Hypokalemia: Definition, Causes, and Management
Hypokalemia is defined as a serum potassium level less than the laboratory lower limit of normal, with severity classified as mild (serum potassium <3.5 to ≥3.0 mEq/L), moderate (<3.0 to ≥2.5 mEq/L), or severe (<2.5 mEq/L). 1
Definition and Classification
- Hypokalemia occurs when serum potassium levels fall below 3.5 mEq/L 1, 2, 3
- Severity is classified as:
Common Causes
Decreased Intake
Increased Losses
Renal Losses
- Diuretic therapy (especially thiazides and loop diuretics) 2, 3, 5
- Primary hyperaldosteronism 2
- Secondary hyperaldosteronism 2
- Bartter syndrome and Gitelman syndrome 2
- Magnesium deficiency (causes renal potassium wasting) 2
Gastrointestinal Losses
Transcellular Shifts
- Insulin administration 3, 5
- Beta-adrenergic stimulation 4
- Metabolic alkalosis 3
- Hypokalemic periodic paralysis 7
Clinical Manifestations
Cardiac Effects
- ECG changes: T-wave flattening, ST-segment depression, prominent U waves 2
- Cardiac arrhythmias (especially ventricular) 2, 3
- First or second-degree atrioventricular block 2
- Atrial fibrillation 2
- Risk of progression to ventricular fibrillation, PEA, or asystole if untreated 2
- Increased risk of digitalis toxicity in patients taking digoxin 2
Neuromuscular Effects
- Muscle weakness 2, 6
- Flaccid paralysis (in severe cases) 2
- Paresthesia 2
- Depressed deep tendon reflexes 2
- Respiratory difficulties due to respiratory muscle weakness 2
Other Effects
- Ileus 8
- Polyuria 6
- Progression of chronic kidney disease 8
- Exacerbation of systemic hypertension 8
- Increased mortality 8
Diagnosis
- Serum potassium measurement 3
- ECG to assess for cardiac conduction abnormalities 3, 5
- Assessment for underlying causes 3
- Note: Serum potassium is an inaccurate marker of total-body potassium deficit; mild hypokalemia may be associated with significant total-body potassium deficits 8
Management
Indications for Urgent Treatment
- Serum potassium ≤2.5 mEq/L 2, 3
- Presence of ECG abnormalities 2, 3
- Neuromuscular symptoms 2, 3
- Cardiac ischemia 8
- Patients on digitalis therapy 8
Treatment Approach
Oral Replacement (Preferred)
- For patients with functioning GI tract and potassium >2.5 mEq/L 3, 8
- Potassium chloride is the preferred supplement 7
- Controlled-release formulations should be reserved for patients who cannot tolerate liquid or effervescent preparations 7
Intravenous Replacement
- For severe hypokalemia (≤2.5 mEq/L) 2, 3
- When ECG changes or neuromuscular symptoms are present 2, 3
- Slow infusion recommended (bolus administration can be dangerous) 2
- In diabetic ketoacidosis, begin potassium replacement with fluid therapy if potassium is low 2
Addressing Underlying Causes
- Consider lower doses of diuretics if hypokalemia is due to diuretic therapy 7
- Correct magnesium deficiency if present (potassium repletion may be difficult until magnesium is corrected) 2
- Dietary counseling to increase potassium intake 2, 3
- Consider potassium-sparing diuretics in patients requiring long-term diuretic therapy 2
Prevention and Monitoring
- Regular monitoring of serum potassium in high-risk patients 2, 4
- Maintain serum potassium ≥4.0 mEq/L in patients with heart failure 2
- Dietary modifications to increase potassium intake 2
- Consider potassium-sparing diuretics in patients requiring long-term diuretic therapy 2
Common Pitfalls
- Failing to address magnesium deficiency when treating hypokalemia 2
- Overlooking secondary hyperaldosteronism as a cause in volume-depleted patients 2
- Not recognizing that mild hypokalemia can be associated with significant total-body potassium deficits 8
- Inadequate monitoring of patients on diuretics with suspected malnutrition 4
- Failing to recognize that even chronic mild hypokalemia can have serious consequences like progression of chronic kidney disease 8