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Nephrology Approach to Acid-Base Problem Solving Answer these four questions when solving acid-base problems: 1. What is the primary disturbance? 2. Is compensation appropriate? 3. What is the anion gap? 4. Does the change in the anion gap equal the change in the serum bicarbonate concentration (a value called the delta delta)? When diagnosing a primary acid-base disorder, remember that: . Acidemia is defined as apH <7.37. Metabolic acidosis = [HCO3] <22 mEq/L. Respiratory acidosis = arterialPcor>44 mm Hg. . Alkalemia is defined as a pH >7.44.Metabolic alkalosis = [HCOJ >26 mEq/L. Respiratory alkalosis = arteria] Pco, <36 mm Hg. STUDY TABLE: Compensatory Response to a Primary Acid-Base Disturbance Condition Expected Compensation lnterpretation Metabolic Acute: A arterial Pco2 = (1.5)[HCO3-] + 8 + 2 Failure of the arterial Pco2 to decrease to expected acidosis value = complicating respiratory acidosis Excessive decrease of the arterial Pco2 - complicating respiratory alkalosis Respiratory Acute: 1 mEq/L 1 in [HCO,-] for each 10 mm Hg t in Failure of the IHCO3-]to increase to the expected value = acidosis arterial Pco2 complicating metabolic acidosis Chronic: 3.5 mEq/L t in [HCO3 ]for each 10 mm Hg Excessive increase in IHCO3-] = 66mplicating metabolic t in arterial Pco2 alkalosis Metabolic 0.7 mm Hg 1 in arterial Pco2 for each 1 mEq/L t in This response is limited by hypoxemia alkalosis IHCO3-l Respiratory Acute: 2 mEq/L J in [HCOg-] for each 10 mm Hg I in Failure of the IHCO,-]to decrease to the expected alkalosis arterial Pco2 value = complicating metabolic alkalosis Chronic: 4-5 mEq/L J in [HCOa-] for each 10 mm Hg Excessive decrease in IHCO3 ]= complicating J in arterial Pco2 metabolic acidosis

. Acidemia is defined as apH <7.37. Metabolic acidosis = [HCO3] <22 mEq/L. Respiratory acidosis = arterialPcor>44 mm Hg. . Alkalemia is defined as a pH >7.44.Metabolic alkalosis = [HCOJ >26 mEq/L. Respiratory alkalosis = arteria] Pco, <36 mm Hg. STUDY TABLE: Compensatory Response to a Primary Acid-Base Disturbance Condition Expected Compensation lnterpretation Metabolic Acute: A arterial Pco2 = (1.5)[HCO3-] + 8 + 2 Failure of the arterial Pco2 to decrease to expected acidosis value = complicating respiratory acidosis Excessive decrease of the arterial Pco2 - complicating respiratory alkalosis Respiratory Acute: 1 mEq/L 1 in [HCO,-] for each 10 mm Hg t in Failure of the IHCO3-]to increase to the expected value = acidosis arterial Pco2 complicating metabolic acidosis Chronic: 3.5 mEq/L t in [HCO3 ]for each 10 mm Hg Excessive increase in IHCO3-] = 66mplicating metabolic t in arterial Pco2 alkalosis Metabolic 0.7 mm Hg 1 in arterial Pco2 for each 1 mEq/L t in This response is limited by hypoxemia alkalosis IHCO3-l Respiratory Acute: 2 mEq/L J in [HCOg-] for each 10 mm Hg I in Failure of the IHCO,-]to decrease to the expected alkalosis arterial Pco2 value = complicating metabolic alkalosis Chronic: 4-5 mEq/L J in [HCOa-] for each 10 mm Hg Excessive decrease in IHCO3 ]= complicating J in arterial Pco2 metabolic acidosis Anion Gap The anion gap = [Na*] ([CI ]+ [HCO3 ]). The normal anion gap is B 10 + 2mBqlL. Acidoses can be divided into normal anion gap acidosis and increased anion gap acidosis. Always calculate the anion gap, regardless of the metabolic disturbance.

. Acidemia is defined as apH <7.37. Metabolic acidosis = [HCO3] <22 mEq/L. Respiratory acidosis = arterialPcor>44 mm Hg. . Alkalemia is defined as a pH >7.44.Metabolic alkalosis = [HCOJ >26 mEq/L. Respiratory alkalosis = arteria] Pco, <36 mm Hg. STUDY TABLE: Compensatory Response to a Primary Acid-Base Disturbance Condition Expected Compensation lnterpretation Metabolic Acute: A arterial Pco2 = (1.5)[HCO3-] + 8 + 2 Failure of the arterial Pco2 to decrease to expected acidosis value = complicating respiratory acidosis Excessive decrease of the arterial Pco2 - complicating respiratory alkalosis Respiratory Acute: 1 mEq/L 1 in [HCO,-] for each 10 mm Hg t in Failure of the IHCO3-]to increase to the expected value = acidosis arterial Pco2 complicating metabolic acidosis Chronic: 3.5 mEq/L t in [HCO3 ]for each 10 mm Hg Excessive increase in IHCO3-] = 66mplicating metabolic t in arterial Pco2 alkalosis Metabolic 0.7 mm Hg 1 in arterial Pco2 for each 1 mEq/L t in This response is limited by hypoxemia alkalosis IHCO3-l Respiratory Acute: 2 mEq/L J in [HCOg-] for each 10 mm Hg I in Failure of the IHCO,-]to decrease to the expected alkalosis arterial Pco2 value = complicating metabolic alkalosis Chronic: 4-5 mEq/L J in [HCOa-] for each 10 mm Hg Excessive decrease in IHCO3 ]= complicating J in arterial Pco2 metabolic acidosis Anion Gap The anion gap = [Na*] ([CI ]+ [HCO3 ]). The normal anion gap is B 10 + 2mBqlL. Acidoses can be divided into normal anion gap acidosis and increased anion gap acidosis. Always calculate the anion gap, regardless of the metabolic disturbance. . When the primary disturbance is a metabolic acidosis, the anion gap differentiates increased anion gap from norrnal anion gap acidosis. . A reduced anion gap (<4 mEq/L) suggests multiple myeloma or hypoalbuminemia.

Anion Gap The anion gap = [Na*] ([CI ]+ [HCO3 ]). The normal anion gap is B 10 + 2mBqlL. Acidoses can be divided into normal anion gap acidosis and increased anion gap acidosis. Always calculate the anion gap, regardless of the metabolic disturbance. . When the primary disturbance is a metabolic acidosis, the anion gap differentiates increased anion gap from norrnal anion gap acidosis. . A reduced anion gap (<4 mEq/L) suggests multiple myeloma or hypoalbuminemia. lncreased Anion Gap Acidosis Common causes of increased anion gap metabolic acidosis include: . DKA r CKD o lactic acidosis (usuallybecause of tissue hypoperfusion) o aspirin toxicity . alcoholicketoacidosis o methanol and ethylene glycol poisoning (also typically associated with an osmolar gap) 267