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1、氧供需平衡Balance of Oxygen Supply and Demand,四川大学华西医院 麻醉科魏蔚,氧输送 oxygen transport (O2T),肺通气肺换气氧在血液中的运输氧在组织中释放,氧瀑布 O2 Cascade,氧从空气进入细胞的线粒体内要经历一系列过程，包括：肺通气、肺换气、氧在血液中的运输及氧在组织的释放四个步骤。也有学者把氧运输过程中，从空气中氧分压159mmHg 至细胞内的34mmHg的巨大落差形象地称为氧瀑布。,空气 上呼吸道,饱和蒸汽压=47mmHgPiO2=(760-47)0.2094=149mmHg, 肺泡,二氧化碳 - PACO2, 约等于 PaC
2、O2.PAO2 = PIO2 PaCO2/R.- R 为呼吸商.- R 0.8.- PAO2 = 149 (40/0.8) = 100mmHg,动脉血,氧从肺泡进入肺静脉氧分压通常下降 5 10 mmHg. PAO2=95mmHg, 毛细血管 静脉血,毛细血管和组织间液间的较大的氧分压差（ 30 mmHg）使得氧气迅速由血液向组织弥散。,Summary,The factors influence transport of oxygen,Cardiac output Blood oxygen content (CaO2)The affinity of hemoglobin for oxygen,
3、血红蛋白与氧的结合量,1g 血红蛋白最多可结合1.34ml的氧气。 (1.39ml when the hemoglobin is chemically pure)如果 Hb=15g/100ml, 最大结合的氧量 =15*1.34=20.1ml/100ml,在组织内释放的氧量,动脉血: SaO2=97%, CaO2=19.4ml/100ml混合静脉血: PvO2=40mmHg, SvO2=75% CvO2=14.4ml/100mlC(a-v)O2=19.4-14.4=5ml/100ml,摄氧率（utilization coefficient/oxygen extraction）,The perc
4、entage of the blood that gives up its oxygen as it passes through the tissue capillaries is called the utilization coefficient.-normal value 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
5、and DO2 do not affect oxygen consumption.,Pathological supply dependency,Relationship between DO2 and VO2 seen in critically ill patients, when increases in CO or increases in oxygen delivery, result in parallel increases in VO2.,氧-血红蛋白解离曲线,Effects on Oxygen-Hemoglobin Dissociation Curve,The causes
6、of a left-shifted oxy-Hb curve(P5027mmHg),Alkalosis the Bohr effectHypothermiaAbnormal and fetal HbCarboxyhemoglobin, MethemoglobinDecreased 2,3-diphosphoglycerate,The causes of a right-shifted oxy-Hb curve (P5027mmHg),Increased hydrogen ionsIncreased CO2Increased temperatureIncreased 2,3-diphosphog
7、lycerate (DPG),氧供Oxygen delivery DO2,DO2 是每分钟供给机体的氧量。 DO2=(0.0031PaO2+1.34HbSaO2)CODO2=1.34HbSaO2CO如果CO=5L,Hb=15g，DO2=1.3415015=1005ml/L,氧耗Oxygen consumption (VO2),Oxygen consumption is the actual amount of oxygen consumed per minute. VO2=CO(CaO2-CvO2)(ml/min) 正常情况下， 200250ml/min.,.,氧需Oxygen demand,
8、Oxygen demand is the actual amount of oxygen needed per minute.-is closely related to the oxygen consumption;-Under some conditions, demand may exceed consumption.,氧供需失衡时机体的代偿机制,CO.血流再分布.细胞摄氧率.,Monitoring?,理想部位：线粒体难点：细胞内的氧合状况无法直接监测思路：对氧输送过程进行监测,测定Hct及Hb的方法,全血细胞分析仪- Hct、Hb血气分析仪 Hct、Hb血红蛋白分光光度仪- Hb离心机
9、Hct,SpO2 monitored by Pulse oximetry since 1980 SO2=O2Hb/(O2Hb+HHb)(%),If R940/R660=1, SO2=85%,Transcutaneous SpO2 monitoring,Two types oximetry:,反射式脉搏氧饱和度探头,The esophageal probe (ESOX, ARISTO Medical, Chicago, IL),Blood gas tension measurement,Oxygen pressure (PO2) PO2 is to measure directly from a
10、 blood sample, usually by using a Clark electrode.Carbon dioxide pressure (PCO2) PCO2 electrodes work by measuring the change in pH induced when blood equilibrates with a potassium chloride/sodium bicarbonate solution.,Mixed venous blood oxygen saturation (SvO2),SvO2 monitoring,连续颈内静脉血氧饱和度监测,经气管混合静脉
11、血氧饱和度监测,术中常用的CO监测方法,右心飘浮导管Picco(外周动脉) FloTrac 传感器TEE,由动脉压力波形计算CO,CO = HR * Sd(AP) * ,PiCCO,Using PiCCO typically requires insertion of a thermodilution catheter in the femoral or axillary artery instead of a standard arterial line. Any available central venous catheter can be used to inject the solu
12、tion for the thermodilution analysis.,术中TEE测量CO,M型法短轴缩短率： FAC=(EDA-ESA)/EDA ; 自动边缘识别系统（ABD）二维Simpson法 SV=LVEDV-LVSDV 多谱勒法 SV=时间速度积分X横截面积 三维法,Calculation of the shunt fraction,Qt = total cardiac output Qs = shunted portion of cardiac output Qns = normal pulmonary end-capillary blood flow that is not
13、shunted past abnormal alveoli Qt = Qs + Qns or Qns = Qt - Qs,Calculation of the shunt fraction,Qt (CaO2) = total oxygen delivered to the body (DO2) Qs (CvO2) = oxygen content of shunted blood Qns (CcO2) = oxygen content of end-capillary blood Total oxygen delivered equals the sum of oxygen in both s
14、hunted and non-shunted blood Qt (CaO2) = Qs (CvO2) + Qns (CcO2),Calculation of the shunt fraction,Substituting (Qt - Qs) for QnsQt (CaO2) = Qs (CvO2) + (Qt - Qs)(CcO2) Qt (CaO2) = Qs (CvO2) + Qt (CcO2) - Qs (CcO2) Qs (CcO2 - CvO2) = Qt (CcO2 - CaO2) The intrapulmonary shunt equationQs/Qt = CcO2 - Ca
15、O2 /CcO2 - CvO2,氧供需平衡的监测,SvO2 60%80%Oxygen extraction ratio (O2ER) O2ER=(CaO2-CvO2)/CaO2Lactic acid 7.32,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
16、 using the PCO2 value determined by gastric tonometry and the bicarbonate concentration in arterial blood.,Baigorri et al. Critical Care 2019 1:61 doi:10.1186/cc104,决定DO2与VO2的因素,DO2,VO2,Hb,SaO2,CO,SvO2,Hb,CO,SaO2,.,术中影响氧供的因素,DO2,CO/Hb,100%,50%,25%,缺氧,低氧血症：PaO260mmHg缺氧类型Hypotonic anoxiaAnemic anoxiaC
17、irculatory anoxiaHistogenous anoxia,氧治疗,Controlled oxygen treatment 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
18、, and then reduce it, guided by blood gas measurements.(2) Oxygen 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,Venturi mask. The colour of the masks aperture reflects the FiO2 achieved (24%: blue; 28%: white; 35%: yellow;40%: red; 60%: green),Complications,CO2 Absorption atelectasisOxygen intoxication,请讨论,术中监测氧供和氧耗的指标？术中引起氧供下降的因素？根椐氧供与氧耗的相关知识，试推一下肺内分流率的计算公式。,
