Polycythaemia is defined as a venous haematocrit greater than 65% and occurs in 0.4 - 4% of newborn infants. This may result in increased blood viscosity and therefore reduced blood flow, impaired tissue oxygenation and a tendency to microthrombus formation exacerbated by hypoxia, acidosis and/or poor perfusion. Thrombosis may result in renal venous thrombosis, adrenal insufficiency, necrotising enterocolitis and cerebral infarction that may affect long-term neurological outcome.
Although most cases of polycythaemia occur in normal healthy infants, polycythaemia may result from
Many polycythaemic infants are asymptomatic. When present, the signs and symptoms of polycythaemia are non-specific and include
The diagnosis of polycythaemia is made on central or peripheral venous blood with a haematocrit over 65%. Because capillary blood haematocrit is not reliable, a peripheral venous haematocrit should be performed if the capillary haematocrit is above 65%. The haematocrit peaks at 2 hours of age, then falls by 6 hours of age and thereafter.
Volume of exchange (ml) = blood volume*(observed - desired haematocrit)/ observed haematocrit
*Term blood volume is 85 ml/kg
This is best performed through peripheral arterial and venous lines.
Treatment of polycythaemia with PET is controversial. Whilst it may improve symptoms, there is no evidence that it improves long-term outcome in either asymptomatic or symptomatic polycythaemic infants. Partial exchange transfusion may be associated with earlier improvement of symptoms. In spite of inconclusive evidence, some still advocate PET when the venous haematocrit is above 70% in asymptomatic infants. Necrotising enterocolitis is probably increased by partial exchange transfusion. Long term outcome is more likely related to the underlying cause of polycythemia.
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