Calcium Balance Flashcards
Approximately what percent of calcium is bound and
what percent is ionized?
About half of the circulating calcium is bound to proteins or
inorganic anions and half is ionized. The ionized portion is the
physiologically active portion that is regulated by homeostasis.
Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC,
Ortega R. Clinical Anesthesia. 7th ed. Philadelphia, PA:
Lippincott Williams and Wilkins; 2013: 352.
How does the concentration of free calcium in the
extracellular space compare to that found in the
intracellular space?
The concentration of free calcium in the intracellular space is
about 10,000 times lower than that found in the extracellular
space.
Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC,
Ortega R. Clinical Anesthesia. 7th ed. Philadelphia, PA:
Lippincott Williams and Wilkins; 2013: 352.
How do acidosis and alkalosis affect ionized calcium
concentrations?
Acute acidosis increases ionized calcium levels and alkalosis
decreases ionized calcium levels.
Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC,
Ortega R. Clinical Anesthesia. 7th ed. Philadelphia, PA:
Lippincott Williams and Wilkins; 2013: 352.
What are the two most important hormones in the
regulation of serum calcium levels and how do they
function?
Parathyroid hormone and calcitriol promote the mobilization of
calcium from bone, promote the reabsorption of calcium from
the renal tubules, and increase intestinal absorption of calcium.
Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC,
Ortega R. Clinical Anesthesia. 7th ed. Philadelphia, PA:
Lippincott Williams and Wilkins; 2013: 352.
What are the normal calcium lab values?
The normal calcium level can be expressed in a number of
ways. The normal ranges for each unit of expression are: Total
Calcium = 8.5-10.5 mg/dL, Ionized Calcium = 4.75-5.3 mg/dL,
Ionized Calcium = 2.38-2.66 mEq/L, and Ionized Calcium =
1.19-1.33 mmol/L.
Butterworth JF, Mackey DC, Wasnick JD. Morgan & Mikhail’s
Clinical Anesthesiology. 5th ed. New York, NY: McGraw-Hill;
2013: 1130.
A patient exhibits hypocalcemia with
hyperphosphatemia. What causes would you
suspect?
Hypocalcemia with hyperphosphatemia is usually indicative of
renal failure or hypoparathyroidism.
Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC,
Ortega R. Clinical Anesthesia. 7th ed. Philadelphia, PA:
Lippincott Williams and Wilkins; 2013: 353-354.
What are the cardiovascular manifestations of
hypocalcemia?
Dysrhythmias, ECG changes, heart failure, hypotension, and
resistance to digitalis and beta-adrenergic drugs.
Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC,
Ortega R. Clinical Anesthesia. 7th ed. Philadelphia, PA:
Lippincott Williams and Wilkins; 2013: 353.
What are the neuromuscular manifestations of
hypocalcemia?
Weakness, tetany, muscle spasms, and seizures
Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC,
Ortega R. Clinical Anesthesia. 7th ed. Philadelphia, PA:
Lippincott Williams and Wilkins; 2013: 353.
What respiratory changes would you expect to see
with hypocalcemia?
Bronchospasm, laryngospasm, and apnea
Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC,
Ortega R. Clinical Anesthesia. 7th ed. Philadelphia, PA:
Lippincott Williams and Wilkins; 2013: 353.
What are some causes of hypocalcemia?
Hypocalcemia does not occur due to a decrease in calcium
intake. It is caused by a deficiency of parathyroid hormone from
surgical removal of the glands or from suppression of
parathyroid hormone. Parathyroid hormone can be suppressed
by hypo- or hypermagnesemia, burns, sepsis, and pancreatitis.
Hypocalcemia may also occur due to hyperphosphatemia.
Massive blood transfusions can result in hypocalcemia by
chelation of calcium with the citrate preservative in blood.
Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC,
Ortega R. Clinical Anesthesia. 7th ed. Philadelphia, PA:
Lippincott Williams and Wilkins; 2013: 352-353.
An otherwise healthy patient has hypocalcemia, but
has a normal phosphate concentration. What do you
think may be the cause?
Hypocalcemia in the presence of a low or normal phosphate
level is usually indicative of a vitamin D or magnesium deficit.
Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC,
Ortega R. Clinical Anesthesia. 7th ed. Philadelphia, PA:
Lippincott Williams and Wilkins; 2013: 353.
What is the preferred treatment for acute
hypocalcemia?
10 mL of 10% calcium gluconate over 10 minutes followed by a
calcium infusion at 0.3-2 mg/kg/hour.
Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC,
Ortega R. Clinical Anesthesia. 7th ed. Philadelphia, PA:
Lippincott Williams and Wilkins; 2013: 354.
In what solution should calcium be diluted when
administered intravenously?
Calcium should be diluted in 50-100 mL of D5W to limit venous
irritation and thrombosis. They will precipitate if mixed with
bicarbonate.
Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC,
Ortega R. Clinical Anesthesia. 7th ed. Philadelphia, PA:
Lippincott Williams and Wilkins; 2013: 354.
What should you monitor during initial calcium
replacement therapy?
ECG monitoring is mandatory during initial intravenous
treatment to observe for signs of cardiotoxicity such as heart
block or ventricular fibrillation.
Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC,
Ortega R. Clinical Anesthesia. 7th ed. Philadelphia, PA:
Lippincott Williams and Wilkins; 2013: 354.
What patients are at particular risk for developing
hypocalcemia?
Decreased ionized calcium levels are seen in about 88% of
critically ill patients and 26% of patients hospitalized in nonacute
care beds. Patients with multiple traumas and those who
have undergone cardiopulmonary bypass are at particular risk.
Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC,
Ortega R. Clinical Anesthesia. 7th ed. Philadelphia, PA:
Lippincott Williams and Wilkins; 2013: 353.
