機(jī)械通氣的呼吸力學(xué)基礎(chǔ)

1、機(jī)械通氣的呼吸力學(xué)基礎(chǔ),,,,,,,,,,,,,,主要內(nèi)容,臨床重要的呼吸力學(xué)指標(biāo)呼吸力學(xué)指標(biāo)測(cè)定的方法和意義呼吸力學(xué)曲線的分析,呼吸力學(xué)應(yīng)用進(jìn)展,呼吸力學(xué)監(jiān)護(hù)已成為呼吸監(jiān)護(hù)的重要內(nèi)容壓力、阻力、順應(yīng)性、 auto-PEEP呼吸力學(xué)曲線監(jiān)測(cè)應(yīng)用日趨廣泛提倡呼吸力學(xué)指導(dǎo)下的個(gè)體化通氣治療肺保護(hù)通氣策略的實(shí)施需要呼吸力學(xué)指導(dǎo),,,,Volume Change,Gas Flow,Pressure Difference,自 主 呼

2、 吸,,,,,,,,,,,Volume Change,Time,Gas Flow,Pressure Difference,,機(jī) 械 通 氣,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

3、 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—?jiǎng)討B(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

4、）流速呼吸功 P-V曲線P0.1,呼吸力學(xué)三要素,壓力（P）、阻力（R）、流速（V）ΔP= R×V壓力和流速為可控因素流速對(duì)時(shí)間積分得到容量控制壓力時(shí)阻力改變可導(dǎo)致容量降低控制流速時(shí)阻力增大可導(dǎo)致壓力增高,,,,time,Pressure,,,,PEEP,PIP,Pplat,,,Alveolar Distending (recoil) Pressure difference (Pdis),Flow-Resi

5、stive Pressure difference (Pres),壓力組成,dP = R x Flow + dV / C st,壓力監(jiān)測(cè)部位,流速監(jiān)測(cè)部位,床旁監(jiān)測(cè)氣道壓力的意義,峰壓力增高而平臺(tái)壓無改變 —?dú)獾雷枇υ龈撸ǚ置谖锒氯?、氣管痙攣）峰壓力與平臺(tái)壓同時(shí)增高 —提示肺或胸壁擴(kuò)張受限 明顯腹脹肺不張氣胸肺水腫、ARDS、肺炎autoPEEP人-機(jī)對(duì)抗氣道峰壓降低（管路漏氣、氣囊漏氣）,

6、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(cè)病變的性質(zhì)和部位,,,,,Paw (cm H2O),,Normal PPlat(Normal Compliance),Increased PIP,},,Increased PTA(increased Airway Resistance),Increased Airway Resistance,,,,,DECREASED COMPLIANCE,,,,,

7、,,Time (sec),Paw (cm H2O),,Normal PPlat(Normal Compliance),Increased PPlat(Decreased Compliance),,Normal,,PIP,小結(jié),壓力升高或降低都應(yīng)進(jìn)一步查找原因壓力增高肺或胸腔順應(yīng)性下降（變硬）氣流阻力增高順應(yīng)性降低和阻力增高處理原則不同,阻 力,氣道阻力的計(jì)算公式和意義,RI=（PIP—Ppla）/吸氣末流速RE=（

8、Ppla—PEEP）/最大呼氣流速 氣管插管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(zhǎng)度氦-氧混合氣也可減低吸氣阻力，減少呼吸功,氣道阻力,大氣道以湍流為主，占總阻力的80%小氣道以層流為主，占總阻力的20%正常人氣道阻力為1cmH2O/L/S哮喘和COPD患者氣道阻力為5-10cmH2O/L/S8號(hào)氣管插管阻力為5 cmH2O/L/S7號(hào)氣管插管阻力為8 cmH2O/L/S 氣

9、管插管時(shí)氣道阻力相當(dāng)于中度哮喘發(fā)作,氣道阻力的計(jì)算方法,Volume Change = Pressure Difference x Compliance of the Balloon,,,,,,,,,C =,,D V,D P,順應(yīng)性,靜態(tài)順應(yīng)性與動(dòng)態(tài)順應(yīng)性,順應(yīng)性—肺的“硬度”或彈性變性能力Static—No flowdynamic—flow and resistance,肺順應(yīng)性監(jiān)測(cè)的意義,靜態(tài)順應(yīng)性（Cs）

10、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(shì)更有意義,順應(yīng)性測(cè)定要求,The gold standard for measuring compliance and resistance utilizes a volume breath delivered with a square wave f

11、low and adequate plateau,,,,,,,,,,,,,,,Compliance Calculations,VTE 500 cc,10 cmH20,,,,區(qū)分肺順應(yīng)性和胸壁順應(yīng)性的意義,CRS=（CL×CW）/（CL+CW）胸壁順應(yīng)性相對(duì)穩(wěn)定時(shí)，CRS的動(dòng)態(tài)變化可代表肺的順應(yīng)性改變?cè)u(píng)價(jià)PEEP對(duì)血流動(dòng)力 學(xué)的影響,Crs = Vt / dPdist (aw)Ccw = Vt / dPdist (

