Abstract
Ex utero intrapartum therapy, or EXIT procedures, are performed in cases in which prenatal imaging suggests a low probability of survival with conventional treatments at birth. The intervention performed varies by indication. Both the mother and fetus are exposed to significant risk during and after the EXIT procedure. EXIT procedures often require general anesthesia for both the mother and fetus in addition to epidural placement in the mother preoperatively. Maintenance of uteroplacental perfusion and preservation of placental perfusion and gas exchange through hemodynamic stability are important factors to consider intraoperatively. Here we present a typical case and then review appropriate preoperative, intraoperative, and postoperative management of such patients.
Keywords
EXIT (ex utero intrapartum therapy), hemodynamic stability, placental perfusion, rapid sequence induction, uterine tone, uteroplacental perfusion
Case Synopsis
A 28-year-old gravida II, para I woman at 36{2/7} weeks’ gestation presents with a fetus prenatally diagnosed with a large cystic left lung mass. Ex utero intrapartum therapy is planned to establish an airway before delivery and possibly transition the fetus onto extracorporeal membrane oxygenation.
Acknowledgment
The authors wish to thank Dr. Marnie Robinson for her contribution to the previous edition of this chapter.
Problem Analysis
Definition
Fetal surgery encompasses many different procedures that can be divided into three broad categories: (1) minimally invasive surgery (fetoscopy), (2) midgestation or open fetal surgery, and (3) ex utero intrapartum therapy (EXIT). Fetoscopic, or minimally invasive, procedures ( Table 32.1 ) involve manipulation of the placenta or umbilical cord through an endoscope, and only local or regional anesthesia is required. Open fetal surgical procedures ( Table 32.2 ) require complete uterine relaxation, usually with high concentrations of volatile anesthetics in addition to regional anesthesia for control of postoperative pain. Both fetoscopy and open fetal surgeries are performed in midgestation to allow for fetal growth after the procedure.
| Disease | Procedure |
|---|---|
| Twin-twin transfusion syndrome | Laser photocoagulation of placental vessels |
| Twin reversed arterial perfusion | Coagulation of umbilical cord |
| Amniotic band syndrome | Division of amniotic bands |
| Disease | Procedure |
|---|---|
| Myelomeningocele | Repair of neural canal defect |
| Sacrococcygeal teratoma | Resection or debulking of teratoma |
| Intrathoracic masses | Resection of mass |
| Congenital diaphragmatic hernia with low lung-to-head ratio | Tracheal occlusion |
In contrast, the EXIT procedure is used for neonates in which prenatal imaging suggests a low probability of survival with conventional treatments at birth. The procedure is usually deferred until as late in gestation as possible, based on both the maternal and fetal condition. The particular intervention performed in an EXIT procedure varies by indication ( Table 32.3 ) and may involve securing an airway, resecting an intrathoracic mass, resecting a neck mass in a controlled setting, special circumstances with thoraco-omphalopagus conjoined twins, or inserting cannulas for extracorporeal membrane oxygenation (ECMO). The role of EXIT to ECMO is controversial, as it is difficult to assess the actual need for ECMO in the first few minutes of ventilation, especially while the fetus is still on placental support. In the case synopsis, the large lung mass puts the fetus at risk for perinatal asphyxia if it proves difficult or impossible to oxygenate and ventilate the lungs after conventional delivery. EXIT allows extended uteroplacental support while the airway is secured by direct laryngoscopy, rigid or fiberoptic bronchoscopy, and possible insertion of an ECMO cannula if required. With emphasis on techniques aimed to maximize uterine relaxation and maintain uteroplacental blood flow, it is now possible to maintain placental support for up to 180 minutes before delivery and separation from placental circulation.
| Disease | Procedure |
|---|---|
| Severe aortic stenosis or left lung hypoplasia | ECMO cannulation |
| Congenital diaphragmatic hernia | Removal of tracheal clip or balloon that was placed in utero ECMO cannulation |
| Congenital high upper airway obstruction syndrome | Tracheostomy |
| Giant cervical neck mass | Resection of mass |
| Severe pulmonary hypoplasia from intrathoracic mass (congenital pulmonary airway malformation or CPAM) | Resection of mass ECMO cannulation |
| Anticipated difficult intubation | Obtain surgical airway |
Recognition
Access to prenatal care is essential for prenatal diagnosis of fetal anomalies, and advances in ultrasound and magnetic resonance imaging have led to better delineation of structural anomalies and their potential impact on the fetus or newborn. Most fetal disease is initially detected by ultrasonography and abnormal findings prompt further testing. Optimal imaging techniques include high-resolution fetal sonography, three-dimensional fetal sonography, ultrafast fetal magnetic resonance imaging, and fetal echocardiography. An in-depth ultrasound examination is used to assess fetal weight and overall health. Estimated fetal weight is important to prepare accurate doses for fetal analgesia, muscle relaxation, and resuscitation drugs. Amniocentesis provides amniotic fluid for analysis, including karyotyping. Structural or functional cardiac defects can be identified using fetal echocardiography. Prenatal imaging of all fetal anomalies is used to visualize areas of involvement, determine the relationship to normal structures, and determine tracheal location. Serial radiographic examinations are also important to monitor the growth of masses, response to treatment medications, and the development of hydrops fetalis. Hydrops fetalis is a life-threatening condition that causes edema in two or more organ systems as a result of immune incompatibility, heart and lung problems, severe fetal anemia, or developmental defects. Care must be taken to assess placental location, as abnormal placentation such as placenta previa or evidence of subchorionic hemorrhage might increase the risk of intraoperative complications.
