5.2 Electrolytes

Electrolyte Fundamentals

Electrolytes are minerals that carry an electric charge when dissolved in body fluids. They regulate everything from how your nerves fire to how your heart beats, so even small imbalances can become clinically significant fast. For nurses, recognizing these imbalances early and knowing how to treat them is a core skill.

The major electrolytes you need to know are sodium ($Na^+$), potassium ($K^+$), calcium ($Ca^{2+}$), magnesium ($Mg^{2+}$), chloride ($Cl^-$), and bicarbonate ($HCO_3^-$).

Key Body Functions

• Fluid balance: Electrolytes regulate osmotic pressure, controlling how water distributes between intracellular and extracellular compartments.
• Nerve and muscle function: They generate action potentials, the electrical impulses that allow nerves to signal and muscles to contract.
• Acid-base balance: Electrolytes (especially bicarbonate) act as buffers to keep blood pH within the narrow normal range of 7.35–7.45.
• Metabolic processes: Many enzymatic reactions, including ATP production and protein synthesis, depend on electrolytes as cofactors.

Electrolyte Homeostasis

• Membrane potential: The charge difference across cell membranes depends on electrolyte concentrations (particularly $Na^+$ and $K^+$). This gradient is what makes nerve impulse transmission and muscle contraction possible.
• Hydration: Sodium is the primary driver of extracellular fluid volume. Where sodium goes, water follows.
• Renal regulation: The kidneys are the main regulators of electrolyte balance. They adjust levels through filtration, reabsorption, and excretion. Hormones like aldosterone and ADH fine-tune this process.

Electrolyte Imbalances and Management

Common Electrolyte Imbalances

Sodium

• Hyponatremia (serum $Na^+$ < 135 mEq/L): Water shifts into brain cells, causing cerebral edema. Watch for nausea, vomiting, headache, confusion, seizures, and in severe cases, coma.
• Hypernatremia (serum $Na^+$ > 145 mEq/L): Cells lose water and shrink (cellular dehydration). Signs include intense thirst, dry mucous membranes, altered mental status, and muscle twitching.

Potassium

• Hypokalemia (serum $K^+$ < 3.5 mEq/L): Impairs nerve and muscle function. Look for muscle weakness, fatigue, constipation, diminished reflexes, and cardiac arrhythmias (flattened T waves, U waves on ECG).
• Hyperkalemia (serum $K^+$ > 5.0 mEq/L): Alters cardiac conduction dangerously. Signs include muscle weakness, paresthesia, bradycardia, and classic ECG changes: peaked T waves → widened QRS → sine wave pattern. This can progress to cardiac arrest.

Calcium

• Hypocalcemia (serum $Ca^{2+}$ < 8.6 mg/dL): Increases neuromuscular excitability. Presents with muscle cramps, tetany, paresthesia, seizures, and prolonged QT interval. Two bedside tests to remember: positive Chvostek's sign (facial twitching when tapping the facial nerve) and positive Trousseau's sign (carpopedal spasm with BP cuff inflation).
• Hypercalcemia (serum $Ca^{2+}$ > 10.2 mg/dL): Reduces neuromuscular excitability. Think of the classic mnemonic "stones, bones, groans, and moans": kidney stones, bone pain, constipation (groans), and fatigue/confusion (moans). ECG shows a shortened QT interval.

Magnesium

• Hypomagnesemia (serum $Mg^{2+}$ < 1.5 mEq/L): Causes muscle weakness, tremors, and cardiac arrhythmias. Importantly, low magnesium often causes low calcium too, because magnesium is needed for proper parathyroid hormone function.
• Hypermagnesemia (serum $Mg^{2+}$ > 2.5 mEq/L): Depresses the CNS and neuromuscular system. Signs progress from lethargy and hypotension to loss of deep tendon reflexes, respiratory depression, and cardiac arrest. Most commonly seen in patients with renal failure who are taking magnesium-containing medications (antacids, laxatives).

Treatment of Electrolyte Disturbances

Sodium imbalances:

• Hyponatremia: Restrict free water intake. For severe or symptomatic cases, administer hypertonic saline (3% NaCl). Correct slowly (no more than 8–12 mEq/L in 24 hours) to avoid osmotic demyelination syndrome. Loop diuretics like furosemide may be used to promote free water excretion.
• Hypernatremia: Replace free water using hypotonic fluids (0.45% NaCl or D5W). Correct gradually to prevent cerebral edema from rapid fluid shifts.

