Maternal and fetal colloid osmotic pressure following fluid expansion during cesarean section

Objectives: To characterize the changes in colloid osmotic pressure during delivery and to determine the relationship between maternal and fetal colloid osmotic pressures. Design: Clinical, prospective study. Setting: Obstetrical operating theater in a tertiary care university hospital. Patients: Thirty healthy parturient patients, at term gestation receiving spinal anesthesia for elective cesarean section. Interventions: None. Measurements and Main Results: Maternal colloid osmotic pressure samples were obtained at the time of intravenous insertion and delivery. Fetal umbilical vein and umbilical artery colloid osmotic pressure samples were measured from the umbilical cord at delivery. The volume of intravenous infusion and dose of ephedrine were recorded for each patient. Maternal colloid osmotic pressure at delivery was significantly less than that value measured at the time of intravenous catheter insertion in each patient (15.8 ± 0.3 vs. 23.1 ± 0.3 mm Hg; p < .0001). Umbilical artery colloid osmotic pressure was consistently higher than umbilical vein colloid osmotic pressure (21.0 ± 0.4 vs. 19.4 ± 0.3 mm Hg; p < .0001). Both umbilical artery colloid osmotic pressure and umbilical vein colloid osmotic pressure were significantly higher than maternal colloid osmotic pressure at delivery (p < .0001). The volume of intravenous infusion and the dose of ephedrine both correlated inversely with maternal colloid osmotic pressure measured at delivery (p < .05). Conclusions: The reduction in maternal colloid osmotic pressure during delivery is, in part, related to intravenous fluid expansion and the amount of vasopressor administered. Despite the significant fluctuations in maternal colloid osmotic pressure, the placenta and fetus possess the capability to alter colloid osmotic pressure.