动脉血气分析6

动脉血气分析 Arterial blood gas analysis /sections/clinical-information/critical care/abgs.html,蚌医一附院ICU 汪华学 2010、7,动脉血气分析六步法 6-step Approach in ABGs,H+ = 24 (PaCO2 )HCO3-如果 pH 和 H+ 数值不一致, 该血气结果可能是错误的,Step 1: 根据 Henderseon- Hasselbach 公式评估血气数值的内在一致性：,Step 2: 是否存在碱血症或酸血症？ pH 7.45 alkalemia 通常这就是原发异常 记住：即使pH值在正常范围（7.357.45），也可能存在酸中毒或碱中毒 你需要核对PaCO2, HCO3- ,和阴离子间隙,Step 3：是否存在呼吸或代谢紊乱？pH值改变的方向与PaCO2改变方向的关系如何？ 在原发呼吸障碍时，pH值和PaCO2改变方向相反 在原发代谢障碍时，pH值和PaCO2改变方向相同,Step 4: 针对原发异常是否产生适当的代偿？ 通常情况下，代偿反应不能使pH恢复正常(7.35-7.45) 如果观察到的代偿程度与预期代偿反应不符，很可能存在一种以上的酸碱异常,Step 5: 计算阴离子间隙(如果存在代谢性酸中毒) AG = Na+ (Cl- + HCO3-) = 12 2 正常的阴离子间隙约为12 mEq/L 对于低白蛋白血症患者, 阴离子间隙正常值低于12mEq/L 低白蛋白血症患者血浆白蛋白浓度每下降1mg/dL,阴离子间隙“正常值”下降约2.5 mEq/L 例如：血浆白蛋白下降2.0 mg/dL，患者AG约为7mEq/L,如果阴离子间隙增加，在以下情况下应计算渗透压间隙 AG升高不能用明显的原因(DKA，乳酸酸中毒，肾功能衰竭)解释 怀疑中毒 OSM间隙 = 测定OSM -(2Na+-血糖/18BUN/2.8) OSM间隙应当 10,Step 6: 如果阴离子间隙升高，评价阴离子间隙升高与HCO3- 降低的关系 计算阴离子间隙改变(AG)与HCO3-改变(HCO3-)的比值：AGHCO3- 如果为非复杂性阴离子间隙升高代谢性酸中毒, 此比值应当介于1.0和2.0之间,如果这一比值在正常值以外, 则存在其他代谢紊乱 如果 AG/HCO3- 2.0，则可能并存代谢性碱中毒 记住患者阴离子间隙的预期“正常值”非常重要，且这一正常值须根据低白蛋白血症情况进行校正（见第五步）,酸碱失衡的原因分析,表1：酸碱失衡的特征,表2：呼吸性酸中毒部分病因,表3：呼吸性碱中毒部分病因,表4：代谢性碱中毒部分病因,表5：代谢性酸中毒部分病因,表6：部分混合性和复杂性酸碱失衡,Case 1,A 22-year of man with diabetes mellitus develops a severe upper respiratory infection Na=128 K=5.9 Cl=94 HCO3=6 PCO2=15 PO2=102 pH=7.19 BG=324,Are the data internally consistent? Is the patient acidemic or alkalemic? Is the primary disorder respiratory? Is the compensation for the metabolic acidosis appropriate? Since the patient has a metabolic acidosis, is this a hyerchloriemic or high anion gap type metabolic acidosis? Is there another (metabolic alkalosis) acid-base disturbance present? What is the delta anion gap (gap)? What are the causes of an increase in anion gap, especially in this patient?,Step 1: Internal Consistency,Henderseon-Hasselbach eqationH+ = 24(PaCO2 )HCO3-,Case 1: Internal Consistency,H+ = 24(PaCO2 )HCO3-= 24156 = 60The data are internally consistent.,Step 2: Alkalemia or Acidemia,Is there alkalemia or acidemia present? pH 7.45 alkalemia,This is usually the primary disorder? Remember: an acidosis or alkalosis may be present even if the pH is in the normal rage (7.35 7.45). Need to check the PaCO2, HCO3-, and anion gap.,Case 1: Alkalemia or Acidemia,The arterial pH = 7.19 7.40 The patient is acidemic,Step 3: Respiratory or Metabolic,What is the relationship between direction of change in the pH and the direction of change in the PaCO2?,Case 1: Respiratory or Metabolic,pH = 7.19, PaCO2 = 15 The primary disorder is a metabolic acidosis,Step 4: Compensation Appropriate?,Case 1: Compensation Appropriate?,The expected PaCO2 = 1.5 6 + 8 2 = 17 2 (1519)Therefore, the measured PaCO2 of 15 is within the predicted rage (15 to 19) for normal compensation,Step 5: Anion Gap,AG = Na+ - (Cl- + HCO3-) = 12 2 A normal AG is approximately 12 mEq/L In patients with hypoalbuminemia, the normal AG is about 2.5 mEq/L lower for each 1 mg/dL decrease in the plasma albumin concentration,Case 1: Anion Gap,AG = Na+ - (Cl- + HCO3-) = 12 2 AG = 128 94 6 = 28 The normal AG is 10 to 14 Therefore, the patient has a high anion gap metabolic acidosis,Step 6: AG,AG = measured AG normal AG Predicted starting HCO3- = AG + measured HCO3- If 26, metabolic