METABOLIC DISORDERS IN THE NEWBORN INFANT
Saturday, August 16, 2008
HYPERGLYCEMIA
Hyperglycemia may develop in preterm infants, particularly those of very low birth weight who are also SGA. Glucose concentrations may exceed 200–250 mg/dL, particularly in the first few days of life. This transient diabetes-like syndrome usually lasts approximately 1–2 weeks.
Management may include simply reducing glucose intake while continuing to provide supplemental calories with intravenous amino acids and lipids, coupled with small milk feedings by gavage. Insulin infusions intravenously have also been used to permit a larger intravenous glucose intake without hyperglycemia. This is usually reserved for infants in whom it has not been possible to begin any gavage milk feedings and in whom caloric intake in the form of amino acids and lipids is small. However, this approach requires careful direct monitoring of blood glucose concentrations. Hyperglycemia can also be a problem in infants treated with dexamethasone for chronic lung disease.
HYPOCALCEMIA
Calcium concentration in the immediate newborn period decreases in all newborn infants. The concentration in fetal plasma is higher than that of the neonate or adult. Hypocalcemia is usually defined as a total serum concentration less than 7 mg/dL (equivalent to a calcium activity of 3.5 mEq/L), although the physiologically active fraction, ionized calcium, should be measured whenever possible. Ionized calcium is usually normal even when total calcium is as low as 6–7 mg/dL. An ionized calcium of greater than 0.9 µmol/L (1.8 mEq/L; 3.6 mg/dL) is not likely to be detrimental.
Clinical Findings
The clinical signs of hypocalcemia and hypocalcemic tetany include a high-pitched cry, jitteriness, tremulousness, and seizures.
Hypocalcemia tends to occur at two different times in the neonatal period. Early-onset hypocalcemia occurs in the first 2 days of life and has been associated with prematurity, maternal diabetes, asphyxia, and, rarely, maternal hypoparathyroidism. Late-onset hypocalcemia occurs at approximately 7–10 days and is observed in infants receiving modified cow’s milk rather than infant formula (high phosphorus intake) or in infants with hypoparathyroidism or hypomagnesemia. Mothers in third-world countries often have vitamin D deficiency, which can also contribute to late-onset hypocalcemia.
Treatment
A. Oral Calcium Therapy: The oral administration of calcium salts is a preferred method of treatment for chronic forms of hypocalcemia resulting from hypoparathyroidism but is rarely used in early-onset hypocalcemia. Calcium in the form of calcium gluconate can be given as a dilute solution or added to formula feedings several times a day. A dose of 0.5–1 g/kg/d provides approximately 45–90 mg of elemental calcium per kilogram per day. If a 10% solution of calcium gluconate is used, the dose is 5–10 mL/kg/d given in divided doses every 4 hours or every 6 hours.
B. Intravenous Calcium Therapy: Intravenous calcium therapy is usually needed for infants with symptomatic hypocalcemia or an ionized calcium less than 0.9 µmol/L. A number of precautions must be observed when calcium gluconate is given intravenously. The infusion must be given slowly so that there is no sudden increase in calcium concentration of blood entering the right atrium, which could cause severe bradycardia and even cardiac arrest. Furthermore, the infusion must be observed carefully, because an intravenous infiltrate containing calcium can cause full-thickness skin necrosis requiring grafting. For these reasons, intravenous calcium therapy should be given judiciously and through a central venous line if possible. Intravenous administration of 10% calcium gluconate is usually given as a bolus of 100–200 mg/kg over approximately 10–20 minutes, followed by a continuous infusion (0.5–1 g/kg/d) over 1–2 days. Ten percent calcium chloride (20 mg/kg per dose) may result in a larger increment in ionized calcium and greater improvement in mean arterial blood pressure in sick hypocalcemic infants and thus may have a role in the newborn. Note: Calcium salts cannot be added to intravenous solutions that contain sodium bicarbonate because they precipitate as calcium carbonate.
Prognosis
The prognosis is good for neonatal seizures entirely caused by hypocalcemia that is promptly treated.
INBORN ERRORS OF METABOLISM
The individual inborn errors of metabolism are rare, but collectively all such disorders create significant clinical problems. The diseases are considered in detail in Chapter 31, but the diagnoses should be entertained in infants who were initially well that present with sepsis-like syndromes, recurrent hypoglycemia, neurologic syndromes (seizures, altered levels of consciousness), and unexplained acidosis.
In the immediate neonatal period, urea cycle disorders commonly present as altered level of consciousness secondary to hyperammonemia. A clinical clue that supports this diagnosis is hyperventilation with primary respiratory alkalosis. The other major diagnostic category to consider consists of infants with severe acidemia secondary to organic acidemias.
