Model Surgical Training: Skills Acquisition in Fetoscopic Laser Photocoagulation of Monochorionic Diamniotic Twin Placenta Using Realistic Simulators

Summary

Practicing the specific skills required for fetoscopic laser coagulation of monochorionic placental anastomoses on realistic models can aid less experienced surgeons in overcoming the steep learning curve associated with this procedure that is now regarded as the standard of care for twin-twin transfusion syndrome.

Abstract

Fetoscopic laser coagulation of arterio-venous anastomoses (AVA) in a monochorionic placenta is the standard of care for twin-twin transfusion syndrome (TTTS), but is technically challenging and can lead to significant complications. Acquiring and maintaining the necessary surgical skills require consistent practice, a critical caseload, and time. Training on realistic surgical simulators can potentially shorten this steep learning curve and enables several proceduralists to acquire procedure-specific skills simultaneously. Here we describe realistic simulators designed to allow the user familiarity with the equipment and specific steps required in the surgical treatment of TTTS, including fetoscopic handling, approaches to anterior and posterior placenta, recognition of anastomoses, and efficient coagulation of vessels. We describe the skills that are especially important in conducting placental laser coagulation that the surgeon can practice on the model and apply in a clinical case. These models can be adapted easily depending on the availability of materials and require standard fetoscopy equipment. Such training systems are complementary to traditional surgical apprenticeships and can be useful aids for fetal medicine units that provide this clinical service.

Introduction

The acquisition of a new, minimally-invasive surgical technique often employs the traditional surgical apprenticeship model in which an individual learns from observing an expert surgeon operate on a live patient and eventually performs the technique under close supervision¹. This time-honored model often limits the passage of knowledge from mentor to individual trainee and relies heavily on the availability of resources such as training funds and patient case-load². Fetoscopic surgery is an example of a high-risk minimally-invasive surgery, performed on a preterm individual during pregnancy in which there are risks to both the mother and fetus. As with any surgical procedure, higher complication rates arise at the initial steep slope of the learning curve. Thus, surgeries are usually performed by the most senior or skilled surgeon in order to meet the critical volume of cases to optimize patient outcomes³.

Good fetoscopy skills are important for the future of fetal therapy, which strives to be minimally invasive, even with respect to the correction of structural defects^4,5,6. Fetoscopic surgery is technically challenging and there are inherent risks to patient safety associated with practicing and developing new skills in the real-life theater environment. Even established surgeons require time and consistent practice on multiple patients to acquire expertise, skills in troubleshooting when difficulties arise, and the instinct to predict and avoid pitfalls in a new and complex procedure. There is less tolerance for suboptimal outcomes usually associated with novice proceduralists⁷. While it is important not to compromise patient safety during the initial implementation of fetoscopic surgery, there is also a need to enhance the efficiency with which skills and expertise are acquired by all proceduralists, particularly in smaller clinical units just beginning to practice fetoscopy. An alternative system complementary to traditional apprenticeship is needed to meet the challenges of limited training funds and a small patient base on which to master these highly specialized procedures. Procedural learning curves can be shortened, and complications reduced by training on high-fidelity machines or cadaveric animal models, with dedicated traditional mentoring or distant proctorship and procedure-focused stepwise learning^8,9,10,11. Familiarization with the fetoscope manipulation, intrauterine orientation of the vascular equator, and laser coagulation before performing the actual surgery has the potential to reduce operative complications^12,13. This training may shorten the learning curve for new operators as they master basic skills on a realistic tissue model.

Monozygotic twinning occurs with uniform frequency worldwide affecting 3-5 per 1,000 pregnancies, and the 75% of monozygotic twins with monochorionic diamniotic (MCDA) placentation are at significant risk for TTTS, which currently complicates about 10-15% of MCDA pregnancies, or 1-3 per 10,000 births¹⁴. The incidence is expected to increase with the frequency of in vitro fertilization (IVF) in which there is a 2 to 12-fold increase in monozygosity^{15,16,17,18,19}. TTTS arises from unidirectional inter-fetal blood flow via deep intraplacental AVA. Untreated, this carries a 60-100% mortality and significant morbidity for surviving fetuses^20,21,22.