alkalosis,Step 6: AG,HA = H+ + A- H+ + HCO3- = H2CO3 H2CO3 = H2O + CO2Increase of A-= Decrease of HCO3- AG = HCO3-,AG,Case 1: AG,AG = 28 10 = 18 Predicted starting HCO3- = 18 + 6 = 24 There is no underlying metabolic alkalosis This, then, is a simple compensated metabolic acidosis,Case 1: Causes,Causes of anion gap metabolic acidosis Diabetic ketoacidosis, alcoholic ketoacidosis, lactic acidosis Drug and toxins: toxic alcohols (methanol, ethylene glycol) The most likely cause of metabolic acidosis in this patient is diabetic acidosis,Case 2,A 32-year old man h/o chronic alcohol use is brought to the emergency center after 3 days of nausea, vomiting, and abdominal pain. Four hours ago he took “something” to help with the pain. He is awake and alert, and physical examination is unremarkable. Na=132 K=3.9 Cl=82 HCO3=4 PCO2=10 PO2=110 pH=7.25 BG=68 BUN=14 blood alcohol=106 Urinalysis: no protein or ketones, +vs for crystals,Are the data internally consistent? Is the patient acidemic or alkalemic? Is the primary disorder respiratory? Is the compensation for the metabolic acidosis appropriate? Since the patient has a metabolic acidosis, is this a hyerchloriemic or high anion gap type metabolic acidosis? Is there another (metabolic alkalosis) acid-base disorder present? What is the gap? What are the causes of an increase in anion gap? How does one make the diagnosis of ethylene glycol ingestion? What are the possible causes of metabolic alkalosis?,Case 2: Internal Consistency,H+ = 24(PaCO2 )/HCO3-= 2410/4= 60The data are internally consistent.,Case 2: Alkalemia or Acidemia,The arterial pH = 7.25 7.40 The patient is acidemic,Case 2: Respiratory or Metabolic,pH=7.25, PaCO2=10 The primary disorder is a metabolic acidosis as the PaCO2 is not elevated,Case 2: Compensation Appropriate?,The expected PaCO2 = 1.5 4 + 8 2 = 14 2 (1216)As the measured PaCO2 is 10, the compensation is close enough to say that it is appropriate.,Case 2: Anion Gap,AG = Na+ - (Cl- + HCO3-) = 12 2 AG = 132 82 4 = 46 The normal AG is 10 to 14 This is a high anion gap type metabolic acidosis,Case 2: AG,AG = 46 10 = 36 The potential fate of this anion is to become bicarbonate. The bicarbonate level before the acid base disturbance was 36 + 4 = 40 Therefore, there is an underlying metabolic alkalosis as well.,Case 2: Causes,Diabetic or alcoholic ketoacidosis? Pro: Chronic alcohol use Anion gap metabolic acidosis Con: Blood glucose WNL No ketones in urine,Case 2: Causes,Implication from history and lab results? Taking something Anion gap metabolic acidosis Crystals in urine,Case 2: Causes,Methanol Anion gap metabolic acidosis No crystals in urine,Ethylene glycol Anion gap metabolic acidosis Crystals in urine Especially calcium oxalate crystals,Case 2: Causes of metabolic alkalosis,The vomiting, presumably due to ulcer, gastritis, or pancreatic disease, lead to alkalosisFinal answer: This is a double acid-base disorder: a metabolic acidosis secondary to ethylene glycol ingestion and a metabolic alkalosis due to vomiting,Case 3,A 46-year old woman with COPD is brought to the emergency center with increasing SOB. CXR reveals a RLL infiltrate.Na=140 K=4.1 Cl=98 HCO3=30 PCO2=66 PO2=38 pH=7.28,Are the data internally consistent? Is