Physiological effects of partial amniotic carbon dioxide insufflation with cold, dry vs heated, humidified gas in a sheep model

OBJECTIVE: Partial amniotic carbon dioxide (CO(2)) insufflation (PACI) is used to improve visualization and facilitate complex fetoscopic surgery. However, there are concerns about fetal hypercapnic acidosis and postoperative fetal membrane inflammation. We assessed whether using heated and humidified, rather than cold and dry, CO(2) might reduce the impact of PACI on the fetus and fetal membranes in sheep. METHODS: Twelve fetal lambs of 105 days' gestational age (term = 145 days) were exteriorized partially, via a midline laparotomy and hysterotomy, and arterial catheters and flow probes were inserted surgically. The 10 surviving fetuses were returned to the uterus, which was then closed and insufflated with cold, dry (22 °C at 0–5% humidity, n = 5) or heated, humidified (40 °C at 100% humidity, n = 5) CO(2) at 15 mmHg for 180 min. Fetal membranes were collected immediately after insufflation for histological analysis. Physiological data and membrane leukocyte counts, suggestive of membrane inflammation, were compared between the two groups. RESULTS: After 180 min of insufflation, fetal survival was 0% in the group which underwent PACI with cold, dry CO(2), and 60% (n = 3) in the group which received heated, humidified gas. While all insufflated fetuses became progressively hypercapnic (PaCO(2) > 68 mmHg), this was considerably less pronounced in those in which heated, humidified gas was used: after 120 min of insufflation, compared with those receiving cold, dry gas (n = 3), fetuses undergoing heated, humidified PACI (n = 5) had lower arterial partial pressure of CO(2) (mean ± standard error of the mean, 82.7 ± 9.1 mmHg for heated, humidified CO(2) vs 170.5 ± 28.5 for cold, dry CO(2) during PACI, P < 0.01), lower lactate levels (1.4 ± 0.4 vs 8.5 ± 0.9 mmol/L, P < 0.01) and higher pH (pH, 7.10 ± 0.04 vs 6.75 ± 0.04, P < 0.01). There was also a non‐significant trend for fetal carotid artery pressure to be higher following PACI with heated, humidified compared with cold, dry CO(2) (30.5 ± 1.3 vs 8.7 ± 5.5 mmHg, P = 0.22). Additionally, the median (interquartile range) number of leukocytes in the chorion was significantly lower in the group undergoing PACI with heated, humidified CO(2) compared with the group receiving cold, dry CO(2) (0.7 × 10(–5) (0.5 × 10(–5)) vs 3.2 × 10(–5) (1.8 × 10(–5)) cells per square micron, P = 0.02). CONCLUSIONS: PACI with cold, dry CO(2) causes hypercapnia, acidosis, hypotension and fetal membrane inflammation in fetal sheep, raising potential concerns for its use in humans. It seems that using heated, humidified CO(2) for insufflation partially mitigates these effects and this may be a suitable alternative for reducing the risk of fetal acid–base disturbances during, and fetal membrane inflammation following, complex fetoscopic surgery. © 2018 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of the International Society of Ultrasound in Obstetrics and Gynecology.