Nephrology Book

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Metabolic Acidosis

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  1. See Also
    1. Arterial Blood Gas
    2. ABG Interpretation
  2. Types
    1. Elevated Anion Gap metabolic acidosis
    2. Hyperchloremic metabolic acidosis (normal Anion Gap)
      1. See Hyperchloremia
  3. Causes: Elevated Anion Gap (Mnemonic: "MUD PILERS")
    1. Methanol
    2. Uremia
    3. Diabetic Ketoacidosis (DKA) or starvation ketosis
    4. Paraldehyde, Phenformin
    5. Isopropyl Alcohol, Isoniazid
    6. Lactic Acidosis
    7. Ethylene Glycol, Ethyl Alcohol
    8. Rhabdomyolysis
    9. Salicylates
    10. Other Causes: Hyperalbuminemia, administered anions
  4. Causes: Normal Anion Gap (Hyperchloremia)
    1. Hypokalemia with Metabolic acidosis
      1. Diarrhea
      2. Ureteral diversion
        1. Uretero-sigmoidostomy
        2. Ileal bladder
        3. Ileal ureter
      3. Renal Tubular Acidosis (proximal or distal)
      4. Mineralocorticoid Deficiency
        1. Angiotensin Deficiency: Liver Failure
        2. ACE Inhibitor
        3. Renin Deficiency
          1. Aging
          2. Extracellular fluid volume expansion
          3. Lead
          4. Beta Blockers
          5. Prostaglandin Inhibitor
          6. Methyldopa
      5. Carbonic Anhydrase Inhibitor
        1. Acetazolamide
        2. Mefenamic acid
      6. Post-hypocapnia
    2. Hyperkalemia (or normal potassium) Metabolic Acidosis
      1. Renal Failure (Early)
      2. Renal Disease
        1. SLE Interstitial Nephritis
        2. Amyloidosis
        3. Hydronephrosis
        4. Sickle Cell Nephropathy
      3. Acidifying agents
        1. Ammonium Chloride
        2. Calcium Chloride
        3. Arginine
      4. Sulfur toxicity
  5. Labs
    1. Arterial Blood Gas
      1. Arterial pH decreased
      2. Serum bicarbonate decreased
      3. PaCO2 decreased
        1. PaCO2 drops 1.2 mmHg per 1 meq/L bicarbonate fall
        2. Calculated PaCO2 = 1.5 x HCO3 + 8 (+/- 2)
          1. Useful in High Anion Gap Metabolic Acidosis
          2. Measured PaCO2 discrepancy: respiratory disorder
    2. Serum Chemistry panel
      1. Anion Gap
        1. Increased in high Anion Gap metabolic acidosis
      2. Excess Anion Gap <23 mEq/L
        1. Suggests Non-Anion Gap metabolic acidosis
      3. Serum Potassium
        1. Investigate normal Anion Gap metabolic acidosis
        2. See above
      4. Serum Chloride
        1. Elevated in normal Anion Gap metabolic acidosis
      5. Serum bicarbonate
        1. Decreased in increased Anion Gap metabolic acidosis
        2. Bicarbonate decrease matches Anion Gap increase
    3. Urinalysis with Urine pH
      1. Urine pH >6: Suggests Renal cause
      2. Urine pH <6: Suggests Gastrointestinal cause
    4. Urine Anion Gap (obtain urine electrolytes)
      1. Decreased Urine Anion Gap <-10
        1. Extrarenal non-Anion Gap Metabolic Acidosis
      2. Increased Urine Anion Gap >+10
        1. Renal non-Anion Gap Metabolic Acidosis
  6. References
    1. Arieff (1993) J Crit Illn 8(2):224
    2. Narins (1982) Am J Med 72:496
    3. Narins (1980) Medicine 59:161
    4. Ghosh (2000) Fed Pract p. 23-33
    5. Rutecki (Dec 1997) Consultant, p. 3067-74
    6. Rutecki (Jan 1998) Consultant, p. 131-42

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