What is Hypokalemia?

Hypokalemia is serum potassium <3.5 mEq/L. It can cause muscle weakness, cardiac arrhythmias, and other complications.

Symptoms:

• Mild (3.0-3.4 mEq/L): Often asymptomatic
• Moderate-Severe (<3.0 mEq/L):
  • Muscle weakness, cramps, fatigue
  • Constipation, ileus
  • Polyuria (nephrogenic DI)
  • Cardiac arrhythmias (PACs, PVCs, Torsades de Pointes)
  • EKG: Flattened T waves, U waves, ST depression

Causes:

1. GI Losses:

• Vomiting, diarrhea, laxative abuse

2. Renal Losses:

• Diuretics (Most Common): Thiazides, loop diuretics
• Hyperaldosteronism (Primary or Secondary): High aldosterone → kidney excretes potassium
• Cushing's Syndrome: High cortisol has mineralocorticoid effect
• Renal Tubular Acidosis (RTA Type 1, Type 2)
• Bartter, Gitelman Syndromes: Genetic tubular defects
• Hypomagnesemia: Causes renal potassium wasting

3. Transcellular Shift (Potassium Moves into Cells):

• Insulin: DKA treatment
• Beta-Agonists: Albuterol
• Alkalosis
• Hypokalemic Periodic Paralysis: Genetic; attacks of paralysis with low K

4. Inadequate Intake (Rare Alone)

Endocrine Causes to Consider:

• Primary Hyperaldosteronism (Conn's Syndrome): High aldosterone, low renin, HTN
• Cushing's Syndrome: High cortisol
• Thyrotoxicosis: Can cause hypokalemic periodic paralysis

Diagnosis:

• Urine Potassium:
  • <20 mEq/L: Extrarenal losses (GI)
  • >40 mEq/L: Renal losses (diuretics, hyperaldosteronism)
• Check Magnesium: Hypomagnesemia causes refractory hypokalemia
• Blood Pressure: HTN suggests hyperaldosteronism, Cushing's
• Acid-Base Status: Acidosis vs. alkalosis
• If Suspected Endocrine Cause:
  • Plasma renin, aldosterone (hyperaldosteronism)
  • 24-hour urine cortisol, dexamethasone suppression test (Cushing's)
  • TSH, free T4 (thyrotoxicosis)

Treatment:

• Oral Potassium Replacement: Potassium chloride (KCl) 20-40 mEq 2-3x/day
• IV Potassium: If severe (<2.5 mEq/L), symptomatic, or unable to take PO
  • Peripheral: Max 10 mEq/hour
  • Central line: Up to 20-40 mEq/hour (monitored)
• Replete Magnesium: Essential (hypokalemia won't correct if Mg low)
• Potassium-Sparing Diuretics: Spironolactone, amiloride (if on loop/thiazide diuretics)
• Treat Underlying Cause: Stop offending medications, treat hyperaldosteronism, etc.