CORE EM: Hypocalcemia

Originally published at CoreEM.net, dedicated to bringing Emergency Providers all things core content Emergency Medicine available to anyone, anywhere, anytime. Reposted with permission.

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Written by: Anand Swaminathan, MD

 

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
  • Ca2+ 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
  • Ca2+ plays numerous critical roles including muscle contraction (skeletal and smooth), clotting factor activity and nerve conduction

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:

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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