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Anesthetic Complications of Fetal Surgery : EXIT Procedures
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.
TABLE 32.1
Indications for Minimally Invasive Fetoscopic Surgery
| 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 |
TABLE 32.2
Indications for Open Midgestation Fetal Surgery
| 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.
TABLE 32.3
Indications for Ex Utero Intrapartum Therapy (EXIT)
| 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 |
CPAM, congenital pulmonary airway malformation; ECMO, extracorporeal membrane oxygenation.
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.
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