Literature Review
Anesthesia for Fetal Surgery.
Myers LB, Cohen D, Galinkin J, Gaiser R, Kurth CD. Paediatric Anaesthesia 2002;12:569-578
Review: The National Institute of Child Health and Development was recently asked to predict the state of health care in the new millennium. The Institute predicted, that by the year 2020, routine diagnosis and treatment of congenital malformation in utero, prior to development of secondary morbidity. Fetal surgery was specifically predicted to be standard therapy for most disabling malformations that are currently treated in young infants. If this prediction proves to be correct, anesthesia for neonatal surgical emergencies will be reduced. This paper reviews the indications, anesthetic issues, and postoperative pain management for fetal surgery as practiced in the year 2002.
I was excited when I read this paper and wished that I were once again young, seeking new horizons on the frontiers of research in this fascinating field. I mentioned this dream to some of my friends who are now in leadership roles. To my utter dismay, some were not the least bit interested. I sincerely hope this to be an aberration. I therefore strongly felt that I should review this paper and maybe light a few sparks.
To date, there are only three medical institutions where major fetal surgical procedures are performed in the USA: The Children's Hospital of Philadelphia, Vanderbilt University Medical Center, and University of California, San Francisco. They have years of experience with animal research and human fetal surgery since early 1990.
Whereas, for maternal surgery such as Caesarean section, the fetus is a bystander, while for fetal therapy, such as amniotic fluid reduction, the mother is a bystander. Anesthesia for fetal surgery involves two patients simultaneously. Surgery is considered appropriate only when the risk of death or severe injury to the fetus is greater then no intervention, and the risk to the mother is low. Hydrops fetalis is the common final pathway for a number of fetal anomalies, and an almost certain fetal demise follows. Hence, these anomalies are considered for surgical intervention. Contraindications include lethal or disabling genetic disease in the fetus and serious medical disease in the mother, e.g., preeclampsia and mirror syndrome.
Fetal surgery involves either open procedure requiring a hysterotomy on the mother, with major airway, thoracic, cardiovascular, and neurological procedures on the fetus; or a minimally invasive fetal procedures such as insertion of a stent and shunt, occlusion or coagulation of fetoplacental structures, and transfusion of medications or blood products. These minimally invasive procedures can be performed with sedation, regional anesthesia, or general anesthesia, depending on maternal and fetal factors. After open fetal surgery, all pregnancies require delivery by Caesarean section but after minimally invasive procedures, vaginal delivery is permissible..
Anesthesia for fetal surgery requires general anesthesia because both mother and fetus mutt be anesthetized and the uterus must be atonic. An anesthetist experienced in fetal surgery screens the mother at the time of surgical and obstetrical workup. The anesthesiologist informs the surgical team of any issues, and discusses the anesthesia with the mother. On the morning of surgery, the obstetrician examines the mother for premature labor and fetal wellbeing. Availability of type specific blood for the mother and 50 ml aliquots of O-negative blood for the fetus is ascertained. The operating room is warmed to 26 C. Drugs for the fetus, atropine 0.02 mg/kg, epinephrine 1 ug/kg, vecuronium 0.2 mg/kg, and fentanyl 20 ug/kg are prepared and given to the scrub nurse. If the mother has not received the tocolytic drug indomethecine, 50 mg rectal suppository, prior to arrival, it is administered after induction. The mother receives 30 ml of 0.3 M of sodium bicitrate orally and 10 mg metachlorpromide i.v. A lumber epidural catheter is then placed for postoperative pain management. The mother is positioned to achieve left uterine displacement. Following preoxygenation, a rapid sequence induction is performed with thiopental 5 mg/kg, succinylcholine 2 mg/kg, and fentanyl 1-2 ug/kg. Anesthesia is maintained with 0.5 MAC of isoflurane or desflurane in oxygen. While an ultrasound examination is being done for surface anatomy with respect to the fetus and placenta, a second large bore intravenous catheter, arterial catheter, urinary catheter, and nasogastric tube are inserted. Fetal hemodynamics are measured by continuous fetal echocardiogram. The location of the placenta is important, as surgical access to the fetus via hysterotomy is more difficult if the placenta is attached to the anterior wall of the uterus, as compared to the posterior wall. This difficulty increases the risk of bleeding, and requires greater manipulation of the uterus, which predisposes to hypotension and fetal hypoxia. Before maternal skin incision, volatile anesthetic is increased to 2 MAC, and maternal relaxation is achieved with vecuronium. Maternal systolic blood pressure is kept above 100 mm Hg, with ephedrine if necessary. Total intravenous fluid is limited to 500 