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For further information, see CMDT Part 21-20: Metabolic Alkalosis

Key Features

Essentials of Diagnosis

  • High HCO3 with alkalemia

  • Evaluate effective circulating volume by physical examination

  • Urinary chloride concentration differentiates saline-responsive alkalosis from saline-unresponsive alkalosis

General Considerations

  • Etiology can be classified into saline responsive or saline unresponsive (Table 21–15)

  • Saline responsive

    • A sign of extracellular volume contraction

    • Much more commonly encountered than saline-unresponsive alkalosis, which implies excessive total body bicarbonate with either euvolemia or hypervolemia

    • Characterized by normotensive extracellular volume contraction and hypokalemia

    • Hypotension or orthostatic hypotension may be seen

    • Generally associated with hypokalemia, due partly to the direct effect of alkalosis on renal potassium excretion and partly to secondary hyperaldosteronism from volume contraction

  • Saline unresponsive

    • Implies a volume-expanded state as from hyperaldosteronism with accompanying hypokalemia from the renal mineralocorticoid effect

Table 21–15.Metabolic alkalosis.

Clinical Findings

Symptoms and Signs

  • No characteristic symptoms or signs

  • Hypotension and orthostasis may occur

  • Weakness and hyporeflexia occur if serum K+ is markedly low

  • Tetany and neuromuscular irritability occur rarely

Diagnosis

  • Arterial blood pH and bicarbonate are elevated

  • With respiratory compensation, arterial PCO2 is increased

  • Serum potassium and chloride are decreased

  • There may be an increased anion gap

  • The urine chloride can differentiate between saline-response (< 25 mEq/L) and unresponsive (> 40 mEq/L) causes

Treatment

Medications

Saline-responsive

  • Correct the extracellular volume deficit with isotonic saline

  • Discontinue diuretics

  • H2-blockers or proton pump inhibitors may be helpful in patients with alkalosis from nasogastric suctioning

  • If pulmonary or cardiovascular disease prohibits adequate resuscitation, acetazolamide will increase renal bicarbonate excretion

  • Hypokalemia may develop because bicarbonate excretion may induce kaliuresis

  • Dialysis with low-bicarbonate dialysate may be required in severe cases, especially when reduced kidney function is present

Saline-unresponsive

  • Blockage of ...

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