Signs and Symptoms of Hypokalemia
Hypokalemia presents with a spectrum of clinical manifestations ranging from weakness and fatigue to life-threatening cardiac arrhythmias, with severity typically correlating with the degree of potassium depletion. 1, 2
Classification of Severity
- Mild hypokalemia: 3.0-3.5 mEq/L
- Moderate hypokalemia: 2.5-3.0 mEq/L
- Severe hypokalemia: <2.5 mEq/L 1
Neuromuscular Manifestations
- Muscle weakness (often beginning in lower extremities and ascending)
- Fatigue
- Muscle cramps
- Flaccid paralysis (in advanced cases)
- Impaired ability to concentrate urine 2
- Quadriplegia (in severe cases) 3
- Carpopedal spasm (rare presentation) 4
- Rhabdomyolysis (in severe cases) 4
Cardiovascular Manifestations
- Cardiac rhythm disturbances (primarily ectopic beats)
- Prominent U-waves on electrocardiogram 2
- ST-segment depression
- T-wave flattening
- Prolonged QT interval
- Sinus bradycardia 3, 4
- Increased risk of cardiac arrest and sudden death in severe cases 5
Gastrointestinal Manifestations
Other Manifestations
- Metabolic alkalosis (especially with concurrent chloride depletion) 2
- Polyuria (due to impaired concentrating ability) 7
- Increased blood pressure (chronic hypokalemia can exacerbate hypertension) 6
Electrocardiographic Changes
The ECG is a crucial diagnostic tool for assessing the severity and cardiac impact of hypokalemia:
- Flattened T waves
- Prominent U waves
- ST-segment depression
- Prolonged QT interval
- Increased risk of ventricular arrhythmias 3, 4
Risk Factors and Common Causes
- Diuretic therapy (especially thiazides and loop diuretics)
- Gastrointestinal losses (vomiting, diarrhea)
- Primary or secondary hyperaldosteronism
- Diabetic ketoacidosis
- Inadequate replacement during parenteral nutrition 2, 5
- Renal tubular disorders
- Magnesium deficiency (often coexists and impairs potassium correction) 1
Clinical Pearls and Pitfalls
- Serum potassium concentration is an inaccurate marker of total-body potassium deficit; mild hypokalemia may be associated with significant total-body potassium deficits 6
- Hypokalemia can accelerate the progression of chronic kidney disease and increase mortality even when mild 6
- Patients on digitalis therapy are at particularly high risk for cardiac arrhythmias when hypokalemic 6
- Hypokalemia often coexists with hypomagnesemia, which must be corrected for effective potassium repletion 1
- Rapid correction of severe hypokalemia is indicated in the presence of ECG changes, neurologic symptoms, cardiac ischemia, or digitalis therapy 6
When to Suspect Severe Hypokalemia Requiring Urgent Intervention
- Presence of ECG changes
- Muscle paralysis or severe weakness
- Respiratory compromise
- Rhabdomyolysis
- Serum potassium <2.5 mEq/L
- Concurrent cardiac disease or digitalis therapy 1, 5, 3
Recognizing the signs and symptoms of hypokalemia early is crucial for preventing progression to life-threatening complications and initiating appropriate treatment.