1、2022-7-302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）2022-7-303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）2022-7-304PaCO2 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。2022-7-305碳酸氢根（HCO3-）HCO3-是反映代谢方面情况的指标。实际碳酸
2、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。2022-7-306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 2022-7-307剩余碱（BE）在标准条件下，Hb充分氧合、38度、
3、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 2022-7-308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。2
4、022-7-309CO2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 2022-7-3010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）2022-7-3011PaO2 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
5、)mmHg。2022-7-3012SaO2 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%。2022-7-3013CaO2 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%2022-7-3014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。P5
6、0 ：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 2022-7-3015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。2022-7-3016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）2022-7-3017分清酸中毒或碱中毒？PH 7.40提示原发失衡可能为碱中毒2022-7-3018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 PaC
7、O2同时伴HCO3-，必为呼碱合并代碱 2022-7-3019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 =2022-7-3020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
8、+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2022-7-3021Example 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 ex
9、cess+8Saturation86%Click to continueClick to continue2022-7-3022Example 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 continue2022-7-3023Example 4.pH7.34Pa
10、CO28.0PaO27.5HCO3-32.1Base excess+8Saturation86%2.Is there an acid base or ventilation problem?YES.YES.Click to continue2022-7-3024Example 4.There is:Mild acidosisPaCO2 is elevated RESPIRATORY ACIDOSISpH7.34PaCO28.0PaO27.5HCO3-32.1Base excess+8Saturation86%Diagnose disturbance Click to continue2022-
11、7-3025Example 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
12、 continue2022-7-3026Example 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 examples2022-7-3027Example 5.A 35 year old woman with a history of an
13、xiety attacks presents to ER.1.Is she hypoxic?pH7.54PaCO222.5PaO291HCO3-22Base excess+2Saturation100%Click to continue2022-7-3028Example 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 continue202
14、2-7-3029Example 5.2.Is there an acid base or ventilation problem?YES.pH7.54PaCO22.9PaO212.1HCO3-22Base excess+2Saturation100%Click to continue2022-7-3030Example 5.There is:Alkalosis PaCO2 is decreased RESPIRATORY ALKALOSISpH7.54PaCO22.9PaO212.1HCO3-22Base excess+2Saturation100%Diagnose disturbance C
15、lick to continue2022-7-3031Example 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 continue2022-7-3032Example 5.pH
16、7.54PaCO22.9PaO212.1HCO3-22Base 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 examples2022-7-3033Example 6.pH7.23PaCO225PaO2225HCO3-12Base excess-10Saturation100%A 42 year old diabe
17、tic 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 continue2022-7-3034Example 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 ven
18、tilation problem?Click to continue2022-7-3035Example 6.pH7.23PaCO23.3PaO229.9HCO3-12Base excess-10Saturation100%2.Is there an acid base or ventilation problem?YES.YES.Click to continue2022-7-3036Example 6.pH7.23PaCO23.3PaO229.9HCO3-12Base excess-10Saturation100%There is:Acidosis PaCO2 is decreased N
19、OT respiratory acidosisLook at HCO3-HCO3-is reduced Base excess is negative METABOLIC ACIDOSISClick to continue2022-7-3037Example 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
20、 METABOLIC ACIDOSISWhat is the anion gap?What is the anion gap?Click to continue2022-7-3038Example 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=24 mmol/l/l There is an anion gap a
21、cidosis due to accumulation of organic acids caused by diabetic ketoacidosisClick to continue2022-7-3039Example 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 exa
22、mples2022-7-3040Example 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 continue2022-7-3041Example 7.NO.This is a normal PaO2 for a patient this age breathing room air2.Is
23、there an acid base or ventilation problem?pH7.5PaCO246.5PaO280HCO3-38Base excess+8Saturation96%Click to continue2022-7-3042Example 7.YES.pH7.5PaCO26.2PaO210.6HCO3-38Base excess+8Saturation96%Click to continue2022-7-3043Example 7.There is:Alkalosis PaCO2 is elevated NOT respiratory alkalosisLook at H
24、CO3-HCO3-is increased Base excess is positive METABOLIC ALKALOSISpH7.5PaCO26.2PaO210.6HCO3-38Base excess+8Saturation96%Click to continue2022-7-3044Example 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 examples2022-7-3045
