First, and most importantly, metabolic abnormalities should be corrected, including hypoglycemia and hypocalcemia, and other less common derangements, if present. The choice of which patients must be treated remains somewhat controversial, but significant agreement exists in several areas.

1. If a baby has symptoms that could be related to polycythemia/hyperviscosity, and the peripheral venous hematocrit exceeds 65%, a partial exchange transfusion should be performed. As noted in earlier questions, the timing, site, and method of determination all affect the hematocrit, and partial exchange transfusion may not in fact be indicated if there are untreated causes of a late hematocrit elevation. For example, a newborn might have an initial hematocrit of 60%, which rises to 66% after 36 hours of poor breastfeeding. At the time of hematocrit determination, the baby is noted to be mildly hypoglycemic. Are both factors related to dehydration, which can be more rapidly and more appropriately corrected with hydration? If so, this is the better choice of therapy.
2. If a baby whose hematocrit (peripheral venous) is between 60 and 70% is without symptoms, they are usually managed by maintaining adequate hydration and repeating the hematocrit 4 to 6 hours later. Overhydration or excessive volume infusion does not make sense, if the baby is normally hydrated.
3. If the hematocrit exceeds 70%, even if there are no symptoms, a partial volume plasma exchange transfusion is usually indicated. Some reports (1,2) suggest little or no significant benefit to the procedure. Little data exists examining the impact of the procedure in these infants with an extremely high hematocrit, where the risk of excessive viscosity is almost certain. Thus, a policy of treating asymptomatic infants in this apparently high-risk group makes good sense.

How is partial exchange transfusion performed?

The procedure is usually accomplished using a "low" umbilical venous catheter, placed to the point of blood return, which should place the tip at about the level of the ductus venosus. Using this catheter, the procedure can usually be accomplished as a single line "push-pull" technique. If this method is not possible, two peripheral venous catheters can be used instead. In either case, the goal is to reduce the peripheral hematocrit to 50-55%, by exchanging a volume of blood with saline. Use of adult plasma offers no benefit, and may worsen viscosity (3). The volume, VE, for exchange (ml) is:

VE= Blood Volume * ((Observed Hct - Desired Hct)/Observed Hct).

where

Blood Volume = Weight (kg) * 80-100 ml

The blood volume of most term infants is 80-100 ml/kg, but it may be increased in polycythemic infants (4). Thus, the above formula will only provide an approximate volume for exchange transfusion, as the blood volume is estimated. In practice, the calculated volume will be about 20 ml/kg, but a hematocrit should be determined about an hour after the end of the procedure to ascertain success.

What are the risks of partial exchange transfusion?

The risks to the procedure include those associated with placing and maintaining an umbilical venous catheter, including the risk of thrombosis, embolism, or disruption of the vessel. The short-term benefits of the procedure include amelioration of metabolic, cardiovascular, and renal abnormalities, and improvement in acute and minor neurologic symptoms. As discussed in previous questions, the benefit in terms of improvement in long term neurologic function is uncertain at best.