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Serum Potassium (K⁺)

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Serum Potassium (K⁺)

TestNormal RangeCritical Values
Serum Potassium (K⁺)3.5–5.1 mEq/L<3.0 mEq/L or >6.0 mEq/L — immediate cardiac monitoring and provider notification required

Clinical Significance

NCLEX Pattern

Potassium questions focus on: (1) NEVER IV push — can stop the heart; (2) ECG changes (peaked T waves = hyperkalemia; depressed/absent T waves = hypokalemia); (3) loop diuretics deplete potassium; (4) kayexalate/insulin for hyperkalemia treatment.

Potassium is the most abundant electrolyte in the intracellular fluid (ICF) and is critical for normal cardiac function, neural function, and muscle contractility. Potassium regulation is controlled by aldosterone (promotes renal excretion) and insulin (drives K⁺ into cells). It is poorly conserved by the body and lost significantly in urine.

IV Potassium Safety Rule

Potassium must NEVER be administered IV push — it can immediately stop the heart. IV potassium must always be mixed with IV fluid and infused slowly via an IV pump. Concentrated potassium solutions require central line administration.

Hypokalemia (K⁺ <3.5 mEq/L)

  • Causes: Excessive vomiting or diarrhea, potassium-wasting diuretics (loop, thiazide), insulin use, inadequate dietary intake
  • Signs and symptoms: Muscle weakness, fatigue, cramps, lethargy, thready pulse, cardiac dysrhythmias (depressed T waves, prolonged PR interval, absent P waves on ECG)
  • Treatment: Increase dietary potassium (bananas, oranges, tomatoes); oral potassium supplements with a full glass of water; IV potassium in fluids for severe cases — never IV push; continuous cardiac telemetry monitoring
  • Nursing priority: Place on telemetry; administer IV potassium slowly over several hours; monitor serum levels after replacement

Hyperkalemia (K⁺ >5.1 mEq/L)

  • Causes: Kidney failure (decreased renal excretion), metabolic acidosis (K⁺ shifts out of cells), potassium-sparing diuretics, excess oral/IV potassium supplementation
  • Signs and symptoms: Irritability, muscle cramping, diarrhea, cardiac dysrhythmias (peaked T waves, bradycardia → ventricular fibrillation, cardiac arrest) — K⁺ >6.0 mEq/L = emergency
  • ECG progression: Peaked T waves → widened QRS → sine wave pattern → ventricular fibrillation
  • Treatment:
    • Dietary restriction of potassium for mild cases
    • Sodium polystyrene sulfonate (Kayexalate) PO or enema — binds K⁺ in GI tract for excretion in stool
    • IV insulin + dextrose — insulin drives K⁺ into cells (monitor glucose hourly; administer dextrose concurrently)
    • IV calcium gluconate — protects the heart temporarily from potassium effects (temporary measure — does not lower serum K⁺)
    • Loop diuretics (furosemide) — promote renal potassium excretion
    • Hemodialysis for severe refractory hyperkalemia

Graph View

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