Case Studies In Acid Base Disorders

1. Case Studies on Acid-Base
Disorders
William T. Browne, M.D.

2. Important concepts
•-emia refers to a pH
•-osis refers to an abnormal
condition or process

3. Normal ranges
•pH 7.36-7.44
•pCO
2
38-42 mm Hg
•HCO
3
-
22-28 mEq/L

4. Fact or Fiction?
•A pCO
2
< 40 mm Hg always
implies a respiratory alkalosis
•FICTION!

5. Fact or Fiction?
•A patient cannot have a
metabolic acidosis and a
metabolic alkalosis
simultaneously
•FICTION!

6. Fact or Fiction?
•A patient can have a metabolic
acidosis with a compensatory
respiratory alkalosis
•FICTION!

7. Important concepts
•-emia refers to a pH
•-osis refers to an abnormal
condition or process

8. Six Steps for Acid-Base
Analysis

9. Six Steps for Acid-Base Analysis
Step 1. Is there an acidemia or alkalemia?

10. Six Steps for Acid-Base Analysis
Step 2.Is the primary process metabolic
or respiratory?

11. Six Steps for Acid-Base Analysis
Step 3:If the primary process is
respiratory, is it acute or chronic?

12. Six Steps for Acid-Base Analysis
Step 4:Is there an
anion gap?
Na
+
- Cl
-
- HCO
3
-
> 12?

13. Six Steps for Acid-Base Analysis
Step 5:Is the respiratory
compensation adequate?
Expected pCO
2
range =
[1.5(measured HCO
3
-
)]+8+/- 2

14. Six Steps for Acid-Base Analysis
Step 6:Are there any other
metabolic disturbances?
Corrected HCO
3
-
=
(Measured HCO
3
-
) + (AG-12)

15. Problem #1
•60 yo male presents to the ED from a
nursing home. You have no history other
than he has been breathing rapidly and is
less responsive than usual.
•Na
+
123 Cl
-
99HCO
3
-
5

•pH 7.31pCO
2
10

16. Six Steps for Acid-Base Analysis
Step 1. Is there an acidemia or alkalemia?
Acidemia

17. Six Steps for Acid-Base Analysis
Step 2.Is the primary process metabolic
or respiratory?
pCO
2
= 10 should drive pH ↑
HCO
3
-
= 5 should drive pH ↓

18. Six Steps for Acid-Base Analysis
Step 3:If the primary process is
respiratory, is it acute or chronic?
Skip this step as primary process is
metabolic!

19. Six Steps for Acid-Base Analysis
Step 4:Is there an
anion gap?
Na
+
- Cl
-
- HCO
3
-
> 12?
123 - 99 -5 = 19
Anion Gap Metabolic Acidosis

20. Causes of anion gap metabolic
acidosis
•Methanol
•Uremia
•Diabetic ketoacidosis
•Paraldehyde
•Isopropyl alcohol
•Lactic acidosis
•Ethylene glycol
•Salicylates
•Rhabdomyolysis

21. Six Steps for Acid-Base Analysis
Step 5:Is the respiratory compensation
adequate?
Expected pCO
2
range =
[1.5(measured HCO
3
-
)]+8+/- 2
[1.5 (5) +8] +/- 2 = [13.5 – 17.5]
pCO
2
= 10, therefore it IS a respiratory alkalosis

22. Six Steps for Acid-Base Analysis
Step 6:Are there any other metabolic
disturbances?
Corrected HCO
3
-
=
(Measured HCO
3
-
) + (AG-12)
(5) + (19-12) = 12
Since this does not correct bicarbonate back to
normal, there is a non anion gap acidosis

23. Causes of non anion gap acidosis
with hypokalemia
•Diarrhea
•Ureteral diversion
•Renal tubular acidosis
–Proximal
–Distal
•Mineralcorticoid
deficiency
•Carbonic anydrase
inhibitor
–Acetazolamide
–Mefenamic acid
•Post hypocapneic
state