Selective fetoscopic laser coagulation (SFLP) is the only curative intervention aimed at the rescue of both twins via fetoscopic identification and ablation of the offending AVA, and is considered the standard of care in TTTS stages II-IV (~ 93% of all cases) in pregnancies at < 26 weeks of gestation, with clinical studies in progress to determine if it should also be applied to selected stage I disease^23,24,25. SFLP carries an overall perinatal survival of ~ 70% with a higher likelihood of more advanced gestation and higher birth weights at delivery^26,27 and is considered superior to other interventions as it directly rectifies the underlying pathology of TTTS^28,29,30. The intervention itself is not without complications, and laser-treated TTTS is associated with recurrence (0-16%), perinatal mortality (~ 35%), and a 5-20% chance of long-term neurologic handicap²³. Acquisition of the correct skills, building expertise over a steep learning curve, adherence to international standards of fetoscopic practice, and maintaining surgical dexterity are essential to providing the best outcomes in this complex disease^13,31,32,33. This is often dependent on financial and human resources and a critical volume of cases that may take significant time to acquire³⁴. Established fetal therapy centers are currently concentrated in Western Europe and North America, but the predicted population boom (and thus new pregnancies) will mostly affect Asia and Africa^35,36. Therefore, an increase in the incidence of fetal anomalies amenable to intrauterine treatment can be expected in these lower-resource populations. The dissemination of specialized services such as fetoscopic surgery is a challenge that needs to be addressed as a regional priority³⁷. New fetal therapy centers in these regions must reliably provide SFLP services to meet the needs of their communities, but significant investment and time is needed for new centers to achieve equivalent outcomes as established ones^38,39,40,41.

Departing from the resource-heavy apprenticeship model will facilitate a much-needed dissemination of skills and expertise to communities in which there is a great demand for it. The traditional surgical apprenticeship is still relevant but less practical for many smaller clinical units, as it is time- and resource-consuming and limits the passage of knowledge and skills to one trainee at a time. Simulator training under proctorship is more applicable on a wider scale and facilitates the passage of knowledge and skills passed from one expert to multiple persons through workshops and regular skills training on reliable tissue models^13,42,43. It has been suggested that, because of its rarity, TTTS treatment should be accumulated in high-volume fetal centers to improve its outcomes. Yet, there is also a need to establish new fetal care centers to improve patient access to treatment. Emerging fetal care centers, like the National University Hospital in Singapore (NUH), will need to adhere to certain guidelines in order to maintain their surgical outcomes, i.e., Siriraj-NUH proctorship system as seen in Figure 1³⁷.

In this article we will describe a model-based system with which new proceduralists can undergo skills training in tandem under the guidance of an expert proctor, and by which skills can be practiced to maintain surgical dexterity during long intervals between patients. We will share practical points from our experiences at the Siriraj Hospital in Bangkok and the NUH in Singapore in initiating fetal therapy^6,44,45.

Protocol

The collection of human placenta from term deliveries was approved by the Domain Specific Review Board of the NUH of Singapore (DSRB C/00/524) and by the Siriraj Institutional Review Board (SIRB 704/2559) of Siriraj Hospital in Bangkok. In all cases, patients gave separate informed written consent for the use of the collected specimen. The pig bladders were collected from a local butcher in Singapore and were a kind donation from Dr. Ying Woo Ng (NUH). The non-human primate (NHP) placentas were waste material collected from breeding Macaca fascicularis under the Ministry of Health (Singapore) National Medical Research Council grant NMRC/CSA/043/2012, strictly adhering to the Institutional Animal Care and Use Committee (IACUC) at the National University of Singapore and Singapore Health Services Pte Ltd (IACUC 2009-SHS-512) and were a kind donation from A/Prof Jerry Chan.

