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department: Diagnostic Update

Correct that calcium

Avent, Yvonne RN, APRN,BC, MSN

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doi: 10.1097/01.CCN.0000281586.47372.c4
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In Brief

Calcium is located in the body's skeletal system, primarily in the teeth and bones. The small amount of calcium that's located in serum is partly ionized. Calcium functions in the transmission of nerve impulses and assists with muscle contraction and relaxation. This includes contraction and relaxation of the cardiac muscle.

What's normal?

Normal total serum calcium levels range from 8.5 to 10.5 mg/dL. About 50% of the total serum calcium exists in ionized form. Ionized calcium is important for neuromuscular activity and blood coagulation. Normal ionized calcium levels range from 4.5 to 5.1 mg/dL. Ionized calcium is the only clinically significant form of calcium.1

Table
Table:
Hypocalcemia vs. hypercalcemia3,4

Serum calcium levels are controlled by parathyroid hormone (PTH) and calcitonin. When ionized calcium levels decrease, PTH is secreted by the parathyroid gland, causing an increase in calcium absorption from the gastrointestinal tract, release of calcium from bones, and increased reabsorption from the renal tubule. The increase in serum ionized calcium then decreases PTH secretion. The thyroid gland will secrete calcitonin if calcium levels rise excessively. Calcitonin inhibits reabsorption of calcium from bone and decreases serum calcium levels.1

Hypocalcemia can be defined as a calcium level below 8.5 mg/dL. Calcium levels above 10.5 mg/dL are classified as hypercalcemia. Levels less than than 7 mg/dL and greater than 12 mg/dL can be classified as critical values.2 (See Hypocalcemia vs. hypercalcemia.)

Serum albumin levels must be considered when evaluating serum calcium levels. Serum calcium levels may be decreased in the presence of hypoalbuminemia. Consequently, it may be necessary to calculate a corrected calcium level if the serum albumin level is abnormal. Use the following formula:

Clinicians may ignore a low serum calcium level in the presence of a decreased albumin level. This is one reason ionized calcium levels may be beneficial. Ionized calcium levels are typically normal in patients with both decreased serum albumin and total calcium levels.1

Treatment of hypocalcemia

Chronic hypocalcemia can be treated by increasing dietary calcium intake to 1,000 to 1,500 mg/day for adults. Patients can achieve this by eating foods such as milk products, canned salmon, sardines, and green leafy vegetables.

Mild hypocalcemia can be treated with the administration of vitamin D to increase calcium absorption from the gastrointestinal tract or oral calcium supplements.5 Oral calcium carbonate (such as Tums or Os-Cal) is most commonly used. Calcium carbonate is affordable and contains 40% elemental calcium.

Severe hypocalcemia can be life-threatening. Patients can present with cardiac dysrhythmias, prolonged QT interval, seizures, and tetany. (See Assess for Trousseau's and Chvostek's signs.) This condition requires prompt treatment with I.V. administration of a calcium salt.6 Calcium chloride produces higher ionized calcium; however, calcium gluconate is preferred because it's less irritating to the tissues. Extravasation of a calcium chloride or gluconate infusion can cause tissue sloughing.

Calcium infusions can cause hypotension and bradycardia. Dysrhythmias can also occur in patients receiving calcium and digoxin.7 Calcium gluconate should be diluted in D5W and not 0.9% sodium chloride solution because 0.9% sodium chloride solution will increase renal calcium loss.8 Calcium will also precipitate when given with solutions containing bicarbonate, sulfate, or phosphate.

Nursing interventions should include clarification of the calcium salt, calcium chloride, or calcium gluconate that should be administered. Calcium chloride contains 13.6 mEq/gram of calcium; calcium gluconate provides 4.6 mEq/gram of calcium.8 Cardiac and vital sign monitoring are essential to monitor for hypotension and bradycardia. Monitor respiratory function because laryngeal spasm or bronchospasm may occur with tetany. Interventions also include monitoring intake and output, calcium levels, and other pertinent lab values. Institute seizure precautions for patients with severe hypocalcemia.

