Electrolyte Imbalances: Sodium, Potassium, Calcium, and Magnesium

Electrolyte imbalances are high-yield on nursing exams and in real practice because they affect nerve conduction, muscle contraction, and cardiac rhythm. This guide reviews the four major electrolytes — sodium, potassium, calcium, and magnesium — with causes, signs, ECG findings, treatments, and critical nursing actions.

Sodium Imbalances (Normal: 135–145 mEq/L)

Hyponatremia (Na⁺ < 135 mEq/L)

• Results from excess water relative to sodium or sodium loss.
• Causes: SIADH, heart failure, cirrhosis, renal failure, excessive water intake, diuretics.
• Early symptoms: nausea, headache, malaise.
• As sodium falls further: confusion, seizures, and coma from cerebral edema.
• Severe symptomatic hyponatremia is treated with cautious hypertonic saline (3% NaCl).
• Correct sodium slowly — rapid correction causes osmotic demyelination syndrome.

Hypernatremia (Na⁺ > 145 mEq/L)

• Results from water loss exceeding sodium loss or excess sodium intake.
• Causes: dehydration, diabetes insipidus, excessive sodium administration, inability to access water.
• Symptoms: thirst, dry mucous membranes, restlessness, confusion, seizures.
• Severe cases cause brain shrinkage and risk of intracranial hemorrhage.
• Treat by correcting the water deficit with hypotonic fluids or D5W.
• Correct slowly to avoid cerebral edema.

Potassium Imbalances (Normal: 3.5–5.0 mEq/L)

Hypokalemia (K⁺ < 3.5 mEq/L)

• Causes: GI losses (vomiting, diarrhea), diuretics, poor intake, alkalosis.
• Symptoms: muscle weakness, cramping, fatigue, constipation, leg cramps.
• ECG: flattened T waves, U waves, ST depression.
• Severe hypokalemia → arrhythmias, paralysis, respiratory failure.
• Treatment: oral or IV potassium replacement.
• IV potassium is NEVER given as a bolus or IV push. Maximum rate is 10 mEq/hour.
• Verify adequate urine output and renal function before replacement.

Hyperkalemia (K⁺ > 5.0 mEq/L)

• Causes: renal failure, potassium-sparing diuretics, ACE inhibitors, tissue breakdown.
• Symptoms: muscle weakness, paresthesias, ascending paralysis.
• ECG: peaked T waves → widened QRS → loss of P wave → sine wave.
• Severe hyperkalemia causes cardiac arrest.
• Emergency treatment:
  • Calcium gluconate — stabilizes the cardiac membrane (does NOT lower K⁺).
  • Insulin with glucose and albuterol — shift K⁺ into cells.
  • Kayexalate (sodium polystyrene sulfonate) — removes K⁺ via the gut.
  • Hemodialysis — definitive treatment for severe cases.

Calcium Imbalances (Normal: 8.5–10.5 mg/dL)

Hypocalcemia (Ca²⁺ < 8.5 mg/dL)

• Causes: hypoparathyroidism, vitamin D deficiency, chronic kidney disease, pancreatitis.
• Symptoms: paresthesias, muscle cramps, tetany, positive Chvostek and Trousseau signs.
  • Chvostek sign: facial twitching when tapping the facial nerve.
  • Trousseau sign: carpal spasm when the BP cuff is inflated.
• ECG: prolonged QT interval.
• Treatment: oral or IV calcium supplementation.
• Monitor for laryngospasm and seizures; keep airway equipment available.

Hypercalcemia (Ca²⁺ > 10.5 mg/dL)

• Causes: hyperparathyroidism, malignancy, excessive vitamin D.
• Symptoms: constipation, polyuria, polydipsia, confusion, bone pain.
• ECG: shortened QT interval.
• Severe cases → renal stones and cardiac arrest.
• Treatment: IV fluids, loop diuretics, bisphosphonates.

