When is intravenous (IV) calcium replacement indicated?

Indications for Intravenous Calcium Replacement

IV calcium replacement is primarily indicated for hypocalcemia, hyperkalemia, hypermagnesemia, and calcium channel blocker toxicity, especially in cases where these conditions cause hemodynamic instability or cardiac arrest.

Specific Indications for IV Calcium Administration:

Hypocalcemia

• IV calcium is indicated for symptomatic hypocalcemia or when ionized calcium levels fall below normal range (normal range: 1.1-1.3 mmol/L) 1
• Acute hypocalcemia requiring immediate treatment may present with:
  • Neuromuscular irritability and tetany 2
  • Seizures 2
  • Cardiac arrhythmias 2
  • Hypotension 1
• IV calcium is particularly important during massive transfusion protocols, as citrate in blood products chelates calcium 1

Hyperkalemia

• IV calcium is recommended for cardiac stabilization in severe hyperkalemia 1
• Calcium administration protects the myocardium from the effects of hyperkalemia while other treatments take effect 1

Hypermagnesemia

• IV calcium (calcium chloride 10% 5-10 mL or calcium gluconate 10% 15-30 mL over 2-5 minutes) may be administered during cardiac arrest associated with hypermagnesemia 1
• Calcium directly antagonizes the effects of magnesium on the myocardium 1

Calcium Channel Blocker Toxicity

• IV calcium is indicated for hemodynamically unstable calcium channel blocker overdose refractory to other treatments 1
• Limited evidence supports its use in this setting, but it may be considered when other measures fail 1

Cardiac Arrest Situations

• IV calcium may be considered when hyperkalemia or hypermagnesemia is suspected as the cause of cardiac arrest 1
• For cardiac resuscitation, calcium is only recommended in cases of documented hyperkalemia, hypocalcemia, hypermagnesemia, or calcium channel blocker toxicity 1

Dosing and Administration:

For Hypocalcemia:

• Calcium chloride: 20 mg/kg (0.2 mL/kg for 10% CaCl₂) IV/IO 1
  • Give by slow push for cardiac arrest
  • Infuse over 30-60 minutes for other indications
• Calcium gluconate: 60 mg/kg IV/IO (may be substituted if calcium chloride is not available) 1
• For moderate to severe hypocalcemia (iCa <1 mmol/L), 4g of calcium gluconate infused at 1g/hour has shown 95% success in achieving iCa >1 mmol/L 3

For Calcium Channel Blocker Toxicity:

• Initial dose: 0.3 mEq/kg of calcium (0.6 mL/kg of 10% calcium gluconate or 0.2 mL/kg of 10% calcium chloride) IV over 5-10 minutes 1
• May be followed by an infusion of 0.3 mEq/kg per hour 1

Important Considerations and Precautions:

• Calcium chloride administration results in a more rapid increase in ionized calcium concentration than calcium gluconate and is preferred for critically ill patients 1
• Administration through a central venous catheter is preferred; extravasation through a peripheral IV line may cause severe skin and soft tissue injury 1
• Stop injection if symptomatic bradycardia occurs 1
• Do not mix sodium bicarbonate with calcium 1
• Monitor serum ionized calcium levels to prevent hypercalcemia, especially during continuous infusions 1
• Severe hypercalcemia (ionized calcium levels greater than twice the upper limits of normal) should be avoided 1

Pitfalls to Avoid:

• Relying solely on adjusted calcium (AdjCa) measurements instead of ionized calcium (iCa) in critically ill patients - AdjCa<2.2 mmol/L has only 78.2% sensitivity and 63.3% specificity for predicting iCa<1.1 mmol/L 4
• Failure to monitor for hypocalcemia during massive transfusion protocols 1
• Inadequate dosing for moderate to severe hypocalcemia - 1-2g of IV calcium gluconate may be insufficient for patients with iCa <1 mmol/L 5
• Peripheral administration of calcium chloride, which can cause tissue necrosis if extravasation occurs 1

In critically ill trauma patients, failure to normalize severely low calcium levels by day 4 may be associated with increased mortality, highlighting the importance of appropriate calcium replacement 4.