Question

Why is deep general anesthesia required during fetal surgery for mom/baby?

Answer 1

The concept of the fetus as a patient has evolved from prenatal diagnosis and serial observation of fetuses with anatomical abnormalities.. Surgical intervention is considered when a fetus presents with a congenital lesion that can compromise or disturb vital function or cause severe postnatal morbidity. Hydronephrosis, saccrococcygeal teratoma, hydrocephalus, meningomyelocoele and diaphragmatic hernia are some of the defects that can be diagnosed by imaging and are amenable to intervention.

The combination of underdeveloped organ function and usually life-threatening congenital malformation places the fetus at a considerable risk. Fetal surgery also leads to enhanced surgical and anaesthetic risk in the mother including haemorrhage, infection, airway difficulties and amniotic fluid embolism.

There are 3 basic types of surgical interventions: 1.Ex utero intrapartum treatment(EXIT), 2.Midgestation open procedures, 3.Minimally invasive midgestation procedures. These procedures require many manipulations and monitoring in both the mother and the unborn fetusIntroduction

The concept of the fetus as a patient has evolved from prenatal diagnosis and serial observation of fetuses with anatomical abnormalities. Rh isoimmunisation provided the first successful example of fetal intervention wherein intravenous blood transfusion was undertaken in a hydropic fetus. Since then several fetal medical interventions like prenatal bone marrow transplantation and prenatal induction of lung maturity have been done1. The use of prenatal means of diagnosing anatomical defects is increasing with ultrasound and fetal magnetic resonance imaging. Surgical intervention is considered when a fetus presents with a congenital lesion that can compromise or disturb vital function or cause severe postnatal morbidity. Hydronephrosis, saccrococcygeal teratoma, hydrocephalus, meningomyelocoele and diaphragmatic hernia are some of the defects that can be diagnosed by imaging and are amenable to intervention2.

Correcting an anatomical malformation in utero with open fetal surgery jeopardizes the pregnancy and entails potential surgical and anaesthetic risks to the mother as well as the fetus. For this reason fetal surgery remains limited to conditions which if allowed to continue, would irreversibly interfere with fetal organ development but which if alleviated, would allow normal development to proceed. Malformations that qualify for consideration of fetal surgery should satisfy the following prerequisites:

Prenatal diagnostic techniques should identify the malformation and exclude other lethal malformations with a high degree of certainty.

The defect should have a defined natural history and cause progressive injury to the fetus that is irreversible after delivery.

Repair of the defect should be feasible and should reverse or prevent the injury process.

Surgical repair must not entail excessive risk to the mother or her future fertility

If new surgical techniques, physiological support systems and tocolytic therapy can reduce fetal and maternal risk to that of elective postnatal surgery, indications for fetal surgery may be liberalized.

Risks

The combination of underdeveloped organ function and usually life-threatening congenital malformation places the fetus at a considerable risk. Surgery and anaesthesia lead to significant risks to the fetus and can result in fetal death and morbidity. Altered coagulation factors predispose the fetus to bleeding and cause difficulty in achieving surgical haemostasis during fetal surgery. This problem is compounded by the small blood volume of the fetus. Fetal surgery can result in premature labor and birth. Initially surgeries were only performed in cases of impending fetal death.With the advancements in anaesthetic and surgical techniques, the risks have decreased and the indications broadened.

Fetal surgery also leads to enhanced surgical and anaesthetic risk in the mother including haemorrhage, infection, airway difficulties and amniotic fluid embolism. Only ASA class I and II mothers with very sick fetuses are taken up for fetal surgery. Fetal saccrococcygeal tumour leads to the ‘maternal mirror syndrome’, wherein the mother experiences progressive symptoms of preecclampsia due to release of toxins from the placenta.This syndrome is terminated by delivery of the fetus and placenta but not by the excision of the tumour.

Fetal surgery

There are 3 basic types of surgical interventions:

1.Ex utero intrapartum treatment(EXIT)3 These are also known as OOPS i.e, operation on placental support. These interventions are performed on vaginal delivery or caesarean section. Only a portion of the fetus is delivered and brief procedures such as endotracheal intubation or examination of neck mass done while the fetus is still connected to the placenta through the umbilical cord.Only brief procedures were possible as placental support rarely lasts for more than 10 minutes during routine births. Techniques are being evolved to allow placental support to continue for an hour or longer. It is possible to secure airway in cases ranging from cystic hygroma to complete high airway obstruction syndrome.The following procedures are being done as EXIT procedures:2.Midgestation open procedures Recognition of foetal defect in early pregnancy allows intervention in midgestation to prevent irreversible damage or development of secondary disease.Hysterotomy is required to access the foetus who is returned to the uterus after completion of surgery for the rest of the gestation. Fetal surgery is performed through a low transverse abdominal incision. Placental location is determined by ultrasonography and a wide uterine incision is given by a specially designed absorbable stapler for performing bloodless hysterotomy. The fetal part is exteriorized for surgery and after completion of the surgery the fetus is placed back into the uterus which is closed.

The fetus continues to grow for the rest of the gestation with reversal of the disease process that prompted the fetal intervention. Example is repair of meningomyelocoele at 22 weeks of gestation to prevent damage to central nervous system tissues due to prolonged exposure to amniotic fluid. The sequelae of bladder and bowel dysfunction and clubfeet may be prevented. The indications for open midgestation fetal surgery are:3.Minimally invasive midgestation procedures4 Because the uterus is a fluid filled organ, small endoscopes allow excellent visualization of fetal and placental structures as long as uterine distention is maintained with irrigating fluid.These are basically of 2 types:

1.Fetendo procedures-Aberrant placental vessels providing imbalance of blood flow to twins can be identified and ligated in this way to prevent fetal death due to twin-twin transfusion syndrome.Other surgeries possible with this technique are radiofrequency ablation or coagulation of non viable twin's umbilical cord in twin reversed arterial perfusion and division of amniotic bands in amniotic band syndrome. Using fetoscopy, these aberrant vessels and bands can be identified and coagulated. Fetal procedures, such as fetal cystoscopy with laser ablation of posterior urethral valves, are also now technically possible and are being undertaken.

2. FIGS-IT- This is a term used for fetal image guided surgery for intervention or therapy, and describes the method of manipulating the fetus without either an incision in the uterus or an endoscopic view inside the uterus. The manipulation is done entirely under realtime cross-sectional view provided by the sonogram. This is the same sonogram as is used for diagnostic purposes, but in this case is used to guide instruments.

Like Fetendo, it can be done either through the mother's skin or, in some cases, with a small opening in the mother's abdomen. It can often be done under a regional anaesthesia like an epidural or a spinal, or even under local anaesthesia. This is the least invasive of the fetal access techniques and, thus, causes the least problem for mother in terms of hospitalization and discomfort

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