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1、氧供需平衡氧供需平衡 Balance of Oxygen Supply and Demand 四川大學(xué)華西醫(yī)院四川大學(xué)華西醫(yī)院 麻醉科麻醉科 魏蔚魏蔚 氧輸送氧輸送 oxygen transport (O2T) 外呼吸外呼吸 血液血液 循環(huán)循環(huán) 組織組織 肺 通氣 肺換氣 氧在血液中的運(yùn)輸 氧在組織中釋放 氧瀑布氧瀑布 O2 Cascade 氧從空氣進(jìn)入細(xì)胞的線粒體內(nèi)要經(jīng)歷一系 列過程，包括：肺通氣、肺換氣、氧在血液中 的運(yùn)輸及氧在組織的釋放四個(gè)步驟。也有學(xué)者 把氧運(yùn)輸過程中，從空氣中氧分壓 159mmHg 至細(xì)胞內(nèi)的 34mmHg的巨大落差形象地稱為 氧瀑布。 空氣空氣 上呼吸道上呼吸道 飽

2、和蒸汽壓 =47mmHg PiO2=(760-47)0.2094=149mmHg 肺泡肺泡 v二氧化碳 - PACO2, 約等于 PaCO2. vPAO2 = PIO2 PaCO2/R. - R 為呼吸商 . - R 0.8. - PAO2 = 149 (40/0.8) = 100mmHg 動(dòng)脈血?jiǎng)用}血 w 氧從肺泡進(jìn)入肺靜脈氧分壓通常下降 5 10 mmHg. PAO2=95mmHg 毛細(xì)血管毛細(xì)血管 靜脈血靜脈血 w 毛細(xì)血管和組織間液間的較大的氧分壓差 （ 30 mmHg） 使得氧氣迅速由血液向組 織彌散 。 Summary The factors influence transport

3、 of oxygen w Cardiac output w Blood oxygen content (CaO2) w The affinity of hemoglobin for oxygen 外呼吸外呼吸 血液血液 循環(huán)循環(huán) 組織組織 血紅蛋白與氧的結(jié)合量血紅蛋白與氧的結(jié)合量 w 1g 血紅蛋白最多可結(jié)合 1.34ml的氧氣。 (1.39ml when the hemoglobin is chemically pure) w 如果 Hb=15g/100ml, 最大結(jié)合的氧量 =15*1.34=20.1ml/100ml 在組織內(nèi)釋放的氧量在組織內(nèi)釋放的氧量 w 動(dòng)脈血 : SaO2=97%,

4、 CaO2=19.4ml/100ml w 混合靜脈血 : PvO2=40mmHg, SvO2=75% CvO2=14.4ml/1 00ml w C(a-v)O2=19.4-14.4=5ml/100ml 攝氧率攝氧率 （ utilization coefficient/oxygen extraction） w The percentage of the blood that gives up its oxygen as it passes through the tissue capillaries is called the utilization coefficient. -normal v

5、alue is about 25%. -during exercise, can increase to 7585%. Physiological supply dependency The normal relationship is for a 4:1 ratio between DO2 and VO2. or in CO and DO2 do not affect oxygen consumption. Pathological supply dependency w Relationship between DO2 and VO2 seen in critically ill pati

6、ents, when increases in CO or increases in oxygen delivery, result in parallel increases in VO2. 氧氧 -血紅蛋白解離曲線血紅蛋白解離曲線 Effects on Oxygen-Hemoglobin Dissociation Curve PaO2 700 90-100 60 40 26.7 SaO2 100 95-98 90 75 50 The causes of a left-shifted oxy-Hb curve (P5027mmHg) Increased hydrogen ions Incre

7、ased CO2 Increased temperature Increased 2,3-diphosphoglycerate (DPG) 氧供氧供 Oxygen delivery DO2 w DO2 是每分鐘供給機(jī)體的氧量。 w DO2=(0.0031PaO2+1.34HbSaO2)CO w DO2=1.34HbSaO2CO 如果 CO=5L,Hb=15g， DO2=1.3415015=1005ml/L 氧耗氧耗 Oxygen consumption (VO2) w Oxygen consumption is the actual amount of oxygen consumed per

8、minute. VO2=CO(CaO2 -CvO2)(ml/min) 正常情況下， 200250ml/min. . 氧需氧需 Oxygen demand wOxygen demand is the actual amount of oxygen needed per minute. -is closely related to the oxygen consumption; -Under some conditions, demand may exceed consumption. 氧供需失衡時(shí)機(jī)體的代償機(jī)制氧供需失衡時(shí)機(jī)體的代償機(jī)制 wCO. w 血流再分布 . w 細(xì)胞攝氧率 . Moni