Although specific criteria for identifying a fetus that would benefit from an EXIT procedure vary by indication, some conditions have similar presentations. For example, cervical neck masses prevent the swallowing of amniotic fluid, resulting in polyhydramnios. Pulmonary amniotic fluid accumulation causes the lungs to appear large and echogenic. Chronic fetal disease from many causes can lead to hydrops fetalis, progressive ascites, pleural and cardiac effusions, and generalized edema that without intervention will ultimately lead to fetal demise.
Risk Assessment
Fetal Risk
The fetus is at risk for adverse events both during and after the EXIT procedure. During surgery, maintenance of normothermia is hampered by exposure of the fetus, whose thin skin is susceptible to evaporative fluid and heat loss. In a preterm fetus, the effects and duration of anesthetic agents are increased owing to immature organ function, incomplete myelination, and delayed elimination.
As a result of decreased fetal heart contractility, the fetus may not be able to compensate for hemodynamic changes. Changes in fetal heart rate, such as tachycardia with fetal incision or bradycardia from inadequate uteroplacental perfusion or umbilical cord compression, may be tolerated for only a brief period. Maternal hypoxia, increased systemic vascular resistance, or the negative inotropic effects of anesthetic agents may further compromise fetal cardiac function. Decreased cardiac preload from impaired venous return during surgical manipulation or blood loss can lead to fetal hypotension, bradycardia, shock, and cardiac arrest. Warm fetal blood products should be readily available to treat poor fetal cardiac function as a result of hypovolemia.
During an EXIT procedure, the fetus remains on the sterile field until division of the umbilical cord, limiting monitoring options to detect physiologic derangements. Hemodynamic data are obtained from a sterile fetal pulse oximeter (normal fetal oxygen saturation being in the range of 60%–70%) and intermittent fetal echocardiography. The use of fetal echocardiography helps identify early problems such as decreased filling, fetal bradycardia, decreased myocardial contractility, ductal constriction, and atrioventricular valve incompetence. Ideally, the surgeon places a fetal intravenous catheter, permitting the administration of inotropic medications, blood, and fluids by the anesthesiologist. If fetal intravenous access is not available, resuscitation is limited to intramuscular injections by the surgeon and maternal interventions by the anesthesiologist. The intramuscular mixture of atropine, fentanyl, and a nondepolarizing muscle relaxant is often administered as soon as the shoulder is exposed by the surgeon. Maintenance of maternal blood pressure and adequate oxygen (O 2 ) delivery is essential to fetal well-being, as is ensuring complete uterine atony and unobstructed umbilical cord blood flow.
The greatest risk to the fetus is fetal demise or severe disability from the underlying disease process. To be considered for EXIT, the fetus must have a dismal prognosis without intervention. With intervention, in addition to the risks already mentioned, there are risks specific to the disease process and its treatment. An adjacent operating room with a separate team of surgeons, anesthesiologists, and nurses is sometimes necessary to continue care of the neonate after delivery. Finally, depending on the timing of EXIT, the infant’s condition may be further complicated by premature birth. From a fetal standpoint, EXIT procedures are normally well tolerated in terms of acid-base status, indicating a well-preserved uteroplacental perfusion despite the prolonged use of high concentrations of volatile agents.
Maternal Risk
The mother is also exposed to significant risk during an EXIT procedure. Like any parturient, she has experienced the physiologic changes of pregnancy and is subject to the associated risks of general anesthesia ( Table 32.4 ). An edematous airway might make intubation difficult, and an increase in gastric reflux and the gravid uterus place the mother at increased risk for aspiration pneumonitis. The thrombophilic state of pregnancy combined with a prolonged surgical procedure places the mother at risk for venous thromboembolic events, thus pneumatic compression boots are indicated until the patient is fully ambulatory. She is also at risk for amniotic fluid embolism during labor or intraabdominal surgery, and at risk for postoperative wound infection. Additional maternal risks unique to EXIT include the following:
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Obligate cesarean section for all future deliveries. EXIT generally requires a larger incision than standard cesarean delivery and the varying location of the hysterotomy location increases the risk of uterine rupture during subsequent labor and vaginal delivery.
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Risks of invasive monitoring. Because the welfare of the fetus depends on uteroplacental perfusion, which in turn is dependent on maternal blood pressure, continuous monitoring of maternal blood pressure during EXIT and open midgestation procedures is indicated.
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Increased risk of blood loss requiring transfusion. The profound uterine relaxation required to maintain uteroplacental support during EXIT in addition to maternal circulatory instability increases the risk of uterine atony after the third stage of labor. Even if uterine tone is reestablished expeditiously, the likelihood of transfusion of blood products is greater with an EXIT procedure than with routine cesarean delivery. Blood products should be readily available if needed.
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