體液平衡與酸堿平衡紊亂第四節(jié)血氣分析

1、1體液平衡和酸堿平衡紊亂（II)第四節(jié) 血氣分析2第四節(jié) 血氣分析血氣分析（analysis of blood gas）與酸堿指標測定是臨床急救和監(jiān)護病人的一組重要生化指標，尤其對呼吸衰竭和酸堿平衡紊亂病人的診斷治療起著關(guān)鍵的作用。 3血氣分析儀的發(fā)展歷史 20世紀五十年代末，丹麥的PoulAstrup研制出第一臺血氣分析儀大致可將其分為三個發(fā)展階段 50年代末-60年代 手動、笨重、樣品用量大、項目少70年代-80年代 自動定標、自動進樣、自動清洗、自動檢測儀器故障和電極狀態(tài)，并自動報警，電極的使用壽命和穩(wěn)定性不斷提高，儀器的預熱和測量時間也逐步縮短。幾百幾十微升 ，測量+計算90年代-90

2、年代以來 血氣電解質(zhì)分析儀 便攜式、免維護、易操作 4血氣分析儀指標血液氧分壓（PO2）pH值二氧化碳分壓（PCO2）HCO3-三個主要項目并由這三個指標計算出其它酸堿平衡相關(guān)的診斷指標，從而對病人體內(nèi)酸堿平衡、氣體交換及氧合作用作出比較全面的判斷和認識。 5一 血液中的氣體及運輸6（一）血液中的氣體及運輸血液中的氣體分壓：根據(jù)Dalton定律，混合氣體的總壓強等于各氣體分壓之和(P=Pi)。氣體分壓強可由下式計算： 氣體分壓強=混合氣體總壓強該氣體容積百分比7溶解度系數(shù)根據(jù)Henry定律，在一定溫度下某種氣體在血液中的溶解量與其分壓呈正比，而且隨溫度升高其數(shù)值減少。氣體的溶解量用溶解度系數(shù)(

3、Bunsen coefficient)表示。 溶解度系數(shù)：指壓力為760mmHg(101kPa)和特定溫度時1ml液體中溶解氣體的毫升數(shù)。 8（二）血中的氧血液氧含量(ct o2)ct o2 = cd o2 + o2 Hb 1.5% 98.5%血紅蛋白(hemoglobin Hb) 對氧的運輸：血漿中PO2的改變會直接影響O2與Hb結(jié)合 9血氧飽和度：血液中HbO2的量與Hb總量（包括HHb和HbO2）之比 血氧飽和度=HbO2/（HHb+HbO2）氧的運輸與氧解離曲線10以血氧飽和度對PO2作圖，所得的曲線稱為氧解離曲線。 氧解離曲線呈S型具有重要的生理意義 氧解離曲線（Oxygen dis

4、sociation curve） 11由組織擴散入血漿，其中少量溶于水 8.8%向紅細胞內(nèi)擴散，在紅細胞內(nèi)碳酸酐酶（carbonic anhydrase， CA）作用下與水結(jié)合成H2CO3 77.8%與Hb結(jié)合成氨基甲酸血紅蛋白（HbNHCOOH) 13.4%（三）CO2的運輸1213（一）血氣分析標本的采集與處理1. 動脈血2. 動脈化毛細血管血3. 靜脈血4. 取血前病人的準備5. 抗凝劑及采血器6. 標本的貯存 二、血氣分析標本的采集和質(zhì)量控制14儀器分析性能的保證 控制物 采集合格的血液標本制定統(tǒng)一的操作規(guī)程 溫度的控制 對精密度和準確度的要求二、血氣分析標本的采集和質(zhì)量控制15采集標

5、本的標準化 注射器和針頭的標準化2ml注射器比5ml注射器為佳死腔量小肝素與血之比約為1202ml注射器針蕊較輕，當針刺入動脈后，血液進入針筒較快，這時無需抽拉注射器的針蕊造成負壓，氣泡不易混入 16采集標本的標準化 抗凝劑的標準化肝素是血氣分析的最佳抗凝劑 使用液體肝素，要最大限度地減小標本的稀釋。 把吸入針筒的抗凝劑盡量排出，肝素的濃度必須足夠低，標本的最終濃度要在50100ul/ml之間。 殘留肝素愈多，使標本中PH值偏低，PO2偏高，PCO2偏低，實驗證明對PCO2影響最大。 17采集標本的標準化 血液和肝素混合的標準化取樣后要認真混勻，將注射器放在手心中慢慢滾動1分鐘，并上下翻轉(zhuǎn)5次

