[医学]血气分析课件.ppt

7/7/20222反映机体酸碱状态的主要指标 1、酸碱度（pH） 2、PaCO2 3、碳酸氢根（HCO3-） 4、剩余碱（BE） 5、缓冲碱（BB） 6、CO2结合力（CO2-CP）7/7/20223酸碱度（pH） 反映H+浓度的指标，以H+浓度的负对数表示。 正常值：7.35 7.45。 pH7.45 碱中毒（失代偿）7/7/20224PaCO2 PaCO2是判断呼吸性酸碱失衡的重要指标，代表溶解于血浆中的CO2量，反映肺泡通气效果。 正常值：35 45mmHg。 PaCO245mmhg，原发性呼酸或继发性代偿性代碱 。7/7/20225碳酸氢根（HCO3-） HCO3-是反映代谢方面情况的指标。 实际碳酸氢根（AB）：直接从血浆测得数据，受代谢和呼吸双重影响（当PaCO2升高时，HCO3-升高）。正常值：21 27mmol/L。 标准碳酸氢根（SB）：在隔绝空气、38度、PaCO2为40mmHg、 SaO2为100%时测得的HCO3- 含量。不受呼吸因素的影响， 基本反映体内HCO3-储量的多少，比AB更为准确，但不能测出红细胞内缓冲作用，也不能反映全部非呼吸酸碱失衡的程度。正常值：22 27mmol/L。7/7/20226碳酸氢根（HCO3-） 健康人AB = SB，撒播碱失衡时两值不一致： AB SB：存在呼酸 AB SB：存在呼碱 7/7/20227剩余碱（BE） 在标准条件下，Hb充分氧合、38度、PaCO2 40mmHg时将1L全血用酸或碱滴定至pH=7.40时所需的酸或碱量。反映总的缓冲碱的变化，较SB更全面，只反映代谢变化，不受呼吸因素影响。正常值：-3 +3mmol/L（全血）。 BE +3mmol/L：代碱 7/7/20228缓冲碱（BB） 是1升全血（BBb）或1升血浆（BBp）中所具有缓冲作用的阴离子总和，主要是和血浆蛋白，反映机体在酸碱紊乱时总的缓冲能力。正常范围：4555mmol/L，与HCO3-有所不同，由于其受Hb、血浆蛋白的影响，当出现BB降低，而HCO3-正常时，说明存在HCO3-以外碱储备不足，如低蛋白血症、贫血等，纠正这种碱储不足，补充HCO3-是不适宜的。7/7/20229CO2结合力（CO2-CP） 将静脉血在室温下与含5.5% CO2的空气平衡，然后测定血浆之CO2含量，减去物理溶解的CO2，即得出CO2结合力。受呼吸和代谢因素的影响，目前已不受重视。 CO2-CP ：呼酸或代碱 CO2-CP ：呼碱或代酸 7/7/202210反映血氧合状态的指标 1、PaO2 2、SaO2 3、CaO2 4、氧解离曲线和P50 5、肺泡-动脉血氧分压差（P(A-a)O2）7/7/202211PaO2 动脉血浆中物理溶解的氧分子所产生的分压，是确定SaO2的重要因素。 正常值：80 100mmHg。随年龄增大而降低。 P a O2 = ( 1 0 0 0 . 3 3 年龄)mmHg。7/7/202212SaO2 动脉血中Hb实际结合的氧量与所能结合的最大氧量之比。与PaO2和Hb氧解离曲线直接相关。 正常值：93% 99%。7/7/202213CaO2 血液实际结合的氧总量（Hb氧含量和物理溶解量）。 血红蛋白氧含量 = 1.34Hb SaO2% 物理溶解氧含量 = PaO20.003ml% 正常人：20.3ml% 7/7/202214氧解离曲线和P50 氧解离曲线：PaO2与SaO2间的关系曲线，呈S型。 P50：pH=7.40、PaCO2=40mmHg条件下，SaO2为50%时的PaO2。 正常值：2428mmHg。 P50 ：曲线右移，Hb与O2亲和力降低，有利于释氧。 P50 ：曲线左移，Hb与O2亲和力增加，不有利于释氧。 影响因素：pH、温度、2,3-DPG 7/7/202215肺泡-动脉血氧分压差（P(A-a)O2） 正常值：5 15mmHg。 P(A-a)O2增大：肺泡弥散障碍；生理性分流或病理性左-右分流； 通气/血流比例失调。7/7/202216酸碱失衡的诊断 1、分清原发和继发（代偿）？酸中毒或碱中毒？ 2、分清单纯性或混合性酸碱失衡？ 3、阴子间隙（anion gap，AG）7/7/202217分清酸中毒或碱中毒？ PH 7.40提示原发失衡可能为碱中毒7/7/202218分清单纯性或混合性酸碱失衡？ PaCO2同时伴HCO3- ，必为呼酸合并代酸 PaCO2同时伴HCO3- ，必为呼碱合并代碱 7/7/202219不同酸碱失衡类型的血气改变酸碱失衡类型酸碱失衡类型 pH PaCO2 HCO3- BE 呼吸性酸中毒呼吸性酸中毒 （稍） = 呼吸性酸中毒代偿呼吸性酸中毒代偿 = 呼吸性碱中毒呼吸性碱中毒 （稍） =呼吸性碱中毒代偿呼吸性碱中毒代偿 = 代谢性酸中毒代谢性酸中毒 = 代谢性酸中毒代偿代谢性酸中毒代偿 = 代谢性碱中毒代谢性碱中毒 = 代谢性碱中毒代偿代谢性碱中毒代偿 = 呼酸并代酸呼酸并代酸 呼碱并代碱呼碱并代碱 呼酸并代碱呼酸并代碱 = 呼碱并代酸呼碱并代酸 = 7/7/202220阴子间隙（AG） 血清中所测得的阳离子总数和阴离子总数之差。 