Physiological effects of cold-dry versus heated-humidified partial amniotic carbon dioxide insufflation in sheep.

Objective Partial amniotic carbon dioxide (CO2) 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, CO2 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 degrees C at 0-5% humidity, n = 5) or heated, humidified (40 degrees C at 100% humidity, n = 5) CO2 at 15mmHg 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 CO2, and 60% (n = 3) in the group which received heated, humidified gas. While all insufflated fetuses became progressively hypercapnic (PaCO2 > 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 CO2 (mean +/- standard error of the mean, 82.7 +/- 9.1mmHg for heated, humidified CO2 vs 170.5 +/- 28.5 for cold, dry CO2 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 CO2 (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 CO2 compared with the group receiving cold, dry CO2 (0.7x10(-5) (0.5x10(-5)) vs 3.2x10(-5) (1.8x10(-5)) cells per square micron, P = 0.02). Conclusions PACI with cold, dry CO2 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 CO2 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. (c) 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.