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Metabolic Acidosis

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Metabolic Acidosis, Non-Anion Gap Metabolic Acidosis, Hypochloremic Metabolic Acidosis, Anion Gap Metabolic Acidosis, Metabolic Acidosis with Anion Gap

  • Types
  1. Elevated Anion Gap Metabolic Acidosis
  2. Hyperchloremic Metabolic Acidosis (normal Anion Gap)
    1. See Hyperchloremia
  • Causes
  • Common
  1. Most common causes of Anion Gap Metabolic Acidosis in seriously ill patients
    1. Lactic Acidosis
    2. Acute Renal Failure
    3. Diabetic Ketoacidosis
  2. Most common causes of Non-Anion Gap Metabolic Acidosis
    1. Gastrointestinal or renal losses of bicarbonate
    2. Volume Resuscitation with Normal Saline
  • Causes
  • Metabolic Acidosis and Elevated Anion Gap (Mnemonic: "MUD PILERS")
  1. Methanol, Metformin
  2. Uremia
  3. Diabetic Ketoacidosis (DKA), Alcoholic Ketoacidosis or Starvation Ketosis
  4. Paraldehyde, Phenformin (neither used in U.S. now)
    1. Propofol Infusion Syndrome has been proposed as a replacement in mnemonic
  5. Iron, Isopropyl Alcohol, and Isoniazid (due to Seizures)
  6. Lactic Acidosis
  7. Ethylene Glycol, Ethyl Alcohol
  8. Rhabdomyolysis
  9. Salicylates (do not miss Chronic Salicylate Poisoning)
  10. Other Causes
    1. Hyperalbuminemia
    2. Administered anions
  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
    7. Excessive Normal Saline infused (liters)
  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
  3. Mnemonic: USED CARP (incomplete)
    1. Ureteral diversion
    2. Small Bowel Fistula
    3. Extra Chloride (ammonium chloride, Calcium Chloride)
    4. Diarrhea
    5. Carbonic anhydrase inhibitors (Acetazolamide, Mefenamic acid)
    6. Adrenal Insufficiency
    7. Renal Tubular Acidosis
    8. Pancreatic Fistula
    9. (2016) CALS Manual, 14th ed, 1: 44
  1. Toxic Alcohol ingestion
    1. Eythylene glycol
    2. Methanol
  2. Serum Ketones are increased (Ketosis)
    1. Alcoholic Ketoacidosis
    2. Diabetic Ketoacidosis
  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. See labs below to further differentiate cause of Metabolic Acidosis with Anion Gap
    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
  • Labs
  • Consider in Metabolic Acidosis with Increased Anion Gap
  1. Basic chemistry panel as above (Serum Glucose, Blood Urea Nitrogen)
  2. Serum Lactate
  3. Serum Ketones (or Beta hydroxybutyrate)
  4. Salicylate Level
  5. Blood Alcohol level
  6. Ethylene Glycol level
  7. Osmolal Gap
    1. Elevated in toxic Alcohol ingestion (Alcohol, Ethylene Glycol, Methanol, isopropanol)
    2. Note that Isopropanol (Isopropyl Alcohol) does not increase Anion Gap, but does increase Osmolal Gap
      1. Isopropanol is the most common ingested toxic Alcohol
      2. It also causes a Ketosis without acidosis (due to acetone which has no charge)
  8. Creatinine Phosphokinase (CPK)
  9. Iron level
  10. Serum Albumin
  • References
  1. Arieff (1993) J Crit Illn 8(2): 224-46 [PubMed]
  2. Narins (1982) Am J Med 72:496 [PubMed]
  3. Narins (1980) Medicine 59:161-95 [PubMed]
  4. Ghosh (2000) Fed Pract p. 23-33
  5. Rutecki (Dec 1997) Consultant, p. 3067-74
  6. Rutecki (Jan 1998) Consultant, p. 131-42