Hypocalcaemia

Acute severe hypocalcaemia most often occurs following extensive neck surgery e.g. for thyroid cancer. This emergency guide outlines a strategy to prevent this complication and to treat it and other causes of severe hypocalcaemia.

 

Pre-operative prevention with vitamin D

Check vitamin D and replace with ergocalciferol 300,000 units by intra muscular injection one month prior to surgery, or give a daily oral replacement dose for three months prior to surgery if <25nmol/l.

Post op routine management

Start calcium supplements  

Start Sandocal 1000 TM 2 tablets twice daily empirically for patients at risk of hypocalceamia e.g. post total thyroidectomy, neck exploration.

Check PTH and calcium levels at 4 and 12 hours.

PTH >1.6pmol/l = low risk  

If the post op PTH level is >1.6pmol/l the patient is low risk.

If the post op PTH is >1.6pmol/l and the second post op serum calcium >2.1mmol/l, stop calcium supplements. The patient should be metabolically fit for discharge.

PTH 0.6-1.6pmol/l = medium risk  

If the post op PTH is 0.6-1.6pmol/l, the patient is medium risk. Continue calcium supplements and recheck calcium, Trousseau and Chvostek signs 12 hourly.

If the patient remains well (both signs negative), calcium stablises to above 2.0mmol/l at 48 hours, stop calcium supplements. The patient should be metabolically fit for discharge.

For medium and high risk patients during post op monitoring, if the serum calcium remains above 1.8mmol/l and the patient is asymptomatic with negative signs, continue monitoring as above but increase their oral calcium supplements to 3 tablets twice daily.

If the patient is still hypocalcaemic by 72hours, start 1alphacalcidol as for high risk patients.

PTH <0.6pmol/l = high risk  

If the post op PTH level is <0.6pmol/l the patient is high risk for permanent HPTH. Start 1alphacalcidol 0.25mcg daily, continue calcium supplements, and monitor serum calcium, Trousseau and Chvostek signs at 12 hours then daily.

If serum calcium is >2.1mmol/l at 24 or 48 hours, stop calcium supplements but continue 1alpha calcidol. The patient should be metabolically fit for discharge but will need ongoing monitoring and long term follow up.

For medium and high risk patients during post op monitoring, if the serum calcium remains above 1.8mmol/l and the patient is asymptomatic with negative signs, continue monitoring as above but increase their oral calcium supplements to 3 tablets twice daily.

If the patient is still hypocalcaemic by 72hours, start 1alphacalcidol as for high risk patients.

Calcium <1.8mmol/l

At any time, if the serum calcium is below 1.8mmol/l or the patient is symptomatic with positive signs, continue monitoring and treatment as above, but also give intravenous calcium gluconate as below.

Emergency management of hypocalcaemia  

Patients with symptoms of tetany, with a positive Trousseau sign, or in whom calcium is falling rapidly post operatively, or whose serum calcium is <1.8mmol/L usually require intravenous calcium gluconate supplementation.

Administer (1.7x patient's weight in kg) mls 10% calcium gluconate in 1l 0.9%saline over a 4 hour infusion. This standardised dose can be administered repeatedly until corrected calcium is >1.8ml/l.

Recheck serum calcium  one hour post infusion, then at least 12 hourly for 24 hours, then daily.

Also check the patient's serum magnesium level and replace as necessary, and continue monitoring and treatment with oral calcium and 1alphacalcdol as above. This is almost always necessary if the post operative PTH level is <0.6pmol/l or for prolonged hypocalcaemia beyond 72 hours post op. 

Hypomagnesaemia  

Any patient presenting with hypocalcaemia should also have their serum magnesium level checked. If this too is low, replacement should be given (intravenously for emergency cases) as without this, the hypocalcaemia will not correct.