metabolic alkalosis

Etiology

• chloride-responsive (urine Cl- < 10-15 meq/L)
  • contraction alkalosis (volume depletion) most common
  • vomiting/NG suction: upper GI loss of HCl
  • thiazide & loop diuretics: renal loss of HCl
  • cirrhosis or heart failure may cause hypervolemia with hypotension due to low effective arterial volume
  • cystic fibrosis
  • villous adenoma
  • congenital chloridorrhea
  • nephrotic syndrome
• chloride-resistant (urine Cl- > 15-20 meq/L) [much less common]
  • hypertensive
    • primary hyperaldosteronism
    • Cushing's syndrome
    • renal artery stenosis
    • glucocorticoid/mineralocorticoid therapy
    • renin-secreting tumor
    • inhibitors of 11-beta hydroxysteroid dehydrogenase
      • licorice ingestion
      • tobacco chewing
      • Liddle's syndrome
    • diuretics & K+ depletion
    • hypercalcemia
    • hypoparathyroidism
  • normotensive or hypotensive
    • Bartter's syndrome
    • Gitelman's syndrome
    • gentamicin
• pCO2 higher than expected
  • COPD & diuretics
  • ARDS & diuretics
• pCO2 lower than expected
  • CHF & diuretics
  • cirrhosis & diuretics
  • hyperemesis

Clinical manifestations

• respiratory compensation with hypoventilation
• weakness
• muscle cramps
• hyperreflexia
• dysrhythmias
• hypertension suggests chloride-resistance (see etiology)
• hypotension more common
• hypervolemia may occur with hypotension (cirrhosis, heart failure) or hypertension (hyperaldosteronism, renin-secreting tumor)

Laboratory

• arterial blood gas
  • increased pH (pH > 7.44)
  • increased pCO2
• electrolytes
  • serum bicarbonate: increased HCO3-
  • serum K+: hypokalemia
  • serum chloride: hypocloremia
• serum aldosterone: may be increased
• urine chloride
  • < 25 meq/L (chloride-responsive)
  • > 40 meq/L (chloride-resistant)
  • diuretic use may initially cause a rise in urine chloride followed by a decline to < 25 meq/L

* Predicted pCO2 (respiratory) compensation for pure metabolic alkalosis (PaCO2, arterial)

• pCO2 (mm Hg) +/- 5 = 0.9 x HCO3- (meq/L) + 15
• pCO2 increases 0.7 mm Hg for each 1 meq/L rise in [[[A18927|HCO3-]]]
• response is limited by hypoxemia

Management

• correct underlying disorder
  • remove renin-secreting tumor
  • remove aldosterone-secreting tumor
  • discontinue offending agents
  • correct hypovolemia
• chloride-responsive (saline-responsive) alkalosis
  • normal saline to correct hypovolemia
  • NaCl tablets
  • treat hypokalemia with KCl
  • acetazolamide 250-500 mg PO or IV every 8 hours
    • CHF with edema present
    • cor pulmonale
    • hepatic cirrhosis
    • post-hypercapnic state
  • reduction of gastric HCl loss
    • proton-pump inhibitor
      • lansoprazole
      • omeprazole
    • H2-receptor antagonist
      • ranitidine
      • cimetidine
• chloride-resistant alkalosis
  • discontinue offending agents
    • thiazides
    • loop diuretics
  • correct Mg+2 deficiency
  • correct K+ deficits
  • amiloride, triamterene or spironolactone
• treatment of severe metabolic alkalosis (pH > 7.55)
  • particularly if contraindication to NaCl administration
    • heart failure
    • renal failure
  • HCl solution
    • 150 mL of 1.0 N HCL in 1 L H2O (H+ 130 meq/L)
    • administer through central line @< 0.2 meq/kg/hr
    • do not infuse directly into the right atrium
    • H+ deficit:
      • 0.5 x LBM* (measured - desired) [[[A18927|HCO3-]]]
      • replace 1/2 the deficit in the 1st 12 hours, & the remainder in the following 24 hours
  • hemodialysis

* LBM: lean body mass in kg.

More general terms

• alkalosis