Background

Definition: A serum potassium level < 3.5 mEq/L. Severe hypokalemia < 2.5 mEq/L

Epidemiology

  • Common electrolyte disorder – 20% of hospitalized patients
  • 10-40% of patients on thiazide diuretics (Rosen 2014)

Causes

  • Renal Losses (diuretics, steroid use, DKA, hyperaldosteronism)
  • Increased non-renal losses (vomiting, diarrhea, sweating)
  • Decreased intake (malnutrition)
  • Intracellular shift (metabolic alkalosis)
  • Endocrine (Cushing’s disease, Insulin therapy)

Clinical Manifestations

  • Mild hypokalemia often asymptomatic
  • Non-specific Symptoms
    • Palpitations
    • Nausea
    • Muscle Weakness
    • Myalgias
    • Fatigue
  • Neurological Effects
    • Paresthesias
    • Weakness
    • Confusion
    • Decreased Deep Tendon Reflexes
    • Hypokalemic Periodic Paralysis (rare)

Diagnostics

  • Serum potassium
  • 12-Lead EKG
    • Classic Findings
      • Flattened T waves
      • U waves
      • Prolonged QT Interval
      • Non-specific ST segment changes
    • Note: Hypokalemia is a common predisposing condition for Torsades de Pointes
  • Urine potassium level (spot): Elevation of urine potassium indicates renal losses as cause of hypokalemia

Life in the Fastlane: Hypokalemia ECG Library

Management

Basics: ABCs, IV, Cardiac Monitor and, 12-lead EKG

Potassium Repletion

  • Every drop in serum potassium of 0.3 mEq = 100 mEq total body depletion (Gennari 1998)
  • Oral Replacement
    • Potassium chloride (KCl) typically used
    • Readily absorbed
  • Intravenous Replacement
    • Rapidly raises serum potassium levels
    • Mild to moderate symptoms: 10-20 mEq/hour
    • Severe symptoms/critically ill
      • Up to 40 mEq/hour
      • Consider administration through central line
      • Keep patient on cardiac monitor
      • Check serum potassium hourly
    • Magnesium Co-administration
      • Hypokalemia is associated with hypomagnesemia (Boyd 1984)
      • Potassium will not move intracellularly (and thus will not replete total body stores) without concomitant magnesium repletion
      • Dose: 0.5-1 g/hour

Note: Potassium replacement (particularly IV) is a leading cause of hyperkalemia. Replete cautiously

Take Home Points

  • Severe hypokalemia can lead to lethal dysrhythmias typically by prolongation of the QT interval.
  • Patients receiving intravenous potassium repletion at more than 20 mEq/hour should have continuous cardiac monitoring and frequent serum potassium evaluations.
  • Always replete magnesium when repleting potassium.

 

Read More

Emergency Medicine Updates – Correction of Critical Hypokalemia

LITFL – Hypokalemia

 

References

Pfenning CL, Slovis CM: Electrolyte Disorders; in Marx JA, Hockberger RS, Walls RM, et al (eds): Rosen’s Emergency Medicine: Concepts and Clinical Practice, ed 8. St. Louis, Mosby, Inc., 2014, (Ch) 125: p 1636-1653.

Gennari FJ: Hypokalemia. N Engl J Med 1998; 339:451-458. PMID: 9700180

Boyd JC et al. Relationship of potassium and magnesium concentrations in serum to cardiac arrhythmias. Clin Chem 1984; 30(5): 754-7. PMID: 6713638