The overall goal of this surgical training model is to allow novice surgeons to familiarize themselves with the techniques used in selective fetoscopic laser photocoagulation in twin-twin transfusion syndrome, and to refine these techniques prior to surgery in patients. These training models are designed to help fetal surgeons refine their skills in fetoscopic ablation of the communicating vessels which cause twin-twin transfusion syndrome. The main advantage of this process is that the entire procedure can be learned before approaching the patient, which helps to overcome the procedural learning curve when a low case load is a significant limitation.
So individuals new to this method will be challenged by the dual use of ultrasound and fetoscope understanding the placenta orientation and navigating the vascular equator. The visual demonstration of these steps is critical as it emphasizes the importance of pre-surgical planning and allows for a better understanding of the surgical process. Begin with setting up the fetoscopy simulator and equipment.
First, take note of the 2.0 millimeter fibro straight fetoscope design. There is the lens, which is zero or 30 degrees and has a standard or remote eye cap. Next, it has a three millimeter double lumen operating chief and a sharp obturator tip that gets directly inserted into the amniotic cavity under ultrsound guidance.
For operation, remove the obturator and place the fetocope into an operating sheath which makes it semi-flexible and able to curve around to the interior placenta. Then connect the eye cap to the laparoscope camera. Next, position the laparoscope tower and ultrasound machine near each other so that the ultrasound probe can be manipulated while operating the fetoscope.
Next, through one of the one way valve ports, fill the fetoscopy simulator to the brim with water. Then, position the simulator on the plastic base as needed. The upper surface of the simulator represents the interior maternal abdomen.
Now, use the curvilinear ultrasound probe with aqueous gel to visualize the placenta within the fetoscopy simulator. Identify the placenta location and a window adjacent to it in which to place the fetoscope. Next, select the 0 degrees straight fetoscope for a posterior placenta or the 0 degree curved fetoscope for an anterior placenta.
Then, under continuous ultrasound guidance, insert the fetoscope in the operating sheath through the port. Monitor the insertion and depth of the fetoscope by ultrasound and bring the placenta in to view. Adjust the focus of the camera to bring the vision into sharper leaf.
Then, systematically explore the vasculature from one end to the other to identify the typical AVA's for ablation. Such anastomosis will be seen runnning along the chorionic surface. The artery is darker and always runs over the vein.
Now, reorientate the simulator for a view of the placenta in the opposite orientation and repeat the procedure. For this placenta in a box model, use a standard store bought plastic container that can be locked water tight. Cut out a wide window of the plastic cover and replace it with ultrasound transparent rubber skin stitched to the margins of the cover.
This skin forms the interior surface of the simulated maternal abdomen through which the fetoscope is placed. Next, mount a rubber latex sheet along the bottom of the box to prevent sonographic reverberation. At the maternity ward, wash the surface of the donated human placenta with tap water in the sink.
Clean all of the blood off of the surface. Then, cut the umbilical cord using strong tissue scissors to a manageable length of about five centimeters. Next, tie the free end of the umbilical cord using suture band or cotton cord tape to prevent blood from running out of the cut end.
At the laboratory, to simulate an interior placenta fix the placenta to the refashioned lid of the container with clear plastic thread or a plastic net. To simulate a posterior placenta, hold it in place with a plastic net or small weights. Fix the placenta to the rubber sheet at the bottom of the container after installing either configuration, fill the container with tap water and lock the lid in place.
Next, prepare the appropriate fetoscope and it's operating sheath with a working channel. Then, connect the eye cap to the camera. Now, perform an ultrasound assessment of the placenta.
For an anterior placenta, find a window into which the fetoscope can be placed such that the lens lies above the center of the placenta. For a posterior placenta, find a window for the fetoscope where the zero degree lens will be perpendicular to the center of the placenta. Now perform direct fetoscopy starting with a two millimeter stab incision into the skin.
Then, under continuous ultrasound guidance, insert the operating trocar with its pyramidal obturator into the fluid filled container which replicates the amniotic sac of the recipient twin. To avoid piercing the placenta, advance the fetoscope slowly. Then, slowly remove the pyramidal obturator from the operating trocar.
Next, carefully place the lens of the fetoscope into the operating trocar in the channel previously occupied by the obturator. Then, bring the placenta and surface vasculature into sharp focus. Now, insert the laser fiber into the operating side channel.
Advance the fiber slowly as the tip nears the end of the sheath, ultimately positioning it five to ten millimeters beyond the operating sheath. If the laser tip advances too far, it may lacerate the vessel. If it doesn't advance far enough, the coagulation effect may be comprimised.
The laser fiber tip should be two to three millimeters from the surface of the vessel and should not touch the vessel when the laser is fired. Now, identify the umbilical cord and placental vessels. Review the placental vaculature from end to end using a combination of ultrasound and direct fetoscopic vision.
The fetoscope should be directed at a 90 degree angle to the target vessel. When it is perpendicular to the vessel or anastomosis use the foot pedal to fire the laser to coagulate the vessel or anastomosis. Continue coagulating the vessel until in blanches and expect to do this across a one to two centimeter segment for a complete cessation of flow.
Afterwards, the vessel should appear flattened and pale. Systematically practice coagulation of vessels from one placental end to the other. Laser coagulate the thick vessels from the periphery towards the center to prevent rupture.
A thick turgid vessel can be narrowed down safely in this manner. Also, practice laser coagulating the smaller feeding vessels first before the larger ones to decongest the region and mitigate the chances of a vascular rupture. The basic requirements for a fetoscopy simulator are a transparent skin that enables ultrasound visualization of the placenta within the model and a representative model of the MCDA placenta.
Use of this model will familiarize novice surgeons with placental orientation, fetoscope placement and handling of straight and curved fetoscopes. Surgeons should gain ample practice in examining vessels along the full length of the placenta and performing laser coagulations. Complete coagulation is evident through the absence of deep anastomosis.
Furthermore, surgeons will become familiar with the common pitfalls such as rapid vascular bleeding and ruptured vessels. After watching this video, you should have a good understanding of placenta orientation on ultrasound and fetoscopic view, how to manipulate the fetoscope correctly to navigate the vascular equator and the safe laser ablation technique. Once mastered, this technique can be done in 40 to 60 minutes, if performed properly.
While attempting this procedure, it's important to remember that there is only one instrument and one entry point. There is rarely a chance to correct mistakes and incorrect fetoscopy placement can make it impossible to safely complete laser ablation. To conclude, carefully plan the surgical approach by mapping the placenta on ultrasound and choosing the right entry site.
These are the most critical steps to practice on the relevant models before approaching the patient.
