FETAL RESPONSE TO CARBON-DIOXIDE PNEUMOPERITONEUM IN THE PREGNANT EWE

Objective: To determine the effects of maternal abdominal carbon dioxide (CO2 insufflation on placental blood now and fetal blood gas measurements in the pregnant ewe. Method: Five time-bred ewes at 110 days' gestation were surgically prepared with maternal and fetal catheters placed for subsequent measurement of vascular pressures, blood gas tensions, and placental blood flows. On surgical recovery day 3, the ewe was anesthetized, placed on her right side, intubated, and manually ventilated to maintain a constant maternal carbon dioxide pressure (PCO2) range (37.1 +/- 3.3 mmHg) for the duration of the experiment. The maternal abdomen was inflated with CO2 to maintain an intraabdominal pressure of 20.7 +/- 0.6 mmHg. Maternal and fetal blood flows and blood gases were determined at 30 minutes of ventilation, 60 minutes of insufflation, and 40 minutes of desufflation. Simultaneous maternal and fetal organ blood flows were determined using the radioactive microsphere technique. Results: Maternal perfusion pressure fell 22% (P = .01) in response to insufflation, whereas pressure in the inferior vena cava rose 53% (P = .003). Maternal placental blood now fell to 61% (P = .002) of control. Seventy-seven percent of this blood-flow change was in response to the decreased perfusion pressure, with 23% resulting from an increased placental vascular resistance of 32% (P = .02). Maternal blood gas values did not change with insufflation or desufflation. Despite the marked decrease in maternal placental blood now, the fetal placental perfusion pressure and blood flow, pH, and blood gas tensions were unaffected by insufflation or desufflation. Conclusion: The sheep fetus has sufficient placental flow reserves or compensatory responses to maintain adequate gas exchange during a 1-hour, 20 mmHg maternal pneumoperitoneum. Laparoscopic surgical procedures may prove to safe alternative to laparotomy during pregnancy.