1. Familiarization with Fetoscope Handling and Placental Orientation Using a Fetoscopy Simulator

1. Set up the fetoscopy simulator and equipment (Figure 2A - C).
   1. Identify the parts of the 2.0 mm fiber straight fetoscope: the lens (0° or 30°), standard or remote eye-cap (Figure 2A); the 3.0 mm double lumen operating sheath with sharp obturator tip for direct insertion into amniotic cavity under ultrasound guidance, for use with the 2.0 mm fetoscope (Figure 2B).
   2. Place the fetoscope into the operating sheath after removal of the obturator and connect the eye-cap to the laparoscope camera.
      NOTE: These straight fiber-endoscopes are semi-flexible and operating sheaths can be carefully bent up to 20-35° from the midline axis to provide the appropriate curvature for use with anterior placentas. Bend the operating sheath without the endoscope inside. Other suitable fetoscopes for posterior and anterior placentas are listed in the Table of Materials.
2. Arrange the laparoscope tower and ultrasound machine near the "operator" so that the ultrasound probe can be manipulated at the same time during the fetoscope insertion.
   1. Fill the fetoscopy simulator to the brim with water through one of the one-way valve ports.
   2. Position the filled simulator on the plastic base in the desired orientation to represent either an anterior or posterior placenta (Figure 2C).
      NOTE: The upper surface of the simulator will now represent the anterior maternal abdomen where the ultrasound probe is placed and where the fetoscope should be inserted.
3. Use the curvilinear ultrasound probe with aqueous gel on the transparent skin of the "anterior maternal abdomen" to visualize the placenta within the fetoscopy simulator. Identify the placental location and a window adjacent to it (for an anterior placenta) in which to place the fetoscope.
4. Insert the appropriate fetoscope in the operating sheath through the port under continuous ultrasound guidance (Figure 2C).
   1. Use the 0° straight fetoscope for a posterior placenta and the 0° curved fetoscope for an anterior placenta (Table of Materials).
   2. Monitor the insertion and depth of the fetoscope by ultrasound and bring the placenta into view.
   3. Adjust the focus of the camera to bring the vision into sharp relief (Figure 2D - F).
5. Identify the inter-twin membranes which are juxtaposed to the vascular equator.
   1. Identify the vascular equator on the surface of placenta and explore the vasculature moving from end-to-end systematically to identify the typical AVAs for ablation.
      NOTE: These anastomoses will be seen running on the chorionic surface; the artery is darker and always runs over the vein (Figure 2C,E).
6. Change the orientation of the simulator to represent the posterior placenta if practice has been done with an anterior placenta, or vice versa.
   1. Repeat the process of ultrasound assessment, planning fetoscope entry, and inserting the fetoscope.
      Note: The orientation of the simulator and thus of the placenta can be changed each time to practice the fetoscopic placement for various positions of placenta, and also to test out different (curved, straight) fetoscopes.

