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