Calcium imbalance
Calcium imbalance: Excerpt from Professional Guide to Diseases (Eighth Edition)
Calcium plays an indispensable role in cell permeability, bone and teeth formation, blood coagulation, transmission of nerve impulses, and normal muscle contraction. Nearly all (99%) of the body’s calcium is found in the bones. The remaining 1% exists in the blood, with 50% of the remainder bound to plasma proteins and 40% ionized or free. The ionized calcium in the serum is critical to healthy neurologic function. The parathyroid glands regulate ionized calcium and determine its resorption into bone, absorption from the GI mucosa, and excretion in urine and feces. Severe calcium imbalance requires emergency treatment because a deficiency (hypocalcemia) can lead to tetany and seizures; an excess (hypercalcemia), to cardiac arrhythmias and coma. (See Clinical effects of calcium imbalance.)
Causes
Common causes of hypocalcemia include:
❑ inadequate intake of calcium and vitamin D, in which inadequate levels of vitamin D inhibit intestinal absorption of calcium
❑ hypoparathyroidism as a result of injury, disease, or surgery that decreases or eliminates secretion of parathyroid hormone (PTH), which is necessary for calcium absorption and normal serum calcium levels
❑ malabsorption or loss of calcium from the GI tract, caused by increased intestinal motility from severe diarrhea or laxative abuse; can also result from inadequate levels of vitamin D or PTH, or a reduction in gastric acidity, decreasing the solubility of calcium salts
❑ severe infections or burns, in which diseased and burned tissue traps calcium from the extracellular fluid
❑ overcorrection of acidosis, resulting in alkalosis, which causes decreased ionized calcium and induces symptoms of hypocalcemia
❑ pancreatic insufficiency, which may cause malabsorption of calcium and subsequent calcium loss in feces. In pancreatitis, participation of calcium ions in saponification contributes to calcium loss
❑ renal failure, resulting in excessive excretion of calcium secondary to increased retention of phosphate
❑ hypomagnesemia, which causes decreased PTH secretion and blocks the peripheral action of that hormone.
Causes of hypercalcemia include the following:
❑ hyperparathyroidism, which increases serum calcium levels by promoting calcium absorption from the intestine, resorption from bone, and reabsorption from the kidneys
❑ hypervitaminosis D, which can promote increased absorption of calcium from the intestine
❑ tumors, which raise serum calcium levels by destroying bone or by releasing PTH or a PTH-like substance, osteoclast-activating factor, prostaglandins and, perhaps, a vitamin D-like sterol
❑ multiple fractures and prolonged immobilization, which release bone calcium and raise the serum calcium level
❑ multiple myeloma, which promotes loss of calcium from bone.
Other causes include milk-alkali syndrome, sarcoidosis, hyperthyroidism, adrenal insufficiency, thiazide diuretics, and loss of serum albumin secondary to renal disease.
Signs and symptoms
Calcium deficit causes nerve fiber irritability and repetitive muscle spasms. Consequently, characteristic symptoms of hypocalcemia include perioral paresthesia, twitching, carpopedal spasm, tetany, seizures and, possibly, cardiac arrhythmias. Chvostek’s sign and Trousseau’s sign are reliable indicators of hypocalcemia. (See Trousseau’s sign. Also see Chvostek’s sign, page 918.)
Clinical effects of hypercalcemia include muscle weakness, decreased muscle tone, lethargy, anorexia, constipation, nausea, vomiting, dehydration, polydipsia, and polyuria. Severe hypercalcemia (serum levels that exceed 15 mg/dl) may produce cardiac arrhythmias and, eventually, coma.
Diagnosis
Confirming diagnosis A serum calcium level less than 8.5 mg/dl confirms hypocalcemia; a level more than 10.5 mg/dl confirms hypercalcemia. (However, because approximately one-half of serum calcium is bound to albumin, changes in serum protein must be considered when interpreting serum calcium levels. A common conversion formula is calcium corrected = calcium actual + 0.8 x [4.0 – albumin level]. Ionized calcium levels are 4.65 to 5.28 mg/dl and are a measure of the fraction of serum calcium in ionized form.)
The Sulkowitch urine test shows increased calcium precipitation in hypercalcemia. In hypocalcemia, an electrocardiogram (ECG) reveals lengthened QT interval, prolonged ST segment, and arrhythmias; in hypercalcemia, shortened QT interval and heart block. (See Diagnosing hypercalcemia, pages 916 and 917.)
Treatment
Treatment varies and requires correction of the acute imbalance, followed by maintenance therapy and correction of the underlying cause. Mild hypocalcemia may require nothing more than an adjustment in diet to allow adequate intake of calcium, vitamin D, and protein, possibly with oral calcium supplements. Acute hypocalcemia is an emergency that needs immediate correction by I.V. administration of calcium gluconate or calcium chloride. Chronic hypocalcemia also requires vitamin D supplements to facilitate GI absorption of calcium. To correct mild deficiency states, the amounts of vitamin D in most multivitamin preparations are adequate. For severe deficiency, vitamin D is used in four forms: ergocalciferol (vitamin D 2), cholecalciferol (vitamin D3), calcitriol, and dihydrotachysterol, a synthetic form of vitamin D2.