2. Tissue Models for Practice of Direct Fetoscopic Entry, the Seldinger Technique, and Laser Coagulation of Vessels

1. Tissue model #1 - Placenta in a box
   1. Create the box model using a standard, store-bought plastic container of 35 x 18 x 15 cm³ dimensions with a watertight lock (Figure 3A).
      1. 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 forms the anterior surface of the simulated maternal abdomen through which the fetoscope is placed. Mount a rubber latex sheet along the bottom of the box to prevent sonographic reverberation (Figure 3A - C).
   2. Collect human placentas after term births, with the proper consent for sample collection. Wash the surface of the placenta with tap water in the sink (it is best to do so in the utility room of the labor ward before transport). Ensure that the placental surface is clean of blood and cut the umbilical cord using strong tissue scissors to a manageable length, e.g., 5 cm.
      1. Transport the placenta in a sealed biohazard plastic bag within a secondary container to the laboratory.
         NOTE: Always handle the placenta and other biological substances using personal protective equipment (disposable gloves, eye shields, etc.). Ensure the proper institutional ethical approvals are in place before carrying out this work.
      2. Tie the free end of the umbilical cord by a suture band or cotton cord tape to prevent the blood running out of the cut end.
         NOTE: The blood in the vessels will also help simulate vessel laceration from over-coagulation during laser practice.
   3. To simulate an anterior placenta, fix the placenta to the re-fashioned lid of the container with clear plastic thread or a plastic net to hold it in place.
   4. To simulate a posterior placenta, fix the placenta to the rubber sheet at the bottom of the container and hold it in place with a plastic net or small weights (Figure 3B).
   5. Fill the container with tap water and lock the lid in place.
   6. Prepare the 0° straight fetoscope for a posterior placenta and its operating sheath with working channel, and the multichannel 0° curved fetoscope for anterior placenta (Table of Materials). Connect the eye-cap to the camera.
      1. Prepare the laser. For example, if using the diode laser with a 400-μm or 600-μm laser fiber, set the initial voltage at 15-30 W and gradually increase if needed for effective coagulation.
   7. Perform the ultrasound assessment of the placenta as described in step 1.3.
      1. Find a placenta-free window adjacent to the anterior placenta in which to insert the curved fetoscope such that the lens lies above the center of the placenta (where the inter-twin equator is expected to be in a MCDA placenta).
      2. Determine where to insert the straight fetoscope for the posterior placenta such that the 0° lens is positioned perpendicular to the center of the placenta.
   8. Perform direct fetoscopic entry by making a 2-mm stab incision with a sharp blade in the "skin". Insert the operating trocar with its pyramidal obturator into the fluid-filled container (the "amniotic sac") under continuous ultrasound guidance (this is the sac of the recipient twin in a patient).
      1. Avoid piercing the placenta by advancing the fetoscope slowly under ultrasound vision. Remove the pyramidal obturator from the operating trocar slowly under continuous ultrasound vision.
      2. Place the lens of the fetoscope carefully into the operating trocar in the channel previously occupied by the obturator, and bring the placenta and surface vasculature into sharp focus (Figure 3C).
   9. Insert the laser fiber into the operating side-channel and advance slowly as the tip nears the end of the sheath.
      ​NOTE: Keep the laser beam as perpendicular as possible to the target vessel in order to maximize the laser effect^46,47.
      1. Advance the laser fiber tip to approximately 5-10 mm beyond the operating sheath.
         NOTE: If the laser tip advances too far from the sheath, it may lacerate the vessel. If the tip is too close, the coagulation effect may be compromised (Figure 3D). The laser fiber tip should be 2-3 mm from the vessel surface and should not touch the vessel when fired (yellow arrow in Figure 3D).
   10. Identify the umbilical cord (Figure 3E) and placental vessels (Figure 3F). Review the placental vasculature end-to-end using a combination of ultrasound and direct fetoscopic vision.
       NOTE: The fetoscope should be directed at a 90° angle to the target vessel. Figure 3G shows the actual monochorionic AVA in a monochorionic placenta. Use the foot pedal to fire the laser when in position perpendicular to the vessel or anastomosis.
   11. Coagulate the vessel until it blanches with the no-touch technique and aim to coagulate a segment of 1-2 cm until complete cessation of flow is accomplished. The vessel should appear flattened (collapsed) and pale for coagulation to be deemed effective.
       1. Systematically practice coagulation of vessels from one placental end to the other. Laser coagulate the thick vessels from the periphery towards the center of the vessel to prevent rupture (thus "shaving" a thicker turgid vessel into a narrower less congested one). Alternatively, coagulate the smaller feeding vessels first before the larger ones to allow decongestion and prevent vascular rupture.
   12. Practice the Solomon technique after individual vessels have been coagulated to complete placental dichorionisation^48,49. Create a line on the placental surface by superficial coagulation with the laser until all the individually-coagulated anastomoses are joined.
2. Tissue model #2 - Pig bladder "uterus"
   ​NOTE: A hybrid tissue model combining a pig bladder and a mid-trimester human placenta may also be considered for simulation if the materials are readily available. This model can be used to practice insufflation and removal of fluid from the "uterus" to recreate commonly encountered complications of fetoscopy like blood-stained liquor, and to practice the Seldinger technique of fetoscope insertion.
   1. Acquire a cleaned pig bladder. Position it with the broader curved perimeter as the upper cephalad pole and the narrower portion as the lower caudal pole, so that the user can bisect along the cephalad border and proceed caudally, such that the bladder opens like a clamshell (Figure 4A, broken line).
      NOTE: Perform all procedures with human and animal tissues in a biological safety cabinet wearing personal protective equipment and with the appropriate institutional approval for handling biological tissues.
   2. Acquire a small mid-gestation human placenta after delivery or medically-induced pregnancy termination. Ensure that the proper consent is attained, and the specimen is anonymized.
   3. Trim the excess amniotic membranes from the placenta (filmy, white tissue attached to the fetal/umbilical surface) using tissue scissors and suture the placenta (red arrow, fetal surface outwards, maternal surface inwards) around its perimeter to one half of the pig bladder. Suture the second half of the pig bladder (black arrow) to the first around the incision in a water-tight fashion (Figure 4B, C).
   4. Place the "uterus" in the model pelvis as shown in Figure 4D. Orientate the uterus to simulate either an anterior or posterior placenta (Figure 4D).
   5. Under ultrasound guidance (if the rubber skin is transparent to ultrasound) practice direct insertion of the trocar and fetoscope within its operating sheath.
   6. Practice the Seldinger technique using a sharp hollow trocar inserted into the amniotic space under real-time ultrasound guidance. Advance the soft J-tipped guidewire through the lumen and withdraw the trocar, passing a blunt cannula loaded with a dilator over the guidewire into the amniotic space before withdrawing the guidewire and dilator altogether, leaving the cannula in place. Finally, insert the fetoscope into the uterus via the cannula (Figure 4E).
   7. Examine the vessels on the placental surface fetoscopically. Reduce or add fluid via the operating channel with a 50-mL syringe to increase or decrease "intrauterine" pressure and to replace blood-stained or turbid fluid with fresh saline.
   8. Practice laser coagulation of vessels in the same manner described in steps 2.1.11-2.1.12.
   9. Dispose the model as biohazardous material according to institutional protocol.