Hyperglycemia may develop in preterm infants, particularly those of very low birth weight who are also SGA. Glucose concentrations may exceed 200–250 mg/dL, particularly in the first few days of life. This transient diabetes-like syndrome usually lasts approximately 1–2 weeks.
Management may include simply reducing glucose intake while continuing to provide supplemental calories with intravenous amino acids and lipids, coupled with small milk feedings by gavage. Insulin infusions intravenously have also been used to permit a larger intravenous glucose intake without hyperglycemia. This is usually reserved for infants in whom it has not been possible to begin any gavage milk feedings and in whom caloric intake in the form of amino acids and lipids is small. However, this approach requires careful direct monitoring of blood glucose concentrations. Hyperglycemia can also be a problem in infants treated with dexamethasone for chronic lung disease.
HYPOCALCEMIA
Calcium concentration in the immediate newborn period decreases in all newborn infants. The concentration in fetal plasma is higher than that of the neonate or adult. Hypocalcemia is usually defined as a total serum concentration less than 7 mg/dL (equivalent to a calcium activity of 3.5 mEq/L), although the physiologically active fraction, ionized calcium, should be measured whenever possible. Ionized calcium is usually normal even when total calcium is as low as 6–7 mg/dL. An ionized calcium of greater than 0.9 µmol/L (1.8 mEq/L; 3.6 mg/dL) is not likely to be detrimental.
Clinical Findings
The clinical signs of hypocalcemia and hypocalcemic tetany include a high-pitched cry, jitteriness, tremulousness, and seizures.
Hypocalcemia tends to occur at two different times in the neonatal period. Early-onset hypocalcemia occurs in the first 2 days of life and has been associated with prematurity, maternal diabetes, asphyxia, and, rarely, maternal hypoparathyroidism. Late-onset hypocalcemia occurs at approximately 7–10 days and is observed in infants receiving modified cow’s milk rather than infant formula (high phosphorus intake) or in infants with hypoparathyroidism or hypomagnesemia. Mothers in third-world countries often have vitamin D deficiency, which can also contribute to late-onset hypocalcemia.
Treatment
A. Oral Calcium Therapy: The oral administration of calcium salts is a preferred method of treatment for chronic forms of hypocalcemia resulting from hypoparathyroidism but is rarely used in early-onset hypocalcemia. Calcium in the form of calcium gluconate can be given as a dilute solution or added to formula feedings several times a day. A dose of 0.5–1 g/kg/d provides approximately 45–90 mg of elemental calcium per kilogram per day. If a 10% solution of calcium gluconate is used, the dose is 5–10 mL/kg/d given in divided doses every 4 hours or every 6 hours.
B. Intravenous Calcium Therapy: Intravenous calcium therapy is usually needed for infants with symptomatic hypocalcemia or an ionized calcium less than 0.9 µmol/L. A number of precautions must be observed when calcium gluconate is given intravenously. The infusion must be given slowly so that there is no sudden increase in calcium concentration of blood entering the right atrium, which could cause severe bradycardia and even cardiac arrest. Furthermore, the infusion must be observed carefully, because an intravenous infiltrate containing calcium can cause full-thickness skin necrosis requiring grafting. For these reasons, intravenous calcium therapy should be given judiciously and through a central venous line if possible. Intravenous administration of 10% calcium gluconate is usually given as a bolus of 100–200 mg/kg over approximately 10–20 minutes, followed by a continuous infusion (0.5–1 g/kg/d) over 1–2 days. Ten percent calcium chloride (20 mg/kg per dose) may result in a larger increment in ionized calcium and greater improvement in mean arterial blood pressure in sick hypocalcemic infants and thus may have a role in the newborn. Note: Calcium salts cannot be added to intravenous solutions that contain sodium bicarbonate because they precipitate as calcium carbonate.
Prognosis
The prognosis is good for neonatal seizures entirely caused by hypocalcemia that is promptly treated.
INBORN ERRORS OF METABOLISM
The individual inborn errors of metabolism are rare, but collectively all such disorders create significant clinical problems. The diseases are considered in detail in Chapter 31, but the diagnoses should be entertained in infants who were initially well that present with sepsis-like syndromes, recurrent hypoglycemia, neurologic syndromes (seizures, altered levels of consciousness), and unexplained acidosis.
In the immediate neonatal period, urea cycle disorders commonly present as altered level of consciousness secondary to hyperammonemia. A clinical clue that supports this diagnosis is hyperventilation with primary respiratory alkalosis. The other major diagnostic category to consider consists of infants with severe acidemia secondary to organic acidemias.
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