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

Abstract

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 ...

Heated humidified carbon dioxide for partial uterine insufflation in fetoscopic myelomeningocele repair: insights from animal model

“…To conclude, the work of Amberg and colleagues supports the use of heated and humidified, rather than cold and dry, CO 2 gas for uterine insufflation during fetoscopic MMC repair. This alternative approach is likely to mitigate the detrimental metabolic effects of using cold, dry gas, with reduced inflammation in the fetal membranes.…”

“…Amberg et al ,. in this issue of the Journal, present a well‐designed study performed on pregnant ewes with the objective of assessing whether using heated, humidified CO 2 for uterine insufflation would have less metabolic impact on the sheep fetuses, with reduced signs of inflammation in the fetal membranes.…”

“…This could occur due to mechanisms like those involved in peritoneal damage seen after laparoscopic surgery using CO 2 gas under similar conditions. Such inflammatory changes could predispose to a higher risk for preterm prelabor rupture of membranes (PPROM); indeed, although not assessed by Amberg et al ,. this risk is known to be increased in cases undergoing fetoscopic MMC repair using cold, dry CO 2 gas (100% PPROM rate, with mean ± SD gestational age (GA) at PPROM of 30.2 ± 2.7 weeks; and 84.3% PPROM, with GA at PPROM of 29.7 ± 3.1 weeks) when compared with those receiving heated, humidified gas (23% PPROM, with median (interquartile range) GA at PPROM of 34 (30.1–35.9) weeks), despite the prolonged duration of surgery in the latter group.…”

“…An important limitation of Amberg et al . 's study is the paucity of data regarding the pathological examination of the membranes. For example, it would have been informative to examine the apoptosis count in both groups.…”

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“…Recent work demonstrated that this can be mitigated by maternal hyperventilation, along with heating and humidifying the gas. 40,41 Dry CO 2 also has an effect on the fetal membranes but, based on biomechanical studies published this year, heating and humidifying the gas may also reduce the risk for membrane rupture. 42,43 While the debate continues over whether or not minimally invasive surgery is equally neuroprotective as open surgery and which surgical techniques have the least prematurity risk, [44][45][46] it is worth considering the experience required to complete the learning curve for prenatal spina bifida repair.…”