9、toring? 理想部位：線粒體 難點(diǎn)：細(xì)胞內(nèi)的氧合狀況無法直接監(jiān)測(cè) 思路：對(duì)氧輸送過程進(jìn)行監(jiān)測(cè) 測(cè)定 Hct及 Hb的方法 全血細(xì)胞分析儀 - Hct、 Hb 血?dú)夥治鰞x Hct、 Hb 血紅蛋白分光光度儀 - Hb 離心機(jī) Hct SpO2 monitored by Pulse oximetry since 1980 SO2=O2Hb/(O2Hb+HHb)(%) If R940/R660=1, SO2=85% Transcutaneous SpO2 monitoring Two types oximetry: 反射式脈搏氧飽和度探頭 The esophageal probe (ESOX,

10、ARISTO Medical, Chicago, IL) Blood gas tension measurement wOxygen pressure (PO2) PO2 is to measure directly from a blood sample, usually by using a Clark electrode. w Carbon dioxide pressure (PCO2) PCO2 electrodes work by measuring the change in pH induced when blood equilibrates with a potassium c

11、hloride/sodium bicarbonate solution. Mixed venous blood oxygen saturation (SvO2) SvO2 monitoring 連續(xù)頸內(nèi)靜脈血氧飽和度監(jiān)測(cè) 經(jīng)氣管混合靜脈血氧飽和度監(jiān)測(cè) 術(shù)中常用的 CO監(jiān)測(cè)方法 w 右心飄浮導(dǎo)管 wPicco w(外周動(dòng)脈 ) FloTrac 傳感器 wTEE 由動(dòng)脈壓力波形計(jì)算 CO CO = HR * Sd(AP) * PiCCO w Using PiCCO typically requires insertion of a thermodilution catheter in the fe

12、moral or axillary artery instead of a standard arterial line. Any available central venous catheter can be used to inject the solution for the thermodilution analysis. 術(shù)中 TEE測(cè)量 CO wM型法 短 軸縮 短率： FAC=(EDA-ESA)/EDA ; 自動(dòng)邊緣識(shí)別系統(tǒng)（ ABD） w 二維 Simpson法 SV=LVEDV-LVSDV w 多譜勒法 SV=時(shí)間速度積分 X橫截面積 w 三維法 Calculation o

13、f the “shunt fraction“ w Qt = total cardiac output w Qs = shunted portion of cardiac output w Qns = normal pulmonary end-capillary blood flow that is not shunted past abnormal alveoli w Qt = Qs + Qns w or Qns = Qt - Qs Calculation of the “shunt fraction“ w Qt (CaO2) = total oxygen delivered to the b

14、ody (DO2) w Qs (CvO2) = oxygen content of shunted blood w Qns (CcO2) = oxygen content of end-capillary blood Total oxygen delivered equals the sum of oxygen in both shunted and non-shunted blood w Qt (CaO2) = Qs (CvO2) + Qns (CcO2) Calculation of the “shunt fraction“ Substituting (Qt - Qs) for Qns w

15、 Qt (CaO2) = Qs (CvO2) + (Qt - Qs)(CcO2) w Qt (CaO2) = Qs (CvO2) + Qt (CcO2) - Qs (CcO2) w Qs (CcO2 - CvO2) = Qt (CcO2 - CaO2) The intrapulmonary shunt equation w Qs/Qt = CcO2 - CaO2 /CcO2 - CvO2 氧供需平衡的監(jiān)測(cè)氧供需平衡的監(jiān)測(cè) w SvO2 60%80% w Oxygen extraction ratio (O2ER) O2ER=(CaO2-CvO2)/CaO2 w Lactic acid 7.32

16、 w Gastric tonometry determines intraluminal PCO2 which is assumed to be in equilibrium with PCO2 in the gastric mucosa. Intramucosal pH (pHim) can be calculated by the Henderson- Hasselbach equation using the PCO2 value determined by gastric tonometry and the bicarbonate concentration in arterial b

17、lood. oBaigorri et al. Critical Care 1997 1:61 doi:10.1186/cc104 決定 DO2與 VO2的因素 DO2 VO2 Hb SaO2 CO SvO2 Hb CO SaO2. 術(shù)中影響氧供的因素 DO 2 CO/Hb 100% 50% 25% 缺氧 w 低氧血 癥： PaO260mmHg w 缺氧類型 Hypotonic anoxia Anemic anoxia Circulatory anoxia Histogenous anoxia 外呼吸外呼吸 血液血液 循環(huán)循環(huán) 組織組織 氧治療 wControlled oxygen treatm

18、ent is used in those who need supplemental oxygen but not rely on their hypoxic drive to continue breathing. -an increase in PaCO2 show they rely on hypoxic drive. The rules of oxygen treatment (1) Give oxygen as much as you can at first, and then reduce it, guided by blood gas measurements. (2) Oxy

19、gen treatment will work only if the patient has a patent airway and is breathing. (3) Definitive treatment of hypoxia depends on the underlying cause. Giving oxygen is a holding measure. Oxygen therapy PaO260mmHg Complications wCO2 wAbsorption atelectasis wOxygen intoxication 請(qǐng)討論 w 術(shù)中監(jiān)測(cè)氧供和氧耗的指標(biāo)？ w 術(shù)中引起氧供下降的因素？ w 根椐氧供與氧耗的相關(guān)知識(shí)，試推一下肺 內(nèi)分流率的計(jì)算公式。