Body water estimates in neonatal polycythemia.

To determine whether neonatal polycythemia and its treatment by partial exchange transfusion affect body water estimates, 10 normocythemic and eight polycythemic neonates were studied within 12 hours of birth. Total body water, extracellular water, and plasma volume were estimated immediately prior to and following exchange. Intracellular and interstitial water contents were calculated. There were no significant differences between normocythemic and preexchange polycythemic neonates in mean total body water, extracellular water, interstitial water, and intracellular water contents. In the polycythemic group, exchange did not affect mean total body water, but was associated with decreases in mean extracellular water and mean interstitial water and an increase in mean intracellular water. Mean transcapillary escape rate of T-1824 was not affected by exchange but was quite rapid both before (35 +/- SE 3%/hr) and after the procedure (30 +/- 4.9%/hr). These data suggest that moderate polycythemia in normal term neonates does not affect total and extravascular body water estimates, but that a fluid shift from the extracellular to the intracellular space may accompany the exchange procedure.