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Polycythemia
is an abnormal increase in RBC mass, defined in neonates as a venous
Hct ≥ 65%; this can lead to
hyperviscosity with sludging of blood within vessels and sometimes thrombosis.
The main symptoms and signs of neonatal polycythemia are very ruddy
complexion, feeding difficulties, lethargy, and seizures. Diagnosis
is made clinically and with a spun Hct. The main symptoms and signs
of hyperviscosity syndrome are cyanosis, jaundice, tachypnea, and
renal failure. Treatment is with partial exchange transfusion.
The terms polycythemia and hyperviscosity are often used interchangeably but are not equivalent. Polycythemia is significant only because it increases risk for hyperviscosity syndrome. Hyperviscosity syndrome is symptoms and signs caused by sludging of blood within vessels. Sludging occurs because increased RBC mass causes a relative decrease in plasma volume and a relative increase in proteins and platelets.
Incidence of polycythemia ranges between 0.4% and 12%. Hyperviscosity occurs in 6.7% of neonates. Only 47% of infants with polycythemia exhibit hyperviscosity; 24% of infants with hyperviscosity have polycythemia.
Etiology
Dehydration causing relative hemoconcentration and an elevated Hct mimics polycythemia but RBC mass is not increased. Causes of true polycythemia include intrauterine hypoxia, placental transfusion, some congenital abnormalities (eg, cyanotic congenital heart disease, renovascular malformations, congenital adrenal hyperplasia), certain delivery procedures (eg, delayed cord clamping, holding neonate below the level of the mother before cord clamping, stripping the cord toward the neonate at delivery), maternal insulin -dependent diabetes, Down syndrome, Beckwith-Wiedemann syndrome, intrauterine growth restriction, twin-to-twin transfusion, and perinatal asphyxia. Premature infants rarely develop hyperviscosity syndrome.
Symptoms and Signs
Symptoms and signs of hyperviscosity syndrome are those of heart failure, thrombosis (cerebral and renal vessels), and CNS dysfunction, including tachypnea, respiratory distress, cyanosis, plethora, apnea, lethargy, irritability, hypotonia, tremulousness, seizures, and feeding problems. Renal vein thrombosis may also cause renal tubular damage and/or proteinuria.
Diagnosis
Diagnosis of polycythemia is by Hct; diagnosis of hyperviscosity syndrome is clinical. Capillary samples often overestimate Hct so a venous Hct, preferably spun, should be obtained before the diagnosis is made; most published studies of polycythemia use spun Hcts, which are generally higher than those obtained on automated counters. Laboratory measure of viscosity is not readily available.
Other laboratory abnormalities may include low blood glucose and Ca levels secondary to poor feeding, maternal diabetes, or both, and RBC lysis; thrombocytopenia (secondary to consumption with thrombosis); hyperbilirubinemia (from turnover of a higher number of RBCs); and reticulocytosis and increased peripheral nucleated RBCs (from increased erythropoiesis secondary to fetal hypoxia).
Treatment
Asymptomatic infants should be treated with IV hydration (see Dehydration and Fluid Therapy: Treatment). Symptomatic infants should undergo an isovolumic partial exchange transfusion to reduce the Hct to ≤ 55% and thereby decrease blood viscosity; blood is removed in 5 mL/kg (about 10 to 12 mL) aliquots and replaced with an equal volume of 0.9% saline. Asymptomatic infants whose Hct remains persistently > 70% despite hydration may also benefit from this procedure.
Although many studies show immediate measurable effects of partial exchange, the long-term benefits remain in question. Most studies have failed to document differences in long-term growth or neurodevelopment between children who received a partial exchange transfusion in the neonatal period and those who did not.
Last full review/revision November 2005
Content last modified November 2005
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