Calcium

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Normal levels: 8.5 to 10.5 mg/dL (2.1 to 2.7 mmol/L)

Physiology:

Calcium plays an important role in the propagation of neuromuscular activity, regulation of endocrine functions, blood coagulation, and bone and tooth metabolism. Calcium homeostasis is closely regulated by a complex interaction among PTH, serum phosphate, vitamin D system, and target organ. Balance is achieved largely by control of absorption rather that regulation of excretion.

Empiric daily requirement

Adults: 10 to 30 mEq/day

Infants//children: 0.5 to 3 mEq/kg/day

Hypocalcemia: levels below 8.5 mg/dL

Causes:

•	The most common cause of hypocalcemia is low serum albumin. Any decrease in albumin results in a decrease in serum calcium . Alkalosis may increase the amount of calcium bound to the albumin.

•	Reduced intestinal absorption due to vitamin D deficiency or small bowel disease.

•	Increased loss through fistulas, damaged skin or burns, renal disease or use of loop diuretics.

•	Medications such as phenytoin and phenobarbital can affect calcium levels because they after the hepatic metabolism of vitamin D.

•	Because of the reciprocal relationship of calcium and phosphorus, excess phosphorus results in decreased calcium levels.

•	Hypomagnesemia is also associated with calcium deficits.

•	Other causes include hypoparathyroidism, acute pancreatitis and alkalosis.

Assessment:

Symptoms primarily involve the neuromuscular system (muscle cramps, fatigue, depression, memory loss and confusion, and in severe cases, tetany and convulsions). The earliest signs of hypocalcemia are numbness and tingling of extremities. As hypocalcemia worsens the cardiovascular system may be affected, as evidenced by myocardial failure, cardiac arrhythmias and hypotension.

Labs:

Serum calcium levels below 8.5 mg/dL. Increased potassium and magnesium levels may also occur.

Correction:

Replace orally if possible. Acute symptomatic hypocalcemia requires intravenous administration of calcium.

TPN correction:

Increase the calcium content of the TPN solution to a maximum of 9 mEq per liter. The total daily calcium dosage should not exceed 27mEq.

Hypercalcemia: levels above 11 mg/dL

Causes:

•	Excessive calcium administration.

•	Malignancies can increase serum calcium by several mechanisms.

•	Hyperparathyroidism

•	Hyperthyroidism

•	Chronic immobilization

•	Paget's disease

•	Medications: vitamin D, vitamin A, thyroid hormone, tamoxifen, androgens, estrogen and progesterone.

Assessment:

GI complaints include nausea, vomiting, abdominal pain, dyspepsia, peptic ulcer disease and acute pancreatitis. Severe hypercalcemic symptoms primarily involve the neuromuscular system (weakness, confusion, diminished reflexes, and in severe cases, coma). Renal affects include polyuria, polydipsia and renal failure. Cardiac signs of hypercalcemia are arrhythmias and an increased risk of digoxin toxicity.

Labs:

Serum calcium levels above 10.5 mg/dL

Correction:

Reduce calcium administration, encourage mobilization and increase fluid intake. Administer IV saline in combination with a loop diuretic in order to inhibit calcium reabsorption and to increase calcium excretion.

TPN correction:

If calcium > 10.5 mg/dL discontinue the current TPN infusion if it contains calcium and begin an infusion of D10NS at the current TPN infusion rate. Reorder a TPN solution without calcium and continue to hold calcium from the TPN solution and all other intravenous fluids until the serum calcium returns to normal.