🫀 Physiological Adaptation · Lesson 2 of 10 · 8 min

Sodium, Calcium and Magnesium: Twitching, Seizing and Going Flat

😮 Tap a client's cheek and the lip twitches: low calcium. Inflate a blood pressure cuff and the hand spasms: low calcium. Lose the knee reflexes on a magnesium drip: stop the drip. The exam shows you the sign and wants the electrolyte.

💡 Key idea

Low calcium and low magnesium twitch and spasm; high calcium and high magnesium go weak and quiet. Sodium is corrected slowly in both directions to protect the brain.

🧠 Why it matters

SODIUM, normal 135 to 145: HYPONATREMIA causes headache, nausea, confusion and seizures, from fluid excess, SIADH, diuretics or hypotonic fluids; treat with fluid restriction and, when severe, hypertonic saline raised slowly, generally no more than 8 to 12 mEq/L in 24 hours, because rapid correction causes osmotic demyelination. HYPERNATREMIA causes thirst, dry mucous membranes, restlessness and seizures, from dehydration or diabetes insipidus; correct slowly with hypotonic fluids to avoid cerebral edema. CALCIUM, normal about 9 to 10.5 mg/dL: HYPOCALCEMIA, after thyroid or parathyroid surgery, with low vitamin D, pancreatitis or kidney disease, causes tingling, muscle cramps, TETANY, laryngospasm, a positive CHVOSTEK'S sign (facial twitch) and TROUSSEAU'S sign (carpal spasm with a cuff), and a prolonged QT; treat with IV calcium gluconate and keep it at the bedside after thyroidectomy. HYPERCALCEMIA, from hyperparathyroidism, cancer and immobility, causes lethargy, constipation, kidney stones, muscle weakness and a shortened QT; treat with fluids, loop diuretics, calcitonin and bisphosphonates. MAGNESIUM, normal about 1.5 to 2.5 mEq/L: HYPOMAGNESEMIA, common in alcohol use disorder and malnutrition, causes tremors, hyperreflexia, tetany and torsades de pointes; HYPERMAGNESEMIA, from kidney failure or magnesium infusions, causes loss of reflexes, lethargy, hypotension, bradycardia and respiratory depression, treated by stopping magnesium and giving calcium gluconate.

🏥 In the real world

🦋 Twelve hours after a thyroidectomy a client reports tingling around the mouth and in the fingertips. The nurse taps in front of the ear and the client's lip twitches. The parathyroid glands were disturbed during surgery and calcium is falling. Calcium gluconate, already at the bedside per protocol, is given. Laryngospasm, the next step in untreated hypocalcemia, never happens.

📌 Takeaways

Hyponatremia: confusion and seizures; correct no faster than 8 to 12 mEq/L a day
Hypocalcemia: Chvostek's, Trousseau's, tetany; calcium gluconate at the bedside after thyroidectomy
Hypermagnesemia: lost reflexes and slow breathing; stop the drip, give calcium gluconate

📖 Terms in this lesson

Hyponatremia: Sodium below 135 mEq/L, causing confusion and seizures; corrected slowly to protect the brain.

Chvostek's sign: A facial twitch when the cheek is tapped, a sign of low calcium.

Trousseau's sign: A hand spasm when a blood pressure cuff is inflated, a sign of low calcium.

SALT LOSS (hyponatremia signs): Seizures, Abdominal cramps, Lethargy, Tendon reflexes diminished, Loss of urine and appetite, Orthostatic hypotension, Shallow breathing, Spasms: the signs of sodium below 135 mEq/L.

FRIED (hypernatremia signs): Fever and flushed skin, Restlessness, Increased fluid retention and blood pressure, Edema, Decreased urine output and dry mouth: the signs of sodium above 145 mEq/L.

CATS (hypocalcemia signs): Convulsions, Arrhythmias, Tetany, Spasms and stridor: the signs of calcium below about 9 mg/dL, the picture to watch for after thyroid or parathyroid surgery.

Sodium (Na+): Normal 135 to 145 mEq/L; below 135 brings confusion and seizures when it falls fast, above 145 thirst and restlessness; critical below 120 or above 160, and correction runs no faster than about 8 to 12 mEq/L a day.

Total calcium (Ca): Normal 9 to 10.5 mg/dL; low brings tingling, tetany, Chvostek's and Trousseau's signs and laryngospasm, high brings weakness, constipation, stones and confusion, and below about 6 or above about 13 is critical.

Ionized calcium: The active, unbound calcium, normally about 4.5 to 5.6 mg/dL (1.1 to 1.4 mmol/L); it is the value to trust when albumin is low, because a low albumin drags the total calcium down without changing the ionized fraction.

Magnesium (Mg): Normal about 1.5 to 2.5 mEq/L (some labs 1.3 to 2.1); low brings tremor, hyperreflexia and torsades, high brings lost reflexes, hypotension and respiratory depression, and below about 1 or above about 5 is critical.

Hypertonic saline (3%): A concentrated salt infusion for severe symptomatic hyponatremia that pulls water out of swollen brain cells; run it slowly by pump, check sodium every few hours, and never correct faster than about 8 to 10 mEq/L in 24 hours, or the brain demyelinates.

✅ Test yourself

A client with a sodium level of 118 mEq/L is receiving 3% saline. Why does the nurse monitor sodium levels every few hours?

The client may develop nephrogenic diabetes insipidus
Sodium levels affect the heart rate only
Rapid correction risks osmotic demyelination
Hypertonic saline causes hypokalemia and muscle cramps

Answer: C · Rapid correction risks osmotic demyelination

Raising sodium too fast shrinks brain cells and can cause permanent neurologic damage; correction is limited to about 8 to 12 mEq/L in 24 hours.

Which finding indicates hypocalcemia in a client after a parathyroidectomy?

Constipation, lethargy and kidney stones
Polyuria, flank pain and muscle weakness
Hand spasm when a cuff is inflated
Shortened QT interval

Answer: C · Hand spasm when a cuff is inflated

Trousseau's sign (carpal spasm with cuff inflation) indicates neuromuscular irritability from low calcium.

A client with chronic kidney disease has a magnesium level of 4.8 mEq/L. Which assessment finding would the nurse expect?

Hyperactive deep tendon reflexes
Positive Chvostek's and Trousseau's signs
Tachypnea with muscle cramps and tremor
Diminished deep tendon reflexes

Answer: D · Diminished deep tendon reflexes

High magnesium depresses the neuromuscular system, producing hyporeflexia, lethargy and respiratory depression.

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