7.5
mg/dL
1
mg/dL
140
mg
2,000
mg
20
mL
105
mg/hr
1.1
mL/hr
7.5
mg/dL
1
mg/dL
140
mg
2,000
mg
20
mL
105
mg/hr
1.1
mL/hr
The Calcium Infusion Calculator assists clinicians in managing hypocalcemia by calculating corrected calcium levels, estimating calcium deficits, and providing intravenous calcium dosing recommendations based on symptom severity. Hypocalcemia is a common and potentially life-threatening electrolyte disorder encountered in emergency departments, ICUs, and post-surgical settings, particularly after thyroid and parathyroid surgery.
Calcium is the most abundant mineral in the body, with 99% stored in bones and teeth and 1% in blood and soft tissues. Serum calcium exists in three forms: ionized (free) calcium (~45%, biologically active), protein-bound calcium (~40%, primarily to albumin), and complexed calcium (~15%, bound to citrate, phosphate, bicarbonate). Total serum calcium levels must be corrected for albumin to avoid misdiagnosis — low albumin (hypoalbuminemia) causes falsely low total calcium while ionized calcium may be normal.
Hypocalcemia is defined as corrected total calcium <8.5 mg/dL (2.1 mmol/L) or ionized calcium <1.1 mmol/L. Common causes include hypoparathyroidism (post-surgical being most common), vitamin D deficiency, chronic kidney disease, pancreatitis, sepsis, massive blood transfusion (citrate chelation), hungry bone syndrome (post-parathyroidectomy), and certain medications (bisphosphonates, denosumab, cinacalcet).
Symptomatic hypocalcemia requires urgent intravenous calcium replacement. Symptoms range from perioral tingling and paresthesias (mild) to carpopedal spasm, Chvostek and Trousseau signs (moderate), to tetany, laryngospasm, seizures, and cardiac arrhythmias (severe). The severity of symptoms generally correlates with both the degree and the rate of calcium decline — acute hypocalcemia is more symptomatic than chronic.
The preferred IV calcium formulation is calcium gluconate 10% because it is less irritating to veins and safer if extravasation occurs. Each 10 mL ampule contains 93 mg of elemental calcium. Calcium chloride 10% contains 272 mg elemental calcium per 10 mL but requires central venous access due to tissue necrosis risk. This calculator provides dosing for calcium gluconate.
The calculator performs the following computations:
Corrected Calcium = Measured Ca + 0.8 x (4.0 - Albumin)
Approximate Deficit (mg) = (8.5 - Corrected Ca) x Weight(kg) x 0.2 x 10 (using 0.2 L/kg as the calcium distribution volume approximation)
IV Bolus (Calcium Gluconate): Severe/moderate symptoms: 2000 mg (2 ampules of 10%) over 10-20 min; Mild: 1000 mg over 10-20 min; Asymptomatic: no bolus needed.
Continuous Infusion: Severe: 1.5 mg/kg/hr; Moderate: 1.5 mg/kg/hr; Mild: 1.0 mg/kg/hr; Asymptomatic: 0.5 mg/kg/hr. All rates refer to elemental calcium from calcium gluconate.
10% Calcium Gluconate: 100 mg/mL (9.3 mg elemental Ca/mL). Volumes are calculated accordingly.
The Corrected Calcium adjusts for albumin — if corrected calcium <8.5 mg/dL, true hypocalcemia is confirmed. The Calcium Deficit provides a rough estimate of the total body deficit — this cannot be replaced acutely; use it to guide multi-day replacement. The Bolus Dose is for immediate symptom relief. Administer over 10-20 minutes with cardiac monitoring (rapid infusion can cause arrhythmias). The Continuous Infusion maintains levels after bolus. Monitor ionized calcium every 4-6 hours and adjust rate accordingly. Target corrected calcium 8.0-9.0 mg/dL. Also check and replace magnesium — hypomagnesemia causes PTH resistance and refractory hypocalcemia.
Inputs
Results
Corrected Ca 7.4 with muscle cramps: give 2g Ca gluconate bolus over 15 min, then infuse at ~105 mg/hr. Recheck ionized Ca in 4-6 hours.
Inputs
Results
Corrected Ca is 8.4 (near normal) despite total Ca 7.8 due to low albumin. Mild symptoms: 1g bolus then infuse at 60 mg/hr. Also address vitamin D and magnesium.
Symptoms range from tingling around the mouth and fingertips (mild) to muscle cramps, Chvostek sign (facial twitch with tapping), and Trousseau sign (carpopedal spasm with BP cuff) to tetany, laryngospasm, seizures, and cardiac arrhythmias (prolonged QT, heart block) in severe cases.
About 40% of serum calcium is bound to albumin. When albumin is low (common in hospitalized patients), total calcium appears low even though ionized (active) calcium may be normal. The correction adds 0.8 mg/dL of calcium for each 1 g/dL that albumin is below 4.0 g/dL.
Calcium gluconate is safer for peripheral IV administration. Calcium chloride provides 3x more elemental calcium per volume but causes severe tissue necrosis if it extravasates from the vein. Calcium chloride should only be given through a central venous catheter.
Bolus calcium gluconate should be infused over 10-20 minutes (never pushed rapidly). Rapid administration can cause bradycardia, cardiac arrest, and vasodilation. Continuous infusion should not exceed 200 mg/hour without cardiac monitoring. ECG monitoring is recommended for all IV calcium.
Magnesium is essential for PTH secretion and PTH receptor function. Hypomagnesemia (Mg <1.5 mg/dL) causes functional hypoparathyroidism and resistance to PTH action, making hypocalcemia refractory to calcium replacement alone. Always check and correct magnesium first.
Thyroidectomy and parathyroidectomy can damage or remove the parathyroid glands, causing transient or permanent hypoparathyroidism. Incidence is 10-30% transiently after total thyroidectomy. Hungry bone syndrome after parathyroidectomy causes rapid calcium uptake by bones, sometimes requiring very aggressive supplementation.
Continue IV calcium until: symptoms resolve, corrected calcium is consistently >8.0 mg/dL, oral calcium and vitamin D are tolerated and taking effect (24-48 hours). Taper the infusion gradually while monitoring levels. Abrupt discontinuation may cause symptom recurrence.
Transition to oral calcium carbonate (1-3 g elemental calcium/day in divided doses) with active vitamin D (calcitriol 0.25-1 mcg twice daily). Calcium citrate is preferred in patients on proton pump inhibitors. Doses are titrated based on serial calcium levels.
Yes, severe hypocalcemia can cause prolonged QT interval, ventricular tachycardia, ventricular fibrillation, and asystole. Ionized calcium <0.7 mmol/L is life-threatening. Patients with severe hypocalcemia should be on continuous cardiac monitoring.
Yes, ionized calcium directly measures the biologically active fraction and is not affected by albumin, pH, or protein levels. It is the preferred measurement in critically ill patients, during blood transfusion, and when albumin-corrected calcium is unreliable. Normal ionized calcium is 1.1-1.3 mmol/L.
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