What is the management of hypocalcemic tetany in a patient, considering their potential history of thyroid or parathyroid surgery and possible underlying causes such as vitamin D deficiency or impaired renal function?

Management of Hypocalcemic Tetany

Immediately administer 100-200 mg of elemental calcium intravenously (10-20 mL of 10% calcium gluconate) over 10 minutes to abort acute tetany, followed by continuous calcium infusion if symptoms persist. 1

Acute Emergency Management

Immediate IV Calcium Administration

• Give 10-20 mL of 10% calcium gluconate (100-200 mg elemental calcium) IV over 10 minutes as the first-line treatment for acute hypocalcemic tetany 1
• For severe or persistent symptoms (laryngospasm, generalized tonic muscle cramps, seizures), follow with continuous IV calcium infusion of 360 mg elemental calcium per day in divided doses 2
• Use a central venous catheter for calcium infusion to avoid tissue necrosis from extravasation 3
• Monitor ionized calcium levels closely, targeting >0.75 mmol/L to resolve neuromuscular irritability 1

Critical Monitoring During Acute Phase

• Check ionized calcium (not total calcium), as alkalosis can falsely normalize total calcium while ionized calcium remains dangerously low 4
• Obtain ECG immediately to assess for QT prolongation, which indicates cardiac risk 5
• Measure serum magnesium—if <1.5 mg/dL, replace magnesium first, not calcium, as hypomagnesemia prevents calcium correction 1

Identifying the Underlying Cause

Post-Surgical Hypocalcemia

• Most common cause in adults is thyroid or parathyroid surgery, typically manifesting within 24-72 hours postoperatively 1, 3
• Measure intact PTH: suppressed or inappropriately normal PTH confirms hypoparathyroidism 3
• This represents permanent hypoparathyroidism requiring lifelong treatment 6

Other Critical Causes to Exclude

• Check serum phosphorus: elevated phosphorus with low calcium suggests acute intravascular calcium binding (tumor lysis, rhabdomyolysis) or chronic kidney disease 5
• Measure 25-hydroxyvitamin D: severe deficiency (<10 ng/mL) can cause symptomatic hypocalcemia 5
• Review medications: bisphosphonates, foscarnet, and citrate (from massive blood transfusions) can acutely bind calcium 1
• Assess for 22q11.2 deletion syndrome in younger patients with recurrent hypocalcemia, especially if there is history of cardiac defects or immune deficiency 5

Transition to Chronic Management

Oral Calcium Supplementation

• Start calcium carbonate 1-2 grams elemental calcium three times daily with meals once acute tetany resolves 5, 7
• If refractory to calcium carbonate despite adequate dosing, suspect achlorhydria—switch to calcium chloride solution (10% solution, 10-30 mL) which does not require gastric acid for absorption 2
• Monitor serum chloride when using calcium chloride to avoid hyperchloremic acidosis 2

Vitamin D Therapy

• For hypoparathyroidism, initiate calcitriol 0.25-2.0 mcg daily (active vitamin D) rather than ergocalciferol, as PTH deficiency impairs 1-alpha hydroxylation 6, 3
• Calcitriol effects begin within days, whereas ergocalciferol or cholecalciferol require 15-25 days to normalize calcium 8
• For chronic kidney disease patients (not on dialysis) with secondary hyperparathyroidism, use calcitriol only if PTH >100 pg/mL and calcium <8.4 mg/dL 5, 6
• Never start vitamin D therapy if serum calcium is already >9.5 mg/dL or phosphorus >4.6 mg/dL, as this risks hypercalcemia and vascular calcification 9

Magnesium Repletion

• If serum magnesium <1.5 mg/dL, provide magnesium supplementation (magnesium oxide 400-800 mg daily) as hypomagnesemia impairs PTH secretion and calcium correction 5, 1

Special Populations

Post-Parathyroidectomy Patients

• Expect "hungry bone syndrome" with severe, prolonged hypocalcemia after removing large parathyroid adenomas 7
• Require aggressive calcium supplementation (up to 6 grams elemental calcium daily) plus calcitriol up to 2 mcg/day 7
• Monitor ionized calcium every 4-6 hours for first 48-72 hours postoperatively 7

Chronic Kidney Disease Patients

• Target calcium 8.4-9.5 mg/dL (NOT normal range) to avoid adynamic bone disease 5, 9
• Use intermittent IV calcitriol (more effective than daily oral) for dialysis patients with PTH >300 pg/mL 5
• Monitor calcium and phosphorus every 2 weeks for 1 month after initiating or increasing vitamin D, then monthly 5

22q11.2 Deletion Syndrome

• Hypocalcemia recurs throughout life despite childhood resolution, especially during biological stress (surgery, pregnancy, infection) 5
• Recommend daily calcium and vitamin D supplementation for all adults with this syndrome, even if currently normocalcemic 5
• Avoid alcohol and carbonated beverages (especially colas) which worsen hypocalcemia 5

Critical Pitfalls to Avoid

• Never rely on total calcium alone—alkalosis can mask severe ionized hypocalcemia by shifting calcium binding 4
• Never give calcium without checking magnesium first—calcium infusions are ineffective in hypomagnesemia 1
• Never use ergocalciferol or cholecalciferol for acute management—their onset of action is 15-25 days, far too slow for symptomatic hypocalcemia 8
• Never overcorrect calcium in chronic hypoparathyroidism—target low-normal range (8.0-8.5 mg/dL) to avoid hypercalciuria, nephrolithiasis, and renal failure 5, 3
• Never target normal PTH levels (<100 pg/mL) in dialysis patients—this causes adynamic bone disease 5, 9

Long-Term Monitoring

• Measure ionized calcium, PTH, magnesium, phosphorus, and creatinine every 3-6 months in stable hypoparathyroidism 5
• Check 24-hour urine calcium annually to detect hypercalciuria (>300 mg/day), which indicates overtreatment and renal stone risk 3
• Obtain renal ultrasound every 1-2 years to screen for nephrocalcinosis and nephrolithiasis 3
• Consider recombinant PTH 1-84 (subcutaneous) for patients with persistent symptoms despite adequate calcium levels or those requiring excessive calcium/vitamin D doses 3