Diagnosis

Metabolic alkalosis

Etiology

Cause [nd9]

1. Excess loss of hydrogen ions: [nd9]

   • Loss of hydrogen ions (gastric acid):

     • Vomiting (hyperemesis gravidarum, pyloric stenosis)

     • Nasogastric suction tubes

     • Zollinger-Ellison syndrome

     • Diarrhea/high-volume ileostomy losses

   • Hypovolemia and diuretic (loop diuretics, thiazide diuretics):

     • reduced GFR --> RAAS --> aldosterone --> Na and H2O retention in exchange for K and H-ions excretion

   • Overcorrection of acidosis: Hypoventilation --> hypercapnia --> increased CO2 --> respiratory acidosis --> renal compensation with excess bicarbonate retention --> metabolic alkalosis

   • Cystic Fibrosis: loss of sodium chloride in the sweat

2. Increased bicarbonate in the extracellular compartment: [nd9]

   • Milk Alkali Syndrome

   • Bicarbonate tablets, baking soda

   • Alkali therapy (bicarbonate) or antacids for peptic ulcer or hyperacidity

   • Blood product administration (sodium citrate --> sodium bicarbonate)

   • TPN (gain of HCO3)

   • Decreases in albumin and phosphate

3. Increased renal reabsorption of bicarbonate (Urine chloride > 20 mEq/L): [nd9]

   • Hypokalemia --> K shifts out of the cells --> H shifts into the cells (increased pH) to maintain electrical neutrality

   • Hyperaldosteronism:

     • Conn syndrome (primary hyperaldosteronism)

     • Cushing's Syndrome

     • Congenital adrenal hyperplasia

     • Mineralcorticoid therapy

     • Liddle syndrome

   • Bartter's Syndrome

   • Hypomagnesemia (can result in recalcitrant hypokalemia) [swt]

   • Hypercalcemia

Pathophysiology and classification [ugn][6pv]

1. The primary pH buffer system in the human body is the bicarbonate (HCO3)/carbon dioxide (CO2) chemical equilibrium system:

   H + HCO3 <--> H2CO3 <--> CO2 + H2O

2. Hypovolemic states:

   • GI losses (vomiting, nasogastric tube, ileostomy, diarrhea)

   • Diuretics

   • Syndromes: Bartter, Gitelman, Cystic fibrosis

3. Hypervolemic states:

4. Respiratory alkalosis: Hyperventilation

5. Central alkalosis:

   • Head injury 

   • Stroke Hyperthyroidism

   • Anxiety

   • Pain

   • Fear

   • Drugs and toxins, such as salicylates, beta-agonists, and endotox

6. Hypoxemia: High altitude, pulmonary disease

7. Cardiopulmonary causes:

   • Pulmonary embolism

   • Pneumothorax

   • Pneumonia

   • Acute asthma

   • Chronic obstructive pulmonary disease exacerbations

   • Cardiogenic edema

8. Iatrogenic causes:

   • Hyperventilation in intubated patients on mechanical ventilation

   • Extracorporeal membranous oxygenation

9. Physiologic causes:

   • Pregnancy

   • Hyperthermia, including fever

10. Multiple disease states affect the equilibrium:

    • Hypokalemia --> Intracellular shift of hydrogen ions

    • GI loss of hydrogen ions

    • Renal hydrogen ion loss

    • Retention or addition of bicarbonate ions

Epidemiology

Incidence per 100.000 [fhu]

Approach

• Blood test: electrolytes (Cl, K, Ca), blood urea nitrogen, and creatinine

• Blood gas: pH and pCO2

• Urine chemistry

• ECG

1. What is the pH? Alkalemia? [swt]

2. Is the primary disturbance metabolic or respiratory?

   • Metabolic alkalosis: high serum HCO3−

   • Respiratory alkalosis: low pCO2

   • Mixed metabolic and respiratory alkalosis: serum HCO3− is high and pCO2 is low

3. Determination of respiratory compensation. For every 1 mmol/l rise in HCO3 above 24 mmol/l, there is a 0.6 mmHg rise in pCO2 as per the following equation:

   • pCO2 (mmHg) = 40 + 0.6 × (HCO3 - 24 mmol/l)

Treatment

1. If suspicion for hypovolemic chloride-responsive metabolic alkalosis:

   • Isotonic saline (0.9 NaCl) + 40 mmol/L KCl (potassium chloride) intravenously

   • Correct electrolytes: hypokalemia, hypomagnesemia

   • Discontinue diuretics or replace with K+ sparing diuretic (spironolactone)

   • Acetazolamide: bicarbonaturic and kaliuretic necessitating aggressive K+monitoring

2. Normovolemic (Cl-resistant) metabolic alkalosis:

   • Treat the underlying cause(s)

     • adrenal adenoma

     • bilateral adrenal hyperplasia --> aldosterone blockers (spironolactone)

   • Correct hypokalemia

   • Low Na+ diet

   • Avoid licorice

3. Severe cases:

   • Slow acid administration

   • Dialysis

Differential diagnoses

Anxiety, Apparent mineralocorticoid excess syndrome, Asthma, Atrial fibrillation, Blood transfusion, Colorectal polyp, Congenital adrenal hyperplasia, COPD, Cushing syndrome, Drug side effects, Heatstroke, Hyperaldosteronism, Hyperthyroidism, Meningitis, Metabolic acidosis, Milk-alkali syndrome, Myocardial infarction, Panic attack, Pneumonia, Pneumothorax, Pulmonary edema, Pulmonary embolism, Pulmonary fibrosis, Renal failure, Ringer's lactate, Salicylate intoxication, Sepsis, Thyrotoxicosis