REBEL Core Cast 88.0 – Hypocalcemia

Take Home Points

Severe hypocalcemia can cause hypotension and QTc prolongation leading to Torsades de Pointes.
Treat moderate to severe symptoms and any EKG changes with IV calcium salts
Always search for and treat the underlying cause of hypocalcemia

Definition: A serum calcium level < 8.5 mg/dL or an ionized calcium level < 2.0

mEq/L

Background

Exists in two states
- Free ionized form (approx. 50%)
- Bound to other molecules (primarily albumin)
Ionized Ca²⁺ concentration is inversely proportional to pH
Calcium metabolism
- Vitamin D: aids in intestinal Ca²⁺ absorption
- Parathyroid hormone (PTH)
  - Increases renal Ca²⁺ reabsorption
  - Arbitrates Vit D stimulated intestinal Ca²⁺ absorption
  - Mobilizes Ca²⁺ from bone
- Calcitonin
  - PTH antagonist
  - Inhibits renal Ca²⁺ reabsorption
  - Inhibits Ca²⁺ mobilization from bone

Causes

Clinical Manifestations

Cardiac Effects
- Hypotension
- QTc prolongation
- Congestive heart failure
- Cardiovascular collapse (severe hypocalcemia)
Neuromuscular Effects
- Muscle cramping
- Paraesthesias
- Tetany
- Chvostek’s sign: facial muscle twitching with tapping over facial nerve (commonly seen in patients without hypocalcemia)
- Trousseau’s sign: carpal spasms induced by inflation of a blood pressure cuff 20 mm Hg above systolic BP X 3 minutes
Other symptoms
- Altered mental status
- Coarse hair
- Cataracts
- Poor dentition
- Dry skin
- Laryngospasm
- Bronchospasm, wheezing
- Fatigue

Diagnosis

Serum calcium < 8.5 mg/dL
- Correct for hypoalbuminemia:1 g/dL drop in serum albumin below 4 g/dL = 0.8 mg/dL drop in serum calcium
- 50% of serum calcium is protein bound, 50% ionized (free)
Ionized calcium < 2.0 mEq/L
- More accurate assessment as no correction required

Management

Asymptomatic/Minimally symptomatic
- Oral supplementation with calcium salts (i.e. calcium carbonate or calcium citrate)
- Disposition: Discharge home with outpatient follow up
Moderate/Severe Symptoms
- Intravenous calcium supplementation: 100-300 mg Ca²⁺ raises serum Ca²⁺ by 0.5 – 1.5 mEq
- Calcium Chloride (CaCl₂)
  - Standard “ampule”: 10 ml of 10% CaCl₂ = 270 mg of Ca²⁺
  - Caustic to veins – should be administered in large peripheral IV or central line preferably
- Calcium Gluconate
  - Standard “ampule”: 10 ml of 10% CaGluconate = 90 mg of Ca²⁺
  - For equivalent dosing to CaCl, give 3 “amps” of CaGluconate
- Despite classic teaching, CaCl₂ is not more bioavailable than CaGluconate and does not raise serum Ca²⁺faster. (Hayes 2013)
- Disposition: Admission to monitored setting if ongoing intravenous repletion (bradycardia and hypertension may occur)
Consider giving prophylactic calcium supplementation in patients receiving massive transfusions.
Magnesium supplementation: Concomitant hypomagnesemia is common.

Take Home Points

Severe hypocalcemia can cause hypotension and QTc prolongation leading to Torsades de Pointes.
Treat moderate to severe symptoms and any EKG changes with IV calcium salts
Always search for and treat the underlying cause of hypocalcemia

References

Pfenning CL, Slovis CM: Electrolyte Disorders; in Marx JA, Hockberger RS, Walls RM, et al (eds): Rosen’s Emergency Medicine: Concepts and Clinical Practice, ed 8. St. Louis, Mosby, Inc., 2014, (Ch) 125: p 1636-53.
Hayes BD. (2013, July 2). Mythbuster: Calcium Gluconate Raises Serum Calcium as Quickly as Calcium Chloride [ALiEM]. Retrieved from http://www.aliem.com/posts/

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Post Peer Reviewed By: Salim R. Rezaie, MD (Twitter: @srrezaie)

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