What are the causes and complications of hypokalemia (low potassium levels)?

Causes and Complications of Hypokalemia

Hypokalemia (serum potassium <3.5 mEq/L) is primarily caused by decreased intake, increased renal losses, gastrointestinal losses, or transcellular shifts, with diuretic therapy being the most common cause in clinical practice. 1, 2

Major Causes of Hypokalemia

Decreased Intake

• Inadequate dietary intake (normal dietary intake is 50-100 mEq per day) 3
• Prolonged parenteral nutrition with insufficient potassium supplementation 3

Increased Renal Losses

• Diuretic therapy (especially thiazides and loop diuretics) - most common cause 1, 2
• Primary hyperaldosteronism 1, 4
• Secondary hyperaldosteronism 1, 4
• Bartter syndrome and Gitelman syndrome 1
• Magnesium deficiency causing renal potassium wasting 1
• Renal tubular acidosis 3, 4
• Severe hyperglycemia with osmotic diuresis 2, 5

Gastrointestinal Losses

• Vomiting and diarrhea 1, 2
• High-output enterocutaneous fistulas 1
• Biliary drainage 4

Transcellular Shifts

• Insulin administration (shifts potassium into cells) 2, 5
• Catecholamine excess (beta-adrenergic stimulation) 2, 5
• Alkalosis (metabolic or respiratory) 6
• Familial periodic hypokalemic paralysis 5
• Thyrotoxic hypokalemic paralysis 5

Other Causes

• Medication-induced (besides diuretics) 2, 4
• Excessive sweating (minor contributor) 3
• Diuretic misuse (e.g., in bodybuilders) 5

Complications of Hypokalemia

Cardiovascular Complications

• ECG changes: T-wave flattening, ST-segment depression, and prominent U waves 1, 2
• Cardiac arrhythmias, particularly ventricular arrhythmias 1
• First or second-degree atrioventricular block or atrial fibrillation 1
• Risk of progression to ventricular fibrillation, pulseless electrical activity (PEA), or asystole 1
• Increased risk of digitalis toxicity in patients taking digoxin 1, 5

Neuromuscular Complications

• Muscle weakness, ranging from mild to severe 2, 7
• Flaccid paralysis in severe cases 1, 5
• Paresthesia and depressed deep tendon reflexes 1
• Respiratory difficulties due to respiratory muscle weakness 1, 5

Renal Complications

• Impaired ability to concentrate urine 3
• Acceleration of chronic kidney disease progression 7
• Structural and functional defects in the kidneys 4

Gastrointestinal Complications

• Ileus due to decreased smooth muscle motility 7, 5
• Constipation 4

Other Complications

• Urinary retention 5
• Rhabdomyolysis (rare) 5
• Metabolic alkalosis (especially with chloride depletion) 3, 4
• Exacerbation of systemic hypertension 7
• Increased mortality 7

Important Clinical Considerations

• Hypokalemia severity is classified as mild (3.0-3.5 mEq/L), moderate (2.5-2.9 mEq/L), or severe (<2.5 mEq/L) 1
• Serum potassium is an inaccurate marker of total-body potassium deficit; mild hypokalemia may be associated with significant total-body potassium deficits 7
• Hypomagnesemia frequently coexists with hypokalemia and can make potassium repletion difficult until magnesium is corrected 1
• Urinary potassium excretion of ≥20 mEq/day in the presence of hypokalemia suggests inappropriate renal potassium wasting 4
• Severe hypokalemia (≤2.5 mEq/L), ECG abnormalities, or neuromuscular symptoms require urgent treatment 2
• The World Health Organization recommends a potassium intake of at least 3,510 mg per day for optimal cardiovascular health 2

Common Pitfalls in Management

• Failing to address magnesium deficiency when treating hypokalemia 1
• Overlooking secondary hyperaldosteronism as a cause in volume-depleted patients 1
• Not recognizing that chronic mild hypokalemia can accelerate chronic kidney disease progression 7
• Failing to identify diuretic misuse in certain populations (e.g., bodybuilders) 5
• Not considering transcellular shifts as a cause, which may lead to rebound potassium disturbances 6