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Repair
the defect before the damage occurs is the principle behind the fetal
interventions and surgery. However there are risks to the mother namely
premature labour, Chorioamnionitis, amniotic fluid leak, mandatory cesarean for
the current and subsequent deliveries. The risks to the fetus are prematurity
and even fetal demise. These risks have to be weighed against the benefits from
fetal interventions. Every fetus has to be evaluated for other associated anomalies.
If another life threatening or non-salvageable anomaly, either anatomical or
chromosomal, is present then implications of that should be discussed with
parents before attempting interventions. Karyotyping will be helpful in this
regard. With the advancement in technology and better outcome in the management
of premature babies the overall risk of fetal surgery has become lesser. This
has given rise to a renewed interest in fetal surgery.  Fetal surgery has become an extension of
pediatric surgery.

Fetal Interventions:

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Fetal surgery:

Fetal
surgery was first attempted at the University of California, San
Francisco in
1980 by Dr. Michael R. Harrison and his colleagues in animal models. In
1981 Dr. Michael Harrison performed the first successful vesicoamniotic
shunting for a baby with Posterior urethral valves 1.Later on open fetal
surgery for diaphragmatic hernia was done. Fetoscopic surgery became popular
for some conditions since fetoscopic surgery reduces maternal morbidity and
avoids the use of upper segment caesarian section. Techniques, risks and
outcomes vary with different procedures.

 

Anesthesia:

Relaxation of uterus is essential for fetal
surgery. Uterine contraction will lead to volume loss and repositioning the
baby in the uterus will become impossible. Uterus is not relaxed with muscle
relaxants. Uterine relaxation can be achieved by increasing the depth of
anesthesia but this in turn will produce myocardial depression of the mother
and fetus. This will reduce the placental circulation leading to hypoxic damage
to the fetus. The balancing act between the depth of anesthesia and sufficient
uterine relaxation is very critical for the survival of the mother and fetus. Tocolytics
can be used to help in uterine relaxation and prevent premature delivery.
Indomethacin a commonly used tocolytic, can constrict the fetal ductus
arteriosus, magnesium sulfate can produce maternal pulmonary edema.

Anesthetic preparation for open fetal surgery
is briefly as follows. Indomethacin 50mg suppository is given 2hrs prior to surgery.
Inhalational isoflurane or desflurane anesthesia is given. An epidural catheter
is placed. Ephedrine can be used to increase maternal blood pressure if needed.

Surgical steps:

Mother’s abdomen is opened and uterus exposed. Placental
position is marked with ultrasound scan. Uterine incision is made away from
placenta. If oligohydramnios is present Ringer lactate is infused into the
amniotic cavity to restore volume. Four through and through stiches are put in
a circular manner to get an avascular area in the middle of the sutures. An
incision is made here entering the amniotic cavity. A uterine stapler with
absorbable staples is used to make 6 to 8 cm long incision. The staples not
only gives hemostasis but also holds the amnion and chorion together preventing
their separation which if it occurs can lead to fetal loss.  Fetal anesthesia is given by injecting 10 to
20µg/kg fentanyl, 20µg/kg atropine 0.2mg/kg Vecuronium I/M. An I/V cannula is
put in one of the hands of the fetus which is delivered out. Fetal
echocardiography is continuously done to ascertain the right atrial load and
cardiac output which will indicate the need for blood transfusion. A pulse
oximeter probe is put on the hand to monitor saturation. However the fetal
saturation is only around 46 to 52% Nikolov so change in saturation is a
better indicator of hypoxia. Fetus responds to hypoxia with bradycardia so a
change in heart rate should be watched for.

The area of interest of the baby is delivered
out, not the whole baby, and surgery is performed. Fetus is put back into the
uterus and uterus closed in two layers after restoring the amniotic fluid
volume with warm ringer lactate. First through and through interrupted sutures
are placed and but not tied. After this, uterus is closed with a continuous
layer of absorbable suture. Interrupted sutures are tied after this. Mother is
put on Tocolytics post op. Epidural analgesia for about 3 days. 50 mg
Indomethacin suppository is given 6 hrly. for 48 hrs. Magnesium sulphate loading dose of
6gms is given and then 2 to 4 gms per hour infusion for 48 to 72 hrs. Then Mg.sulphate is tapered. Oral Nifidipine or Sub cut. Terbutaline pump is
given after this.

Most of these pregnancies go into preterm
labour 10 to 14 weeks after the initial surgery. Since the incision for the
fetal surgery is in the upper segment a second cesarean is mandatory to prevent
scar dehiscence.

Fetal interventions can be broadly divided into
two groups. Conditions that are lethal and conditions that are not lethal.
There are no ethical problems when we intervene when the life of mother or
fetus is at risk examples are fetal Congenital pulmonary malformations or
Sacrococcygeal teratoma where the fetus is going into hydrops. Decision making
becomes complex when surgery is attempted for non-lethal conditions like myelomeningocele
and posterior urethral valves. Here the baby can survive even if ante natal
intervention is not done. At the same time doing intervention cannot assure a
normal baby.