AG = （Na+ + K+）（Cl + HCO3- ） 可简化为 AG = Na+（Cl + HCO3- ） 正常值：8 16mmol/L AG ：代酸、脱水、低K+，Ca2+、Mg2+ AG ：未测定阴离子浓度（细胞外液稀释、低蛋白血症） 未测定阳离子浓度（高K+，Ca2+、Mg2+、多发性骨髓瘤7/7/202221Example 4.A patient with COPD has a ABG taken in out-patient clinic to assess his need for home oxygen. He is breathing room air.pH7.34PaCO260PaO256HCO3-32.1Base excess+8Saturation86%Click to continueClick to continue7/7/202222Example 4.pH7.34PaCO28.0PaO27.5HCO3-32.1Base excess+8Saturation86%1. Is he hypoxic?Is he hypoxic?YES.YES.The (A-a) PO2 = 2.4 kPa The (A-a) gradient is increased, and home oxygen might be appropriateClick to continue7/7/202223Example 4.pH7.34PaCO28.0PaO27.5HCO3-32.1Base excess+8Saturation86%2. . Is there an acid base or ventilation problem?YES.YES.Click to continue7/7/202224Example 4.There is:Mild acidosisPaCO2 is elevated RESPIRATORY ACIDOSISpH7.34PaCO28.0PaO27.5HCO3-32.1Base excess+8Saturation86%Diagnose disturbance Click to continue7/7/202225Example 4.There is:HCO3- = 32.1Expected HCO3- = 24 + (8.0 5.3) x 3.0 = 32.1This is the expected HCO3- if there has been significant renal compensation over a long period; in addition the base excess has increased. CHRONIC RESPIRATORY ACIDOSISpH7.34PaCO28.0PaO27.5HCO3-32.1Base excess+8Saturation86%Click to continue7/7/202226Example 4.There is:pH change: 8.0 5.3 x 0.02 = 0.054pH = 7.4 0.054 = 7.346 CONSISTENT WITH SIMPLE CHRONIC RESPIRATORY ACIDOSIS; NO ADDITIONAL DISTURBANCEpH7.34PaCO28.0PaO27.5HCO3-32.1Base excess+8Saturation86%Return to examples7/7/202227Example 5.A 35 year old woman with a history of anxiety attacks presents to ER . 1. Is she hypoxic?pH7.54PaCO222.5PaO291HCO3-22Base excess+2Saturation100%Click to continue7/7/202228Example 5.NO. This is a normal PaO2 for room air 2. Is there an acid base or ventilation problem?pH7.54PaCO22.9PaO212.1HCO3-22Base excess+2Saturation100%Click to continue7/7/202229Example 5.2. Is there an acid base or ventilation problem?YES.pH7.54PaCO22.9PaO212.1HCO3-22Base excess+2Saturation100%Click to continue7/7/202230Example 5.There is: Alkalosis PaCO2 is decreased RESPIRATORY ALKALOSISpH7.54PaCO22.9PaO212.1HCO3-22Base excess+2Saturation100%Diagnose disturbance Click to continue7/7/202231Example 5.pH7.54PaCO22.9PaO212.1HCO3-20Base excess+2Saturation100%There is:HCO3- = 20Expected HCO3- = 24 - (5.3 2.9) x 1.5 = 20.4This is the expected HCO3- if there has only been a small amount of renal compensation ACUTE RESPIRATORY ALKALOSISClick to continue7/7/202232Example 5.pH7.54PaCO22.9PaO212.1HCO3-22Base excess+2Saturation100%There is:pH change: 5.3-2.9 x 0.06 = 0.144pH = 7.4 + 0.144 = 7.54 CONSISTENT WITH SIMPLE ACUTE RESPIRATORY ALKALOSIS; NO ADDITIONAL DISTURBANCEReturn to examples7/7/202233Example 6.pH7.23PaCO225PaO2225HCO3-12Base excess-10Saturation100%A 42 year old diabetic woman present with UTI symptoms; she has deep