Effects of amniodistention with carbon dioxide on fetal acid-base status during fetoscopic surgery in a sheep model

Background: Because the data from previous experiments on the fetal effects of carbon dioxide (CO2) amniodistention in endoscopic fetal surgery are co nflicting, we set out to evaluate the fetal acid-base status during CO2 amn iodistention. with or without maternal hyperventilation. using a sheep mode l 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: grou p I had fetal surgery + no maternal hyperventilation (n = 10); group II had fetal surgery + maternal hyperventilation (n = 10); group IU. had no fetal surgery + maternal hyperventilation (n = 6), Hyperventilation kept CO2 at 29-31 mmHg: in its absence, pCO(2) ranged from 38 to 41. Fetal surgery cons isted of fetoscopic tracheal clipping. Maternal blood pressure (mean, 98/69 mmHg) and heart rate (mean, 72. br,m) were kept at values comparable to hu man pregnancy:. Fetal and maternal blood as measurements were taken every 1 5 min during 1 h of amniodistention. Results: The ranges for baseline mean fetal pCO(2) (mmHg) and pH were 51-55 and 7.24-7.25, respectively, in all study groups. After 1 h of amniodisten tion, mean + SEM values of fetal pCO(2) and pH were 88 +/- 3 and 7.06 +/- 0 .03 in group I, 69 +/- 4 and 7.13 +/- 0.02 in group Il, and 71 +/- 5 and 7. 14 +/- 0.04 in group III, respectively. Therefore, maternal hyperventilatio n attenuated but could not prevent significant fetal hypercarbia and acidos is. Fetal surgical manipulation had no effect on these observations. Conclusion: CO2 amniodistention should not be considered for clinical pract ice until wars of preventing,g its effects on the fetal acid-base status ca n be demonstrated.