Reducing the deleterious effects of intrauterine CO₂ during fetoscopic surgery

The fetoscopic approach to fetal intervention is a promising minimally invasive technique for correcting congenital anomalies in utero. However, expansion of the amniotic cavity with CO₂ to visualize the fetus causes fetal hypercarbia and acidosis. We assessed whether maternal hyperventilation during intrauterine CO₂ insufflation could attenuate the fetal hypercarbic acidosis. Seven fetal lambs of 105 ± 2 days (mean ± SEM) gestation (term = 145 days) were instrumented with a carotid arterial catheter in utero. After 7 ± 1 days of recovery, fetoscopic exposure was obtained with intrauterine insufflation of CO₂ at 10 mmHg of intraamniotic pressure. After 30 min, the ewe was hyperventilated at a mean respiratory rate of 23/min for 30 min under continuous insufflation. The uterus was then deflated and following 1 hr of stabilization, and the same protocol of CO₂ pneumometrium was repeated. Fetal and maternal arterial blood was sampled at baseline and at 15 min intervals. Fetal PaCO₂ increased during 30 min of CO₂ insufflation (50.8 ± 2.8 vs. 72.3 ± 5.0 mmHg, P < 0.01); however, this change was reversed (to 51.5 ± 3.0 mmHg, P < 0.01) by 30 min of maternal hyperventilation. The fetus developed acidosis after 30 min of CO₂ pneumometrium (pH 7.350 ± 0.012 vs. 7.236 ± 0.026, P < 0.01); this was also reversed (to 7.366 ± 0.019, P < 0.01) by maternal hyperventilation. These results were reproducible during the second CO₂ insufflation challenge. Fetal hypercarbic acidosis during fetoscopy with CO₂ insufflation is reduced by maternal hyperventilation.