the patient acidemic or alkalemic? Is the primary disorder respiratory? Is the compensation appropriate? What are the various type of metabolic alkalosis? What are the causes of a chloride resistant metabolic alkalosis? What is the most likely cause of chloride resistant metabolic alkalosis in this patient?,Case 3: Internal Consistency,H+ = 24(PaCO2 )/HCO3-= 2466/30 = 53The data are internally consistent.,Case 3: Alkalemia or Acidemia,The arterial pH = 7.28 7.40 The patient is acidemic,Case 3: Respiratory or Metabolic,pH=7.28, PaCO2=66 The primary disorder is a respiratory acidosis as the PaCO2 is high.,Case 3: Compensation Appropriate?,Respiratory acidosis can be acute or chronic. In acute respiratory acidosis, the HCO3- = 24 + PaCO2/10; here is 24 + (66-40)10, or 27 In chronic respiratory acidosis, the HCO3- = 24 +3.5 PaCO2/10; here is 24 + 3.5(66-40)10, or 33 In this case, the HCO3- = 30, midway between, suggesting an acute and chronic process.,Case 3: Causes,The most likely cause in this patient is chronic obstrutive pulmonary disease with acute pneumonia.Final answer: Respiratory acidosis, acute on chronic.,Case 4,A 47-year old woman presents with a history of drinking with nausea, vomiting, and fever. Na=140 K=2.9 Cl=96 HCO3=18 PCO2= 49 PO2= 45 pH=7.15 BG=96 Urinalysis: 4 + ketones CXR reveals LUL, RML, and RLL infiltrates,Are the data internally consistent? Is the patient acidemic or alkalemic? Is the primary disorder respiratory? What about the compensation? Since the patient has a metabolic acidosis, is this a hyperchloriemic or high anion gap type metabolic acidosis? What are the causes of a high anion gap metabolic acidosis? What is the most likely explanation for the patient clinical syndrome?,Case 4: Internal Consistency,H+ = 24(PaCO2 )/HCO3-= 2449/18=65The data are internally consistent.,Case 4: Alkalemia or Acidemia,The arterial pH = 7.15 7.40 The patient is acidemic,Case 4: Respiratory or Metabolic,pH=7.15, PaCO2=49 There is a primary respiratory acidosis , but its magnitude is insufficient to cause this degree of acidemic (all else being equal, raising the PaCO2 to 49 should lower the pH to 7.33). Thus, there must be another basis for part of the acidosis (ie, metabolic acidosis ) This must be a double acid-base disturbance, in other words, a metabolic and a respiratory acidosis,Case 4: Anion Gap,AG = Na+ - (Cl- + HCO3-) = 12 2 AG = 140 96 18 = 26 The normal AG is 10 to 14. This is a high anion gap type metabolic acidosis.,Case 4: AG,AG = 26 10 = 16 The potential fate of this anion is to become bicarbonate. The bicarbonate level before the acid base disturbance was 16 + 18 = 34. Therefore, there is an underlying metabolic alkalosis as well.,Case 4: Diagnosis,Although there are many causes that were discussed in earlier questions, the most diagnosis in this patient is alcoholic ketoacidosis as the patient had 4+ ketones in her urine.Another alternative possibility would be diabetic ketoacidosis, but this is unlikely in view of the normal blood glucose level of 96.,Case 4: Diagnosis,Most likely, this patient is a chronic alcoholic with nausea and vomiting (resulting in a metabolic alkalosis: did you notice that the AG16 + the HCO3- = 34?) who discontinued her