6、，充分混合，動作要慢不能太劇烈，避免溶血。 18采集標本的標準化 確保密閉必須防止外界空氣進入。抽血時必須做到：抽血針筒不漏氣；抽氣時應(yīng)讓血液自動進入注射器，切勿用力拉針蕊，以免空氣沿針筒壁進入；針頭拔出時應(yīng)立刻將針頭刺入橡皮塞內(nèi)，注意針頭不要穿通橡皮塞。隔絕空氣空氣中氧分壓高于動脈血，二氧化碳分壓低于動脈血19采集標本的標準化 抽血后及時送檢細胞離體后還在不斷地進行新陳代謝，使PH下降、PCO2上升、PO2下降，標本存放時間愈長，室溫愈高，變化愈大 ； 如不能及時測定，將標本放置于4，2小時內(nèi)檢測 20采集標本的標準化 測定前標本要充分混合除血液與抗凝劑充分混合外，在測定前血漿和血球要充分混

7、合，特別是對血紅蛋白、紅細胞壓積影響最大。把注射器針頭部位不能混合的血棄去，然后慢慢進行注入。 21儀器的標準化 儀器調(diào)試新購儀器必須進行性能鑒定（電極線性、穩(wěn)定性、氣壓計精密度、重復性試驗），是觀察電子元件及電極的重要方法，并要有詳細的記錄。 22儀器的標準化 儀器的標定在進行標本測定之前必須用三個標準物分別定標，使其各參數(shù)值均在標準物參數(shù)范圍內(nèi)，才能進行標本測定。 23儀器安裝標準化 放置儀器的實驗臺要穩(wěn)固(最好水泥臺)，工作環(huán)境要清潔(最好操作間單獨隔開)，要防潮、防止陽光直射，室內(nèi)溫度應(yīng)在1525之間，相對濕度應(yīng)80%。儀器應(yīng)有穩(wěn)壓器，并有良好的接地。 24制訂嚴格的操作規(guī)程 嚴格的操

8、作規(guī)程是質(zhì)量的保證，將操作規(guī)程張貼在操作臺前，隨時檢查及時對照，同時要建立儀器使用工作記錄，每天記錄儀器的使用情況及故障的發(fā)生與排除。 25其他質(zhì)控物：要定期對儀器進行質(zhì)量監(jiān)控。查找失控之可能原因進行逐項排除直至在控，方可用于病人標本分析。電極的線性：用不同濃度的氣體進行校正，制作曲線。用于驗證電極的質(zhì)量溫度控制：儀器內(nèi)溫度必須設(shè)定在。26三、血氣分析常用指標與參數(shù)及 臨床意義27【參考范圍】動脈血(一)酸堿度（pH） NaHCO3 pH=6.1+log Pco2 pH 電極判斷酸或堿紊亂不能確定紊亂的性質(zhì)28二氧化碳分壓（partial pressure of carbon dioxide，

9、 pCO2）是指物理溶解在血液中的CO2所產(chǎn)生的張力。在HH方程中H2CO3代表了呼吸成分，并直接影響pH值，即：【參考范圍】動脈血PCO2：3545mmHg（）(二)二氧化碳分壓 pCO2 NaHCO3 pH=6.1+log Pco2 是否為呼吸性酸堿紊亂， 代償后的代謝性酸堿紊亂。29氧分壓（partial pressure of oxygen，PO2）是指血漿中物理溶解的O2所產(chǎn)生的張力。 PO2是缺氧的敏感指標，肺通氣和換氣功能障礙動脈血氧分壓（PaO2）的正常參考范圍為75-100mmHg55mmHg 呼吸衰竭 代償變化原發(fā)失衡的變化決定pH偏向 例1：血氣，PaCO230 mmHg

10、，HCO3- 15 mmol/L。判斷原發(fā)失衡因素 例2：血氣， PaCO2 29 mmHg，HCO3- 19 mmol/L。判斷原發(fā)失衡因素 7.45PCO235-45 mmHg 40 mmHgHCO3-2227 mmol/L 24 mmol/L酸堿平衡的判斷概念258代償公式代謝 HCO3-改變?yōu)樵l(fā)時：代酸時：代償后PaCO2 極限10mmHg 代堿時：代償后的PaCO2升高55mmHg59代償公式呼吸( PaCO2）改變?yōu)樵l(fā)時，所繼發(fā)HCO3-變化分急性和慢性（35天），其代償程度不同:急性呼吸（PaCO2）改變時，所繼發(fā)HCO3-變化為34 mmol 慢性呼吸性酸中毒時：代償后的H

