The working environment: fluid or gas

Technical Aspects. The working environment: fluid or gas

Ideally, surgery within the amniotic cavity would be performed under a gas environment, as in standard laparoscopy. Indeed, visualization within gas is superior to that within fluid, both in terms of light transmission as well as in the angle of view which is reduced by 30% in water. 

Working within gas would also be advantageous should bleeding in the amniotic cavity occur. Work within gas would also allow the use of electrosurgery, CO2 laser and other standard surgical techniques. Carbon dioxide is the most widely used gas in laparoscopy because it does not support combustion and dissolves readily in the patient’s blood. 

However, the use of CO2 in the pregnant ewe results in fetal acidosis after 30 minutes.6 Presumably, fetuses are unable to clear the CO2 into the maternal circulation fast enough to avoid lowering of their pH. It is not known whether a similar complication would occur in humans given the differences in placentation. Pelletier et al tested Xenon and CO2 in sheep, and did not show development of fetal acidosis with the former.7 In our lab, nitrous oxide did not result in fetal acidosis (unpublished). However, nitrous oxide allows combustion, which is obviously not desirable. 

Therefore, only CO2 is a viable candidate for gas medium during fetoscopy. Unfortunately, gas within the amniotic cavity interferes with ultrasound imaging. This limitation could be overcome if adequate endoscopic visualization allowed dispensing the use of ultrasound for a short period of time. However, gas instillation may limit adequate monitoring of the fetus and of the procedure. Furthermore, gas may dissect the membranes from the uterine wall, resulting in collapse of the amniotic cavity. 

Lastly, evacuation of the gas from the amniotic cavity may be difficult, and small bubbles may persist at the level of the anterior uterine wall, hampering ultrasound visualization with ultrasound. Despite the above, we have found a very limited application of working within a gas environment in TTTS, specifically, in patients with an anterior placenta and turbid amniotic fluid from prior or intraoperative bleeding. 

In these cases, a small bubble of air can be used to identify vascular anastomoses otherwise not visible through the turbid fluid. The bubble can be placed beneath the anastomoses with lateral tilting of the operating table. The endoscope is then placed in the gas/water interface and the vessels lasered within the gas bubble (Figure 9.1). This small surgical tip may allow completion of an otherwise very difficult surgery.