The document outlines a 5-step process for arterial blood gas analysis: 1) Determine if there is acidosis or alkalosis, 2) Calculate compensatory changes to identify mixed disorders, 3) Calculate anion gap, 4) Correct HCO3 levels if anion gap is high, 5) Correlate results with patient's condition. Examples demonstrate using this process to diagnose a patient with respiratory acidosis and metabolic alkalosis in one case, and high anion gap metabolic acidosis with metabolic alkalosis in another.

1. Arterial blood gas analysis
Dr. Mashfiqul Hasan
 5 steps
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2. Step 1
 Determine the
primary disorder
 Acidosis or alkalosis?
12/11/12  Metabolic or 2

3. Example - 1
 PH = 7.32  WHAT IS
 HCO3 = 40 THE
meq/L (High) DIAGNOSIS
 PaCO2 = 60 ?
mm of Hg
(High)
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4. Respiratory acidosis
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5. Example - 2
 PH = 7.22
 HCO3 = 14 meq/L (Low)
 PaCO2 = 27 mm of Hg (Low)
 WHAT IS THE
DIAGNOSIS?
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6. Metabolic
acidosis
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7. Step - 2
 Calculate the range of
compensatory
mechanism to determine
the presence of mixed
acid base disorder.
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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?
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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 in
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PaCO2 9

10. But here HCO3 is 40
meq/L.
What does it indicate?
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11.  It indicates mixed acid
base disorder.
 Superimposed
metabolic alkalosis
which causes rise of
HCO3 disproportionately
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12. Final diagnoses
 Chronic respiratory
acidosis with metabolic
alkalosis
 Which may develop in a
patient of Corpulmonale
getting diuretics therapy
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13. Example - 2
 PH = 7.22
 HCO3 = 14 meq/L (Low)
 PaCO2 = 27 mm of Hg (Low)
 Metabolic acidosis
 How to calculate the
12/11/12 compensatory change? 13

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/L
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15. PaCO2 is consistent with
calculation
 So there is no mixed acid
base disorder according
to step 2.
 Final diagnosis is
metabolic acidosis.
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16. Step - 3
 Calculate the anion
gap.
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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/L
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18. Calculation of anion gap
 Na+ - (Cl- + HCO3-) = anion
gap
 140 – (90 + 40) = 10
mmol/L
 Anion gap is normal
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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?
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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-
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12=15 20

21. Step - 4
 Calculate the HCO3-
concentration if the
anion gap is
increased.
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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.
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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/L
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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.
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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.
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26. Final diagnosis of
example 2
 High Anion gap Metabolic
acidosis with concomitant
metabolic alkalosis
 Which may be present in
alcoholic ketoacidosis with
excessive vomiting
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27. Final step
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28. Final step
 Examine the patient to
determine whether the
clinical signs are
compatible with the acid
base analysis thus
obtained.
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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.
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30. Thanks for patient
hearing
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