A woman has a total thyroidectomy on Monday. On Tuesday morning her lips feel strange and both hands are tingling. This is the commonest calcium emergency on a surgical ward, it is predictable, and it is usually handed to the most junior doctor present.
Why it happens
- Devascularisation of the parathyroids — far commoner than removing them
- Inadvertent excision — found in the specimen at histology
- Hungry bone after parathyroidectomy for severe disease
- Magnesium depletion — low magnesium blocks both PTH release and its effect on bone. Hypocalcaemia that will not correct is hypomagnesaemia until proved otherwise.
Two signs, one more useful than the other
| Sign | How | Worth |
|---|---|---|
| Chvostek's | Tap over the facial nerve in front of the tragus; the ipsilateral lip twitches | Easy, but positive in up to a quarter of normal people |
| Trousseau's | Inflate a cuff above systolic pressure for three minutes; carpopedal spasm follows | Uncomfortable, but far more specific |
Predict it before it happens
A PTH measured on the evening of surgery, or at four hours, does the work: a PTH below 15 pg/mL predicts hypocalcaemia, so supplements are started before the symptoms arrive. A normal PTH allows early, safe discharge.
Treating it
Two columns, and the decision between them is clinical. A patient with tetany is treated intravenously whatever the number says; a comfortable patient with a mildly low calcium is treated by mouth.
| Mild or asymptomatic — oral | Symptomatic or severe — intravenous |
|---|---|
| Calcium carbonate, 1–3 g elemental calcium daily in divided doses, with food | Calcium gluconate 10%, 10 mL diluted in 50–100 mL of 5% dextrose, over 10 minutes |
| Add alfacalcidol 0.5–1 µg daily if the calcium is slow to respond, or PTH is absent | Repeat until symptoms settle, then an infusion |
| Check the magnesium and replace it | Cardiac monitoring; correct the magnesium |
| Recheck the calcium daily; warn the patient which symptoms to return with | Start oral calcium and alfacalcidol at the same time — the drip is a bridge, not a cure |
Stridor or seizure is an emergency. Call for senior help.
Three errors that cause harm
- Calcium chloride through a peripheral cannula — it is three times as concentrated as gluconate and causes tissue necrosis if it extravasates. Use gluconate peripherally.
- Forgetting magnesium — the calcium will not come up until the magnesium does.
- Rapid intravenous calcium in a patient on digoxin — it can precipitate a fatal arrhythmia. Give it slowly, with monitoring, and tell your senior.
Why alfacalcidol and not ordinary vitamin D
Activating vitamin D needs the renal 1α-hydroxylation step, and that step is driven by PTH. After the parathyroids are damaged there is no PTH to drive it, so giving cholecalciferol simply fills a 25(OH)D store that cannot be activated. Alfacalcidol and calcitriol are already past the missing step.
Handing it over in one sentence
“Day one after total thyroidectomy, corrected calcium 7.4 mg/dL with perioral paraesthesia and a positive Trousseau's sign. Postoperative PTH was undetectable. I have given 10 mL of 10% calcium gluconate intravenously, started oral calcium with alfacalcidol, sent a magnesium, and put her on cardiac monitoring with four-hourly calcium levels.”