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Objective: Our purpose was to evaluate in a sheep model for endoscopic fetal surgery the impact of nitrous oxide-gas amniodistention compared with fluid amniodistention on duration of surgery, hemorrhagic events, and fetomaternal acid-base status., Study Design: Pregnant ewes (n = 16) at 92 to 104 days of gestation (term, 145 days) underwent amniodistention with Hartmann's solution (group I, n = 8) or nitrous oxide (group II, n = 8) at 38 degrees C. Endoscopic tracheal clipping according to a standardized surgical protocol was performed in all animals. The duration of fetoscopy (from insertion of first cannula until removal of last one), fetal surgery (fetal skin incision to skin closure), and number of bleeding episodes was recorded. Maternal and fetal blood gas values (pH, PO2, and PCO2) were measured at baseline and every 15 minutes during the experiment. Videotapes of the operations were assessed independently and scored by a visual analog scale in terms of smoothness of the operation and control of hemorrhagic events., Results: Mean duration of fetoscopy (+/-SEM) (68 +/- 16 minutes vs 92 +/- 23 minutes) and fetal surgery (19 +/- 6 minutes vs 42 +/- 18 minutes) as well as number of bleeding episodes (1.9 +/- 0.8 minutes vs 5.8 +/- 2.1 minutes) was significantly reduced in animals operated with use of nitrous oxide amniodistention. In both groups, fetal and maternal blood gases remained unchanged during the entire experiment. Visual analog scale (VAS) scores were significantly higher for procedures conducted with use of gas distention., Conclusion: In a lamb model for fetal surgery, gas amniodistention with use of nitrous oxide results in a quicker operation procedure with less bleeding compared with fluid amniodistention, and without adverse side effects on fetomaternal acid-base status.

Background: Because the data from previous experiments on the fetal effects of carbon dioxide (CO2) amniodistention in endoscopic fetal surgery are conflicting, we set out to evaluate the fetal acid-base status during CO2 amniodistention, with or without maternal hyperventilation, using a sheep model for endoscopic surgery., Methods: We assigned 26 pregnant ewes undergoing amniodistention with CO2 (4-5 mmHg intraamniotic pressure) to one of the following three groups: group I had fetal surgery + no maternal hyperventilation (n = 10); group II had fetal surgery + maternal hyperventilation (n = 10); group III had no fetal surgery + maternal hyperventilation (n = 6). Hyperventilation kept CO2 at 29-31 mmHg; in its absence, pCO2 ranged from 38 to 41. Fetal surgery consisted of fetoscopic tracheal clipping. Maternal blood pressure (mean, 98/69 mmHg) and heart rate (mean, 72 bpm) were kept at values comparable to human pregnancy. Fetal and maternal blood gas measurements were taken every 15 min during 1 h of amniodistention., Results: The ranges for baseline mean fetal pCO2 (mmHg) and pH were 51-55 and 7.24-7.25, respectively, in all study groups. After 1 h of amniodistention, mean +/- SEM values of fetal pCO2 and pH were 88 +/- 3 and 7.06 +/- 0.03 in group I, 69 +/- 4 and 7.13 +/- 0.02 in group II, and 71 +/- 5 and 7.14 +/- 0.04 in group III, respectively. Therefore, maternal hyperventilation attenuated but could not prevent significant fetal hypercarbia and acidosis. Fetal surgical manipulation had no effect on these observations., Conclusion: CO2 amniodistention should not be considered for clinical practice until ways of preventing its effects on the fetal acid-base status can be demonstrated.