3. Transferring Skills Learned on the Model to the Human Patient

1. On the patient with a MCDA twin pregnancy, perform ultrasound examination of the placenta and identify the cord insertion points of both fetuses on the placenta.
   ​NOTE: In this case, one of the cords may be inserted close to the margin of the MCDA placenta. Imagine a line joining the two placental cord insertions and determine the midpoint of this line which indicates the location of the vascular equator and may be closer to the smaller donor twin rather than equidistant to both cords especially with a significant amniotic sac size discrepancy. The vascular equator lies perpendicular to the line joining the cords.
2. Determine the site of fetoscope insertion.
   1. For an anterior placenta, find a window under ultrasound visualization of the placenta, free from placental tissue, from which the curved fetoscope can be manipulated such that the lens lies over the vascular equator.
   2. For a posterior placenta, insert the fetoscope at the approximate midpoint between the cords directly over the vascular equator. Move the fetoscopic lens up and down the vascular equator using a sweeping movement while maintaining an approximately 90° angle to the equator, optimal for laser coagulation.
      NOTE: This may require the insertion site to be lateral to the vascular equator, just beyond the periphery of the placenta on the side of the polyhydramnios sac.
3. Check for completion of placental dichorionization after the delivery of the fetuses to assess for residual anastomoses (Figure 5A - C). Inject the umbilical cord vessels with different colored dyes to distinguish between the donor and recipient arteries and veins after the necessary preparation as previously described^44,50.

