How should severe hypocalcemia be treated acutely in an adult patient who is symptomatic (tetany, seizures, cardiac arrhythmia) or has ionized calcium <0.8 mmol/L (total calcium <7 mg/dL)?

Treatment of Severe Hypocalcemia

For symptomatic severe hypocalcemia (tetany, seizures, cardiac arrhythmia) or ionized calcium <0.8 mmol/L, immediately administer intravenous calcium chloride 10% solution 5-10 mL (500-1000 mg calcium gluconate equivalent) over 2-5 minutes with continuous cardiac monitoring, followed by a continuous infusion of 1-2 mg elemental calcium/kg/hour to maintain ionized calcium >0.9 mmol/L. 1, 2

Immediate Acute Management

Choice of Calcium Preparation

• Calcium chloride 10% is the preferred agent over calcium gluconate because it delivers three times more elemental calcium per volume (270 mg vs. 90 mg per 10 mL) and produces more rapid increases in ionized calcium concentration 3, 1, 2
• Calcium chloride is particularly critical in patients with liver dysfunction, hypothermia, hypoperfusion, or shock states where citrate metabolism is impaired and calcium gluconate cannot be efficiently converted to ionized calcium 1, 4
• If calcium chloride is unavailable, calcium gluconate 10% solution 15-30 mL IV can be substituted, but recognize you are delivering only one-third the elemental calcium 1, 2

Initial Bolus Dosing

• Adults: Administer calcium chloride 10% solution 5-10 mL (or calcium gluconate 15-30 mL) IV over 2-5 minutes for cardiac arrest or life-threatening symptoms 3, 1
• Pediatric patients: Administer calcium chloride 20 mg/kg (0.2 mL/kg of 10% solution) or calcium gluconate 50-100 mg/kg IV slowly with continuous ECG monitoring 3
• For non-arrest situations, infuse over 30-60 minutes rather than rapid bolus to minimize cardiac complications 3, 2

Continuous Infusion Protocol

• Following initial bolus, start continuous infusion at 1-2 mg elemental calcium/kg/hour, adjusted to maintain ionized calcium in the normal range (1.15-1.36 mmol/L) 1
• Dilute calcium gluconate injection to 5.8-10 mg/mL concentration in 5% dextrose or normal saline for continuous infusion 2
• Target maintaining ionized calcium >0.9 mmol/L minimum to prevent cardiac dysrhythmias and coagulopathy, with optimal range 1.1-1.3 mmol/L 1

Critical Administration Precautions

Route and Monitoring

• Administer via central venous access whenever possible to avoid severe tissue injury, calcinosis cutis, and skin necrosis from extravasation 3, 1, 4
• If peripheral access must be used, ensure secure IV line and stop infusion immediately if patient complains of tenderness at injection site 4
• Do NOT exceed infusion rate of 200 mg/minute in adults or 100 mg/minute in pediatric patients 2
• Maintain continuous cardiac monitoring during administration; stop infusion if symptomatic bradycardia occurs 3, 2

Drug Incompatibilities

• Never mix calcium with sodium bicarbonate in the same IV line as precipitation will occur 3, 1
• Do not mix calcium gluconate injection with ceftriaxone due to formation of ceftriaxone-calcium precipitates 2
• Concomitant use of ceftriaxone and IV calcium is contraindicated in neonates ≤28 days old 2

Essential Cofactor Correction

• Check and correct magnesium deficiency immediately, as hypomagnesemia is present in 28% of hypocalcemic ICU patients and prevents full calcium correction 1
• Hypocalcemia cannot be fully corrected without adequate magnesium; administer IV magnesium sulfate for replacement before expecting calcium normalization 1

Monitoring During Treatment

• Measure ionized calcium every 4-6 hours initially during intermittent infusions until stable, then twice daily 1, 2
• During continuous infusion, measure ionized calcium every 1-4 hours 2
• Monitor ECG continuously during acute treatment phase 3, 2
• In patients with renal impairment, initiate at lowest recommended dose and monitor calcium every 4 hours 2

Context-Specific Considerations

Tumor Lysis Syndrome

• Exercise extreme caution with calcium administration in tumor lysis syndrome patients 3
• Only treat symptomatic patients, as increased calcium may precipitate calcium phosphate in tissues causing obstructive uropathy 3
• Consider renal consultation if phosphate levels are elevated before administering calcium 3

Massive Transfusion/Trauma

• Hypocalcemia results from citrate-mediated chelation of calcium from blood products (especially FFP and platelets) 1
• Hypothermia, hypoperfusion, and hepatic insufficiency from shock all impair citrate metabolism, worsening hypocalcemia 1
• Colloid infusions (but not crystalloids) independently contribute to hypocalcemia beyond citrate toxicity 1
• Maintain ionized calcium >0.9 mmol/L throughout massive transfusion to preserve coagulation and cardiovascular stability 1

Cardiac Arrest

• Calcium administration is recommended only for cardiac arrest associated with documented hyperkalemia, hypocalcemia, hypermagnesemia, or calcium channel blocker toxicity 3, 1
• Routine use of calcium for undifferentiated cardiac arrest is not recommended 3

Critical Pitfalls to Avoid

• Standard coagulation tests may appear normal despite significant hypocalcemia-induced coagulopathy because laboratory samples are citrated then recalcified before analysis 1
• Even mild hypocalcemia impairs the coagulation cascade (factors II, VII, IX, X activation) and platelet adhesion—do not ignore ionized calcium <1.0 mmol/L in critically ill patients 1
• Low ionized calcium is associated with increased mortality, coagulopathy, platelet dysfunction, decreased clot strength, and cardiovascular dysfunction 1
• Beware of overcorrection—severe iatrogenic hypercalcemia can result in renal calculi and renal failure 1
• Acidosis increases ionized calcium levels, so correction of acidosis may paradoxically worsen symptomatic hypocalcemia 1

Transition to Maintenance Therapy

• When ionized calcium levels stabilize and oral intake is possible, transition to oral calcium carbonate 1-2 g three times daily 1
• Consider adding calcitriol up to 2 μg/day to enhance intestinal calcium absorption 1
• Total elemental calcium intake should not exceed 2,000 mg/day 1
• Check 25-hydroxyvitamin D levels; if <30 ng/mL, initiate vitamin D2 50,000 units orally monthly for 6 months 1
• Continue monitoring corrected total calcium and phosphorus at least every 3 months once stable 1