Updated July 2026 · 8 min read
Part of the ICU Emergencies Hub — browse every related guide in one place.
Calcium runs the heart's contraction, the coagulation cascade, and every nerve and muscle. In the ICU it drops for predictable reasons — transfused blood, CRRT, sepsis, pancreatitis — and the fix is one of the fastest interventions on the unit. But which calcium salt, and how you read the lab, matters more than most bedside teaching admits.
Roughly half the calcium in blood is bound to albumin; only the ionized (free) fraction is biologically active. In critically ill patients — who are frequently hypoalbuminemic — the total calcium can look falsely low while the active ionized level is fine, or the total can look normal while the ionized is dangerously low. Acid-base status shifts it too: alkalosis increases calcium binding to albumin and drops the ionized fraction, which is why a hyperventilating patient can develop perioral tingling and carpopedal spasm with a "normal" total calcium. For any unstable ICU patient, trust the ionized calcium from a blood gas over a calculated correction.
Beyond citrate, the frequent contributors are sepsis and critical illness themselves, acute pancreatitis (calcium saponifies in the inflamed fat), rhabdomyolysis in its early phase, tumor lysis syndrome (hyperphosphatemia binds calcium), hypomagnesemia (low magnesium impairs PTH release and action, so calcium won't correct until the magnesium is fixed), post-thyroid/parathyroid surgery, and rapid correction of acidosis. A low magnesium is the classic reason a calcium level "won't come up" no matter how much you give.
Mild hypocalcemia is often silent. As it worsens, look for neuromuscular irritability: perioral and fingertip numbness, muscle cramps, and frank tetany with carpopedal spasm. Two classic signs support the diagnosis — Chvostek's sign (tapping the facial nerve triggers a facial twitch) and Trousseau's sign (inflating a BP cuff above systolic for a few minutes induces carpal spasm). The dangerous end is cardiac: hypotension refractory to pressors, a prolonged QT interval that can degenerate into torsades, and reduced myocardial contractility. Severe cases produce seizures and laryngospasm.
Symptomatic or severe hypocalcemia is treated with IV calcium. Two salts are used:
Calcium gluconate is the peripheral-line workhorse. It's less irritating to veins and is the default for most repletion. Calcium chloride delivers about three times as much elemental calcium per amp and works faster, which makes it the code-cart and central-line choice for a crashing patient — but it is intensely sclerosing and can cause severe tissue necrosis if it extravasates, so it should run through a central line whenever possible. In both cases, IV calcium is pushed or infused slowly with continuous cardiac monitoring.
| Point | What the nurse does |
|---|---|
| Read the right lab | Trust the ionized calcium from a gas, not the total, in unstable patients |
| Anticipate citrate | Expect and monitor low ionized calcium in massive transfusion and citrate CRRT |
| Check the magnesium | Calcium won't correct if magnesium is low — replace both |
| Pick the salt | Gluconate peripherally; chloride via central line for the crashing patient |
| Protect the vein | Calcium chloride extravasation causes necrosis — central access, watch the site |
| Infuse safely | Slow, on a monitor; never in the same line as bicarb or phosphate |
Related: Calcium chloride vs gluconate · Phosphate replacement · IV magnesium replacement · Massive transfusion protocol
Educational content for licensed clinicians. Always follow your facility's pharmacy dosing protocol and provider orders. Not medical advice.
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