Surgical Treatment of the Fetus

Summary

Over the past half-century, implementation of high-resolution screening prenatal imaging, coupled with increasingly nuanced understanding of embryology and human fetal development, have created a new surgical patient: the fetus. Through decades of rigorous scientific investigation and technical innovation, congenital anomalies that previously carried a grim prognosis are now candidates for fetal intervention. As experience has grown with fetal surgical intervention, we have been able to quantify survival benefit and reduction in morbidity to the fetus for many conditions, while also coming to understand the specific risks for the fetus and the mother.

In fact, the potential impact of fetal surgery on the mother presents difficult ethical decisions. By undergoing general anesthesia, a surgical operation, postoperative recovery, and the remainder of pregnancy, the mother is subject to significant risk but can expect no direct health benefit from fetal surgical intervention. Specifically, short-term morbidity after fetal surgery includes preterm labor, the potential risk of anesthesia, the potential need for blood transfusion, premature rupture of membranes, chorioamniotic separation, chorioamnionitis, and placental abruption. Long-term morbidity related to the hysterotomy used in open fetal cases includes infertility, uterine rupture during future pregnancies, and mandatory cesarean section with future pregnancies. Therefore, it is crucial that the obstetric, medical, and surgical teams consider the protection of the pregnant woman as the utmost priority when making treatment decisions. Additionally, comprehensive discussion of the potential benefit to the fetus and the unique risks to the mother is required while obtaining informed consent. Specifically, women should be informed of and provided access to alternative treatment modalities, including postnatal therapy, palliative delivery, or pregnancy termination.

Fetal Access

Access to the fetus can be considered in three general categories: percutaneous, fetoscopic, and open hysterotomy. Preoperative and intraoperative ultrasound are critical for defining the anomaly (or anomalies), delineating the placental anatomy, determining the position of the fetus, detecting the location of the maternal blood vessels, and monitoring the fetal heart rate during the procedure. Ultrasonography is particularly vital in percutaneous and fetoscopic procedures owing to limited direct visualization of the fetus, placenta, and uterus during the procedure.

Percutaneous Interventions

Needle-based interventions were first reported in 1963, when Liley performed the first fetal transfusion by inserting a 16-gauge needle into the fetal peritoneal space. Since then, advances in imaging and instrumentation have broadened the application of percutaneous techniques in the treatment of the fetus. Percutaneous procedures are performed through small skin incisions on the mother's abdominal wall, utilizing real-time ultrasound to visualize the fetal and maternal anatomy and guide the intervention. Cystic masses, ascites, pleural fluid, or other fluid collections can be aspirated as a diagnostic or therapeutic maneuver. Shunts can be inserted for more definitive drainage of fluid into the amniotic space. Other devices such as radio frequency ablation (RFA) probes can be deployed to treat complications of twin gestation. The needles used to place these catheters, as well as the RFA device, are approximately 1.5 to 2 mm in diameter, minimizing morbidity to the mother and irritation of the uterus.

Fetoscopic Surgery

Fetoscopic procedures are performed using a 1.2- to 3.0-mm fetoscope with or without a working channel, inserted through a 2.3- to 4.0-mm cannula placed into the uterus. For procedures performed through a single port with a fetoscope containing a working port, the uterus can be accessed through a small incision on the mother's abdomen. Procedures requiring multiple instruments and ports may proceed either via multiple small abdominal incisions or a maternal laparotomy allowing port placement directly into the uterus. Fetoscopy permits direct visualization of the lesion at the time of intervention but is still facilitated by the use of fetal ultrasound. Additionally, access to the uterus is performed under ultrasonographic guidance to locate a “window” in the uterus that is devoid of the placenta in hopes of reducing the risk of maternal bleeding, placental abruption, and fetal morbidity. Occasionally, the amniotic fluid is not clear enough for adequate direct visualization with the fetoscope. In such cases, an amnio-exchange may be performed with warmed isotonic crystalloid solution to optimize visualization.

Open Hysterotomy

The early experience in surgically correctable fetal anomalies in utero was conducted through an open hysterotomy. Fortunately, continuing advancements in imaging and minimally invasive techniques have reduced the need for open fetal procedures. Open fetal procedures are usually performed through a low, transverse maternal skin incision. The fascia can be opened in a vertical or transverse fashion, depending on the exposure needed. Preoperative and intraoperative ultrasound is crucial to map out the placenta and determine the ideal placement of the uterine incision to optimize fetal exposure and avoid injury to the placenta. Uterine staplers with absorbable staples were developed specifically for fetal surgery to allow a hemostatic hysterotomy yet avoid infertility from permanent staples functioning as an intrauterine device. Typically, fetal exposure is limited to the site specific to the intervention to avoid hypothermia and unnecessary manipulation of the umbilical cord, which is prone to spasm that can result in fatal fetal ischemia. A fetal extremity may also be exposed for placement of an intravenous cannula if indicated. The uterus should be stabilized within the maternal abdomen to minimize tension on the uterine blood vessels that could impede placental flow. Amniotic fluid volume is maintained using warm, isotonic crystalloid solution. At the conclusion of the procedure, the amniotic fluid is completely restored, and the uterus is closed in multiple layers using absorbable sutures. Postoperatively, the mother and fetus are monitored continuously for uterine contractions and heart rate, respectively. Patients are often discharged with oral nifedipine as a tocolytic.