11、CO3-升高水平(HCO3-）=0.35PaCO25.58 慢性呼吸性堿中毒時：代償后的HCO3-降低水平(HCO3-）60酸堿平衡判斷的四步驟據(jù)pH、PaCO2、HCO3-變化判斷原發(fā)因素據(jù)所判斷的原發(fā)因素選用相關(guān)的代償公式據(jù)實測HCO3-/PaCO2與相關(guān)公式所計算出的代償區(qū)間相比，確定是單純或混合酸堿失衡高度懷疑三重酸堿失衡（TABD）的，同時測電解質(zhì)，計算AG和潛在HCO3-61pH堿中毒?正常?呼吸性堿中毒酸中毒?代謝堿中毒呼吸性酸中毒*代謝性堿中毒#代謝性酸中毒呼吸性堿中毒*代謝性酸中毒#呼吸性酸中毒呼吸性酸中毒代謝性堿中毒正常呼吸性堿中毒代謝性酸中毒呼吸性堿中毒代謝性堿中毒(HC

12、O3-）=0.35(HCO3-）=0.49 呼吸性酸中毒呼吸性堿中毒代謝性酸中毒*實測預計上限實測預計上限實測預計下限呼吸性酸中毒代謝性酸中毒呼吸性酸中毒代謝性堿中毒*呼吸性堿中毒PCO2PCO2PCO245 mmHg45 mmHg45 mmHg路線圖黑體表示起主要作用*可能是代償/病理#臨床觀察62病例分析一男性患者,62歲,因“肺氣腫合并感染”于日入院.入院后經(jīng)常規(guī)治療,病情沒有好轉(zhuǎn),反而加重日出現(xiàn)輕度昏迷,痰多并不能排出,肺部感染難以控制.表:病人入院時和病情嚴重時的血氣分析、電解質(zhì)變化日期 pH Pco2 HCO3- BE AG K+ Cl-請分析該病人酸堿平衡失調(diào)的類型(含診斷依據(jù))

13、 63檢查酸堿平衡的生化指標1.CO2結(jié)合力(CO2CP):主要反映代謝性因素的變化2.血液pH值:反映代償性或失償性酸堿平衡失常的指標3.CO2分壓(Pco2):反映呼吸性酸堿平衡失調(diào)4.緩沖堿(BB):反映代謝性酸堿平衡失調(diào)5.堿剩余(BE):反映代謝性酸堿平衡失調(diào)6.實際HCO3-(AB):主要反映代謝性因素的變化7.標準HCO3-(SB):反映代謝性酸堿平衡失調(diào)8.陰離子隙(AG):有助于診斷代謝性酸中毒64小 結(jié)1.血液pH值正常,不能排除混合型酸堿平衡失調(diào)2.BE:標態(tài)下,用標準酸滴定至所用的量正值 BD:標態(tài)下,用標準堿滴定至所用的量負值3.不受呼吸代謝性酸堿平衡的主要指標:BB

14、、BE、SB4.臨床反映代謝性酸堿平衡的主要指標:BE、AB或SB5.臨床反映呼吸性酸堿平衡的主要指標:Pco26.臨床反映代償或失償酸堿平衡失調(diào)的指標:血液pH值6566小節(jié)不拘小節(jié)膽大心細融會貫通67A step by step guideArterial Blood GasesA step by step guideHCO3- + H+ H2CO3 CO2 + H2068ObjectivesTo be able to interpret simple arterial blood gasTo know the meaning of common terms used in arteria

15、l blood gas interpretationTo know the normal ranges for arterial blood gas valuesHow to Analyze an ABGPO2NL = 80 100 mmHgPCO2NL = 35 45 mmHgAcidotic45Alkalotic35HCO3NL = 22 26 mmol/LAcidotic 26Normal ABG Values?PaO2 pHPaCO2HCO3Base Excess10.0 kPa（75mmHg)4.5 - 6.0 kPa(35-45mmHg)22 - 26-2 - +2Many mod

16、ern gas machines also measureK+ Na+ Cl- SaO2 Hb COHb MetHb Lactate715 steps to analysing an ABGIs the patient hypoxic? Is there a significant degree of lung injury? A a GradientThe gradient between alveolar PAO2 and arterial PaO2 in a person with healthy lungs is 15 20 mmHgThe higher the gradient, t

