1. The document outlines a group session on acid base interpretation that will include examples, concepts, and more examples. 2. It will divide participants into teams to work through questions to interpret acid-base imbalances, including determining if it is acidosis or alkalosis, the primary disorder, compensation, and ruling out mixed disorders. 3. The session provides the equation for calculating pH based on bicarbonate and PCO2, steps for acid-base interpretation including determining the primary change and compensatory change, and tips for interpretation including not considering blood gas data without electrolytes and recognizing that single disorders may result in a normal pH range.

1. S a b a h a t Z a i d i
S e n i o r C l i n i c a l F e l l o w
A I C U
N U H
Group session on acid base
interpretation

2. Layout of the session
1. Examples
2. Concepts
3. Examples again
4. Conclusion

3. Lets make teams!

4. Question!
1. Is it acidosis or alkalosis?
2. What is the primary disorder? (Respiratory or metabolic)
3. If respiratory, acute or chronic?
4. If metabolic acidosis, anion gap acidosis or non anion gap?
5. Is compensation adequate?
6. Ruled-out mixed disorder ?

5. 1. Is it acidosis or alkalosis?
2. What is the primary disorder?
(Respiratory or metabolic)
3. If respiratory, acute or chronic?
4. If metabolic acidosis, anion gap
acidosis or non anion gap?
5. Is compensation adequate?
6. Ruled-out mixed disorder ?

6. 1. Is it acidosis or alkalosis?
2. What is the primary disorder?
(Respiratory or metabolic)
3. If respiratory, acute or chronic?
4. If metabolic acidosis, anion gap
acidosis or non anion gap?
5. Is compensation adequate?
6. Ruled-out mixed disorder ?

7. 1. Is it acidosis or alkalosis?
2. What is the primary disorder?
(Respiratory or metabolic)
3. If respiratory, acute or chronic?
4. If metabolic acidosis, anion gap
acidosis or non anion gap?
5. Is compensation adequate?
6. Ruled-out mixed disorder ?

8. 1. Is it acidosis or alkalosis?
2. What is the primary disorder?
(Respiratory or metabolic)
3. If respiratory, acute or chronic?
4. If metabolic acidosis, anion gap
acidosis or non anion gap?
5. Is compensation adequate?
6. Ruled-out mixed disorder ?

9. Equation
pH = 6.1 + log [HCO3-]/0.03( Pco2)

10. Step 1
 PH < 7.35 – ACIDOSIS
 PH > 7.45 - ALKALOSIS

11. STEP 2
ACID BASE CHANGE
Acid-base disorder Primary change Compensatory change
Respiratory Acidosis pCO2 up HCO3 up
Respiratory Alkalosis pCO2 down HCO3 down
Metabolic Acidosis HCO3 down pCO2 down
Metabolic Alkalosis HCO3 up pCO2 up

12. Compensation

13. The Boston Rule

14. STEP 4 ANION GAP
 The principle of electro-neutrality
(Na + K) – (Cl + HCO3)
 Usually 12-16 mEq/l
 Difference is due to the unmeasured –ve charge on
the proteins (albumin), and SO4 and PO4-

15. Anion Gap
When Hco3 is lost, to maintain electro neutrality
Cl is conserved by the kidney’s and so Anion Gap
is normal.

16. Top Tips
 Do not interpret any blood gas data for acid-base diagnosis
without closely examining the serum electrolytes: Na+, K+, Cl.
 Single acid-base disorders do not lead to normal blood pH,
although pH can end up in the normal range (7.35 - 7.45) with a
single mild acid-base disorder, a truly normal pH with distinctly
abnormal HCO3 and PaCO2 invariably suggests two or more
primary disorders.
 Simplified rules predict the pH and HCO3- for a given change in
PaCO2. If the pH or HCO3- is higher or lower than expected for the
change in PaCO2, the patient probably has a metabolic acidbase
disorder as well.

17. Examples again….

18. Thank you!