Hypercalcaemia needs urgent correction when the albumin-adjusted calcium is above 3.5 mmol/L, with intravenous 0.9% saline of 4 to 6 litres over 24 hours and then a bisphosphonate if more is needed, according to the Society for Endocrinology's emergency guidance. Hypocalcaemia is a medical emergency below 1.9 mmol/L or when symptomatic at any level below the reference range, treated with 10 to 20 ml of 10% calcium gluconate over 10 minutes under ECG monitoring. At the CT1 anaesthetics interview the hypocalcaemia scenario is the tingling, stridulous patient the night after a total thyroidectomy.
Key takeaways
- Hypercalcaemia below 3.0 mmol/L is often asymptomatic; 3.0 to 3.5 usually needs prompt treatment; above 3.5 needs urgent correction because of dysrhythmia and coma (Society for Endocrinology)
- Ninety percent of hypercalcaemia is primary hyperparathyroidism or malignancy; a high calcium with a high PTH is parathyroid, with a low PTH is malignancy or another cause
- Rehydrate with 4 to 6 litres of 0.9% saline in 24 hours, watching for overload; loop diuretics are rarely used and do not lower calcium
- If more is needed: zoledronic acid 4 mg over 15 minutes, or pamidronate 30 to 90 mg at 20 mg/hour; the nadir comes at 2 to 4 days
- Severe hypocalcaemia is below 1.9 mmol/L or symptomatic: 10 to 20 ml of 10% calcium gluconate in 50 to 100 ml of 5% glucose over 10 minutes with ECG monitoring, then an infusion
- Check and replace magnesium, and stop the proton pump inhibitor that may have caused it
How is hypercalcaemia graded?
Hypercalcaemia is graded by the Society for Endocrinology on the albumin-adjusted calcium: below 3.0 mmol/L it is often asymptomatic and does not usually need urgent correction, at 3.0 to 3.5 it may be tolerated if it rose slowly but prompt treatment is usually indicated, and above 3.5 it needs urgent correction because of the risk of dysrhythmia and coma.
Serum calcium is bound to albumin, so the unadjusted value misleads in a dehydrated or malnourished patient. Say adjusted, every time.
The features are polyuria and thirst, anorexia, nausea and constipation, confusion and coma, renal impairment, a shortened QT interval with dysrhythmias, pancreatitis and peptic ulceration.
What causes it, and how do you find out?
Ninety percent of hypercalcaemia is due to primary hyperparathyroidism or malignancy, according to the Society for Endocrinology, and the parathyroid hormone level splits them. A high calcium with a high PTH is primary or tertiary hyperparathyroidism; a high calcium with a low PTH is malignancy or a less common cause.
The bloods are adjusted calcium, phosphate, PTH and urea and electrolytes, with an ECG looking for a shortened QT. The history asks about weight loss, night sweats, cough, family history, and drugs including supplements.
Less common causes the guidance lists include thiazides, lithium, immobilisation, thyrotoxicosis, granulomatous disease, vitamin D excess and adrenal insufficiency. Familial hypocalciuric hypercalcaemia mimics primary hyperparathyroidism but rarely presents as an emergency.
What do you do first for hypercalcaemia?
The first treatment for hypercalcaemia is rehydration with intravenous 0.9% saline, 4 to 6 litres in 24 hours, according to the Society for Endocrinology. Fluid overload is monitored for in renal impairment and the elderly.
Loop diuretics are rarely used, only if overload develops, and the guidance states they are not effective at reducing serum calcium. The old reflex of saline plus furosemide is not the answer.
Dialysis may need to be considered if there is severe renal failure. An ABCDE assessment comes first in a confused or comatose patient, with the airway protected as needed.
When is a bisphosphonate given?
A bisphosphonate is given if further treatment is required after intravenous saline, and the Society for Endocrinology lists three: zoledronic acid 4 mg over 15 minutes, pamidronate 30 to 90 mg depending on severity at 20 mg per hour, or ibandronic acid 2 to 4 mg.
They are given more slowly, with dose reduction considered, in renal impairment. The calcium reaches its nadir at 2 to 4 days, so a repeat dose the next morning is a mistake, and they can cause hypocalcaemia if vitamin D is deficient or PTH is suppressed.
Second-line options are prednisolone 40 mg daily for lymphoma, granulomatous disease or vitamin D poisoning, effective in 2 to 4 days, and calcimimetics, denosumab or calcitonin under specialist supervision. Parathyroidectomy can be considered in a severe acute presentation of primary hyperparathyroidism that does not respond.
How do you recognise hypocalcaemia?
Hypocalcaemia is recognised by peri-oral and digital paraesthesiae, positive Trousseau's and Chvostek's signs, tetany and carpopedal spasm, laryngospasm, a prolonged QT interval with arrhythmia, and seizures. The Society for Endocrinology notes symptoms typically appear when the adjusted calcium falls below about 1.9 mmol/L, though the threshold depends on the rate of fall.
