Disorders of calcium and magnesium

Manage now— do this, in order

• Severe symptomatic hypocalcaemia — secure the airway first (laryngospasm is the immediate threat), then IV calcium gluconate: 10–20 mL of 10% calcium gluconate diluted in 50–100 mL of 5% glucose or 0.9% sodium chloride over 10–20 minutes with continuous cardiac monitoring — first 10 mL over 10 minutes, a second 10 mL may follow and be repeated until tetany ceases. Child: 0.5 mL/kg (max 20 mL) diluted over 10 minutes. Never push IV calcium — rapid administration causes bradycardia, hypotension and asystole; never run it into a line containing bicarbonate or phosphate.Doctor / Nurse
• Then start an infusion — a bolus raises the calcium for only 1–2 hours and the tetany will return: 100 mL of 10% calcium gluconate in 1 litre of 5% glucose at 50–100 mL/hour, titrated to the lower end of normal, rechecking calcium every 4–6 hours. Give magnesium concurrently — hypocalcaemia with magnesium depletion will not correct until magnesium is replaced: the commonest reason for refractory hypocalcaemia. If calcium gluconate is unavailable, 10% calcium chloride 10 mL = 6.8 mmol (three times the calcium) but far more sclerosant — large free-flushing vein or central line only.Doctor / NurseNot available at your setup — Infusion pump.
• Severe hypercalcaemia — fluid first, always, and in volume: 0.9% sodium chloride at least 4–6 litres over the first 24 hours in an adult without heart failure, then 3–4 litres daily for several days; in shock start with 1 litre over the first hour; elderly, cardiac or renal patients — 250–500 mL boluses with reassessment after each; child — 20 mL/kg over 1 hour. Monitor urine output and replace the potassium and magnesium that saline diuresis strips out. Do not give furosemide to a dehydrated patient — it worsens the hypercalcaemia; 20–40 mg IV only if fluid-overloaded, after full rehydration.
• Then a bisphosphonate, after rehydration: pamidronate 30–90 mg in 500 mL of 0.9% sodium chloride IV over 2–4 hours (60–90 mg for corrected calcium above 3.0 mmol/L), or zoledronic acid 4 mg in 100 mL over at least 15 minutes (more potent in malignancy). The calcium will not fall for 24–72 hours — the fluid is the rescue, not the bisphosphonate. Avoid IV bisphosphonates at eGFR below approximately 35 mL/min/1.73 m².Doctor / Nurse
• Hypercalcaemia adjuncts and housekeeping: calcitonin 4–8 units/kg IM or SC every 6 hours works within hours rather than days; prednisolone 30–60 mg orally daily (or hydrocortisone 100 mg/day IV) for myeloma, lymphoma, sarcoidosis and vitamin D or A intoxication; denosumab 120 mg SC for bisphosphonate-refractory malignant hypercalcaemia; dialysis with a low-calcium dialysate where renal failure coexists. Stop thiazides, lithium, calcium supplements, vitamin D and A preparations and calcium-containing antacids; mobilise the patient; withhold digoxin.Doctor / Nurse
• Hypomagnesaemia with torsades de pointes or seizure (adult): magnesium sulphate 2 g (8 mmol) diluted in 10 mL of 5% glucose IV over 10–15 minutes, whatever the measured magnesium; in cardiac arrest the same 2 g as a bolus, repeated once if torsades recurs (50% magnesium sulphate: 2 mL = 1 g = 4 mmol). Symptomatic without arrhythmia: 1–2 g IV over 5–60 minutes, diluted. Child: 25–50 mg/kg (0.1–0.2 mmol/kg), max 2 g, over 20 minutes.Doctor / Nurse
• Replete the stores — a bolus alone is never enough (only 50–70% of an IV dose is retained): magnesium sulphate 24 mmol (6 g) in 500 mL of 0.9% sodium chloride or 5% glucose IV over 24 hours, repeated daily and continued for at least 2 days after the plasma magnesium normalises; cap at 0.5 mmol/kg in the first 24 hours in anyone under about 50 kg or with renal impairment, and reduce by up to 75% in chronic kidney disease. Monitor deep tendon reflexes and respiratory rate throughout any infusion — the earliest signs of overshoot — and check magnesium every 12–24 hours. Mild asymptomatic depletion: oral magnesium 20–30 mmol/day in divided doses.Doctor / NurseNot available at your setup — Infusion pump.
• Hypermagnesaemia — stop every source immediately (infusion, antacid, laxative, enema, purgative) and antagonise with calcium: 10 mL of 10% calcium gluconate IV over 2–10 minutes, repeated as required, with cardiac monitoring; obstetric magnesium toxicity — calcium gluconate 1 g IV over 2 minutes; paediatric — 0.5 mL/kg of the 10% solution by slow IV. Then promote excretion (0.9% sodium chloride with furosemide 20–40 mg IV if the kidneys work; glucose and insulin shift magnesium intracellularly as for hyperkalaemia), support ventilation, and arrange haemodialysis early rather than late in severe hypermagnesaemia with renal failure.Doctor / NurseNot available at your setup — Dialysis / renal replacement. No dialysis: saline with furosemide if urine flows, calcium repeated as required, ventilatory support, and urgent transfer.