Nitrous oxide amniodistention compared with fluid amniodistention reduces operation time while inducing no changes in fetal acid-base status in a sheep model for endoscopic fetal surgery

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 Hartmannʹs solution (group I, N = 8) or nitrous oxide (group II, N = 8) at 38°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, P 2, and P 2) 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. (Am J Obstet Gynecol 2002;186:538-43.)