Nursing care
Why low calcium makes nerves and muscles fire too easily
Written and reviewed by Andrew Wright, ADN, RN, CMSRN · 4 min read · Updated October 2026
Short answer
Hypocalcaemia causes tetany because calcium outside the cell helps keep nerve membranes stable. When ionised calcium falls, nerves become irritable and fire with little or no stimulus, so muscles twitch and cramp. The nurse sees tingling around the mouth and fingers, carpopedal spasm, and positive Chvostek and Trousseau signs; laryngospasm and seizures signal severe hypocalcaemia.
How falling calcium makes nerve membranes unstable
Calcium in the fluid around nerve cells acts like a brake on the membrane. MSD describes the main features of hypocalcaemia as the result of disturbed membrane potential, which produces neuromuscular irritability. In plain terms, when ionised calcium drops, the threshold for firing falls, so nerves send signals far more readily than they should.
Peripheral motor nerves are affected early. They fire repeatedly, so the muscles they supply contract and stay contracted. That sustained, involuntary contraction is tetany. Sensory nerves misfire too, which explains the pins and needles around the lips, tongue, fingers and feet that clients often describe before visible spasm appears.
Why ionised calcium matters more than the total number
Only the ionised, unbound fraction of calcium is active at the membrane. Much of the rest travels bound to albumin. MSD notes that tetany can occur from a fall in ionised calcium without marked total hypocalcaemia, as happens in severe alkalosis, because a higher pH increases protein binding and leaves less free calcium available.
This is why a client who is hyperventilating can develop tingling and carpopedal spasm even with an unremarkable total calcium. It also explains why low albumin can make a total calcium look low while ionised calcium is adequate. Interpret any calcium result alongside albumin, pH and symptoms, and follow local protocol for which value guides treatment.
Bedside signs: Chvostek, Trousseau and laryngospasm
Latent tetany can be unmasked at the bedside. Chvostek sign is twitching of the facial muscles when the facial nerve is tapped just in front of the ear. MSD notes it occurs in some healthy people and may be absent in chronic hypocalcaemia, so it supports the picture but does not settle it alone.
Trousseau sign is carpal spasm provoked by inflating a blood pressure cuff above systolic pressure on the arm for a few minutes, which briefly reduces blood flow to an already irritable nerve. Severe hypocalcaemia can progress to hyperreflexia, laryngospasm and seizures, and the ECG may show a prolonged QT interval, which raises dysrhythmia risk.
Expected and concerning trends after thyroid surgery
Thyroidectomy can bruise or remove parathyroid glands, cutting parathyroid hormone and therefore calcium. MSD states that transient hypoparathyroidism is common after subtotal thyroidectomy and that symptoms usually begin a day or two after surgery, although they can appear much later. Mild, brief tingling may settle once calcium is replaced per protocol.
Concerning trends are spreading numbness, muscle cramps that become sustained spasm, a newly positive Trousseau sign, voice change, stridor or noisy breathing. These suggest calcium is still falling and the airway may be threatened by laryngospasm. Keep emergency airway equipment available as local protocol directs, and report rather than wait for the next scheduled calcium.
Work a hypothetical post-thyroidectomy scenario
Imagine a hypothetical client the day after total thyroidectomy who reports tingling around the mouth and in both hands. While the nurse takes a blood pressure, the hand flexes into spasm. Options include reassuring that tingling is expected after anaesthesia, offering a warm pack for the hand cramp, or assessing airway and breathing and notifying the provider about suspected hypocalcaemia.
Assessing the airway and notifying the provider is the best choice, because cuff-induced carpal spasm is a positive Trousseau sign and the same irritability can affect laryngeal muscles. Reassurance misreads a classic pattern, and a warm pack treats the symptom rather than the cause. Calcium replacement is a prescriber decision made under local protocol.
Sources and further reading
Hypocalcemia (MSD Manual Professional Edition). Neuromuscular irritability from altered membrane potential; tetany features; Chvostek and Trousseau signs; laryngospasm, seizures, QT prolongation; post-thyroidectomy hypoparathyroidism timing; tetany in alkalosis.
Respiratory Alkalosis (MSD Manual Professional Edition). Decreased ionised calcium in alkalosis from increased protein binding; paresthesias and carpopedal spasm.
Hypoparathyroidism (MedlinePlus Medical Encyclopedia). Parathyroid hormone deficiency as a cause of low calcium, including after neck surgery.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our endocrine practice questions are the closest set to what this page covers.
Common questions
Why does alkalosis cause tingling and spasm like hypocalcaemia?
A higher pH increases calcium binding to albumin, so the ionised fraction falls even when total calcium is near normal. Nerves respond to ionised calcium, so they become irritable and can cause paresthesias and carpopedal spasm.
Is a positive Chvostek sign enough to diagnose hypocalcaemia?
No. Chvostek sign can be present in some healthy people and may be missing in chronic hypocalcaemia. It is a supporting finding that prompts a calcium level, symptom review and report, not a diagnosis on its own.
Which hypocalcaemia finding is most urgent to report?
Stridor, voice change or difficulty breathing are most urgent because they may signal laryngospasm. Seizures and new dysrhythmias are also emergencies. Escalate these immediately and support the airway as local protocol directs.