Signs and Symptoms of Hypokalemia
Hypokalemia is defined as serum potassium less than the laboratory lower limit of normal (<3.5 mEq/L), with severity classified as mild (3.0-3.5 mEq/L), moderate (2.5-3.0 mEq/L), or severe (<2.5 mEq/L). 1, 2
Cardiac Manifestations
- ECG changes are common and include T-wave flattening, ST-segment depression, and prominent U waves 2
- Cardiac arrhythmias, particularly ventricular arrhythmias, can occur and may be life-threatening 2, 3
- First or second-degree atrioventricular block or atrial fibrillation may develop 2
- Risk of progression to ventricular fibrillation, pulseless electrical activity (PEA), or asystole if left untreated 2
- Patients taking digoxin are at significantly increased risk of digitalis toxicity due to hypokalemia 2, 3
- Sinus bradycardia and long-QTc can be observed 4
Neuromuscular Symptoms
- Weakness and fatigue are common presentations 5, 6
- Muscle cramps and paresthesias (abnormal sensations) may occur 2, 6
- Depressed deep tendon reflexes are common 2
- In severe cases, flaccid paralysis can develop 2, 5
- Respiratory difficulties due to respiratory muscle weakness can occur 2
- Rhabdomyolysis (muscle breakdown) may develop, especially with severe hypokalemia 4, 7
- Carpopedal spasms have been reported in severe cases, particularly when associated with other electrolyte abnormalities 4
Gastrointestinal Symptoms
- Ileus (intestinal paralysis) can develop, particularly with severe hypokalemia 6
- Constipation may occur 2
Renal Effects
- Impaired urinary concentrating ability leading to polyuria 7
- Increased risk of chronic kidney disease progression with persistent hypokalemia 6
Metabolic Effects
- Glucose intolerance 7
- Often associated with metabolic alkalosis, especially when caused by diuretics or gastrointestinal losses 2, 5
Severity-Related Symptoms
- Mild hypokalemia (3.0-3.5 mEq/L): Symptoms are often vague or absent 3
- Moderate hypokalemia (2.5-3.0 mEq/L): Increasing muscle weakness, fatigue, and ECG changes 3
- Severe hypokalemia (<2.5 mEq/L): Clinical problems become more pronounced with significant risk of cardiac arrhythmias, paralysis, and rhabdomyolysis 3, 4
Common Pitfalls in Recognition
- Failing to recognize that serum potassium is an inaccurate marker of total-body potassium deficit - mild hypokalemia may be associated with significant total-body potassium deficits 6
- Overlooking hypokalemia in patients with chronic or frequent vomiting, diarrhea, polyuria, or those on diuretics, insulin therapy, or total parenteral nutrition 8
- Not addressing concurrent magnesium deficiency, which often coexists with hypokalemia and can make potassium repletion difficult until corrected 2
- Missing hypokalemia as a cause of unexplained cardiac arrhythmias or muscle weakness 8