sighing respiration. This is the ABG on FiO2 0.4 1.Is she hypoxic?Is she hypoxic?Click to continue7/7/202234Example 6.pH7.23PaCO23.3PaO229.9HCO3-12Base excess-10Saturation100%NO. NO. This PaO2 is adequate for an FiO2 of 0.42. Is there an acid base or ventilation problem?Click to continue7/7/202235Example 6.pH7.23PaCO23.3PaO229.9HCO3-12Base excess-10Saturation100%2. Is there an acid base or ventilation problem?YES.YES.Click to continue7/7/202236Example 6.pH7.23PaCO23.3PaO229.9HCO3-12Base excess-10Saturation100%There is: Acidosis PaCO2 is decreased NOT respiratory acidosisLook at HCO3- HCO3- is reduced Base excess is negative METABOLIC ACIDOSISClick to continue7/7/202237Example 6.pH7.23PaCO23.3PaO229.9HCO3-12Base excess-10Saturation100%Using Winters formula:Expected PaCO2 = (1.5 x 12) + (8 2) x 0.133= 3.2 3.7 kPaThe PaCO2 falls within this rangeSIMPLE METABOLIC ACIDOSISWhat is the anion gap?What is the anion gap?Click to continue7/7/202238Example 6.pH7.23PaCO23.3PaO229.9HCO3-12Base excess-10Na+135Cl-99 What is the anion gap?What is the anion gap?= Na+ ( Cl= Na+ ( Cl- - + HCO + HCO3 3- - ) )= 135 ( 99 + 12 ) = 135 ( 99 + 12 ) NaNa= 24 mmol/l= 24 mmol/l There is an anion gap acidosis due to accumulation of organic acids caused by diabetic ketoacidosisClick to continue7/7/202239Example 6.pH7.23PaCO23.3PaO229.9HCO3-12Base excess-10Na+135Cl-99 Corrected bicarbonate = 24 mmol/lThe PaCO2 falls within the expected rangeSIMPLE METABOLIC ACIDOSIS; NO OTHER DISTURBANCEReturn to examples7/7/202240Example 7.A 70 year old man presents with a 3 day history of severe vomiting.Here is his ABG on room air.1.Is he hypoxic?pH7.5PaCO26.2PaO210.6HCO3-38Base excess+8Saturation96%Click to continue7/7/202241Example 7.NO. This is a normal PaO2 for a patient this age breathing room air2. Is there an acid base or ventilation problem?pH7.5PaCO246.5PaO280HCO3-38Base excess+8Saturation96%Click to continue7/7/202242Example 7.YES. pH7.5PaCO26.2PaO210.6HCO3-38Base excess+8Saturation96%Click to continue7/7/202243Example 7.There is: Alkalosis PaCO2 is elevated NOT respiratory alkalosisLook at HCO3- HCO3- is increased Base excess is positive METABOLIC ALKALOSISpH7.5PaCO26.2PaO210.6HCO3-38Base excess+8Saturation96%Click to continue7/7/202244Example 7.3.Is there respiratory compensation?Expected PaCO2= 0.8 kPa per 10 mmol/l in HCO3-= 5.3 + (0.8 x ( 38 24 /10)= 6.4 CONSISTENT WITH SIMPLE METABOLIC ALKALOSISpH7.5PaCO26.3PaO210.6HCO3-38Base excess+8Saturation96%Return to examples7/7/202245结束结束