Results

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. The simulator illustrated here was developed at Siriraj Hospital (Bangkok), and is a closed system that incorporates a silicon replica of a mid-gestation monochorionic placenta (Figure 1). The consistent use of this model should increase the confidence of the n...

Discussion

The skills practiced on a fetoscopy simulator and on the tissue models encompass the majority of technical abilities required for SFLP. The advantages of training on these models include learning to simultaneously handle the ultrasound probe and fetoscope, familiarity with handling the straight and curved fetoscopes, practicing the systematic examination of the vascular equator along the whole length of the inter-twin membrane to identify anastomosing vessels on high-fidelity MCDA placenta, and learning the correct techn...

Materials

Name	Company	Catalog Number	Comments
Fetoscopic Simulator	Maternal-Fetal Medicine unit, Department of Obstetrics and Gynaecology, Siriraj Hospital, Bangkok, Thailand	NA.	Siriraj Fetoscopic Simulator. Customised model of monochorionic anterior/posterior placenta and anastomses produced at the Siriraj Hospital in Bangkok.
Laparoscopy tower with light source, camera and video recorder	Olympus Singapore	Olympus Visera Elite system (Olympus Singapore) with camera OTV-S190 and light source CLV-S190 set at medium intensity (level 0) and video recorder	Laparoscopy tower for fetoscopy and recording of practice
Voluson E8 ultrasound machine with 4CD probe	GE Healthcare Singapore	GE Voluson E8; transabdominal 4CD curved transducer (2-5MHz)	Ultrasound system for guidance of fetoscope introduction and manipulation
Minature straight forward telescope 0o (2mm) for posterior placenta	KARL STORZ GmbH & Co KG, Tuttlingen, Germany	11630AA	Fetoscope. 0° lens, diameter 2mm, length 26cm, autoclavable, fibre optic light transmission incorporated. To use with operating sheath 11630KF.
Operating sheath, straight with pyramidal obturator.	KARL STORZ GmbH & Co KG, Tuttlingen, Germany	11630 KF	Size 9 Fr with working channel 1 mm, for use with 11630AA; working channel for laser fibres up to 400µm core.
Multichannel miniature straight forward telescope 0° set straight for posterior placenta	KARL STORZ GmbH & Co KG, Tuttlingen, Germany	11506AAK	Fetoscope. 0° lens, diameter 3.3 mm, length 30cm , 30,000 pixels, integrated channels, autoclavable, fibre optic light transmission incorporated.
Multichannel miniature straight forward telescope 0° set curved  for anterior placenta	KARL STORZ GmbH & Co KG, Tuttlingen, Germany	11508AAK	Fetoscope. 0° lens, diameter 3.3 mm, length 30cm , 30,000 pixels, integrated channels, autoclavable, fibre optic light transmission incorporated.
Dornier diode laser with 400um or 600um laser fibre	Medilas D Multibeam, Dornier MedTech Asia, Singapore	S/N D60-353	Laser photocoagulation system. Diode (30-60 W)
Laser fibre	400-600µm laser fiber	Disposable LG type D01-6080-BF-0;LOT 1024/0613	Use the provided ceramic cutter to refashion the tip of the fibre once coagulated after burning to maintain the sharp focus of the laser.
Large plastic container with ultrasound transparent skin;	NA	NA.	Container is a simple houshold item with a watertight lid that cn be locked in place. The silicon rubber "skin" produced inhouse allows US visualisation of the placenta within the container. Can be used as a simulator for vascular laser coagulation.
Pig bladder and small mid-gestation placenta	NA	NA.	Obtained from the local butcher. Elastic tissue that can be stretched when filled with large volume of fluid; can incorporate a small human/NHP placenta and used as a simulator for laser coagulation