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Key Features

Essentials of Diagnosis

  • Hallmark of this disorder is that metabolic acidosis (thus low HCO3) is associated with normal serum Cl, so that the anion gap increases

  • Decreased HCO3 is also seen also in respiratory alkalosis, but pH distinguishes between the two disorders

General Considerations

  • Calculation of the anion gap is useful in determining the cause of the metabolic acidosis

  • Normochloremic (increased anion gap) metabolic acidosis

    • Generally results from addition to the blood of organic acids such as lactate, acetoacetate, β-hydroxybutyrate, and exogenous toxins

    • Uremia produces an increased anion gap metabolic acidosis via unexcreted organic acids and anions

Etiology

  • Lactic acidosis

    • Type A: cardiogenic, septic, or hemorrhagic shock; carbon monoxide or cyanide poisoning

    • Type B: metabolic causes (eg, diabetes mellitus, ketoacidosis, liver disease, kidney disease, infection, leukemia, or lymphoma); toxins (eg, ethanol, methanol, salicylates, isoniazid, or metformin); nucleoside analog reverse transcriptase inhibitors

  • Diabetic ketoacidosis

  • Alcoholic ketoacidosis

    • Acid-base disorders in alcoholism are frequently mixed (10% have triple acid-base disorder)

    • Three types of metabolic acidoses: ketoacidosis, lactic acidosis, and hyperchloremic acidosis from bicarbonate loss in urine from ketonuria

    • Metabolic alkalosis from volume contraction and vomiting

    • Respiratory alkalosis from alcohol withdrawal, pain, sepsis, or liver disease

  • Uremic acidosis (usually at glomerular filtration rate < 15–30 mL/min)

  • Ethylene glycol toxicity

  • Methanol toxicity

  • Salicylate toxicity (mixed metabolic acidosis with respiratory alkalosis)

Clinical Findings

Symptoms and Signs

  • Symptoms are mainly those of the underlying disorder

  • Compensatory hyperventilation may be misinterpreted as a primary respiratory disorder

  • When severe, Kussmaul respirations (deep, regular, sighing respirations indicating intense stimulation of the respiratory center) occur

Diagnosis

Laboratory Tests

  • See Table 21–12

  • Blood pH, serum HCO3, and PCO2 are decreased

  • Anion gap is increased (normochloremic)

  • Hyperkalemia may be seen

  • In lactic acidosis, lactate levels are at least 4–5 mEq/L but commonly 10–30 mEq/L

  • The diagnosis of alcoholic ketoacidosis is supported by the absence of a diabetic history and no evidence of glucose intolerance after initial therapy

Table 21–12.Primary acid-base disorders and expected compensation.

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