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
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,
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.