At what calcium level is urgent replacement required?

Urgent Calcium Replacement Thresholds

Urgent calcium replacement is required when ionized calcium is less than 0.9 mmol/L (or corrected total calcium less than approximately 7.6 mg/dL). 1, 2

Assessment of Calcium Status

• Preferred measurement: Ionized calcium (normal range: 1.15-1.36 mmol/L)
• Alternative: Total calcium corrected for albumin using the formula:
  • Corrected calcium (mg/dL) = Total calcium (mg/dL) + 0.8 × [4 - Serum albumin (g/dL)]
  • Normal range for corrected total calcium: 8.4-9.5 mg/dL

Urgent Replacement Protocol

For severe hypocalcemia (ionized calcium <0.9 mmol/L):

1. Intravenous administration options:

   • Calcium gluconate: 1-2 mg elemental calcium per kg body weight per hour 1

     • Administer via secure IV line, preferably in a central or deep vein
     • Monitor ECG during administration, especially with concurrent cardiac glycoside use 3

   • Calcium chloride (provides more elemental calcium per mL than calcium gluconate):

     • Adult dose: 200 mg to 1 g (2-10 mL of 10% solution)
     • Pediatric dose: 2.7-5.0 mg/kg 4
     • Administer slowly (not to exceed 1 mL/min) 4

2. Monitoring during treatment:

   • Measure serum calcium during intermittent infusions every 4-6 hours
   • For continuous infusion, monitor every 1-4 hours 3
   • Monitor ECG for cardiac arrhythmias, especially with rapid administration 3

3. Transition to oral therapy when possible:

   • Calcium carbonate: 1-2 g three times daily
   • Add calcitriol (up to 2 μg/day) 1

Important Clinical Considerations

• Symptoms of severe hypocalcemia requiring urgent treatment:

  • Neuromuscular irritability, tetany, seizures
  • Prolonged QT interval, heart block, cardiac arrest
  • Mental status changes

• Common pitfalls to avoid:

  • Rapid administration: Can cause hypotension, bradycardia, and cardiac arrhythmias 3
  • Extravasation: Can lead to tissue necrosis and calcinosis cutis 3
  • Drug incompatibilities: Calcium is not compatible with fluids containing phosphate or bicarbonate 3
  • Overlooking concurrent magnesium deficiency: Must be corrected to effectively treat hypocalcemia 1, 2

• Special considerations:

  • Patients with renal impairment: Start at lower doses and monitor more frequently 3
  • Patients on cardiac glycosides: Increased risk of arrhythmias with calcium administration 3
  • Patients receiving blood transfusions: Monitor calcium levels due to risk of citrate-induced hypocalcemia 1

Remember that pH affects ionized calcium levels - an increase of 0.1 units in pH decreases ionized calcium by approximately 0.05 mmol/L. Acidosis increases ionized calcium while alkalosis decreases it 1.