機械通氣的呼吸力學基礎

1、機械通氣的呼吸力學基礎,,,,,,,,,,,,,,主要內(nèi)容,臨床重要的呼吸力學指標呼吸力學指標測定的方法和意義呼吸力學曲線的分析,呼吸力學應用進展,呼吸力學監(jiān)護已成為呼吸監(jiān)護的重要內(nèi)容壓力、阻力、順應性、 auto-PEEP呼吸力學曲線監(jiān)測應用日趨廣泛提倡呼吸力學指導下的個體化通氣治療肺保護通氣策略的實施需要呼吸力學指導,,,,Volume Change,Gas Flow,Pressure Difference,自 主 呼

2、 吸,,,,,,,,,,,Volume Change,Time,Gas Flow,Pressure Difference,,機 械 通 氣,重要的呼吸力學指標,壓力 阻力 容量 峰壓力 吸氣阻力 吸氣潮氣量平臺壓力 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,,,,重要的呼吸力學指標,順應性—靜態(tài)順應性—動態(tài)順應性—呼吸系統(tǒng)順應性肺順應性（C=△V/ △P，正常肺0.2-0.3L/cmH2O）胸壁順應性（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時間積分得到容量控制壓力時阻力改變可導致容量降低控制流速時阻力增大可導致壓力增高,,,,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)測部位,流速監(jiān)測部位,床旁監(jiān)測氣道壓力的意義,峰壓力增高而平臺壓無改變 —氣道阻力增高（分泌物堵塞、氣管痙攣）峰壓力與平臺壓同時增高 —提示肺或胸壁擴張受限 明顯腹脹肺不張氣胸肺水腫、ARDS、肺炎autoPEEP人-機對抗氣道峰壓降低（管路漏氣、氣囊漏氣）,

6、肺（氣道）阻力與順應性的改變都可導致氣道壓力的改變,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),,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,壓力升高或降低都應進一步查找原因壓力增高肺或胸腔順應性下降（變硬）氣流阻力增高順應性降低和阻力增高處理原則不同,阻 力,氣道阻力的計算公式和意義,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)徑關系最大流速和氣管插管長度氦-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號氣管插管阻力為5 cmH2O/L/S7號氣管插管阻力為8 cmH2O/L/S 氣

9、管插管時氣道阻力相當于中度哮喘發(fā)作,氣道阻力的計算方法,Volume Change = Pressure Difference x Compliance of the Balloon,,,,,,,,,C =,,D V,D P,順應性,靜態(tài)順應性與動態(tài)順應性,順應性—肺的“硬度”或彈性變性能力Static—No flowdynamic—flow and resistance,肺順應性監(jiān)測的意義,靜態(tài)順應性（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態(tài)順應性（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的水平順應性的動態(tài)變化趨勢更有意義,順應性測定要求,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)分肺順應性和胸壁順應性的意義,CRS=（CL×CW）/（CL+CW）胸壁順應性相對穩(wěn)定時，CRS的動態(tài)變化可代表肺的順應性改變評價PEEP對血流動力 學的影響,Crs = Vt / dPdist (aw)Ccw = Vt / dPdist (

12、pl)CL = Vt / Pdist (aw - pl),胸壁順應性降低對跨肺壓的影響,,機械通氣時氣體分布,,,機械通氣時氣體在肺內(nèi)分布特點,自主呼吸時氣體主要進入肺的下垂區(qū)域和肺周邊胸膜下部位機械通氣時氣體主要分布在肺非下垂區(qū)和大氣道內(nèi)ARDS機械通氣時氣體主要進入非下垂區(qū)域COPD和哮喘患者除存在肺內(nèi)氣體分布不勻外，還存在較嚴重的小氣道塌陷氣流波形（方波和正弦）對氣體的分布無明顯影響,機械通氣時肺內(nèi)氣體分布,,,

13、,提倡應用自主通氣模式,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)氣流法準靜態(tài)順應性測定注意事項鎮(zhèn)靜、肌松近口端壓力和流速監(jiān)測注意干擾因素（如明顯腹脹）,PEEP對血流動力學的影響,ΔPpl=ΔPEEP[CL/（CL+CW）]正常人CL≈CW，故ΔPpl≈1/2×（ΔPEEP）相當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。當肺實變、肺順應性減小時，傳

14、遞比例減少。而胸壁順應性減小時，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。肺順應性增大（肺氣腫）或胸壁順應性減小時較低水平的PEEP就可能干擾肺毛細血管楔壓的判斷，測定值高于實際水平。,PEEP對血流動力 學的影響,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存在嚴重氣道狹窄及氣體陷閉時

16、不能反映真實的肺泡壓力，用平臺壓更準確吸氣末肺容積（VEI）食道內(nèi)壓測定,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,,,痰液栓對呼吸力學評估的影響,auto PEEP臨床跡象,不能解釋的心動過速、低血壓，特別是機械通氣治療剛開始時（由人工通氣過度為機械通氣時）患者觸發(fā)每次呼吸非常費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呼氣（喘鳴音）仍在進行壓力流速圖形顯示異常,動態(tài)過度充氣對循環(huán)功能影響,,,Air Trapping,,,Insp

18、iration,,,Expiration,,,,,Time (sec),Flow (L/min),,},,auto PEEP監(jiān)測,auto PEEP的處理,改變呼吸機參數(shù)增加呼氣時間，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，應用支氣管擴張劑）加用適當?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機械通氣時可明顯增大（延長管、濕化器）肺泡死腔肺栓塞時VD/VT可顯著增大（0.6）COPD、Asthma時V/Q比例失衡， VD/VT增大VD/VT增大將導致分鐘通氣量顯著增大,呼吸力學測定的質(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,呼吸力學是機械通氣理論的重要內(nèi)容