What is the management of tetany, particularly in patients with hypocalcemia, hypomagnesemia, or alkalosis?

Management of Tetany

Immediate Assessment and Stabilization

For acute tetany, immediately check and correct hypomagnesemia first, as hypocalcemia cannot be adequately treated without normalizing magnesium levels—this is the single most critical step that is frequently overlooked. 1, 2

Initial Diagnostic Workup

• Measure pH-corrected ionized calcium (not just total calcium), as this is the physiologically active fraction and most accurate for diagnosis 1, 3
• Check serum magnesium levels in all patients with tetany, as hypomagnesemia is present in 28% of hypocalcemic patients and must be corrected first 4, 1
• Obtain arterial blood gas to assess for respiratory alkalosis from hyperventilation 5, 6
• Check serum phosphate and potassium levels, as multiple electrolyte disturbances often coexist 7, 6

Acute Treatment Algorithm

Step 1: Correct Hypomagnesemia (If Present)

Administer magnesium sulfate 1-2 g IV bolus immediately for symptomatic patients with documented or suspected hypomagnesemia. 4, 1, 2

• Magnesium deficiency impairs PTH secretion and creates end-organ PTH resistance, making calcium supplementation ineffective until corrected 1, 3
• Calcium levels require approximately 4 days to normalize after initiating magnesium therapy, even though PTH levels normalize within 24 hours 1
• Magnesium sulfate is FDA-approved specifically for acute hypomagnesemia accompanied by signs of tetany similar to those observed in hypocalcemia 2

Step 2: Administer Intravenous Calcium

Once magnesium is addressed, give calcium chloride 10 mL of 10% solution (270 mg elemental calcium) IV over 2-5 minutes for adults with symptomatic tetany. 7, 4

• Calcium chloride is strongly preferred over calcium gluconate due to three times higher elemental calcium content (270 mg vs 90 mg per 10 mL) 7, 4
• Administer slowly while monitoring ECG continuously for bradycardia and cardiac arrhythmias 7, 4
• For children, use calcium chloride 20 mg/kg (0.2 mL/kg of 10% solution) IV, given slowly for cardiac manifestations or over 30-60 minutes for tetany 7
• Calcium gluconate 50-100 mg/kg IV may be substituted if calcium chloride is unavailable, but is less effective 7, 4

Step 3: Address Alkalosis (If Present)

• For hyperventilation-induced alkalosis causing tetany, have the patient rebreathe into a paper bag or use controlled breathing techniques to normalize pH 5, 6
• Alkalosis increases protein binding of calcium, reducing ionized calcium levels even when total calcium is normal 5, 6
• Do not administer sodium bicarbonate, as this will worsen alkalosis and tetany 7

Specific Clinical Scenarios

Tumor Lysis Syndrome with Tetany

• Administer calcium gluconate 50-100 mg/kg IV slowly with ECG monitoring for symptomatic hypocalcemia 7
• Use extreme caution when phosphate levels are elevated (>1.62 mmol/L) due to risk of calcium-phosphate precipitation in tissues 7
• Asymptomatic hypocalcemia does not require treatment in this setting 7

Hyperkalemia with Tetany

• Calcium chloride 100-200 mg/kg/dose IV stabilizes myocardial cell membranes and takes priority 7
• Sodium bicarbonate may be added to correct acidosis, but monitor for worsening tetany if alkalosis develops 7

Post-Surgical or Hypoparathyroid Tetany

• Initiate calcium gluconate infusion at 1-2 mg elemental calcium per kg body weight per hour if ionized calcium falls below 0.9 mmol/L 4
• Transition to oral calcium carbonate 1-2 g three times daily plus calcitriol up to 2 mcg/day when oral intake is possible 4, 8
• Measure ionized calcium every 4-6 hours for the first 48-72 hours, then twice daily until stable 4

Chronic Management and Prevention

Long-Term Supplementation

• Prescribe daily calcium carbonate 1,000-1,500 mg elemental calcium divided into 2-3 doses (maximum 500 mg per dose for optimal absorption) 4
• Add vitamin D3 400-800 IU daily, or calcitriol 0.25-2 mcg daily for hypoparathyroidism 4, 8
• Total elemental calcium intake should not exceed 2,000 mg/day from all sources 4

Monitoring Requirements

• Check pH-corrected ionized calcium, magnesium, PTH, and creatinine every 3 months during chronic treatment 4
• Target corrected total calcium in the low-normal range (8.4-9.5 mg/dL) to avoid hypercalcemia complications 4
• Monitor for signs of overcorrection: kidney stones, renal failure, vascular calcification 4, 1

Critical Pitfalls to Avoid

• Never administer calcium without first checking and correcting magnesium levels—this is the most common error and renders calcium therapy ineffective 1, 2
• Do not mix calcium with sodium bicarbonate in the same IV line, as precipitation will occur 7, 4
• Stop calcium injection immediately if symptomatic bradycardia develops during administration 7
• Avoid calcium administration through peripheral IV if possible due to risk of severe tissue necrosis with extravasation; use central venous access when available 7
• Do not give calcium by endotracheal route—it is ineffective and not recommended 7

High-Risk Populations Requiring Enhanced Surveillance

• Patients with 22q11.2 deletion syndrome have 80% lifetime prevalence of hypocalcemia and require daily calcium/vitamin D supplementation plus avoidance of alcohol and carbonated beverages 4, 3
• Neonates in first 24-48 hours require vigilant monitoring due to interrupted placental calcium transfer, though most early hypocalcemia is asymptomatic 3
• Patients receiving massive transfusions need continuous calcium monitoring and replacement due to citrate-mediated chelation 4