The commonest cause of acute symptomatic hypocalcaemia in hospital is disruption of the parathyroid glands after total thyroidectomy, which is why this is an anaesthetic scenario. Other causes are selective parathyroidectomy, severe vitamin D deficiency, magnesium deficiency including proton pump inhibitor-associated hypomagnesaemia, cytotoxic drugs, pancreatitis, rhabdomyolysis and large-volume transfusion.
The investigations are adjusted calcium, phosphate, PTH, urea and electrolytes, vitamin D and magnesium.
How is severe hypocalcaemia treated?
Severe hypocalcaemia, defined by the Society for Endocrinology as a calcium below 1.9 mmol/L or symptoms at any level below the reference range, is a medical emergency treated with 10 to 20 ml of 10% calcium gluconate in 50 to 100 ml of 5% glucose intravenously over 10 minutes with ECG monitoring. The bolus can be repeated until the patient is asymptomatic.
It is followed by an infusion: 100 ml of 10% calcium gluconate, ten vials, diluted in 1 litre of 0.9% saline or 5% glucose and run at 50 to 100 ml per hour, titrated to normocalcaemia until treatment of the cause takes effect.
Calcium chloride is an alternative but is more irritant and given only through a central line. The 2019 addendum states each 10 ml vial of 10% calcium gluconate contains 2.2 mmol of calcium, so 4.4 ml of 7.35% or 2.2 ml of 14.7% calcium chloride is the equivalent.
Laryngospasm and a prolonged QT are the two features that make this the anaesthetist's emergency. Say that you would have airway equipment at the bedside and continuous ECG monitoring throughout.
How is mild hypocalcaemia managed after thyroidectomy?
Mild hypocalcaemia, asymptomatic with a calcium above 1.9 mmol/L, is managed orally: the Society for Endocrinology suggests Sandocal 1000 two tablets twice daily or an equivalent. After thyroidectomy the calcium is repeated 24 hours later.
If the adjusted calcium is above 2.1 mmol/L the patient may be discharged with a recheck within a week. If it stays between 1.9 and 2.1, the Sandocal increases to three tablets twice daily. If mild hypocalcaemia persists beyond 72 hours post-operatively despite supplements, alfacalcidol 0.25 micrograms daily is started with close monitoring.
Vitamin D deficiency is loaded with about 300,000 units of colecalciferol or ergocalciferol over 6 to 10 weeks.
What about magnesium?
Magnesium deficiency causes hypocalcaemia that will not correct until the magnesium does, and the Society for Endocrinology's regimen is 24 mmol over 24 hours, made up as 6 g of magnesium sulphate in 500 ml of 0.9% saline or 5% glucose, with the precipitating drug stopped.
Proton pump inhibitors are the drug to ask about. A patient on omeprazole with tetany and a normal PTH has a magnesium problem until proven otherwise.
Which traps catch candidates?
The calcium traps at interview are furosemide for hypercalcaemia, a second bisphosphonate dose before the nadir, calcium chloride through a peripheral cannula, and hypocalcaemia treated without the magnesium checked.
- Using an unadjusted calcium
- Saline plus loop diuretic as first-line: the guidance says diuretics do not lower calcium
- Re-dosing zoledronic acid at 24 hours when the nadir is at 2 to 4 days
- Peripheral calcium chloride
- Discharging a post-thyroidectomy patient at 2.0 mmol/L: the threshold is above 2.1
What is the interviewer listening for?
In a calcium scenario the assessors are listening for the adjusted value, the threshold that makes it urgent, the first treatment with its volume, and the airway plan in the hypocalcaemic patient.
- Above 3.5 mmol/L is urgent; 4 to 6 litres of saline in 24 hours, then a bisphosphonate
- PTH splits parathyroid from malignancy
- Below 1.9 or symptomatic: 10 to 20 ml of 10% calcium gluconate over 10 minutes with the ECG on
- Then the infusion, and magnesium checked
- Laryngospasm and QT prolongation named as the reasons you stay
How this comes up at the CT1 anaesthetics interview
Calcium comes up in the clinical judgement station as the total thyroidectomy patient who is tingling and anxious at 2 a.m., or the confused oncology patient with a calcium of 3.7 who needs a procedure. The station is one of two 15-minute stations, each marked out of 50, with 60 out of 100 appointable.
The follow-up in the thyroidectomy case is stridor, which tests whether you separate hypocalcaemic laryngospasm from a neck haematoma and call for help either way. anaestheticinterview's 340-question bank includes a post-thyroidectomy scenario with AI-marked spoken practice, so the calcium gluconate dose can be rehearsed out loud.