List the causes of metabolic alkalosis and explain how you will evaluate a patient with metabolic alkalosis.

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College Answer

Evaluation of causes of metabolic alkalosis requires a systematic approach involving history, examination and some specific investigations. Categories of aetiology include
• loss of hydrogen ions (gastrointestinal, renal)

• intracellular shift of hydrogen ions

• administration of alkali

• contraction alkalosis

•    History and examination will reveal, documented fluid losses

-(vomiting & gastric losses, laxative induced diarrhoea),

-signs of volume depletion (loss of bicarbonate free fluids),

- administered drugs (mineralocorticoids, diuretics , and antacids in renal failure) , alkali (bicarbonate, lactate, citrate etc)

• and recent hypercapnia.

• Blood investigations may reveal hypokalemia (with hydrogen shifting into cells), hypochloremia

•    Urinary findings may include excessive potassium excretion (reabsorbing hydrogen), alkaline pH (increased bicarbonate) and inappropriately elevated chloride excretion (diuretic therapy, hypokalaemia).

•          Using Stewart’s physicochemical approach, an isolated increase in Strong ion difference (SID) seen with the use of solutions such as plasmalyte or NaHCO3 or a reduction in ATOT seen with hypoalbuminemia can lead to metabolic alkalosis

Discussion

The diagnostic approach to metabolic alkalosis is discussed in more detail elsewhere.

Instead of a text excess, I will reproduce the diagnostic flowchart which was suggested by a Medscape article, and which seemed like a nice way of remembering this process.

diagnostic algorithm for metabolic alkalosis

This flowchart can be converted into the form of a point-form answer:

  • History and examination
    • Recent exogenous bicarbonate administration
    • Milk-alkali syndrome
    • Hypercalcemia
    • β-lactam use
    • Cystic fibrosis
  • Low urinary chloride
    • Recent diuretic therapy
    • Gastric losses via NG suction or vomiting,
    • Villous adenoma of colon
    • Post-hypercapneic (compensatory) alkalosis
  • High urinary chloride and normal blood pressure
    • Ongoing diuretic therapy (must be effective, the blood pressure is normal...)
    • Bartter syndrome
    • Gitelman’s syndrome
    • Hypokalemia
    • Hypomagnesaemia
  • High urinary chloride, hypertension and high renin activity
    • Ongoing diuretic therapy
    • Renal artery stenosis
    • Renin-secreting tumour
    • Malignant hypertension
  • High urinary chloride, hypertension and normal renin-aldosterone axis
    • Cushing syndrome
    • Corticosteroid use
    • 17-hydroxylase deficiency
    • Liddle’s syndrome
    • Licorice overindulgeance
  • High urinary chloride, hypertension and hyperaldosteronism without high renin levels
    • Adrenal adenoma
    • Adrenal hyperplasia
    • Aldosterone synthase hyperactivity

Thus, the following is a list of the necessary details one will need to determine from the patients history, physical examination, and biochemistry values:

Background history

  • History of congential adrenal hypoplasia
  • History of cystic fibrosis
  • History of CCF (suggesting chronic exposure to diuretics)
  • History of uncontrolled hypertension (malignant hypertension or renal artery stenosis)

Recent history

  • Recent antacic consumption
  • Recent use of calcium supplements
  • β-lactam antibiotic use
  • Massive abuse of licorice
  • History of diarrhoea (villous adenoma) or vomiting (chloride loss)
  • History of recent hypercapneic respiratory failure

Examination

  • Clinically, findings consistent with severe hypertension (eg. retinal changes)
  • Renal artery stenosis bruit
  • Peripheral oedema (suggesting chronic exposure to diuretics)

Biochemistry

  • Serum potassium
  • Serum magnesium
  • Urinary chloride
  • Serum renin levels
  • Serum aldosterone levels

References

References

Gennari, F. John. "Pathophysiology of metabolic alkalosis: a new classification based on the centrality of stimulated collecting duct ion transport." American Journal of Kidney Diseases 58.4 (2011): 626-636.

Tripathy, Swagata. "Extreme metabolic alkalosis in intensive care." Indian journal of critical care medicine: peer-reviewed, official publication of Indian Society of Critical Care Medicine 13.4 (2009): 217.

Galla, John H. "Metabolic alkalosis." Journal of the American Society of Nephrology 11.2 (2000): 369-375.

Pahari, D. K., et al. "Diagnosis and management of metabolic alkalosis."JOURNAL-INDIAN MEDICAL ASSOCIATION 104.11 (2006): 630.

Palmer, Biff F., and Robert J. Alpern. "Metabolic alkalosis." Journal of the American Society of Nephrology 8.9 (1997): 1462-1469.

Gennari, F. John. "Pathophysiology of metabolic alkalosis: a new classification based on the centrality of stimulated collecting duct ion transport." American Journal of Kidney Diseases 58.4 (2011): 626-636.