Patients at risk for osteoporosis will need instruction regarding the risk of falls, the need for increased calcium in the diet, and the possibility of requiring calcium supplementation. Patients should also be advised that high doses of alcohol and caffeine inhibit the absorption of calcium, and cigarette smoking enhances urinary excretion of calcium. Medications such as calcitonin-salmon (Miacalcin), alendronate (Fosamax), raloxifene (Evista), ibandronate (Boniva), or risedronate (Actonel) may be prescribed to reduce the rate of bone loss.1

Treatment of hypercalcemia

In treating hypercalcemia, the goals are calcium correction and treatment of the underlying cause. Asymptomatic patients with mild hypercalcemia may not benefit from calcium correction. However, conservative measures for treating hypercalcemia may be used. These include elimination of high calcium foods from the diet; elimination of medications that impair calcium excretion (such as lithium and thiazide diuretics), if possible; fluid administration to increase renal excretion of calcium; adequate hydration; and increased mobility.3,9

Patients with calcium levels greater than 14 mg/dL or symptomatic patients with calcium levels greater than 12 mg/dL should be treated immediately.2 Patients can present with nausea, vomiting, constipation, abdominal pain, muscle weakness, and shortened QT interval. First-line treatment includes aggressive hydration followed by diuresis. In adults, 0.9% sodium chloride solution should be infused to achieve a urine output of 200 mL/hour.9 This will enhance filtration and excretion of calcium and increase intravascular volume. Aggressive hydration should be used cautiously in the elderly and in patients with heart or renal failure.

Diuresis with a low-dose loop diuretic such as furosemide (Lasix) administered I.V. should be considered after rehydration. Furosemide increases calcium excretion. Thiazide diuretics should be avoided as they cause hypercalcemia.

Calcitonin is used in severe hypercalcemia refractory to hydration and diuresis. The recommended dosage is 4 units/kg body weight dose subcutaneously or I.M. every 12 hours. The dosage may be increased to 8 units/kg every 12 hours after 1 to 2 days if response is unsatisfactory. The maximum dosage is 8 units/kg every 6 hours.8 Calcitonin may be derived from salmon; therefore, it's contraindicated in patients sensitive to salmon. Adverse effects may include nausea, vomiting, skin irritation, flushing, and abdominal pain. The I.M. site and rotation of sites is recommended if the injection volume exceeds 2 mL.8

Bisphosphonates are a group of drugs used to inhibit bone resorption. This group of drugs is useful when hypercalcemia is due to malignancy. Pamidronate disodium (Aredia) can be given for severe hypercalcemia as a one-time dose of 60 to 90 mg as an I.V. infusion. Prehydration is required before use. Retreatment may be considered if hypercalcemia occurs, but it is recommended to wait at least 7 days from the initial infusion to allow for complete response. Dosage may be adjusted for renal or liver impairment.7,8

Another bisphosphonate, zoledronic acid (Zometa), is also useful for hypercalcemia of malignancy. Recommended dosage is 4 mg I.V. infusion over no less than 15 minutes. Again, prehydration is required and clinicians should wait 7 days from initial infusion to allow for full response.9 One study determined that zoledronic acid is a more effective treatment than pamidronate disodium in the treatment of hypercalcemia of malignancy.10

Other treatments include glucocorticoids, dialysis, and parathyroidectomy.

Nursing care

Nursing interventions include encouraging fluid intake and ambulation. Fluids containing sodium should be used unless contraindicated as sodium increases calcium excretion. Cardiac rhythm should be monitored.1 Calcium levels should be monitored as ordered, as well as sodium and potassium levels due to use of diuretics. Intake and output measurement is also critical to assess response to hydration and diuretic therapy.

Hypocalcemia and hypercalcemia can have many varied causes and clinical symptoms. Patients may not exhibit symptoms, or they may present with cardiac dysrhythmias, tetany, and seizures. Knowledge of the medical management and nursing interventions is critical in order to properly care for these patients.

Assess for Trousseau's and Chvostek's signs

Testing for Trousseau's and Chvostek's signs may help in the diagnosis of tetany that can occur with hypocalcemia.

Trousseau's sign

To elicit Trousseau's sign, apply a blood pressure cuff to the patient's upper arm and inflate the cuff to a pressure 20 mm Hg above the patient's systolic pressure. Within 1 to 3 minutes, the patient will experience Trousseau's sign, a carpal spasm, with an adducted thumb, flexed wrist and metacarpophalangeal joints, and extended interphalangeal joints with the fingers together. This indicates tetany associated with hypocalcemia.

Figure
Figure

Chvostek's sign

To elicit Chvostek's sign, tap the patient's facial nerve adjacent to the earlobe and just below the zygomatic bone. Brief repeated contractions of the upper lip, nose, or the side of the face indicate Chvostek's sign.

Figure
Figure

REFERENCES

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    10. Major P, Lortholary A, Hon J, et al. Zoledronic acid is superior to pamidronate in the treatment of hypercalcemia of malignancy: a pooled analysis of two randomized, controlled clinical trials. J Clin Oncol. 2001;19:558–567.
    © 2007 Lippincott Williams & Wilkins, Inc.