 

 

Posterior urethral valves:

The aim of fetal
surgery in Posterior urethral valves (PUV) is to relieve the obstruction before
renal damage occurs. First thing to make sure is that the irreversible damage
has not occurred already. Poor prognosticators are detection before 24 wks, Pelvic
dilatation of > 10mm, renal parenchymal echogenicity or cystic changes. Indications for
intervention are deterioration
in renal function indicated by Oligohydramnios AFI: 2 cm)
multiloculated cysts, type II has smaller uniform cysts, type III is not grossly
cystic, referred to as the adenomatoid type, appears as a solid mass . Compression by the mass leads to hypoplasia of
normal lung tissue, and cardiovascular compromise leading to fetal hydrops and
death .Esophageal compression by the thoracic mass causes interference with
fetal swallowing of amniotic fluid and results in polyhydramnios . Once the
fetus develops hydrops the mother develops maternal mirror syndrome in which she
develops preeclampsia mimicking the signs and symptoms of the fetus. Fetal
surgery does not reverse material condition. Hence it is important to do the fetal
surgery before the maternal mirror syndrome develops. Chromosomal anomalies are
not common in CPAM so karyotyping by amniocentesis and chorionic villus
sampling (CVS) is not warranted.

CCAM volume ratio (CVR) is a good prognostic
indicator.  CCAM volume is calculated by
using the formula for a prolate ellipse (length X height X width X 0.52). This
is divided by head circumference to correct for fetal size.  A CVR > 1.6 is predictive of increased
risk of hydrops Crombleholme. Fetal lung lobectomy is the definitive
treatment. Pre medication, anesthetic consideration and surgical steps are the
same as described before. After opening the uterus the side of the affected
chest is exposed. Chest of the fetus is opened through the fifth intercostal
space. Lobectomy is done. Chest is closed. Fetus put back into the uterus and
uterus closed as described before.  Post-natal
management with tocolytic is continued and baby delivered out as close to term
as possible at the same time not allowing the mother to go into labour for fear
of scar dehiscence.

Myelomeningocele

Damage to spinal cord
in myelomeningocele occurs due to three reasons.

Firstly there is
congenital dysplasia of the involved part. Secondly as the spinal cord floats
up through the vertebral defect there is tearing of the roots leading to
neurological deficit. Thirdly the fetal urine which forms the amniotic fluid in
the third trimester has a high content of urea which is toxic to spinal cord.
It is the second and third cause of damage that fetal surgery tries to prevent.
Spinal cord can regenerate till myelination occurs. Myelination occurs between
15th to 24th weeks of gestation. There for surgery has to
be done before 24 weeks of gestation. Ultra sound diagnosis is based on the
demonstration of cerebral ventriculomegaly, Microcephaly, Obliteration of cysterna magna, vertebral anomalies. Once diagnosis is established
screening tests are done which includes Maternal AFP >1000ng at 20wks, Amniocentesis and fluid assayed for AFP&
acetylcholinesterase, Karyotyping, U/S for leg movements. If ultra sound does not
demonstrate leg movements the damage is already done and fetus may not benefit
from ante natal surgery.

Surgery can be done
either fetoscopic or by open method.

Fetoscopic repair: Selection criteria
19 to 25wks gestation, Normal karyotype, no other anomalies, Lesion higher than
S2, Hind brain herniation with lateral ventricle less than 15mm Thomas Kohl. Mother
is catheterized. Placenta is marked out.  Position of the fetus is confirmed by on table
ultra sound to be in a favorable position. Three 5mm ports are used in the sub
umbilical position depending on the position of the placenta. 30 degree fetoscope
is introduced and the fetus visualized. About 200mls of amniotic fluid id
drained and replaced by carbon dioxide through an insufflator. The pressure at
which the gas starts flowing into the amniotic cavity is the opening pressure.
This pressure is maintained and amniotic fluid is further removed and replaced
with carbon dioxide till the myelomeningocele comes out of the amniotic fluid. The
rest of the baby remains immersed in the amniotic fluid. Insufflation pressure
can be increased up to a maximum of 30cms. Once the myelomeningocele is exposed
incision is made at the junction of the arachnoid and the skin. Skin is lifted
off the placode by undermining it. An absorbable patch is placed underneath the
skin covering the placode. Skin is approximated as much as possible and
attached to the patch. Another Gortex patch is sutured to the periphery of the
wound covering the surgical site and making it water tight. People also have
used a single layer of cellulose patch with good results Denis. Post op
management is same as described earlier.

Fetoscopic repair has
lesser morbidity to the mother compared to open repair in the form of lesser
chances of premature labour and need for a mandatory caesarian section for the
next and subsequent deliveries. However there are higher chances of oligohydramnios
because of the amniotic fluid leak through the trocar sites. This also leads to
Chorioamnionitis and fetal loss. Baby may need a formal repair of the
myelomeningocele after birth. Since numbers of cases done are small it will be
dangerous to make define conclusions at this point of time.

Open repair: Indications are same
as for fetoscopic repair. After opening the uterus as described earlier the
lumbar area of the fetus is exposed .Incision is made along the junction of the
arachnoid and skin. Neural placode is positioned in the vertebral canal. Dura
closed over it with continuous suture. Myofascial flaps closed over it and
finally skin is closed. If defect cannot be closed then patch can be used as in
fetoscopic repair. Uterus is closed after restoring amniotic fluid volume with
Ringer lactate as described earlier.

