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Common causes of hypocalcemia after the first week of life are DiGeorge sequence (lateral displacement of the inner canthi, short palpebral fissures, short philtrum, micrognathia, ear and cardiovascular anomalies, absent parathyroid, and a defect in cell-mediated immunity that results from a primary defect of the fourth bronchial arch), hyperphosphatemic states, magnesium deficiency, and osteopetrosis. Neonates on furosemide, bicarbonate therapy, or undergoing transfusion of citrated blood may develop hypocalcemia.
Neonates with hypocalcemia tend to look healthy between seizures. A clue to the diagnosis of hypocalcemia is a Q-oTC interval (measured from the beginning of the Q to the beginning of the T) greater than 0.2 seconds (prolonged). The immediate treatment of hypocalcemic seizures is calcium gluconate 10% at a dose of 1 to 2 mL/kg intravenously at an infusion rate of less than 1 mL per minute. Calcium gluconate should not be mixed with sodium bicarbonate. The initial dose should be repeated in 10 minutes if seizures continue or recur. If seizures continue after the second dose and the Q-oTC interval is still greater than 0.2 seconds, hypomagnesemia should be suspected. If seizures continue but the Q-oTC is shorter than 0.2 seconds, phenobarbital should be used. The maintenance dose of calcium should be adjusted for each patient. The daily dose is usually 5 to 10 mL/kg of 10% calcium gluconate solution.

Hypomagnesemia
Total serum magnesium under 1.5 mg/dL may induce seizures. Hypomagnesemia should be considered in neonates with hypocalcemia that persists after two appropriate doses of intravenous calcium. The immediate treatment of hypomagnesemia consists of 0.1 to 0.2 mL/kg of 50% magnesium sulfate solution intravenously or intramuscularly. Magnesium sulfate, if given intravenously, should be infused slowly over 10 minutes. If seizures continue and hypocalcemia is not present, antiepileptic drugs are indicated. The usual maintenance dose of magnesium sulfate 50% solution is 0.2 mL/kg per day administered orally or intravenously.

 

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Jones, 1997 Fenichel, 1990 Volpe, 1997 Tsang, 1972