Colloid osmotic pressure of normal newborns and premature infants.

Colloid osmotic pressure (COP) is an important regulator of fluid movement and can now be measured simply and reliably. The authors used the 4100 Wescor Colloid Osmometer to define COP values and its relation to total protein concentration (TP) in different groups of newborns. The mean COP was 19.4 +/- 2.2 (SD) torr in 99 term infants delivered vaginally and 16.0 +/- 2.1 in 40 term infants delivered by cesarean section (p less than 0.005). The COP was lower in those born operatively without preceding labor (14.9 +/- 1.8). COP correlated well with TP (r = 0.92) in term infants. In 60 sick preterm infants with 362 determinations, COP (12.5 +/- 2.5) was different from term infants (p less than 0.001) and the correlation with TP was poor (r = 0.64). Different therapeutic modalities were found to affect COP widely. Crystalloid infusion decreased COP by 22% and surgery by 32%. The authors conclude that COP varies not only with gestational age but also with mode of delivery and experience of labor. In critically ill preterm neonates, because estimations form TP are inadequate, the only way to obtain a quantitative measure of COP is by direct measurement. Repeated measurements of COP will permit precise selection of the fluids and will warn of changes that may lead to pulmonary edema.