Potassium imbalances:

• Hypokalemia: Replace with potassium chloride (KCl), oral or IV. IV potassium must always be diluted and infused slowly (generally no faster than 10–20 mEq/hr via peripheral line) because rapid infusion can cause fatal arrhythmias. Address the underlying cause (diuretic use, vomiting, diarrhea).
• Hyperkalemia: Treatment follows a stepwise approach:
  1. Calcium gluconate IV to stabilize the cardiac membrane (does not lower $K^+$, but protects the heart)
  2. Regular insulin with dextrose (D50) to shift $K^+$ into cells temporarily
  3. Sodium bicarbonate if acidosis is present (also shifts $K^+$ intracellularly)
  4. Sodium polystyrene sulfonate (Kayexalate) or patiromer to promote GI potassium excretion
  5. Dialysis for severe or refractory cases

Calcium imbalances:

• Hypocalcemia: Administer calcium gluconate (preferred for peripheral IV; less irritating to veins) or calcium chloride (for central lines or emergencies; contains 3x more elemental calcium). Add oral calcium supplements and vitamin D for ongoing replacement.
• Hypercalcemia: Aggressive IV fluid hydration (normal saline) followed by loop diuretics to promote calcium excretion. For moderate-to-severe cases, bisphosphonates (e.g., zoledronic acid, pamidronate) inhibit bone resorption. Calcitonin provides a faster but shorter-acting effect.

Magnesium imbalances:

• Hypomagnesemia: Administer magnesium sulfate IV or IM for severe deficiency; oral magnesium supplements for mild cases.
• Hypermagnesemia: Stop all magnesium-containing medications immediately. Give IV fluids with loop diuretics to promote excretion. Calcium gluconate can be given as an antagonist in symptomatic cases. Dialysis may be needed if renal function is impaired.

Pharmacology of Electrolyte Therapy

• Sodium chloride (hypertonic saline, 3% NaCl)
  • Action: Raises serum sodium and osmolality, pulling water from the intracellular space into the extracellular space.
  • Side effects: Fluid overload, hypertension, pulmonary edema. Overly rapid correction risks osmotic demyelination syndrome.
• Potassium chloride (KCl)
  • Action: Directly replaces potassium deficits to restore normal serum levels (3.5–5.0 mEq/L).
  • Side effects: GI irritation with oral forms (take with food and a full glass of water). IV administration can cause phlebitis at the infusion site. Overdose leads to hyperkalemia and cardiac arrhythmias. Never give IV potassium as a bolus push.
• Calcium gluconate / Calcium chloride
  • Action: Replaces calcium deficits. In hyperkalemia, calcium stabilizes the cardiac cell membrane without lowering potassium levels.
  • Side effects: Calcium chloride causes severe tissue necrosis if it extravasates, so it requires a central line. Hypercalcemia and constipation can occur with excessive dosing. Infuse slowly; rapid IV calcium can cause bradycardia or cardiac arrest.
• Magnesium sulfate
  • Action: Replaces magnesium deficits. Also used in eclampsia/preeclampsia for seizure prophylaxis.
  • Side effects: Hypotension, bradycardia, flushing, and respiratory depression at high doses. Monitor deep tendon reflexes during infusion (loss of reflexes is an early sign of toxicity). Keep calcium gluconate at the bedside as the antidote.

Nursing Care for Electrolyte Imbalances

• Monitor labs regularly. Check the basic metabolic panel (BMP) to track electrolyte levels. Know the normal ranges and flag values that are trending in the wrong direction, not just those already out of range.
• Assess vital signs, neuro status, and cardiac rhythm. Many electrolyte imbalances show up first on the ECG or as changes in mental status. Continuous cardiac monitoring is essential for significant potassium or calcium abnormalities.
• Administer replacements safely. Verify the correct dose, route, and rate. IV potassium and calcium both require controlled infusion rates. Use an infusion pump for IV electrolyte replacement.
• Watch for side effects. Monitor IV sites for infiltration or extravasation (especially with calcium chloride). Assess respiratory status during magnesium sulfate infusions. Report signs of overcorrection promptly.
• Track intake and output. Accurate I&O records help evaluate fluid balance and guide therapy adjustments. Daily weights are also useful for tracking fluid shifts.
• Collaborate on dietary modifications. Work with the dietitian to adjust the patient's diet (e.g., sodium restriction for hypernatremia, potassium-rich foods like bananas and oranges for hypokalemia).
• Identify and address root causes. Electrolyte imbalances are often secondary to medications (diuretics, laxatives), chronic conditions (renal failure, heart failure), or GI losses (vomiting, diarrhea). Treating only the number without addressing the cause leads to recurrence.

Patient Education for Electrolyte Disorders

• Dietary guidance: Teach patients which foods support their specific electrolyte needs. For example, patients on potassium-wasting diuretics should eat potassium-rich foods (bananas, potatoes, spinach), while patients with hyperkalemia need to avoid them.
• Hydration: Encourage appropriate fluid intake based on the patient's condition. Patients with hyponatremia may need to restrict fluids rather than drink more, which is counterintuitive and worth explaining clearly.
• Warning signs: Make sure patients can recognize symptoms that need medical attention: persistent muscle cramps, heart palpitations, confusion, extreme fatigue, or numbness/tingling.
• Medication safety: Review electrolyte supplements and any interacting medications. Patients should understand not to double up on missed doses of potassium or take extra magnesium-containing antacids without checking with their provider.
• Follow-up: Stress the importance of regular lab work, especially for patients on diuretics, ACE inhibitors, or other medications that affect electrolyte levels. Imbalances can develop gradually and go unnoticed without monitoring.