A large multicenter
study called MOMS trial was under taken to compare the benefit from antenatal
surgery and post-natal surgery Azdic. At one year of age: Requirement of
shunt occurred in 40% of prenatal surgery group while it was 80% in postnatal
surgery group. Hind brain herniation occurred in 64% of prenatal group while it
was 96% in post-natal group. At 30 months of age 42% walked without support in
prenatal group while only 21% in postnatal surgery group. This clearly
indicated that prenatal repair had a better outcome.

 

EXIT procedure (Ex
utero intrapartum treatment)

This procedure is attempted when there is airway obstruction and baby
will not be able to breath after delivery. Usual conditions that produce this
are large cystic hygromas and mediastinal tumour. Here the baby is intubated
before the cord is clamped and placental separation occurs.  This involves preventing the uterus from
contracting during the procedure at the same time facilitating the uterine
contraction after the procedure to prevent post-partum haemorrhage.

Maternal anesthesia is given by rapid sequence. Thiopental 5mg/kg; succinylcholine 2mg/kg, Fentanyl 1to 2 µg/kg I/V followed by intubation.
Maternal oxygenation & BP maintained within 10% of base line

BP elevated with
Ephedrine to counter act the hypotensive effect
of volitional agents. Ephedrine acts
selectively on the peripheral resistance sparing placental circulation.  Cardiac rate rather than the stroke volume
determines the cardiac output in fetus. Cardiac output of fetus is dependent on
the rate rather than stroke volume. They have a high vagal tone and low baroreceptor
sensitivity. This makes them respond to stress with bradycardia. Inhalational
anesthetic agents can cause myocardial depression and vasodilatation leading to
hypotension. The procedure can be divided into two stages.

Stage 1

Inhalational agents
used at minimum level first and then increased before maternal incision (isoflurane,
sevoflurane).Tocolytic supplementation is given
with indomethacin, Terbutaline or nitroglycerine. Maintenance of uterine volume
is achieved by delivering only the head and neck of the fetus outside the
uterus. Uterine contraction will lead to placental separation.

Fetal anesthesia is
given before fetal incision. 10 to 20µg/kg fentanyl, 20µg/kg atropine, 0.2mg/kg
Vecuronium I/M is given to the fetus to prevent fetal movement. Baby is
intubated and cord clamped if possible otherwise the neck or mediastinal tumour
is dealt with first to facilitate intubation and then cord is clamped.

Stage 2 starts just
before clamping the cord. Volatile anesthetic is reduced to minimum, Oxytocin
20units in 500mls of normal saline is given as bolus followed by 10units in
1000mls drip, uterine massage is done if uterine contraction is not adequate,
0.25mg Methergine & 250µg of F2 alpha prostaglandin is given to augment
uterine contraction. This is followed by reversal of maternal paralysis.

 

Congenital diaphragmatic hernia

Fetal management congenital
diaphragmatic hernia (CDH) is constantly evolving. Initially hysterotomy and
open repair of CDH was tried but most of the mothers went into premature
labour. The advantage lung growth obtained was neutralized by the prematurity
and overall survival rate was not different when compared to standard
post-natal repair. So this was given up. Harrison 1 This was followed by
tracheal occlusion by clipping done either by hysterotomy or fetoscopically.
Tracheal occlusion leads to accumulation of lung fluid in and expansion of the
lung. It also leads to maturation of the pneumocytes. Clip was removed at birth
before the cord was clamped. This was an also associated with premature
delivery and over inflation of the lung. At present a detachable balloon is
used to occlude the trachea. This is introduced through a fetoscope. Fetoscope
is introduced through the abdominal wall of the mother, through the uterus into
mouth of the fetus. It is then passed over the tongue, over the epiglottis into
the trachea till carina is visualized. Balloon is inflated in the trachea just
abov the carina. Twisting of the stem will detach the balloon. Procedure is
done around 26 wks. To prevent over inflation of the lung the balloon is
deflated by ultra sound guided needle puncture by 34 wks. of gestation. If the
deflated balloon does not come out when the child cries after birth it is
removed by a tracheoscope. If balloon deflation is not done antenatally it has
to be removed at birth with a bronchoscope.

Indications for fetal
intervention are left sided hernia, liver in the chest and LHR at 26 to 28 wks is
less than 1. If LHR is more than one then they have a fair chance of survival
with conventional postnatal management and antenatal surgery is not indicated.

So far the number of
cases done is small but the results are encouraging. Ulatra sound scan post
balloon deployment showed an increase in LHR.Deprest An international trial
called FETO trial is going on and the results will make clear the advantage of
FETO over conventional post-natal management.

The main problem with
all fetal surgical care is the onset of premature labour. In some cases like CDH,
posterior urethral valves and myelomeningocele some damage would have already
occurred to the concerned organ that we cannot promise a normal child to the
mother. Parents should be well counselled as to the advantages and risks before
attempting any intervention.

 

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