Arterial blood gas analysis

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Here I have tried to give example of analysis of ABG. This is based on Harrison's & CMDT.

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Arterial blood gas analysis

  1. 1. Arterial blood gas analysis Dr. Mashfiqul Hasan  5 steps12/11/12 1
  2. 2. Step 1  Determine the primary disorder  Acidosis or alkalosis?12/11/12  Metabolic or 2
  3. 3. Example - 1  PH = 7.32  WHAT IS  HCO3 = 40 THE meq/L (High) DIAGNOSIS  PaCO2 = 60 ? mm of Hg (High)12/11/12 3
  4. 4. Respiratory acidosis12/11/12 4
  5. 5. Example - 2  PH = 7.22  HCO3 = 14 meq/L (Low)  PaCO2 = 27 mm of Hg (Low)  WHAT IS THE DIAGNOSIS?12/11/12 5
  6. 6. Metabolic acidosis12/11/12 6
  7. 7. Step - 2  Calculate the range of compensatory mechanism to determine the presence of mixed acid base disorder.12/11/12 7
  8. 8. Example - 1  PH = 7.32  HCO3 = 40 meq/L (High)  PaCO2 = 60 mm of Hg (High) Respiratory acidosis  How to calculate the compensatory change?12/11/12 8
  9. 9. Calculation  Primary change in  So, HCO3 should PaCO2 is : rise by 7 meq/L 60-40=20mm of Hg here. raised  Compensatory  HCO3 level change in HCO3 should be 3.5 should be meq/L rise for per 24+7=31 meq/L 10 mm of Hg rise in12/11/12 PaCO2 9
  10. 10. But here HCO3 is 40 meq/L. What does it indicate?12/11/12 10
  11. 11.  It indicates mixed acid base disorder.  Superimposed metabolic alkalosis which causes rise of HCO3 disproportionately12/11/12 11
  12. 12. Final diagnoses  Chronic respiratory acidosis with metabolic alkalosis  Which may develop in a patient of Corpulmonale getting diuretics therapy12/11/12 12
  13. 13. Example - 2  PH = 7.22  HCO3 = 14 meq/L (Low)  PaCO2 = 27 mm of Hg (Low)  Metabolic acidosis  How to calculate the12/11/12 compensatory change? 13
  14. 14. Calculation  So, PCO2 should  Primary change in HCO3 is : 24-14=10 fall by 13 mm of Hg here. meq fall  Compensatory change in PCO2 should be 1.3  PCO2 level mm of Hg fall for per 1 should be 40- meq fall in HCO3 13=27 meq/L12/11/12 14
  15. 15. PaCO2 is consistent with calculation  So there is no mixed acid base disorder according to step 2.  Final diagnosis is metabolic acidosis.12/11/12 15
  16. 16. Step - 3  Calculate the anion gap.12/11/12 16
  17. 17. Example -1  PH = 7.32  HCO3 = 40 meq/L (High)  PaCO2 = 60 mm of Hg (High)  Na+ = 140 mmol/L  K+ = 4 mmol/L  Cl- = 90 mmol/L12/11/12 17
  18. 18. Calculation of anion gap  Na+ - (Cl- + HCO3-) = anion gap  140 – (90 + 40) = 10 mmol/L  Anion gap is normal12/11/12 18
  19. 19. Example - 2  PH = 7.22  HCO3 = 14 meq/L (Low)  PaCO2 = 27 mm of Hg (Low)  Na+ = 142 mmol/L  K+ = 4.9 mmol/L  Cl- = 101 mmol/L  What is the anion gap?12/11/12 19
  20. 20. Calculation of anion gap  Na+ - (Cl- + HCO3-) = anion gap  142 – (101 + 14) = 27 mmol/L  Anion gap is increased  So the diagnosis is high anion gap metabolic acidosis.  Change of anion gap is 27-12/11/12 12=15 20
  21. 21. Step - 4  Calculate the HCO3- concentration if the anion gap is increased.12/11/12 21
  22. 22. Calculation of HCO3-  Corrected HCO3- = Measured HCO3- + the increase in anion gap  Corrected HCO3- should be the normal value for HCO3-, that is 24 mmol/L if there is no mixed acid base disorder.12/11/12 22
  23. 23. Example 2  PH = 7.22  HCO3 = 14 meq/L (Low)  PaCO2 = 27 mm of Hg (Low)  Na+ = 142 mmol/L  K+ = 4.9 mmol/L  Cl- = 101 mmol/L  Anion gap = 27 mmol/L  Change in anion gap = 15 mmol/L12/11/12 23
  24. 24. Calculation of HCO3-  Corrected HCO3- = Measured HCO3- + the increase in anion gap  Corrected HCO3- = 14+15 = 29 mmol/L  It is higher than normal.12/11/12 24
  25. 25. What does it indicate?  Higher corrected HCO3- indicates concomitant presence of metabolic alkalosis.  Lower corrected HCO3- indicates concomitant presence of non anion gap metabolic acidosis.12/11/12 25
  26. 26. Final diagnosis of example 2  High Anion gap Metabolic acidosis with concomitant metabolic alkalosis  Which may be present in alcoholic ketoacidosis with excessive vomiting12/11/12 26
  27. 27. Final step12/11/12 27
  28. 28. Final step  Examine the patient to determine whether the clinical signs are compatible with the acid base analysis thus obtained.12/11/12 28
  29. 29. 5 steps at a glance 1. Determine the primary disorder. 2. Calculate the compensatory change to determine the presence of mixed acid base disorder. 3. Calculate the anion gap. 4. If anion gap is high, calculate the corrected HCO3- level. 5. Correlate with the patient.12/11/12 29
  30. 30. Thanks for patient hearing12/11/12 30

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