REBEL Core Cast 88.0 – Hypocalcemia

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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

• Hypoalbuminemia (Ca²⁺ bound to albumin)
• Hypoparathyroidism
• Chronic renal failure
• Electrolyte disorders: Hypomagnesemia, Hyperphosphatemia
• Abnormal cell destruction: tumor lysis syndrome, rhabdomyolysis
• Severe pancreatitis
• Drugs: Calcitonin, phosphate, bisphosphonates
• Tox: HFl acid burn
• Massive blood transfusion (due to citrate in blood products)

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

1. 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.
2. Hayes BD. (2013, July 2). Mythbuster: Calcium Gluconate Raises Serum Calcium as Quickly as Calcium Chloride [ALiEM]. Retrieved from http://www.aliem.com/posts/

Read More

• LITFL: Hypocalcemia
• LITFL: Hypocalcaemia

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