⬇️ Hypokalemia

K+ < 3.5 mEq/L - Check Magnesium First!

🔑 CRITICAL FIRST STEP

Check Magnesium Level!

Mg++ must be >1.7 mg/dL for K+ replacement to work effectively*

⚠️ Refractory hypokalemia is often due to concurrent hypomagnesemia

🔍 Systematic Diagnostic Approach

📊 Initial Assessment

  • Check Magnesium: ALWAYS measure Mg++ level
  • Medication Review: Diuretics, insulin, beta-agonists
  • Clinical Context: GI losses, poor intake
  • Acid-Base Status: pH affects K+ distribution

🎯 Etiology by Mechanism

  • Increased Losses: Most common cause
  • Decreased Intake: Dietary, NPO status
  • Transcellular Shift: Into cells (insulin, alkalosis)
  • Dilutional: Massive fluid resuscitation
  • Medications: Many drug-induced causes

⚠️ Clinical Manifestations

  • Cardiovascular: Arrhythmias, prolonged QT
  • Muscular: Weakness, cramping, paralysis
  • GI: Ileus, constipation
  • Renal: Concentrating defect, polyuria
  • Metabolic: Glucose intolerance

🔄 Etiology Classification

💧 Increased Losses

Renal Losses:

  • Diuretics (thiazides, loop diuretics)
  • Hyperaldosteronism (1° or 2°)
  • Bartter/Gitelman syndrome
  • Magnesium deficiency
  • Medications (aminoglycosides, cisplatin)

GI Losses:

  • Diarrhea (most common GI cause)
  • Villous adenoma
  • Fistulas, ileostomy
  • Laxative abuse

🔄 Transcellular Shift

  • Insulin: Drives K+ into cells
  • Beta-2 Agonists: Albuterol, epinephrine
  • Alkalosis: Each 0.1 pH ↑ = 0.5 mEq/L K+ ↓
  • Anabolic States: Refeeding, B12/folate therapy
  • Hypothermia: Rewarming causes shift
  • Familial Periodic Paralysis: Genetic channelopathy

📉 Decreased Intake

  • Poor Dietary Intake: Elderly, eating disorders
  • NPO Status: Prolonged fasting
  • Tea and Toast Diet: Classic presentation
  • Malnutrition: Protein-energy malnutrition
  • Clay Ingestion: Binds potassium

Note: Kidneys conserve K+ well, so dietary deficiency alone rarely causes severe hypokalemia

💊 Treatment Protocol

🎯 Step-by-Step Replacement Strategy

1 CHECK MAGNESIUM: Must be >1.7 mg/dL before K+ replacement
• If Mg++ low: Replace simultaneously • 2g MgSO4 IV over 4 hours
2 CHOOSE ROUTE: PO preferred over IV when possible
• PO: Safer, better tolerated • IV: Only if severe, NPO, or malabsorption
3 CALCULATE DEFICIT: Estimate total body K+ deficit
• Each 1 mEq/L ↓ = ~200-400 mEq total deficit** • More in chronic cases
4 REPLACE SAFELY: Avoid rapid correction
• PO: 40-100 mEq/day divided • IV: ≤10 mEq/hr peripheral, ≤20 mEq/hr central

💊 Replacement Options & Dosing

Oral vs IV Replacement

💊 Oral Replacement (Preferred)

Advantages:

  • Safer (no risk of cardiac arrest)
  • Better tolerated
  • More physiologic
  • Cost-effective

Options:

  • KCl tablets: 10-20 mEq TID
  • KCl liquid: 20-40 mEq BID
  • K-Dur: 20 mEq BID (extended release)

Total Daily Dose: 40-100 mEq/day

💉 IV Replacement (When Necessary)

Indications:

  • Severe hypokalemia (<2.5 mEq/L)
  • Symptomatic (arrhythmias, paralysis)
  • NPO status
  • Malabsorption

Safety Rules:

  • Peripheral line: ≤10 mEq/hr
  • Central line: ≤20 mEq/hr
  • Cardiac monitoring required
  • Check K+ every 4-6 hours

🧮 Interactive Potassium Calculator

Hypokalemia Replacement Calculator

Calculating potassium replacement plan...

⚠️ Special Considerations

🚫 Common Mistakes

  • Ignoring Magnesium: #1 cause of refractory hypokalemia
  • Too Rapid IV Replacement: Risk of cardiac arrest
  • Inadequate Dosing: Underestimating total deficit
  • Stopping Too Early: Not achieving target levels
  • Missing Ongoing Losses: Continuing diuretics

🔍 Refractory Cases

  • Check Magnesium Again: Most common cause
  • Ongoing Losses: Diarrhea, diuretics
  • Medication Review: Hidden K+-wasting drugs
  • Endocrine Workup: Hyperaldosteronism
  • Genetic Testing: Gitelman, Bartter syndrome

📊 Monitoring Parameters

  • Serum K+: Every 4-6 hours during replacement
  • Magnesium: Recheck if initially low
  • ECG: If arrhythmias or severe hypokalemia
  • Daily Weights: Monitor volume status
  • Renal Function: Ensure adequate urine output

📚 Clinical References

*Magnesium Threshold: Normal serum Mg++ 1.46-2.68 mg/dL; hypomagnesemia <1.46 mg/dL. The 1.7 mg/dL threshold represents clinical practice for optimal K+ repletion (StatPearls 2025, Merck Manual 2025).

**Deficit Calculation: "For every 1 mEq/L decrease in serum potassium, the potassium deficit is approximately 200-400 mEq" (Medscape Emergency Medicine 2025, PMC Hypokalemia Review 2018).

🎯 Key Learning Points

🔑 Critical First Steps

  • ALWAYS check magnesium level first
  • Replace Mg++ if <1.7 mg/dL
  • Review medications for K+-wasting drugs

💊 Treatment Priorities

  • PO replacement preferred when possible
  • IV replacement: ≤10 mEq/hr peripheral
  • Estimate 200-400 mEq total deficit

⚠️ Safety Considerations

  • Cardiac monitoring for IV replacement
  • Recheck K+ every 4-6 hours
  • Address ongoing losses