12、pl)CL = Vt / Pdist (aw - pl),胸壁順應(yīng)性降低對(duì)跨肺壓的影響,,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)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)ARDS機(jī)械通氣時(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波形（方波和正弦）對(duì)氣體的分布無明顯影響,機(jī)械通氣時(shí)肺內(nèi)氣體分布,,,

13、,提倡應(yīng)用自主通氣模式,壓力-容積曲線,,,P-V曲線的測(cè)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(cè)定注意事項(xiàng)鎮(zhèn)靜、肌松近口端壓力和流速監(jiān)測(cè)注意干擾因素（如明顯腹脹）,PEEP對(duì)血流動(dòng)力學(xué)的影響,ΔPpl=ΔPEEP[CL/（CL+CW）]正常人CL≈CW，故ΔPpl≈1/2×（ΔPEEP）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

14、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(duì)PCWP讀數(shù)的影響。肺順應(yīng)性增大（肺氣腫）或胸壁順應(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(cè)定值高于實(shí)際水平。,PEEP對(duì)血流動(dòng)力 學(xué)的影響,Compensation of the PCWP for PEEP:Compliant lungs corrected PCWP = PCWP - 

15、9; PEEP (mm Hg)Noncompliant lungs corrected PCWP = PCWP - 1/4 PEEP (mm Hg)PEEP (cm H2O) /1.36 = PEEP (mm Hg),,,,,,Low VT vs High VT,,Low PEEP vs High PEEP,,HFOV,,Prone,,Protective,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)

16、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）食道內(nèi)壓測(cè)定,Auto-PEEP Maneuver,Press Exp Pause key to schedule automatic expiratory pause maneuverDuring the next exhalation, the inspiratory and expiratory valves will close and pressure wil

17、l equilibrate between the circuit and the patient,,,痰液栓對(duì)呼吸力學(xué)評(píng)估的影響,auto 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,動(dòng)態(tài)過度充氣對(duì)循環(huán)功能影響,,,Air Trapping,,,Insp

18、iration,,,Expiration,,,,,Time (sec),Flow (L/min),,},,auto PEEP監(jiān)測(cè),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的75%左右,外源

19、性PEEP改善觸發(fā)的機(jī)理,,重癥哮喘患者外源性PEEP的影響,,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(zhǎng)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(cè)定的質(zhì)量控制,No significant leaksCompliance should subtract out circ

20、uit compliance, especially in pediatricsManual calculations often contribute to errors,Respiratory Mechanics Requirements For Accuracy,The patient must be at rest during peak and plateau pressure measurementsAdding p

21、lateau should not restrict exhalation and create auto-PEEPPlateau time must not be too short or too long,Patient Effort During Inspiratory Plateau,,Plateau Pressure = ??,Plateau Time Too Short,Results in falsely low c

22、ompliance values !,Static Compliance Leaks and/or Too Long a Plateau,Results in falsely high compliance values !,,Air Leak,,,,Volume (ml),Time (sec),,,,,Air Leak,,,,Volume (ml),Pressure (cm H2O),,Air Leak,,Air Leak,Insp

23、iration,Expiration,,,,Volume (ml),Flow (L/min),,,Air Leak in mL,NormalAbnormal,,Response to Bronchodilator,,,Before,Time (sec),Flow (L/min),,,,,PEFR,After,,,,,Long TE,Higher PEFR,Shorter TE,Inadequate Inspiratory Flow,

24、,,Adequate Flow,Time (sec),Inadequate Flow,Paw (cm H2O),,,,,Inadequate Inspiratory Flow,Flow (L/min),Time (sec),,,,,NormalAbnormal,Active Inspiration or Asynchrony,,,,Flow versus Time,,,,,,,,,,,,,,,ACCELERATING,DECEL

25、ERATING,SINE,SQUARE,,Lung Compliance Changes and the P-V Loop,Volume (mL),,,Preset PIP,VT levels,Paw (cm H2O),,,COMPLIANCEIncreasedNormalDecreased,,Pressure Targeted Ventilation,,,,,,,,,V,P,,,V,P,,,,,,Optimising PEEP

26、,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 valve failure of the ventilator,,,Time,Flow,,,,,Insufficient Expira

27、tory Time,Expiratory 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 PEEP,,,T

28、ime,Flow,,,,,,,End-Expiratory Flow,,,,,,F,V,,,,V,F,Airway Obstruction,Pressure-Volume Loop,,,,,,,,,,,,,,Controlled,Assisted,Spontaneous,Vol (ml),Paw (cm H2O),I: InspirationE: Expiration,I,E,E,E,I,I,,總結(jié),呼吸力學(xué)是機(jī)械通氣理論的重要內(nèi)容