Alkalosis, Metabolic

Key Features

Essentials of Diagnosis

• High serum HCO₃^– with alkalemia (high pH)

• 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 chloride responsive or chloride unresponsive (Table 21–15)

• Chloride responsive (U_Cl^– < 20 mEq/L)

  • Involves the loss of chloride and extracellular volume

  • In vomiting and nasogastric suction, loss of acid (HCl) generates the alkalosis and volume contraction from Cl^– loss maintains the alkalosis

  • Distally acting diuretics that cause chloride loss, eg, loop and thiazide diuretics, are a common cause of metabolic alkalosis; U_Cl^– levels can be unreliable when diuretics have been used since they increase U_Cl^– excretion

• Chloride unresponsive (U_Cl^– > 20 mEq/L)

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

Etiology

• Chloride responsive (U_Cl < 20 mEq/L)

  • Excessive body bicarbonate content

    • Renal alkalosis

      • Diuretic therapy

      • Poorly reabsorbable anion therapy (carbenicillin, penicillin, sulfate, phosphate)

      • Posthypercapnia

    • Gastrointestinal alkalosis

      • Loss of HCl from vomiting or nasogastric suction

      • Intestinal alkalosis: chloride diarrhea

      • NaHCO₃ (baking soda)

      • Sodium citrate, lactate, gluconate, acetate

      • Transfusions

      • Antacids

  • Normal body bicarbonate content: Contraction alkalosis

• Chloride unresponsive (U_Cl > 20 mEq/L)

  • Excessive body bicarbonate content

    • Renal alkalosis, normotensive

      • Bartter syndrome (renal salt wasting and secondary hyperaldosteronism)

      • Severe potassium depletion

      • Refeeding alkalosis

      • Hypercalcemia and hypoparathyroidism

    • Renal alkalosis, hypertensive

      • Endogenous mineralocorticoids (primary hyperaldosteronism, hyperreninism, adrenal enzyme deficiency: 11-β- and 17-α-hydroxylase, Liddle syndrome)

      • Exogenous alkali

      • Exogenous mineralocorticoids

      • Licorice

Clinical Findings

Symptoms and Signs

• No characteristic symptoms or signs

• However, hypopnea can be present in severe cases

• Alkalemia decreases oxygen delivery by shifting the oxygen disassociation curve of hemoglobin

• Concomitant hypokalemia may cause weakness and hyporeflexia

Diagnosis

Laboratory ...