17、he worst the lung injury725 steps to analysing an ABGDoes the patient have an acidaemia or an alkalaemia? Is the cause respiratory or metabolic?Is there any attempt at compensation? 73CompensationRespiratory compensation is quickMetabolic compensation is slowCompensation is not usually completePatie

18、nts never over compensate74Acid-Base disorderpHPaCO2HCO3Respiratory acidosisMetabolic acidosisRespiratory alkalosisMetabolic alkalosisRespiratory acidosis with partial renal compensationMetabolic acidosis with partial respiratory compensationRespiratory alkalosis with partial renal compensationMetab

19、olic alkalosis with partial respiratory compensationMixed metabolic & respiratory acidosisMixed metabolic & respiratory alkalosisNNNNFill in the gaps75Scenario 1 Arterial blood gas analysis reveals:FiO20.4 (40%)PaO27.0 kPaPaCO28.9 kPa HCO33565 year old male with known COPD presents in A&E complainin

20、g of increased breathlessness. The paramedics have put him on a venturi mask to give an FiO2 of 40% due to his breathlessness and initial low saturations.Significant findings on your examination is a drowsy patient with a resp rate of 8, SpO2 of 85% and wide-spread coarse cracklesHypoxiaRespiratory

21、acidosis with chronic renal compensationInfective exacerbation of COPD?Hypoxic drive ?tired76Scenario 2 Arterial blood gas analysis reveals:FiO20.3 (30%)PaO222.0 kPaPaCO22.5 kPa HCO310Na135Cl106Anion Gap = ?18 year old male with diabetes has been suffering from D&V for 48 hours and because he has be

22、en unable to eat he has not taken his insulinSignificant findings on your examination are a resp rate of 40, heart rate of 120, BP 95/50, Blood glucose 30mmol/lMetabolic acidosis with respiratory compensationDKA2477Scenario 3 Arterial blood gas analysis reveals:FiO20.21 (21%)PaO215.1 kPaPaCO23.1 kPa

23、 HCO317 year old male has taken his fathers BMW (without asking) to impress his girlfriend and had a altercation with a large bus where the BMW came off much the worse.There is little abnormal to find on examination apart from bruising, a resp rate of 24, a pulse of 110 and a BP of 120/85Respiratory

24、 alkalosisAnxiety78Scenario 4 Arterial blood gas analysis reveals:FiO20.4 (40%)PaO28.2 kPaPaCO23.7 kPaHCO3-12 mmol/LA 75 year old female is on the surgical ward 2 days after a laparotomy for a perforated sigmoid colon secondary to diverticular disease. She has become hypotensive over the last 6 hour

25、s. A nurse has started 40% O2On examination vital signs are: RR 35 min-1, SpO2 92%, HR 120 min-1, warm peripheries, BP 70/40 mmHg, Urine output 50 ml in the last 6 hoursHypoxiaMetabolic acidosis with respiratory compensationShock secondary to Sepsis79Scenario 5 A 75 year old man presents to the emer

26、gency department after a witnessed out-of-hospital VF cardiac arrest. The paramedics arrived after 5 minutes, during which CPR had not been attempted. The paramedics had successfully restored spontaneous circulation after 3 shocks but have been unable to intubate him. He is breathing spontaneously w

27、ith a re breathing mask in situ. On arrival: comatose (GCS 3) Resp rate 8 HR 120 min-1BP 150/95 mmHg.Arterial blood gas analysis reveals:FiO20.85 (85%)PaO210.5 kPaPaCO27.0 kPa HCO314BE- 10Mixed respiratory and metabolic acidosisHypoperfusion and respiratory failure80Any Questions?81SummaryIdentify t

28、he hypoxic patientIdentify an acidosis or alkalosisRecognise when compensation is taking placeFormulate an initial treatment plan for some common scenariosUnderstand the role Arterial Blood Gases play in patient management You should now be able to:Mixed Acid-Base AbnormalitiesCase Study No. 3:56 yo

29、 neurologic dz required ventilator support for severalweeks. She seemed most comfortable when hyperventilatedto PaCO2 28-30 mmHg. She required daily doses of lasix toassure adequate urine output and received 40 mmol/L IV K+each day. On 10th day of ICU her ABG on 24% oxygen & VS:ABG ResultspH7.62BP11

30、5/80 mmHgPCO230 mmHgPulse88/minPO285 mmHgRR10/minHCO330 mmol/LVT1000mlBE10 mmol/LMV10LK+2.5 mmol/L Interpretation:Acute alveolar hyperventilation (resp. alkalosis) and metabolic alkalosis with corrected hypoxemia.Case study No. 427 yo retarded with insulin-dependent DM arrived at ERfrom the institut

