Anion Gap, low and high - causes

AG = Na - (Cl + HCO3)

Normal AG = 10 - 12 mEq/L

Normal anion gap (AG) = serum albumin x 3.

High AG >10-12. mEq/L.

Low AG gap - causes:

    • Hypoalbuminemia (normal AG is largely accounted for anionic plasma proteins - albumin)

    • Halide (Br- or I-) intoxication

    • Severe hyperlipidemia

    • Multiple myeloma (cationic IgG paraproteins)

    • Anion Gap Metabolic Acidosis:

    • MUDPILES:

      • Methanol, metformin, uremia, DKA, paraldehyde, INH, iron tablets, lactic acidosis, ethanol, ethylene glycol, salicylates, rhabdomyolysis

      • Check presence or absence of ketonuria:

      • Ketonuria: DKA, EtOH, paraldehyde poisoning, starvation, isopropyl alcohol intoxication (does not cause acidosis)

      • No ketonuria: uremia, lactic acidosis, methanol

  • Normal Anion Gap Metabolic Acidosis:

      • RTA types 1, 2, and 4

        • Renal HCO3- loss/RTA2

        • ▼ H+ secretion/RTA1

        • Hypoaldosterone related/RTA4

      • Nonrenal HCO3- loss in diarrhea, pancreatic fistula, biliary, urinary diversion, ileostomy.

      • Cholestyramine, or ingestion of Ca and Mg chloride

      • Rapid infusion of NS

      • Spironolactone, TMP, ACE-I, pentamidine, NSAIDs, cyclosporine, acetazolamide (CI inhibitors),beta blockers

Tx:

  • Treat the underlying cause

  • Severe acidosis (pH <7.2) may require treatment with parenteral NaHCO3.

  • Bicarbonate deficit may be calculated as follows:

    • HCO3 deficit in mEq/L = 0.5 x body wt in kg - (24 - measured HCO3).

  • Rapid infusion of sodium bicarbonate should be considered for only severe acidosis.

  • Overaggressive correction should be avoided to prevent overshoot alkalosis.

  • Hypernatremia and fluid overload can occur with NaHCO3 administration.

  • Serum electrolytes should be followed closely

Bicarbonate

  • 1 ampoule of 8.4% NaHCO3 = 50 mEq NaHCO3 = 1000 mEq Na/L

  • Give in D5W.

  • To give HCO3- in acute setting:

    • HCO3- deficit = 0.5 x body wt in Kg (24 - HCO3 measured). Keep the HCO3 desired 15 mEq/L.

    • 0.5 x body wt in kg (15 - bicarb measured).

    • Give 1/2 the dose slowly.

    • D5W + Sodium bicarbonate is generally the fluid of choice in Pts who are oliguric, hyperkalemic, and acidotic.