Neonatal polycythemia: II. Plasma, blood and red cell volume estimates in relation to hematocrit levels and quality of intrauterine growth.

Volumes of plasma (PV), blood (BV), and red cells (RCV) were estimated within 32 hours of birth in 39 neonates with normal growth, 14 neonates with intrauterine growth retardation, and 20 neonates with macrosomia. Total PV, BV, and RCV increased linearly with birth weight and were unaffected by deviation in the quality of fetal growth. In proportion to body weight, PV/kg, BV/kg, and RCV/kg correlated neither with birth weight nor with the quality of intrauterine growth. Neonates with umbilical vein hematocrit (UV Hct) levels 51% to 60%, 61% to 65%, and 66% to 77% had progressively lower, but not statistically different, mean PV/kg (38.1 +/- 4.49, 37.6 +/- 5.41, and 34.8 +/- 5.16 ml/kg, respectively). On the other hand, they had progressively higher mean BV/kg (90 +/- 10.1 vs 101 +/- 13.7 ml/kg, P less than .002, and vs 110 +/- 19.0 ml/kg, P less than .001). They also had progressively higher mean RCV/kg (52 +/- 7.4, 64 +/- 8.7, and 75 +/- 16.4 ml/kg, P less than .001). Although PV/kg did not correlate with UV Hct, both BV/kg and RCV/kg increased linearly with increasing UV Hct (r = .58 and r = .79, respectively). Volume estimates were repeated after partial exchange transfusion in 29 neonates. Mean UV Hct decreased from 63 +/- 5.9% preexchange to 51 +/- 5.2% postexchange (P less than .001), mean PV increased from 37.7 +/- 5.56 to 47.6 +/- 7.99 ml/kg (P less than .001) and mean RCV decreased from 67 +/- 16.5 to 51 +/- 12.3 ml/kg (P less than .001). Despite precautions to keep the partial exchange isovolemic, mean BV decreased from 105 +/- 18.7 to 98 +/- 18.0 ml/kg (P = .001) and the mean PV increase (10 ml/kg) was less than the mean RCV decrease (16 ml/kg). These data suggest that neonates with polycythemic have normal PV but their RCV and BV are elevated in direct proportion to UV Hct. "Isovolemic" partial exchange transfusion decreases UV Hct, RCV, and BV and increases PV.