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BCPS Exam > FEN: Disorders of Calcium Homeostasis > Flashcards

FEN: Disorders of Calcium Homeostasis Flashcards

1
Q

What is the total normal serum calcium conentration?

A

8.5-10.5 mg/dL (total Ca2+ includes bound and unbound Ca2+)

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2
Q

What is the normal serum ionized calcium?

A

4.4-5.3 mg/dL

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3
Q

List four mechanisms for ionized calcium homeostasis

A
  1. Parathyroid hormone
  2. Phosphorus
  3. Vitamin D
  4. Calcitonin
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4
Q

What is the active form of calcium?

A

The active form of Ca2+ is the unbound or ionized Ca2+

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5
Q

About how much of the Ca2+ in the EC compartment is bound to plasma proteins?

A

About half

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6
Q

What plasma protein is Ca2+ primarily bound to?

A

Albumin

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7
Q

Describe the distribution of Ca2+ in the EC and IC compartments

A
  1. 99% of total body stores of Ca2+ are in skeletal bone

2. less than 1% of total body stores of Ca2+ are in EC fluid

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8
Q

Define hypocalcemia

A

Serum calcium concentration less than 8.5 mg/dL

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9
Q

List seven causes of hypocalcemia

A
  1. chronic kidney disease
  2. hypoparathyroidism
  3. vitamin D deficiency
  4. alcoholism
  5. hyperphosphatemia
  6. large amounts of blood products
  7. continuous renal replacement therapy
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10
Q

Describe the mechanism of how continuous renal replacement therapy (CRRT) causes hypocalcemia

A

Ca2+ chelates with citrate used as anticoagulation for plasmaphoresis or CRRT

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11
Q

Describe pseudohypocalcemia

A
  1. Serum calcium is normally bound to proteins in blood, esp. albumin
  2. Low albumin states can give a falsely low total serum calcium level.
  3. Ionized calcium level is usually normal in these states and can be approximated by calculation.
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12
Q

Describe how acidosis and alkalosis can affect hypocalcemia

A
  1. Calcium binding to albumin is depenent on serum pH,
  2. Thus ionized calcium is increased in severe acidosis and decrease in severe alkalosis.
  3. Measurement of ionized calcium is recommended in thesee cases.
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13
Q

What equation is used to correct total calcium in hypoalbuminemia?

A

Add 0.8 mg/dL Ca2+ for every 1 g/dL albumin below normal.

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14
Q

In critically ill patients, how should hypocalcemia in setting of hypoalbuminemia be assessed?

A

Measure ionized calcium level

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15
Q

List two categories of symptoms that can result from hypocalcemia

A
  1. muscular

2. neurologic

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16
Q

List four muscular symptoms of hypocalcemia

A
  1. tetany
  2. muscle spasms
  3. hypoactive reflexes
  4. hypotension
17
Q

List four neurologic symptoms of hypocalcemia

A
  1. anxiety
  2. hallucinations
  3. lethargy
  4. seizures
18
Q

How to treat true asymptomatic hypocalcemia (e.g. not pseudohypocalcemia)

A
  1. Oral Ca2+ supplements

2. May also require vitamin D supplementation

19
Q

Describe how to dose oral calcium supplements

A
  1. Different preparations have different elemental calcium
  2. calcium carbonate 1250 has 500 mg elemental calcium
  3. Dose at 2-4 g elemental calcium/day in 2-3 divided dosing
20
Q

Describe how to treat symptomatic hypocalcemia

A
  1. Intravenous elemental Ca2+ bolus;

2. Sometimes followed by a continuous infusion

21
Q

What is elemental Ca2+ content of 1 g of calcium chloride?

A

273 mg of elemental Ca2+

22
Q

What is elemental Ca2+ content of 1 g of calcium gluconate?

A

90 mg of elemental Ca2+

23
Q

What is dosing of IV calcium bolus in setting of symptomatic hypocalcemia?

A
  1. 200-300 mg of elemental Ca2+ administered IV over 5-10 minutes
24
Q

Which IV calcium product should be administered through a central IV catheter?

A

Calcium chloride

25
Q

Why is calcium gluconate preferred over calcium chloride for peripheral IV?

A

Calcium chloride can cause severe limb ischemia/tissue necrosis if it extravasates

26
Q

What is dosing of calcium chloride in symptomatic hypocalcemia?

A

1 g of calcium chloride (273 mg of elemental Ca2+) administered through central intravenous catheter over 5-10 minutes

27
Q

What is dosing of calcium gluconate in symptomatic hypocalcemia?

A

2-3 g of calcium gluconate (180-270 mg of elemental Ca2+) administered IV (peripheral or central) over 5-10 minutes

28
Q

What is the most rapid infusion rate of Ca2+ permissible?

A

60 mg of elemental Ca2+ per minute

29
Q

What are three risks of rapid administration of Ca2+?

A
  1. Hypotension
  2. Bradycardia
  3. Asystole
30
Q

What is the dosing for a continuous infusion of elemental Ca2+?

A

0.5-2 mg/kg/hour of elemental Ca2+

31
Q

What is the ideal (e.g. safest) duration over which to administer IV calcium

A

1-2 hours

32
Q

When drug toxicity requires additional caution when administering calcium?

A

Digoxin toxicity (cardiac tetany, “stone heart,” sudden death)

33
Q

When might a slower infusion (e.g. 1-4 hours) of calcium be preferred over rapid infusion (e.g. 5-10 minutes) in setting of symptomatic hypocalcemia?

A

Patients with mild to severe hypoglycemia (Ca2+ less than 4 mg/dL) but WITHOUT seizures or tetany are candidates for slower infusion, e.g. calcium gluconate 4 g over 4 hours IV (this is about 1-2 mg/kg/hour)

34
Q

Calcium gluconate shortages: how do you admixture peripheral nutrition?

A
  1. If there is a shortage of calcium gluconate, DO NOT add calcium chloride to PN. 2. Use multielectrolyte products in PN, if possible.
35
Q

Calcium gluconate shortages: how do you give peripheral calcium?

A

The safety of diluted calcium chloride administered peripherally is unknown. Some experts say calcium chloride can be given in emergency situations through a large peripheral vein (e.g. median cubital vein). Known vesicant. Monitor for extravasation and be ready to treat.

36
Q

Define hypercalcemia

A

Serum calcium concentration greater than 10.5 mg/dL

37
Q

What conditions is treatment of hypercalcemia routine?

A
  1. Malignancy (oncology)

2. Hyperparathyroidism (nephrology)

BCPS Exam (34 decks)

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