Acid-Base Disorders

1. Acid-Base Disorders Robert Fields, DO St Joseph’s Mercy Hospital Emergency Dept.

3. 5 Steps is all you need • Check the pH • Find the primary disorder (Look at pCO2 and HCO3) • Calculate the anion gap (AG=Na – (HCO3 + Cl-) • Calculate the excess anion gap (AGp - AGn + HCO3p = X) • Winters formula pCO2 = 1.5(HCO3-) + 8

4. What do you really need to do this? • ABG, with pCO2 and pH • Chem 7 with Na+, Cl-, HCO3-

5. STEP 1, Check the pH • Acidemia, pH < 7.35 • Alkalemia, pH >7.45 • Made Simpler! Acidemia<7.40>Alkalemia • Acidosis/Alkalosis vs. Acidemia/Alkalemia • Know the “normals” of the rest. (This is not to hard as it is printed in the computer)

6. STEP 2, Find the Basic Problem • Look at the pCO2 and the HCO3- • Respiratory problems relate to pCO2 • Metabolic problems relate to HCO3-

7. Respiratory Acidosis • Causes • CNS depression • NMS disorders • Pulmonary edema • Ventilatory dysfunction

8. Respiratory Alkalosis • Causes • Anxiety • Hypoxia • CNS stimulants • Pregnancy • Sepsis • Excessive mechanical ventilation

9. Chloride responsive Vomiting Diuretics Dehydration Chloride unresponsive Excess mineral corticoid activity Cushing's, Conn’s The infamous licorice ingestion Metabolic Alkalosis

10. STEP 3, Check the Anion Gap

11. What is the Anion Gap? • Cations = Anions • Na+ + K+ etc. = HC03- + Cl- + Alb + etc • Simplified • Na+ = HC03- + Cl- + others • We will call the others, AG (anion gap) and solve for AG. • Therefore AG = Na+ - (HCO3- + Cl-)

12. Increased Anion Gap Metabolic Acidosis • Methanol • Uremia • DKA (starvation ketosis, alcohol ketosis) • Paraldehyde • INH, Iron • Lactic Acidemia (type A, B, D) • Ethanol, Ethylene Glycol • Salicylates

13. Columbia Encyclopedia: paraldehyde (pârăl'dəhīd') , nervous system depressant similar to alcohol in its effects and used as a sedative. A colorless flammable liquid with a disagreeable odor, paraldehyde produces sleep for up to 12 hr. with little or no muscle, heart, or respiratory depression. It is often given to alcoholics having delirium tremens, to induce sleep, and is also used to calm psychiatric patients. Like alcohol and other depressants it is addictive (see drug addiction and drug abuse). Paraldehyde is also used in the manufacture of synthetic resins, as a preservative, and in preparing leather. It is produced by treating acetaldehyde with a small amount of sulfuric acid.

14. Gastrointestinal Diarrhea Ureteral diversion Renal Loss RTA Early renal failure Acetozolamide Aldosterone inhibitors Normal Anion GapMetabolic Acidosis

19. Lactic Acid Production H+ +

20. + H++HCO3- CO2 + H2O + H2CO3

21. Buffering Species CO2 + H2O <----> H2CO3 carbonic anyhdrase H2CO3 <----> HCO3- + H+

24. STEP 4, Check the Anion Gap Excess • This is going to help you determine if there is an alkalosis or acidosis that is NOT related to the anion gap. • This done by doing this equation • AGp – AGn + HCO3-p = X • X should equal 24 if there is no additional acidosis or alkalosis.

25. The results of Step 4 • If you calculated < 20 mmol/L There is a an acidosis present that is unrelated to the AG. • If you calculated >30 mmol/L there is an alkalosis present.

26. What we are doing so far ? • 1. Determine the pH • 2. Finding primary disorder • 3. Finding AG Metabolic Acidosis if not already recognized • 4. Finding Metabolic Acidosis (unrelated to the AG) and/or metabolic Alkalosis if not yet recognized.

27. So What’s Left? • Respiratory Alkalosis or Acidosis that may have gone unrecognized. • Winter’s formula • pCO2 = 1.5 (HCO3) + 8 +-2

28. Examples

29. Example 1 • pH, 7.50 • pCO2, 20mm Hg • Na+, 140 mmol/L • Cl-, 103 mmol/L • HCO3-, 15

30. Results • Alkalemia • Primary disorder, respiratory • AG is 22, Therefore metabolic acidosis with AG. A-ha! Two disorders are present. • Excess AG, 22- 12 + 15 = 25 , no alkalosis or acidosis otherwise present. • Don’t need to do Winter’s as you can only have one respiratory problem. • Clinical correlation?

31. Salicylate Toxicity

32. Example 2 • pH, 7.40 • pCO2, 40mm Hg • Na+, 145 mmol/L • Cl-, 100 mmol/L • HCO3-, 24

33. Results • pH? Normal • Primary, What Primary? • Anion Gap = 21 • Excess anion gap = 21-12 + 24 =33, A significant metabolic alkalosis is present too! • Winter’s ? Nothing too bad here. • Clinical Correlation?

34. CRI (AG acidosis) with vomiting as uremia worsened

35. Example 3 • pH, 7.50 • pCO2, 20mm Hg • Na+, 145 mmol/L • Cl-, 100 mmol/L • HCO3-, 15

36. Example 3 • Alkalemia • Respiratory primarily • Anion Gap is 30, AG MA (MUDPILES) • Excess anion gap plus HC03 = 30-12 + 15 = 33, There it is the triple threat. • Don’t need Winter’s, respiratory determined as primary.

37. Clinical Correlation • Vomiting (metabolic alkalosis) • Alcoholic ketoacidosis (AG metabolic acidosis) • Pneumonia, (Respiratory alkalosis)

38. Example 4 • pH, 7.10 • pCO2, 50mm Hg • Na+, 145 mmol/L • Cl-, 100 mmol/L • HCO3-, 15

39. Example 4 • Acidemia • Respiratory and Metabolic • Anion Gap is 30, you know the drill • Excess AG + HCO3 = 30-12+15=33, Metabolic Alkalosis. • Clinical Correlation?

40. Clinical Correlation • DKA with vomiting, followed by aspiration and unresponsive.

41. Example 5 • pH 7.25 • pCO2, 45 • Na+, 137 • Cl-, 79 • HCO3-, 20

42. Example 5 • Acidemia • Metabolic • AG=38 • 38-12 + 20 = 46 • Winter’s ! 1.5(20) + 8 = 38

43. Clinical Correlation • Borhaave’s Esophageal Rupture • Anion Gap Acidosis from lactic acid and ketoacidosis • Metabolic alkalosis from profound dehydration and loss of gastric HCL into chest wall • Respiratory acidosis from large pleural effusion.

44. References • 1991 West J. Medicine, A Practical Approach to Acid-Base Disorders.