31、ion where he lived. On room air ABG & VS:pH7.15BP180/110 mmHgPCO222 mmHgPulse130/minPO292 mmHgRR40/minHCO3 9 mmol/LVT800mlBE-30 mmol/LMV32LInterpretation:Partly compensated metabolic acidosis.Case study No. 574 yo with hx chronic renal failure and chronic diuretic therapywas admitted to ICU comatose

32、 and severely dehydrated. On40% oxygen her ABG & VS:pH7.52BP130/90 mmHgPCO255 mmHgPulse120/minPO292 mmHgRR25/minHCO342 mmol/LVT150mlInterpretation:Partly compensated metabolic alkalosis with corrected hypoxemia.Case study No. 643 yo arrives in ER 20 minutes after a MVA in which heinjured his face on

33、 the dashboard. He is agitated, has mottled,cold and clammy skin and has obvious partial airway obstruction.An oxygen mask at 10 L is placed on his face. ABG & VS:pH7.10BP150/110 mmHgPCO260 mmHgPulse150/minPO2125 mmHgRR45/minHCO318 mmol/LVT? mlBE-15 mmol/LMV? L.Interpretation:Acute ventilatory failu

34、re (resp. acidosis) andacute metabolic acidosis with corrected hypoxemiaCase study No. 717 yo, 48 kg with known insulin-dependent DM came to ERwith Kussmaul breathing and irregular pulse. Room airABG & VS:pH7.05BP140/90 mmHgPCO212 mmHgPulse118/minPO2108 mmHgRR40/minHCO35 mmol/LVT1200mlBE-30 mmol/LMV

35、48LInterpretation:Severe partly compensated metabolicacidosis without hypoxemia. Case No. 7 contdThis patient is in diabetic ketoacidosis.IV glucose and insulin were immediately administered. Ajudgement was made that severe acidemia was adverselyaffecting CV function and bicarb was elected to restor

36、e pH to 7.20.Bicarb administration calculation:Base deficit X weight (kg) 430 X 48 = 360 mmol/LAdmin 1/2 over 15 min & 4 repeat ABGCase No. 7 contdABG result after bicarb:pH7.27BP130/80 mmHgPCO225 mmHgPulse100/minPO292 mmHgRR22/minHCO311 mmol/LVT600mlCase study No. 847 yo was in PACU for 3 hours s/p

37、 cholecystectomy. Shehad been on 40% oxygen and ABG & VS:pH7.44BP130/90 mmHgPCO232 mmHgPulse95/min, regularPO2121 mmHgRR20/minHCO322 mmol/LVT350mlBE-2 mmol/LMV7LSaO298%Hb13 g/dLCase No. 8 contdOxygen was changed to 2L N/C. 1/2 hour pt. ready to be D/Cto floor and ABG & VS:pH7.41BP130/90 mmHgPCO210 m

38、mHgPulse95/min, regularPO2148 mmHgRR20/minHCO36 mmol/LVT350mlBE-17 mmol/LMV7LSaO299%Hb7 g/dLCase No. 8 contd What is going on?Case No. 8 contdIf the picture doesnt fit, repeat ABG!pH7. 45BP130/90 mmHgPCO231 mmHgPulse95/minPO287 mmHgRR20/minHCO322 mmol/LVT350mlBE-2 mmol/LMV7LSaO2 96% Hb13 g/dLTechnic

39、al error was presumed.Case study No. 967 yo who had closed reduction of leg fx without incident.Four days later she experienced a sudden onset of severe chestpain and SOB. Room air ABG & VS:pH7.36BP130/90 mmHgPCO233 mmHgPulse100/minPO255 mmHgRR25/minHCO318 mmol/LBE-5 mmol/LMV18LSaO288% Interpretatio

40、n:Compensated metabolic acidosis withmoderate hypoxemia. Dx: PECase study No. 1076 yo with documented chronic hypercapnia secondary tosevere COPD has been in ICU for 3 days while being tx forpneumonia. She had been stable for past 24 hours and wastransferred to general floor. Pt was on 2L oxygen & ABG &VS:pH7.44BP135/95 mmHgPCO263 mmHgPulse110/minPO252 mmHgRR22/minHCO342 mmol/LBE+16 mmol/LMV10LSaO286%. Interpretation:Chronic ventilatory failure (resp. acidosis)with uncorrected hypoxem