血气分析血气分析血气分析血气分析的常用指标及其意义的常用指标及其意义陈钢陈钢反映机体酸碱状态的主要指标1、酸碱度（pH）2、PaCO23、碳酸氢根（HCO3-）4、剩余碱（BE）5、缓冲碱（BB）6、CO2结合力（CO2-CP）8/22/20242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）8/22/20243PaCO2 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 。8/22/20244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。8/22/20245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 8/22/20246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 8/22/20247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。8/22/20248CO2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 8/22/20249反映血氧合状态的指标1、PaO22、SaO23、CaO24、氧解离曲线和P505、肺泡-动脉血氧分压差（P(A-a)O2）8/22/202410PaO2 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。 PaO2 = (1000.33年龄)mmHg。8/22/202411SaO2 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%。8/22/202412CaO2 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% 8/22/202413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 8/22/202414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。8/22/202415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）8/22/202416分清酸中毒或碱中毒？ PH 7.40提示原发失衡可能为碱中毒8/22/202417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 8/22/202418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 = 8/22/202419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8/22/202420Example 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 continue8/22/202421Example 4.pH7.34PaCO28.0PaO27.5HCO3-32.1Base excess+8Saturation86%1. Is he hypoxic?Is he hypoxic?YES.YES.The (A-a)PO2=2.4kPaThe(A-a)gradientisincreased,andhomeoxygenmightbeappropriateClick to continue8/22/202422Example 4.pH7.34PaCO28.0PaO27.5HCO3-32.1Base excess+8Saturation86%2. . Is there an acid base or ventilation problem?YES.YES.Click to continue8/22/202423Example 4.There is:Mild acidosisPaCO2 is elevated RESPIRATORY ACIDOSISpH7.34PaCO28.0PaO27.5HCO3-32.1Base excess+8Saturation86%Diagnose disturbance Click to continue8/22/202424Example 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 continue8/22/202425Example 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 examples8/22/202426Example 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 continue8/22/202427Example 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 continue8/22/202428Example 5.2. Is there an acid base or ventilation problem?YES.pH7.54PaCO22.9PaO212.1HCO3-22Base excess+2Saturation100%Click to continue8/22/202429Example 5.There is:AlkalosisPaCO2 is decreased RESPIRATORY ALKALOSISpH7.54PaCO22.9PaO212.1HCO3-22Base excess+2Saturation100%Diagnose disturbance Click to continue8/22/202430Example 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 continue8/22/202431Example 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 examples8/22/202432Example 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 continue8/22/202433Example 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 continue8/22/202434Example 6.pH7.23PaCO23.3PaO229.9HCO3-12Base excess-10Saturation100%2. Is there an acid base or ventilation problem?YES.YES.Click to continue8/22/202435Example 6.pH7.23PaCO23.3PaO229.9HCO3-12Base excess-10Saturation100%There is:AcidosisPaCO2 is decreased NOT respiratory acidosisLook at HCO3-HCO3- is reducedBase excess is negative METABOLIC ACIDOSISClick to continue8/22/202436Example 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 continue8/22/202437Example 6.pH7.23PaCO23.3PaO229.9HCO3-12Base excess-10Na+135Cl-99 What is the anion gap?What is the anion gap?= Na+ ( = Na+ ( ClCl- - + HCO + HCO3 3- - ) )= 135 ( 99 + 12 ) = 135 ( 99 + 12 ) NaNa= 24 = 24 mmolmmol/l/lThere is an anion gap acidosis due to accumulation of organic acids caused by diabetic ketoacidosisClick to continue8/22/202438Example 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 examples8/22/202439Example 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 continue8/22/202440Example 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 continue8/22/202441Example 7.YES. pH7.5PaCO26.2PaO210.6HCO3-38Base excess+8Saturation96%Click to continue8/22/202442Example 7.There is:AlkalosisPaCO2 is elevated NOT respiratory alkalosisLook at HCO3-HCO3- is increasedBase excess is positive METABOLIC ALKALOSISpH7.5PaCO26.2PaO210.6HCO3-38Base excess+8Saturation96%Click to continue8/22/202443Example 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 examples8/22/2024448/22/202445