Amniotic fluid exchange

Technical Aspects. Amniotic fluid exchange

The amniotic cavity may be turbid, particularly with advancing gestational age. Visualization may be further hindered by bloody discoloration from previous procedures such as amniocenteses or cordocenteses, from intraoperative intraamniotic bleeding, or from excessive vernix. 

Light transmission in these settings can be significantly compromised. To overcome this problem, we have developed techniques to exchange the amniotic fluid with Ringer’s lactate or 0.9 saline solution. One technique uses a custom-designed suction– irrigation probe or ‘trumpet’ (Figure 9.2) that is inserted through the trocar under ultrasound guidance and directed to a pocket of amniotic fluid. 

Fluid is retrieved in amounts of 300–500 ml at a time, and substituted with physiological solution. The quality of the remaining fluid can be assessed through the clear suction tubing. Amniotic fluid exchange can also be performed simultaneously by infusion of fluid through the trumpet and suctioning through the shaft of the trocar via a side-port. 

A third technique uses infusion of fluid through the operating channel of the endoscope and suctioning through the trocar (Figure 9.3a,b). Once the fluid has become clear, the endoscopic procedure can continue. These amniotic fluid exchange systems can clear the amniotic fluid at a maximum rate of 2250 ml/min without altering the total amniotic fluid volume. 

Despite the speed, up to 45 minutes may be required to clear a bloody discolored amniotic fluid cavity from previous invasive procedures, or from intraoperative bleeding. Precise knowledge of the amount of fluid infused or drained can be obtained with the use of special infusion pumps. 

We currently use the arthroscopic pump made by Davol (Davol, Cranston, RI) (Figure 9.4a,b). This pump has a digital display of the fluid balance, which the surgeon can readily see. The calculation of the balance is based on the weight of the fluid on the stand of the pump. Inaccurate estimates may occur due to fluid leakage through the trocar. Fluid infusion is also based on the sonographic appearance of the amniotic cavity, which provides an overall sense of the amount of fluid present.