ml of normal saline, unless blood loss exceeds 100 ml, in order to prevent postoperative pulmonary edema. The surgeon assesses the uterine tone, and if found tobe still high, inhailational anesthetic is increased and ephedrine used as necessary. A special stapeling device is used to incise the uterus with minimum bleeding and to seal the amniotic membrane. Warm fluid is continuously infused in to the uterine cavity. A small uterine incision is helpful, but requires excellent uterine relaxation. Fentanyl, for intra operative and post operative fetal analgesia; atropine, to ablate fetal bradycardia response to surgical stimulation; and vecuronium to ensure a still fetus are injected i.m. into the fetus. For procedures with potential blood loss, the surgeon applies a pulse oximeter to the fetal forearm, and may also check fetal hemoglobin, pH, and blood gases from the umbilical artery. Fetal desaturation, SpO2 less then 50%, results from hypo perfusion, low cardiac output, or kinking of the umbilical cord. The anesthesiologist infuses blood and medication, as needed, through a surgeon held butterfly needle located in an exposed fetal vessel, e.g., superior vena cava , aorta, or umbilical vein. Durring hysterotomy closure intravenous magnesium sulphate a 6 G bolus over 20 minutes followed by 3 G/hr infusion is given to allow volatile anesthetic to be discontinued and mother to emerge from anesthesia with a quiescent uterus. The epidural catheter is used to deliver 15-20 ml of 0.25% bupivicaine and 3 mg of morphine as the inhailed anesthetic is decreased. Magnesium may potentiate vecuronium, hence neuromuscular transmission should be properly monitored. A smooth emergence and tracheal extubation are required to minimize tension on uterine and abdominal suture lines.
Serious postoperative issues include premature labor, pulmonary edema, amniotic fluid leak, and fetal demise. All patients experience premature uterine contractions in the immediate postoperative period, thus necessitating magnesium sulphate infusion. Bed rest for the remainder of the pregnancy is required. Postoperative pain management is crucial and excellent pain control helps prevent the uterine contractuers.
Anesthesia for the minimally invasive fetal surgery that involves use of a laroscope (fetoscope) and ultrasound depends mainly on surgical factors. It is vital for the anesthesiologist to attend the patient preparation meetings to understand the surgical approach and to select the best anesthetic. Surgical factors to consider include location of the placenta and the umbilical cord, history of uterine activity, position of the fetus, relation of the fetal lesion to other structures, and chance of converting to open fetal surgery. Fetal procedures have been performed under general or regional anesthesia or with sedation techniques. The maternal pre visit and morning evaluation and premedication are the same as in open surgery. Arterial canula and nasogastric tube are not used, and one intravenous catheter is sufficient. General anesthesia is usually a balanced technique, 0.75-1 MAC inhailational agent with fentanyl, rather then deep anesthesia as profound uterine relaxation is not necessary. Skin, uterine, and fetal incisions are small, and postoperative epidural analgesia is generally not required. Tocolytic management is with magnesium sulphate transitioned to subcutaneous terbutaline or oral nifedepine. Tocolytics may be discontinued later in pregnancy, and some maternal activity is permitted.
Various condition amenable to open fetal surgery include, congenital cystic adenomatoid malformation, pulmonary sequestration in which the mass is increasing in size, and other intra thoracic masses that may compress the heart or lungs. The goals here are to remove the masses to allow the lungs to grow, and to unobstruct systemic venous return. These resections are best done at 18-25 weeks of gestation. Airway disease include large neck masses, with anticipated difficult intubation at birth. This entails delivering fetal head through hysterotomy and managing the airway by direct laryngoscopy, bronchoscopy and intubation, while fetal gas exchange is maintained via the placenta. Of all the fetal surgeries, meningomyelocele closure has recently received the most attention. The goal here is to prevent a shunt dependant hydrocephalus and the further loss of spinal cord function. There is growing evidence that this loss of spinal cord function is due to both the embryonic defect and a secondary injury from exposure of neuronal tissue to the amniotic fluid. Unexpected benefits of the fetal closure have been found to be reversal of hind brain herniation, closure of Arnold Chiari defect and lower incidence of shunt dependant hydrocephalus. The procedure is best performed at 22-25 weeks gestation.
Anesthesia for fetal surgery is an exciting new field, the whole effort being a team approach. By constantly refining anesthetic techniques and readdressing important issues such as tocolysis, the anesthesiologist can not only play a vital role, but also help to establish improvements in care and research for years to come.
Reviewed by: Hoshang J. Khambatta, MD
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