Case Studies on 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 • pCO2 38-42 mm Hg • HCO3- 22-28 mEq/L

4. Fact or Fiction? • A pCO2 < 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- - HCO3- > 12?

13. Six Steps for Acid-Base Analysis Step 5: Is the respiratory compensation adequate? Expected pCO2 range = [1.5(measured HCO3-)]+8+/- 2

14. Six Steps for Acid-Base Analysis Step 6: Are there any other metabolic disturbances? Corrected HCO3- = (Measured HCO3-) + (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- 99 HCO3- 5 • pH 7.31 pCO2 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? pCO2 = 10 should drive pH ↑ HCO3- = 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- - HCO3- > 12? 123 - 99 - 5 = 19 Anion Gap Metabolic Acidosis

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

21. Six Steps for Acid-Base Analysis Step 5: Is the respiratory compensation adequate? Expected pCO2 range = [1.5(measured HCO3-)]+8+/- 2 [1.5 (5) +8] +/- 2 = [13.5 – 17.5] pCO2 = 10, therefore it IS a respiratory alkalosis

22. Six Steps for Acid-Base Analysis Step 6: Are there any other metabolic disturbances? Corrected HCO3- = (Measured HCO3-) + (AG-12) (5) + (19-12) = 12 Since this does not correct bicarbonate back to normal, there is a non anion gap acidosis

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

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

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- 80 HCO3- 10 • pH 7.21 pCO2 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? pCO2 = 25 should drive pH ↑ HCO3- = 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- - HCO3- > 12? 130 - 80 - 10 = 40!! Anion Gap Metabolic Acidosis

30. Six Steps for Acid-Base Analysis Step 5: Is the respiratory compensation adequate? Expected pCO2 range = [1.5(measured HCO3-)]+8+/- 2 [1.5 (10) +8] +/- 2 = [21 - 25] pCO2 = 25, therefore this is normal respiratory compensation

31. Six Steps for Acid-Base Analysis Step 6: Are there any other metabolic disturbances? Corrected HCO3- = (Measured HCO3-) + (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- 100 HCO3- 8 • pH 7.07 pCO2 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? pCO2 = 28 should drive pH ↑ HCO3- = 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- - HCO3- > 12? 125 - 100 - 8 = 17 Anion Gap Metabolic Acidosis

37. Six Steps for Acid-Base Analysis Step 5: Is the respiratory compensation adequate? Expected pCO2 range = [1.5(measured HCO3-)]+8+/- 2 [1.5 (8) +8] +/- 2 = [18-22] pCO2 = 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 HCO3- = (Measured HCO3-) + (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 (pCO2)/(HCO3-) = [H+] 80 – [H+] = xx xx should equal the last two digits of the pH. 7.xx

40. brow2110@umn.edu