Open fetal surgery requires cesarean section for the current pregnancy and all future pregnancies owing to the potential for uterine rupture during labor. Although vaginal delivery after cesarean section (VBAC) may be considered for routine, lower uterine segment hysterotomy, VBAC is not an option after hysterotomy for fetal surgery owing to the increased risk of uterine rupture.

Exit Procedure

Ex-utero intrapartum therapy (EXIT) allows for a fetal intervention to be conducted while maintaining uteroplacental circulation, followed by immediate delivery. EXIT procedures are most commonly indicated for airway issues but have been described for extracorporeal membranous oxygenation, separation of conjoined twins, and resection of fetal neoplasms. An EXIT procedure is performed similarly to the open fetal procedure described above. However, at the conclusion of the case, with an established fetal airway, the fetus is delivered. Since uterine relaxation is critical during any fetal intervention, the EXIT procedure carries a significant risk for maternal hemorrhage at the time of delivery, and coordination between the anesthesiologist and the surgeon is critical, as discussed below.

Anesthetic Considerations

In addition to providing amnesia, analgesia, and patient monitoring that are central to all anesthetic encounters, successful maternal-fetal anesthesia must maintain uteroplacental relaxation and circulation. The only exception to this is the EXIT procedure, in which uterine contraction after delivery of the fetus is necessary to prevent bleeding secondary to uterine atony.

In all cases, the mother is positioned supine with her left side down to minimize compression of the inferior vena cava by the gravid uterus. Commonly administered preoperative medications include indomethacin for tocolysis and an antibiotic, such as cefazolin, for infection prophylaxis. The maternal bladder is decompressed by either straight catheterization for short procedures or an indwelling bladder catheter for longer or open procedures.

For minimally invasive percutaneous interventions and fetoscopic procedures, locoregional anesthesia can be administered via epidural, spinal, or local injection, depending on the mother's preference and anticipated length of the procedure. Spinal and epidural anesthesia are especially useful for complex fetoscopic procedures requiring multiple ports or in cases when emergency cesarean section may become necessary. Regional anesthesia can produce maternal hypotension and negatively impact uteroplacental blood flow; therefore, with spinal anesthesia normotension is maintained with a phenylephrine infusion. Both phenylephrine and ephedrine are effective vasopressors that maintain maternal blood pressure while minimizing the effect on umbilical cord blood flow. Additional conscious sedation can be provided intravenously using propofol or inhaled nitrous oxide. Nitrous oxide has the added benefit of enhanced uterine relaxation.

For open fetal procedures, including EXIT, deep maternal general anesthesia is required to ensure adequate uterine relaxation. Volatile inhaled anesthetics are used at high concentrations (usually 2.0 minimal alveolar concentration), but the subsequent relaxation of the myometrium can lead to a drop in placental blood flow. Therefore, maternal blood pressure is augmented in these cases with either ephedrine or phenylephrine. The surgeon should be vigilant about repeated assessment of uterine tone. When the uterus is open, amniotic fluid volume is maintained with warm, isotonic crystalloid solution to prevent compression of the umbilical cord.

For open fetal cases, as the hysterotomy is being closed, the inhaled anesthetic is reduced or turned off and tocolysis with magnesium sulfate is initiated. Amniotic fluid volume is restored. Alternatively, after delivery during an EXIT procedure, the inhaled anesthetic is reduced, and oxytocin is administered to enhance uterine contraction prior to closure of the hysterotomy.

For procedures performed directly on the fetus, additional fetal anesthesia and analgesia is required. In the fetus experiencing pain, systemic vascular resistance can increase, which may decrease umbilical cord blood flow and fetal perfusion. While transplacental passage of the volatile anesthetics does occur, the time needed for fetal levels to reach a therapeutic dose precludes maternal anesthesia from being an adequate source of fetal anesthesia. Furthermore, inhaled anesthetics do not provide analgesia. Thus, additional fetal anesthesia is administered intramuscularly and typically consists of opioid analgesics and non-depolarizing paralytic agents such as rocuronium or pancuronium. Rocuronium and pancuronium have the added benefit of vagal inhibition that can abate bradycardia, which may result from opioid administration; however, atropine is often administered for additional protection against bradycardia.

Transplacental passage of anesthetic from mother to fetus places the fetus at risk for demise. Inhaled anesthetics produce myocardial depression, which can augment the fetal bradycardic response to stress and contribute to malperfusion, as fetal cardiac output and end organ perfusion are primarily determined by heart rate. Other environmental factors such as hypothermia and umbilical cord compression increase the risk for fetal demise. Accordingly, continuous fetal monitoring should be undertaken via transcutaneous pulse oximetry, intraoperative fetal echocardiography, and monitoring of amniotic fluid temperature.

Finally, in light of in vitro and animal data demonstrating lasting neurotoxic effects associated with exposure to all general anesthetics tested, the Food and Drug Administration (FDA) issued a Safety Communication in 2016 acknowledging the potential for adverse effects on fetal brain development and postnatal learning with anesthetic exposure to the pregnant woman. Clinical studies have not demonstrated worsened neurodevelopmental outcomes with brief anesthetic exposure, but data suggest the effect may be dose-dependent, with prolonged and repeated anesthetic exposure placing the developing brain at higher risk. Further clinical studies characterizing the effects of anesthesia on developing brains are necessary and ongoing.

Anomalies Amenable to Fetal Surgery

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