In this episode of Hospital Medicine Unplugged, we blitz through hypocalcemia—measure ionized calcium, treat symptoms now, fix the cause, and avoid reflex over-correction in the ICU.

We open with the do-firsts: confirm with ionized Ca (total Ca lies in hypoalbuminemia), check Mg/Phos/Cr, PTH, 25-OH D, ECG for QT prolongation, and scan the story (neck surgery, CKD, vitamin D deficiency, sepsis, pancreatitis, meds, massive transfusion).

Call the problem when ionized Ca <1.1 mmol/L (or total Ca <8 mg/dL—use with caution). Symptoms span paresthesias → tetany → seizures, laryngospasm, bronchospasm → HF/arrhythmias. Hypomagnesemia can both cause and perpetuate hypocalcemia—correct it.

Etiology buckets you’ll meet fast:
• Low/ineffective PTH: post-op hypoparathyroidism, autoimmune, infiltrative, severe hypoMg.
• PTH resistance / CaSR/GNAS disorders.
• Vitamin D deficiency or low 1,25-(OH)₂D (malabsorption, CKD, meds).
• Chelation/precipitation: citrate from massive transfusion, pancreatitis, TLS, rhabdo.
• Critical illness: impaired PTH action & vitamin D metabolism.

Who needs admission/telemetry right now? Severe symptoms, ionized Ca <0.9 mmol/L, QTc changes, post-thyroid/parathyroid surgery with falling Ca, massive transfusion, pancreatitis/sepsis with instability.

Treatment—build the acute backbone:
• IV calcium for severe/symptomatic: 10–20 mL of 10% calcium gluconate (≈93 mg elemental Ca per 10 mL) over 10–15 min with ECG, then infuse to target low-normal ionized Ca (e.g., ~1.1–1.2 mmol/L).
• Prefer gluconate peripherally; chloride is central-line only (tissue necrosis risk).
• Replete Mg (e.g., MgSO₄ 1–2 g IV; more if renally appropriate) before/with calcium.
• Treat the trigger: stop causative meds, give vitamin D/calcitriol if deficient or hypoparathyroid, manage sepsis/pancreatitis, and in hemorrhage dose calcium during MTP.

Maintenance & chronic plays:
• Oral calcium (carbonate/citrate in divided doses) + vitamin D; add calcitriol when PTH is low/ineffective.
• Target low-normal Ca to limit hypercalciuria/nephrocalcinosis; consider thiazide if urinary Ca high.
• rhPTH/long-acting PTH analogues for select hypoparathyroid patients to cut Ca/calcitriol burden—cost/safety/selection matter.

ICU reality check:
• Hypocalcemia is common and tracks severity of illness. Routine IV Ca for asymptomatic ICU patients (esp. sepsis) hasn’t shown outcome benefit and may be harmful—individualize. Failure to normalize ionized Ca over the first few ICU days correlates with worse outcomes, but causality is uncertain.

Special situations you’ll see:
• Post-thyroidectomy: early Ca + calcitriol, PTH-guided protocols, monitor Mg; escalate to IV if symptomatic or Ca <~7–8 mg/dL.
• CKD/CKD-MBD: tolerate mild asymptomatic hypocalcemia; avoid positive Ca balance/vascular calcification; control phosphate; use active vitamin D selectively.
• Pancreatitis: replace only if symptomatic/severe; no routine calcium to chase numbers.
• Massive transfusion: citrate chelation—aim ionized Ca >1.0–1.2 mmol/L with protocolized Ca (often 1 g gluconate early and intermittently).

Monitoring that sticks:
• During IV therapy: ionized Ca q1–2h while titrating, then q4–6h; continuous ECG.
• Check Mg/Phos and correct; reassess Ca needs after fixing Mg.
• Chronic: Ca/Phos/Mg/Cr q3–6 mo; 24-h urine Ca (goal <4 mg/kg/day); periodic renal imaging if hypercalciuria or rising Cr.

Pitfalls you don’t want to meet:
• Treating numbers, not patients in the ICU.
• Forgetting magnesium—you’ll chase Ca forever.
• Pushing CaCl peripherally—extravasation disaster.
• Overshooting Ca in CKD → vascular calcification.
• Skipping vitamin D in low/ineffective PTH states.

We close with the system moves: a hypocalcemia bundle that (1) defaults to ionized Ca + Mg/Phos/PTH/25-OH D + ECG; (2) triages to IV Ca + Mg for symptomatic/severe; (3) targets low-normal ionized Ca, not “high-normal”; (4) hard-wires Mg repletion; (5) routes special scenarios (post-op, CKD, MTP, pancreatitis) to tailored pathways; (6) sets outpatient labs/urine Ca to prevent stones and nephrocalcinosis.

Fast recognition, ionized-first confirmation, symptom-driven IV calcium, relentless Mg correction, and etiology-specific fixes—treat wisely, not reflexively.