24. Causes of non anion gap acidosis
with hyperkalemia
•Early renal failure
•Renal disease
–SLE interstitial
nephritis
–Amyloidosis
–Hydronephrosis
–Sickle cell
nephropathy
•Acidifying agents
–Ammonium chloride
–Calcium chloride
–Arginine
•Sulfur toxicity

25. Problem #2
•42 yo female has the flu for four days with
incessant vomiting. She presents to the
ED two days after stopping insulin due to
no food intake
•Na
+
130 Cl
-
80HCO
3
-
10

•pH 7.21pCO
2
25

26. Six Steps for Acid-Base Analysis
Step 1. Is there an acidemia or alkalemia?
Acidemia

27. Six Steps for Acid-Base Analysis
Step 2.Is the primary process metabolic
or respiratory?
pCO
2
= 25 should drive pH ↑
HCO
3
-
= 10 should drive pH ↓

28. Six Steps for Acid-Base Analysis
Step 3:If the primary process is
respiratory, is it acute or chronic?
Skip this step as primary process is
metabolic!

29. Six Steps for Acid-Base Analysis
Step 4:Is there an
anion gap?
Na
+
- Cl
-
- HCO
3
-
> 12?
130 - 80 - 10 = 40!!
Anion Gap Metabolic Acidosis

30. Six Steps for Acid-Base Analysis
Step 5:Is the respiratory compensation
adequate?
Expected pCO
2
range =
[1.5(measured HCO
3
-
)]+8+/- 2
[1.5 (10) +8] +/- 2 = [21 - 25]
pCO
2
= 25, therefore this is normal respiratory
compensation

31. Six Steps for Acid-Base Analysis
Step 6:Are there any other metabolic
disturbances?
Corrected HCO
3
-
=
(Measured HCO
3
-
) + (AG-12)
(10) + (40-12) = 38
Since this over corrects bicarbonate there is a
metabolic ALKALOSIS!!

32. Problem #3
•30 year old female BMT patient with
neutropenic fever has been receiving
multiple antibiotics including amphotericin
B. You are called to the bedside for her
fevers, rigors, and dyspnea
•Na
+
125 Cl
-
100HCO
3
-
8

•pH 7.07pCO
2
28 K
+
2.5

33. Six Steps for Acid-Base Analysis
Step 1. Is there an acidemia or alkalemia?
Acidemia

34. Six Steps for Acid-Base Analysis
Step 2.Is the primary process metabolic
or respiratory?
pCO
2
= 28 should drive pH ↑
HCO
3
-
= 8 should drive pH ↓

35. Six Steps for Acid-Base Analysis
Step 3:If the primary process is
respiratory, is it acute or chronic?
Skip this step as primary process is
metabolic!

36. Six Steps for Acid-Base Analysis
Step 4:Is there an
anion gap?
Na
+
- Cl
-
- HCO
3
-
> 12?
125 - 100 - 8 = 17
Anion Gap Metabolic Acidosis

37. Six Steps for Acid-Base Analysis
Step 5:Is the respiratory compensation
adequate?
Expected pCO
2
range =
[1.5(measured HCO
3
-
)]+8+/- 2
[1.5 (8) +8] +/- 2 = [18-22]
pCO
2
= 28, therefore this is a respiratory acidosis
even though the value is below 40!!

38. Six Steps for Acid-Base Analysis
Step 6:Are there any other metabolic
disturbances?
Corrected HCO
3
-
=
(Measured HCO
3
-
) + (AG-12)
(8) + (17-12) = 13
Since this is below the normal range after
correction, there is a non anion gap acidosis

39. If data doesn’t make sense, check
the validity of your data!
24 (pCO
2
)/(HCO
3
-
) = [H
+
]
80 – [H
+
] = xx
xx should equal the last two digits
of the pH. 7.xx

40. [email protected]