Magnesium Imbalances (Normal: 1.5–2.5 mg/dL)

Hypomagnesemia (Mg²⁺ < 1.5 mg/dL)

• Causes: GI losses, diuretics, alcohol use, poor nutrition.
• Symptoms (similar to hypocalcemia): muscle cramps, tremors, paresthesias, tetany.
• ECG: prolonged QT and PR intervals.
• Often coexists with hypokalemia and hypocalcemia — all must be corrected together.
• Treatment: oral or IV magnesium replacement.
• With IV mag, monitor for respiratory depression and hypotension.

Hypermagnesemia (Mg²⁺ > 2.5 mg/dL)

• Causes: renal failure, excessive magnesium intake.
• Symptoms: lethargy, muscle weakness, decreased deep tendon reflexes.
• ECG: prolonged PR interval, widened QRS.
• Severe cases → respiratory depression, bradycardia, cardiac arrest.
• Treatment: IV calcium to antagonize magnesium effects; hemodialysis in severe cases.

ECG Changes Summary

• Hypokalemia: flattened T waves, U waves, ST depression
• Hyperkalemia: peaked T waves, widened QRS, loss of P wave, sine wave
• Hypocalcemia: prolonged QT interval
• Hypercalcemia: shortened QT interval
• Hypomagnesemia: prolonged QT, prolonged PR
• Hypermagnesemia: prolonged PR, widened QRS

Nursing Assessment

• Monitor serum electrolyte levels and report critical values immediately.
• Assess for muscle weakness, cramps, and paresthesias.
• Monitor ECG for characteristic changes.
• Assess for Chvostek and Trousseau signs in hypocalcemia.
• Monitor intake and output, especially with diuretics.
• Watch for signs of dehydration or fluid overload.

Nursing Interventions

• Administer oral or IV electrolytes as ordered.
• For IV potassium: never bolus; infuse slowly with continuous cardiac monitoring.
• For IV magnesium: monitor for respiratory depression and hypotension.
• For hyperkalemia: prepare to administer calcium gluconate, insulin/glucose, and albuterol.
• For hypocalcemia: keep airway equipment at the bedside (laryngospasm risk).
• Provide dietary teaching for electrolyte management.

Patient Teaching

• Eat potassium-rich foods (bananas, oranges, spinach) if hypokalemic; avoid them if hyperkalemic.
• Limit sodium if hypernatremic or fluid-overloaded.
• Take calcium and vitamin D supplements as prescribed.
• Avoid magnesium-containing antacids if renal function is impaired.
• Report muscle cramps, weakness, or palpitations to the provider.

Common Exam Traps

• Hyperkalemia → peaked T waves; hypokalemia → U waves.
• Calcium gluconate stabilizes the heart in hyperkalemia but does not lower potassium.
• Hypocalcemia → positive Chvostek and Trousseau signs.
• Hypomagnesemia must be corrected first — otherwise hypokalemia and hypocalcemia will not resolve.
• IV potassium is never given as a bolus or push; max rate is 10 mEq/hour.
• IV magnesium can cause respiratory depression — monitor closely.
• Hypernatremia causes confusion; correct slowly to avoid cerebral edema.
• Hyponatremia causes seizures; correct slowly to avoid osmotic demyelination syndrome.
• Loop diuretics cause hypokalemia, hypomagnesemia, and hypocalcemia.
• Potassium-sparing diuretics cause hyperkalemia.

Key takeaways

• Sodium imbalances present with neurologic symptoms (confusion, seizures); always correct slowly to avoid cerebral edema or osmotic demyelination syndrome.
• Hyperkalemia is a cardiac emergency: calcium gluconate stabilizes the heart, while insulin/glucose and albuterol shift K⁺ into cells, and Kayexalate or dialysis removes it.
• IV potassium is never pushed — max 10 mEq/hour with cardiac monitoring and adequate urine output.
• Hypocalcemia → tetany, positive Chvostek and Trousseau signs, prolonged QT, and risk of laryngospasm.
• Hypomagnesemia must be corrected before hypokalemia and hypocalcemia will resolve.
• Know the ECG fingerprints: peaked T waves (hyperkalemia), U waves (hypokalemia), prolonged QT (low Ca²⁺ or Mg²⁺), shortened QT (high Ca²⁺).