How do you manage a patient with critically low calcium (total serum calcium <7 mg/dL or ionized calcium <0.8 mmol/L)?

Management of Critical Hypocalcemia

For a patient with critically low calcium (total serum calcium <7 mg/dL or ionized calcium <0.8 mmol/L), immediately administer intravenous calcium chloride 10% solution 5–10 mL (270 mg elemental calcium per 10 mL) over 2–5 minutes with continuous cardiac monitoring, then start a continuous infusion at 1–2 mg elemental calcium/kg/hour, targeting ionized calcium 1.15–1.36 mmol/L. 1, 2

Immediate Assessment & Stabilization

Check for Life-Threatening Manifestations

• Assess immediately for tetany, seizures, laryngospasm, bronchospasm, QT prolongation on ECG, or cardiac arrhythmias—these require emergent IV calcium regardless of the exact calcium level. 1, 2
• Obtain a 12-lead ECG before treatment to document baseline QTc; QTc >500 ms or prolongation >60 ms above baseline mandates immediate correction. 1
• Ionized calcium <0.8 mmol/L carries particularly high risk for cardiac dysrhythmias and must be corrected urgently. 1, 2

Measure Ionized Calcium Directly

• Do not rely on total calcium or corrected calcium formulas in critically ill patients—these are insensitive and lack specificity, with 71% of ICU patients appearing hypocalcemic by total calcium but only 12% truly hypocalcemic by measured ionized calcium. 3
• Direct ionized calcium measurement is the only accurate method in critical illness because circulating factors alter calcium-protein binding unpredictably. 3, 4
• Normal ionized calcium is 1.1–1.3 mmol/L (4.6–5.4 mg/dL); values <0.9 mmol/L require immediate treatment. 1, 5, 2

Acute Intravenous Calcium Replacement

Agent Selection: Calcium Chloride is Preferred

• Calcium chloride 10% is superior to calcium gluconate because 10 mL contains 270 mg elemental calcium versus only 90 mg in calcium gluconate, and it raises ionized calcium three times faster. 1, 2, 6
• Calcium chloride is especially critical when citrate metabolism is impaired by shock, hypothermia, or liver dysfunction. 1, 2

Initial Bolus Dosing

• Adults: Give calcium chloride 10% solution 5–10 mL IV over 2–5 minutes for symptomatic hypocalcemia or cardiac arrest. 1, 2, 6
• Pediatric patients: Give calcium chloride 20 mg/kg (0.2 mL/kg of 10% solution) IV slowly with continuous ECG monitoring. 1, 2
• For non-arrest situations, infuse the bolus over 30–60 minutes rather than rapidly to reduce cardiac complications. 1, 2

Continuous Infusion Protocol

• Start a continuous infusion at 1–2 mg elemental calcium per kg per hour, adjusting based on serial ionized calcium measurements every 4–6 hours initially. 1, 2
• Target ionized calcium 1.15–1.36 mmol/L (normal range) to optimize cardiovascular function and coagulation. 1, 2
• The FDA-approved adult dosage for hypocalcemic disorders is 200 mg to 1 g (2–10 mL of 10% solution) at intervals of 1–3 days, but critical hypocalcemia requires continuous infusion. 6

Administration Route & Monitoring

• Use central venous access whenever possible to avoid severe tissue necrosis from extravasation; peripheral administration of calcium chloride can cause calcinosis cutis and skin necrosis. 1, 2
• Continuous cardiac (ECG) monitoring is mandatory; stop the infusion immediately if symptomatic bradycardia develops. 1, 2, 6
• Never mix calcium with sodium bicarbonate in the same IV line—precipitation will occur. 1, 2

Essential Cofactor Correction: Magnesium First

• Check serum magnesium immediately and correct hypomagnesemia before expecting full calcium normalization—28% of hypocalcemic ICU patients have concurrent hypomagnesemia, and calcium replacement will fail without adequate magnesium. 1, 2
• Hypomagnesemia causes hypocalcemia through two mechanisms: impaired PTH secretion and end-organ PTH resistance. 1
• Give magnesium sulfate 1–2 g IV bolus immediately for symptomatic patients with concurrent hypomagnesemia, followed by calcium replacement. 1

Context-Specific Considerations

Massive Transfusion & Trauma

• Hypocalcemia in trauma patients results from citrate in blood products (especially FFP and platelets) binding calcium; each unit contains approximately 3 g of citrate. 1, 2
• Citrate metabolism is impaired by hypothermia, hypoperfusion, and hepatic insufficiency—these patients require more aggressive calcium replacement and frequent monitoring. 1, 2
• Maintain ionized calcium >0.9 mmol/L minimum during massive transfusion; early hypocalcemia (first 24 hours) predicts mortality better than fibrinogen, acidosis, or platelet counts. 1, 5, 2
• Colloid infusions independently worsen hypocalcemia beyond citrate effects. 1, 2

Chronic Kidney Disease (Stages 3–5)

