Placental Gas Exchange During Amniotic Carbon Dioxide Insufflation in Sheep

Ben Amberg, Philip L.J. DeKoninck, Aidan Kashyap, Sasha Skinner, Karyn Rodgers, Erin Victoria McGillick, Jan A.M. Deprest, Stuart Brian Hooper, Kelly Crossley, Ryan Hodges

Research output: Contribution to journalArticleResearchpeer-review

Abstract

OBJECTIVES: Insufflation of the amniotic cavity with carbon dioxide (CO2 ) is used clinically to improve visibility during complex fetoscopic surgery. Insufflation with heated, humidified CO2 has recently been shown to reduce fetal hypercapnia and acidosis in sheep, but the underlying mechanisms are unclear. We have investigated whether differences in placental CO2 and oxygen (O2 ) exchange could explain these findings.

METHODS: Fetal lambs at 105days gestation (term 146days) were instrumented with an umbilical artery and vein catheter and common umbilical vein flow probe. Arterial and venous catheters and flow probes were also inserted into the maternal uterine circulation. Six ewes were insufflated with cold, dry CO2 (22o C, 0-5% humidity) and seven with heated, humidified CO2 (40o C, 95-100% humidity) at 15mmHg for 180 minutes. Blood flow recordings and paired arterial and venous blood gasses were sampled from uterine and umbilical vessels. Rates of placental CO2 and O2 exchange were calculated. Data are presented as mean±SEM.

RESULTS: After 180 minutes of insufflation fetal survival was 33% (2/6) using cold, dry CO2 and 71% (5/7) using heated, humidified CO2 . By 120 minutes, fetuses insufflated with heated, humidified CO2 had lower arterial CO2 levels and higher pH compared to those insufflated with cold, dry gas. Insufflation significantly decreased placental gas exchange in both groups as measured by rates of both (i) fetal CO2 clearance and O2 uptake and (ii) maternal O2 delivery and CO2 uptake from the fetal compartment.

CONCLUSIONS: Lower arterial CO2 and higher pH levels in fetuses insufflated with heated, humidified, compared to cold, dry CO2 , could not be explained by differences in placental gas exchange. Instead, heated humidified insufflation appeared to reduce fetal CO2 absorption from the uterus supporting its use in preference to cold, dry CO2 .
Original languageEnglish
Number of pages28
JournalUltrasound in Obstetrics and Gynecology
DOIs
Publication statusAccepted/In press - 25 Nov 2019

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