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Fetal response to neutral gas and liquid media for intraamniotic distension
D O Fauza1, J Rawn, S J Fishman
1Harvard Center for Minimally Invasive Surgery, Department of Surgery, Children's Hospital and Harvard Medical School, Boston, MA, USA.
Purpose:
This study was aimed at comparing the effects of a neutral liquid and a neutral gas used as intraamniotic media on umbilical blood flow, O2 delivery, blood pressure, acid-base status, and electrolytes in the fetus at escalating intraamniotic pressures.
Methods:
Eight fetal lambs underwent invasive monitoring of common umbilical blood flow, blood pressure, blood gases, sodium, and hematocrit, as intraamniotic pressure was raised from 0 to 30 mm Hg. The animals were divided equally in two groups depending on the intraamniotic medium used (group I, warmed saline and group II, air). Maternal systemic blood pressure, O2 saturation, and temperature were kept constant.
Results:
In each group, a threshold level of intraamniotic pressure was evident, above which there was a significant decrease in the common umbilical artery blood flow, with concomitant fetal hypoxemia and hypercarbia. This intraamniotic pressure threshold was 20 mm Hg in group I (saline), but only 15 mm Hg in group II (air).
Conclusions:
Although both a neutral liquid and a neutral gas can safely be used as intraamniotic media, a neutral liquid medium allows for a wider range of safe intrauterine working pressure (0 to 20 mm Hg), as compared with a neutral gas (0-15 mm Hg).