alcohol intake and developed alcoholic ketoacidosis (metabolic acidosis), and also developed pneumonia resulting in the respiratory acidosis.Final answer: Triple acid-base disturbance: metabolic acidosis, respiratory acidosis, and metabolic alkalosis.,Case 5,A 62-year old man is admitted to the ICU with SOB. A number of empty bottles had been found in his apartment, including furosemide, enalapril, potassium chloride, aspirin. CXR reveals pulmonary edema. Na=140 K=2.8 Cl=108 HCO3=10 PCO2= 16 PO2= 106 pH=7.42,Are the data internally consistent? Is the patient acidemic or alkalemic? Is the primary disorder respiratory? Since the patient has a metabolic acidosis, is this a hyperchloriemic or high anion gap type metabolic acidosis? Is there a metabolic alkalosis present as well? What is the gap? What is the most likely cause of this acid-base disorder?,Case 5: Internal Consistency,H+ = 24(PaCO2 )/HCO3-= 2416/10=38The data are internally consistent.,Case 5: Acidemia or Alkalemia,The arterial pH = 7.42 Neither. The pH is normal, but this dose not exclude underlying acid-base disorders.,Case 5: Respiratory or Metabolic,For any primary acid-base disorder , one cannot fully return pH to normal. The finding of a normal pH implies 2 primary disorders. There must be a primary respiratory alkalosis （PaCO2=16）but also a primary metabolic acidosis (because the pH is normal).,Case 5: Anion Gap,AG = Na+ - (Cl- + HCO3-) = 12 2 AG = 140 108 10 = 22 The normal AG is 10 to 14. This is a high anion gap type metabolic acidosis.,Case 5: AG,AG = 22 10 = 12 When one adds 12 to the measured bicarbonate of 10 to equal 22, this indicates that there is no underlying metabolic alkalosis.,Case 5: Causes,This patient appears to have ingested salicylate. The finding of a mixed acid-based disturbance of a respiratory alkalosis and metabolic acidosis is very suggestive of this disturbance. In particular, this acid-base disturbance in the setting of pulmonary edema is highly suggestive of salicylate intoxication.,Case 6,A 28-year old woman is admitted for unexplained delirium and acidosis after cleaning her motor cycle with solvents. Na=139 K=1.7 Cl=115 HCO3=12 PCO2=28 PO2=92 pH=7.24 BUN=7 Cr=1.3 Urinalysis pH = 6.5 Specific gravity=1.020 NO cells or casts,Are the data internally consistent? Is the patient acidemic or alkalemic? Is the primary disorder respiratory? Since the patient has a metabolic acidosis, is this a hyperchloriemic or high anion gap type metabolic acidosis? What are the causes of a hyperchlo- riemic metabolic acidosis? How does one distinguish between the possibilites. What are the potential causes of distal renal tubular acidosis in this woman?,Case 6: Internal Consistency,H+ = 24(PaCO2 )/HCO3-= 2428/12 = 56The data are internally consistent.,Case 6: Acidemia or Alkalemia,The arterial pH = 7.24 7.40 The patients is acidemic,Case 6: Respiratory or Metabolic,pH=7.24, PaCO2=28 The primary disorder is a metabolic acidosis as the PaCO2 is not elevated,Case 6: Compensation Appropriate?,The expected PaCO2 = 1.512 + 82 = 26+2 Because the actual PaCO2 is 28, the change in PaCO2 is appropriate, and the hypoventilation is secondary to the metabolic alkalosis. This is a simple, compensalated metabolic alkalosis.,