Treatment of hypercalcemia primarily eliminates excess serum calcium through hydration with normal saline solution, which promotes calcium excretion in the urine. Loop diuretics, such as ethacrynic acid and furosemide, also promote calcium excretion. (Thiazide diuretics are contraindicated in hypercalcemia because they inhibit calcium excretion.) Corticosteroids, such as prednisone and hydrocortisone, are helpful in treating sarcoidosis, hypervitaminosis D, and certain tumors. Plicamycin can also lower serum calcium levels and is especially effective against hypercalcemia secondary to certain tumors. Calcitonin may also be helpful in certain instances. Sodium phosphate solution administered orally or by retention enema promotes calcium deposition in bone and inhibits its absorption from the GI tract.
Special considerations
Watch for hypocalcemia in patients receiving massive transfusions of citrated blood; in those with chronic diarrhea, severe infections, and insufficient dietary intake of calcium and protein (especially in elderly patients); and in those who are hyperventilating.
❑ Monitor serum calcium levels every 12 to 24 hours and report a calcium level less than 8.5 mg/dl immediately. When giving calcium supplements, frequently check the pH level because a pH lower than 7.45 inhibits calcium ionization. Check for Trousseau’s and Chvostek’s signs.
❑ Administer calcium gluconate slow I.V. in 5% dextrose in water (never in saline solution, which encourages renal calcium loss). Don’t add calcium gluconate I.V. to solutions containing bicarbonate; it will precipitate. When administering calcium solutions, watch for anorexia, nausea, and vomiting — possible signs of overcorrection to hypercalcemia. Never infuse more than 1g/hour, except in an emergency. Use a volume-control device to ensure proper flow rate.
❑ If the patient is receiving calcium chloride, watch for abdominal discomfort.
Alert Don’t confuse calcium chloride with calcium gluconate in administration; 1 gm of calcium chloride has three times the calcium as 1 gm of calcium gluconate.
❑ Monitor the patient closely for a possible drug interaction if he’s receiving cardiac glycosides with large doses of oral calcium supplements; watch for signs of digoxin toxicity (anorexia, nausea, vomiting, yellow vision, and cardiac arrhythmias). Administer oral calcium supplements 1 to 1½ hours after meals or with milk.
❑ Provide a quiet, stress-free environment for the patient with tetany. Observe seizure precautions for patients with severe hypocalcemia.
❑ To prevent hypocalcemia, advise all patients — especially elderly patients — to eat foods rich in calcium, vitamin D, and protein, such as fortified milk and cheese. Explain how important calcium is for normal bone formation and blood coagulation. Discourage chronic use of laxatives. Also, warn hypocalcemic patients not to overuse antacids, because these may aggravate the condition.
If the patient has hypercalcemia:
❑ Monitor serum calcium levels frequently. Watch for cardiac arrhythmias if serum calcium levels exceed their normal values of 8.5 to 10.5 mg/dl. Increase fluid intake to dilute calcium in serum and urine, and to prevent renal damage and dehydration. Watch for signs of heart failure in patients receiving normal saline diuresis.
❑ Administer loop diuretics (not thiazide diuretics), as ordered. Monitor intake and output, and check urine for renal calculi and acidity. Provide acid-ash drinks, such as cranberry or prune juice, because calcium salts are more soluble in acid than in alkali.
❑ Check ECG and vital signs frequently. In the patient receiving cardiac glycosides, watch for signs of toxicity, such as anorexia, nausea, vomiting, and bradycardia (often with arrhythmia).
❑ Ambulate the patient as soon as possible. Handle the patient with chronic hypercalcemia gently to prevent pathologic fractures. If the patient is bedridden, reposition him frequently and encourage range-of-motion exercises to promote circulation and prevent urinary stasis and calcium loss from bone.
❑ To prevent recurrence, suggest a low-calcium diet, with increased fluid intake.
Pictures
Book Source Details
- Book Title: Professional Guide to Diseases (Eighth Edition)
- Author(s): Springhouse
- Year of Publication: 2005
- Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2005 Lippincott Williams & Wilkins.
More About Hypocalcemia
More Medical Textbooks Online about Hypocalcemia
Review other book chapters online related to Hypocalcemia:
Medical Books Excerpts
- Carpopedal spasm
- "Alarming Signs and Symptoms: Lippincott Manual of Nursing Practice Series" (2007)
- [ read ]
Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
» Next page: Chvostek's sign (Professional Guide to Signs & Symptoms (Fifth Edition))
Rate This Website
What do you think about the features of this website?
Take our user survey and have your say:
Website User Survey
Medical Tools & Articles:
Next articles:
Tools & Services:
Medical Articles:
Forums & Message Boards
- Ask or answer a question at the Boards:
