The hyperviscosity or polycythemia syndrome is a condition which most frequently develops shortly after birth (Table 4.24). It is characterized by a peripheral venous hematocrit above 69%, involves sludging and stasis of blood flow, and often leads to a number of pathophysiological sequelae, and possibly death.
Incidence in all newborns is reported to be 2.9-5.0%. Associated conditions are transient tachypnea, respiratory distress, increasing pulmonary vascularity, congestive heart failure, cyanosis, cardiomegaly, renal thrombosis, neurological abnormalities, necrotizing enterocolitis, thrombocytopenia, hyperbilirubinemia and jaundice, and persistent fetal circulation. A number of factors affect blood viscosity (Table 4.25)