changes and the P-V LoopVolume (mL)Preset PIPVT levelsPaw (cm H2O)COMPLIANCEIncreasedNormalDecreasedPressure T

24、argeted VentilationOptimising PEEPVPPEEP: 3 cmH2OVPPEEP: 8 cmH2OVolume vs TimeInspirationExpirationTime (sec)Volume (ml)Inspiratory Tidal VolumeTI呼氣阻力增加Prolonged expiratory flow indicates an obstruction to exhalation and may be caused by obstruction of a large airway, bronchospasm, or expiratory val

25、ve failure of the ventilatorTimeFlow吸氣時(shí)間過短Spontaneous inspiration is easy but exp is impededLonger I-times may cause asynchrony123456SEC123456PawcmH2060-20120120SECVL/min.Attempts to ExhaleInsufficient Expiratory TimeExpiratory flow is unable to return to baseline prior to the initiation of the next mechanical breathIncomplete exhalation causes gas trapping, dynamic hyper-expansion and the development of intrinsic PEEPTimeFlowEnd-Expir