北大知名教授讲解动脉血气分析

动脉血气分析,北京大学人民医院呼吸内科高占成2003.09.30,内容提要,一、Review of O2 & CO2 transportation in blood二、Basic concepts三、Acid-base regulation and imbalances四、Diagnosis and analysis of acid-base imbalances五、Examples,Gas transportation-O2,一、reviews,Gas transportation-CO2,一、reviews,Exturnal breathing-O2 loading and CO2 unloading in lungs,一、reviews,Inturnal breathing-CO2 loading and O2 unloading in tissue,一、reviews,DEFINITION,血气分析是利用3个电级（pH、CO2、O2）测定动脉血气中具有生理效应气体（O2、CO2）分压及pH值的技术。其作用在于（1）了解有无缺O2和CO2潴留？程度？；（2）酸碱失衡？类型？程度；（3）重要的重症监护参数，指导临床诊断和治疗。,二、Basic concepts,常用指标及正常值,二、Basic concepts,PaO2SaO2O-H dissociation curveO2CT D(A-a)O2Oxygenation Index,1. 有关氧的指标,二、Basic concepts,（1）PaO2,PaO2：物理溶解于动脉血液中的氧所产生的压力(0.3ml O2/100ml at 37 0C sea level when breathing room air)正常值95mmHg影响因素：1）atmospheric pressure2）temperature3）inspired O2 content4）the patients age：PaO2 = 104-(0.27 x age)意义：缺氧的早期指标（趋势），但不完全反映缺氧,二、Basic concepts,Atmospheric Pressure,二、Basic concepts,（2）SaO2,SaO2：血液在一定氧分压下，HbO2占全部Hb的百分比，每克Hb在氧饱和的情况下可结合1.34 ml O2。SaO2和Hb的多少无关。正常值953%影响因素：1）O2 pressure2）temperature3）pH意义：反映缺氧较为迟钝，但为影响O2CT的主要因素,二、Basic concepts,（3）Oxygen-Hemoglobin Dissociation Curve,O-H curve: 1. PaO2与SaO2有关，但非直线关系； 2. SaO2反映缺氧的程度远不如PaO2敏感； 3. 高原缺氧可保证供养； 4. 有利于肺携带氧，组织释放氧； 5. PaO2 60mmHg为缺氧的治疗点,二、Basic concepts,（4）Oxygen content,O2CT：血液中所含氧量的总和，除了物理溶解于血液中的氧量外，还包括了与Hb结合的氧量O2CT = (1.34 Hb SaO2) + 0.003 PaO2 = (1.34 15 100%) + 0.003 100 = 20.1+0.3 = 20.4 ml 正常值：15-23 ml (15g Hb)意义：有无缺氧的指标，较全面但迟钝,二、Basic concepts,（5）D(A-a)O2,PAO2 = FiO2(760-47) 1.25 PaCO2 = 0.21 713 1.25 PaCO2 = 150 1.25 PaCO2 D(A-a)O2 = PAO2 PaO2正常值: 10 mmHg (30mmHg)意义：判断V/Q比例、弥散能力等的重要指标,二、Basic concepts,（6） Oxygenation Index,Oxygenation Index=PO2/FiO2正常值：400500mmHg反映机体的缺氧状态ALI: 200mmHgOI300mmHgARDS: OI45mmHg为通气不足，CO2潴留，呼酸；SB，通气不足，呼酸；代碱 AB Expected PaCO2, suggesting a primary respiratory acidosis.,四、Diagnosis and analysis of acid-base imbalances,2. 4-5-6-7 Method for Identifying Acid-base Disturbances and Their Compensation Limit,四、Diagnosis and analysis of acid-base imbalances,3. 掌握酸碱变化规律,肺肾间相互代偿规律代偿极限代偿时限代偿只能使pH像正常方向移动（接近7.40），不可能移向相反方向代偿“过失”和代偿“不足”都提示有另一种失调，“过失”为反向失调，“不足”为同向失调在单纯性失调中，与pH方向相同者为原发失调代偿改变应与原发性失调在程度上相匹配，如0.6法（HCO3-/PCO2 =0.6）结合临床,四、Diagnosis and analysis of acid-base imbalances,Sample Problem-Case 1,A 24 year old man presents with confusion. He has had diabetes since age 12, and has been suffering from an intestinal flu for the last 24 hours. He has not been eating much, has vague stomach pain, stopped taking his insulin, and has been vomiting. His glucose is high, and he has the following electrolytes and arterial blood gases:Na+ 130 mEq/L pH 7.20Cl- 80 mEq/L PaCO2 25 mmHgHCO3- 10 mEq/L PO2 68 mmHg,Sample Problem-Case 2,A 68 year old man presents with confusion. He has been diagnosed with COPD since age 40, and has been suffering from an acute respiratory infection for the last 48 hours. He has not been eating much, has dyspnea all the time and hard to talk. He has the following electrolytes and arterial blood gases:Na+ 130 mEq/L pH 7.20Cl- 80 mEq/L PaCO2 85 mmHgHCO3- 46 mEq/L PO2 46 mmHg,Sample Problem-Case 3,A 68 year old man has been diagnosed with Cor pulmonale since COPD. He has the following electrolytes