• In CKD patients with corrected calcium <8.4 mg/dL, **first control serum phosphorus to <5.5 mg/dL before administering calcium** because a calcium-phosphorus product >55 mg²/dL² markedly increases vascular calcification risk. 7, 1
• Use non-calcium-containing phosphate binders (sevelamer or lanthanum) when phosphorus is elevated; calcium-based binders are contraindicated. 7, 1
• Once phosphorus is controlled, give oral calcium carbonate 1–2 g three times daily (1,200–2,400 mg elemental calcium), targeting corrected calcium 8.4–9.5 mg/dL (low-normal range). 7, 1
• Total elemental calcium intake (diet plus supplements) must not exceed 2,000 mg/day to prevent nephrocalcinosis. 7, 1

Tumor Lysis Syndrome

• Use extreme caution with calcium replacement when serum phosphate is elevated—calcium can precipitate as calcium-phosphate crystals in tissues and kidneys, causing obstructive uropathy. 1, 2
• Administer calcium only to symptomatic patients with tumor lysis syndrome; obtain renal consultation before giving calcium if phosphate is high. 1, 2

Post-Parathyroidectomy

• Measure ionized calcium every 4–6 hours for the first 48–72 hours after surgery, then twice daily until stable. 1, 2
• If ionized calcium falls below 0.9 mmol/L, start calcium gluconate infusion at 1–2 mg elemental calcium/kg/hour, titrating to maintain ionized calcium 1.15–1.36 mmol/L. 1, 2
• Once oral intake is feasible, transition to calcium carbonate 1–2 g three times daily plus calcitriol up to 2 µg/day. 1, 2

Transition to Oral Maintenance Therapy

When to Transition

• Once ionized calcium stabilizes in the normal range and the patient can take oral medications, transition from IV to oral calcium supplementation. 1, 2

Oral Calcium Regimen

• Calcium carbonate is the preferred oral supplement due to high elemental calcium content (40%), low cost, and wide availability. 7, 1
• Give calcium carbonate 1–2 g three times daily with meals (providing 1,200–2,400 mg elemental calcium). 7, 1
• Limit individual doses to 500 mg elemental calcium to optimize absorption; divide doses throughout the day. 1

Vitamin D Assessment & Supplementation

• Measure 25-hydroxyvitamin D; if <30 ng/mL, start ergocalciferol 50,000 IU monthly for 6 months. 7, 1
• Daily vitamin D₃ supplementation (400–800 IU/day) is recommended for all adults with chronic hypocalcemia. 1
• Active vitamin D metabolites (calcitriol 0.5–2 µg/day) are reserved for severe or refractory cases, particularly when PTH is above target range despite adequate vitamin D repletion. 7, 1

Monitoring Requirements

Acute Phase

• Measure ionized calcium every 4–6 hours initially until stable, then twice daily. 1, 2
• Continue cardiac monitoring throughout the acute treatment phase. 1, 2

Chronic Management

• Measure corrected total calcium and phosphorus at least every 3 months during chronic supplementation. 7, 1
• Monitor pH-corrected ionized calcium, magnesium, PTH, and creatinine regularly. 1
• Keep the calcium-phosphorus product <55 mg²/dL² to prevent soft-tissue and vascular calcification. 7, 1

Critical Safety Thresholds & Pitfalls

Avoid Over-Correction

• Do not exceed corrected total calcium of 10.2 mg/dL (2.54 mmol/L)—iatrogenic hypercalcemia causes renal calculi, nephrocalcinosis, and renal failure. 7, 1
• Target the low-normal range (8.4–9.5 mg/dL) in CKD patients to minimize hypercalciuria and vascular calcification risk. 7, 1

Phosphate Management is Critical

• Never give calcium when serum phosphorus is >5.5 mg/dL (CKD stage 5) or >4.6 mg/dL (CKD stages 3–4) without first controlling phosphate. 7, 1
• A calcium-phosphorus product >55 mg²/dL² is a hard safety limit that markedly increases calcification risk. 7, 1

pH Effects on Ionized Calcium

• Each 0.1-unit increase in pH decreases ionized calcium by approximately 0.05 mmol/L; correcting acidosis may paradoxically worsen hypocalcemia. 5, 2
• Account for pH changes when interpreting ionized calcium levels. 5

Drug Compatibility

• Never administer calcium through the same line as sodium bicarbonate or vasoactive amines (norepinephrine, epinephrine). 1, 2

Recognize Underlying Causes

• Check intact PTH—low or inappropriately normal suggests hypoparathyroidism; elevated suggests vitamin D deficiency or CKD. 1
• Assess for recent thyroid/parathyroid surgery, bisphosphonates, denosumab, cisplatin, cetuximab, or chronic kidney disease. 1, 8
• Hypothyroidism may be contributory; assess thyroid function annually in high-risk populations. 1

Special Populations

22q11.2 Deletion Syndrome

• 80% have lifetime history of hypocalcemia due to hypoparathyroidism, which may recur at any age despite apparent childhood resolution. 1
• Daily calcium and vitamin D supplementation is recommended for all adults with this syndrome. 1
• Targeted calcium monitoring is critical during biological stress (surgery, childbirth, infection). 1
• Avoid alcohol and carbonated beverages (especially colas) as they worsen hypocalcemia. 1

Cardiac Arrest

• Calcium administration during cardiac arrest is recommended only when arrest is associated with documented hyperkalemia, hypocalcemia, hypermagnesemia, or calcium-channel-blocker toxicity. 2
• Routine calcium use for undifferentiated cardiac arrest is not recommended. 2