氧供需平衡麻醉课件

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1、氧供需平衡氧供需平衡 Balance of Oxygen Supply and Demand 四川大学华西医院四川大学华西医院 麻醉科麻醉科 魏蔚魏蔚 氧输送氧输送 oxygen transport (O2T) 外呼吸外呼吸 血液血液 循环循环 组织组织 肺 通气 肺换气 氧在血液中的运输 氧在组织中释放 氧瀑布氧瀑布 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。 空气空气 上呼吸道上呼吸道 饱

2、和蒸汽压 =47mmHg PiO2=(760-47)0.2094=149mmHg 肺泡肺泡 v二氧化碳 - PACO2, 约等于 PaCO2. vPAO2 = PIO2 PaCO2/R. - R 为呼吸商 . - R 0.8. - PAO2 = 149 (40/0.8) = 100mmHg 动脉血动脉血 w 氧从肺泡进入肺静脉氧分压通常下降 5 10 mmHg. PAO2=95mmHg 毛细血管毛细血管 静脉血静脉血 w 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

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 循环循环 组织组织 血红蛋白与氧的结合量血红蛋白与氧的结合量 w 1g 血红蛋白最多可结合 1.34ml的氧气。 (1.39ml when the hemoglobin is chemically pure) w 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在组织内释放的氧量 w 动脉血 : SaO2=97%,

4、 CaO2=19.4ml/100ml w 混合静脉血 : PvO2=40mmHg, SvO2=75% CvO2=14.4ml/1 00ml w C(a-v)O2=19.4-14.4=5ml/100ml 摄氧率摄氧率 （ 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 -血红蛋白解离曲线血红蛋白解离曲线 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 是每分钟供给机体的氧量。 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) 正常情况下， 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. 氧供需失衡时机体的代偿机制氧供需失衡时机体的代偿机制 wCO. w 血流再分布 . w 细胞摄氧率 . Moni

9、toring? 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 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,

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 连续颈内静脉血氧饱和度监测 经气管混合静脉血氧饱和度监测 术中常用的 CO监测方法 w 右心飘浮导管 wPicco w(外周动脉 ) FloTrac 传感器 wTEE 由动脉压力波形计算 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. 术中 TEE测量 CO wM型法 短 轴缩 短率： FAC=(EDA-ESA)/EDA ; 自动边缘识别系统（ ABD） w 二维 Simpson法 SV=LVEDV-LVSDV w 多谱勒法 SV=时间速度积分 X横截面积 w 三维法 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 氧供需平衡的监测氧供需平衡的监测 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 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 DO 2 CO/Hb 100% 50% 25% 缺氧 w 低氧血 症： PaO260mmHg w 缺氧类型 Hypotonic anoxia Anemic anoxia Circulatory anoxia Histogenous anoxia 外呼吸外呼吸 血液血液 循环循环 组织组织 氧治疗 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 请讨论 w 术中监测氧供和氧耗的指标？ w 术中引起氧供下降的因素？ w 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。