EFFECTS OF INTRAAMNIOTIC HELIUM, CARBON-DIOXIDE, AND WATER ON FETAL LAMBS

The hysteroscopic approach to the correction of congenital anomalies i n utero may be helped by the temporary introduction of clear, electric ally neutral fluids (liquids or gases) into the amniotic cavity. Accor dingly, the authors determined the effects of three candidate fluids ( helium, carbon dioxide, and water) on the oxygenation, acid-base balan ce, electrolyte concentrations, and hemodynamic function of nine sheep fetuses at 120 days' gestation (full term 145 days). Each fetus was e xposed, in random order, to each of the three fluids, at an intraamnio tic pressure of 15 mm Hg. The authors found that helium produced no ch anges in any of the measurements and was well tolerated by the fetus a nd the mother. Carbon dioxide decreased fetal arterial pH, and increas ed both arterial PCO2 and PO2 Although the decrease in pH was explaine d entirely by the increase in PCO2, the increase in arterial PO2 may h ave resulted from vasodilatation of the placental circulation or vasoc onstriction of the fetal circulation with a redistribution of blood fl ow to the placenta. Water caused mild fetal hyponatremia and hypochlor emia, without significant changes in acid base balance or oxygenation. The results suggest that both helium and water may represent viable a lternatives for amniotic fluid replace ment during hysteroscopic surge ry. Copyright (C) 1995 by W.B. Saunders Company