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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5786_Библиотеки_им_академика_М_И_Перельмана.pdf
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In the vast majority of cases, a regular 20 gauge needle with a length of 12–15 cm
excluding the hub will be chosen. This offers a good combination of length and
rigidity and may even be inserted through thick abdominal walls followed by a
rapid fluid withdrawal. There is no strong evidence that the use of smaller bore
needles decreases the procedure's complication rate.
Safety
Fetal loss rates for mid-trimester amniocentesis are best expressed through a randomized clinical trial of genetic amniocentesis involving 4606 low-risk women
who were randomized to have either an amniocentesis or an ultrasound examination.8 All procedures were performed by five physicians at the same institution
using a 20 gauge needle. The study group had a higher rate of spontaneous abortion compared with the control group (1.7% vs 0.7%; OR 95% 2.3(1.3–4.0);
p<0.01). The authors also underlined that 1% might be an underestimation of the
actual procedure-related risk since termination of the affected pregnancies in the
study group and not in the control group may have artificially decreased the spontaneous fetal loss rate. Risk factors included high maternal serum α-fetoprotein
(AFP), perforation of the placenta and discoloured (brown- and green-stained)
amniotic fluid. Technical difficulties and multiple needle insertions have also
been implicated as causes for an increased rate of pregnancy loss.
10,11
Invasive procedures in obstetrics
Amniocentesis in multiple gestations
Amniocentesis in twin pregnancies has traditionally involved puncture of the first
sac, withdrawal of amniotic fluid, injection of a dye and then a new needle insertion to puncture the second sac. When the second sac was sampled, the fluid was
then supposed to be free of dye. The disadvantage is that two punctures of the
skin and of the uterus are necessary, potentially increasing the procedure-related
risk. In addition, with the injection of dyes, a foreign substance is introduced into
the amniotic cavity of one of the fetuses, and neonatal occlusion of the intestinal
tract has been reported after injection of methylene blue.
We therefore recommend a single-needle insertion technique. The site of the needle insertion is determined mainly by the position of the membrane separating the
two sacs. After entry into the first sac and aspiration of amniotic fluid, the stylet is
replaced in the needle which is then advanced sharply through the dividing membrane
into the second sac. To avoid contamination of the second sample with any amniotic
fluid from the first sac still in the needle, the first 1 mL of fluid is discarded.
12
FETAL BLOOD SAMPLING
Ultrasound-guided fetal blood sampling (FBS) or cordocentesis or funipuncture
has developed since its introduction by Daffos et al in 1983.13 In low-risk pregnancies FBS can be performed from 20 weeks onwards when the size of the
umbilical vein allows for the procedure to be safely performed.
FBS shares the same diagnostic indications as amniocentesis or CVS when
this is done after 20 weeks of gestation. FBS has specific therapeutic indications
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NO
NO
YES
YES
Catheterization of the vein
Catheterization of the vein
A
90° to the insertion
90° to the insertion
YES
YES
B
Insertion unattainable
Insertion unattainable
NO
NO
Free loop stuck on the placenta
Free loop stuck on the placenta
such as intrauterine fetal blood or platelet transfusions in severe fetal anaemia or
alloimmune fetal thrombocytopenia respectively.
Technique
The aim is to puncture the cord at the placental cord insertion. All procedures can
be planned as access to either an anterior placenta, with a direct transplacental
access to the umbilical vein, or to a posterior placenta with a transamniotic access
to the vein. Ultrasound examination should therefore carefully assess the entire
placental surface to plan the procedure. Local anaesthetic is not necessary for diagnostic procedures but it is a useful adjunct in intrauterine blood transfusions.
An anterior placenta makes cord insertion technically easier; the umbilical
•
vein insertion on the placenta should be visualized in the ultrasound plane
(Fig. 12.4A) with an angle which allows the needle to be directed to the vein.
Posterior placenta and cord insertion requires a transamniotic approach
•
to the cord insertion. The needle should puncture the umbilical vein at
Ultrasound in obstetrics and gynaecology
an angle as close to 90° as possible; indeed, the smaller the angle, the
higher the risk of hurting the cord and lacerating the vessels (Fig. 12.4B).
Indenting the cord under gentle needle pressure should precede a sharp
and controlled puncture.
When the cord insertion is not accessible, for example in cases with a
•
posterior placenta when the fetus is lying on the insertion, the needle can be
directed towards the intrahepatic umbilical vein. A transverse view of the
fetal abdomen should be obtained with the fetus lying on its back or side.
236
Fig. 12.4 Ultrasound-guided funipuncture in an anterior placenta (A) and a posterior
placenta (B).
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One should avoid aiming at a free loop. The target is mobile and therefore
•
the cord puncture is uncertain; it can lacerate the cord and the vessel to be
punctured cannot be chosen, thus increasing the risk of arterial puncture.
When this situation cannot be avoided, the loop should be pushed onto
the placental surface and then punctured sharply.
When FBS is undertaken after 28 weeks, it should ideally be performed after a
course of steroids for fetal lung maturation. The procedure should be attempted
in an operative theatre to allow an emergency caesarean section if fetal distress
occurs. This should be discussed with the parents prior to the procedure.
A total volume of 2–5 mL of blood is sampled in 1 mL syringes; this may contain a small amount of heparin or citrate, depending on the investigations to be
performed. The sample should be immediately placed in the appropriate containers and the purity of blood assessed by the haematology lab. This will generally
involve comparisons of mean corpuscular volumes (MCV) in fetal and maternal
blood samples. Depending on the indication, determination of white blood cell
count, differential cell evaluation, blood and Rh grouping, anti-I and anti-I antigen,
Kleihauer–Betke test, concentration of β-human chorionic gonadotropin, factors
IX and VIIC, and AFP levels in maternal and fetal blood may be necessary.
Complications
The overall fetal loss rate due to cordocentesis is estimated to be 1% in a low-risk
14
population.
However, there is great variation in the series published, with rates
ranging from 0% to 12%.14 There is a negative correlation between fetal loss rate
and the size of the series published. Furthermore, several authors have pointed
out that there is a distinct learning curve for the performance of cordocentesis.16
The first 100 procedures are critical regarding maximal loss rate and the procedure should be regularly practised.
15
The presumed causes of pregnancy losses following cordocentesis are: chorioamnionitis, premature rupture of the membranes, fetal exsanguination, severe
bradycardia and cord haematoma. The duration and difficulty of the procedure
are major risk factors. These complications are more prone to occur when the cord
is punctured through a transamniotic approach, especially in a free loop. Bleeding
occurs in 60–70% of these cases and lasts for less than 1 minute in the vast majority of cases. Bradycardia below 100 beats/min occurs in 10–20% of arterial punctures, usually as a result of a vasospasm. The mother should be placed on her left
side and breathe oxygen; 0.5 mg of atropine can be used occasionally. A rare but
serious cause of bradycardia is cord haematoma; this can arise as a consequence of
cord laceration in difficult procedures and can lead to cord tamponade.
Invasive procedures in obstetrics
INTRAUTERINE FETAL BLOOD TRANSFUSION
16
The technique of fetal blood transfusion has a lot in common with that of cordocentesis. However, preparation should allow for a good catheterization of the
umbilical vein by inserting the needle in alignment with the cord insertion. Initial
sampling will serve to establish the starting haemoglobin and/or platelet count.
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The former will be quickly established using a proper analyser in the operative
room. In intravascular blood transfusion, either top-up or exchange transfusions
can be used with no clear advantage of one technique over the other. In most centres the top-up technique is used.
The main indications for intrauterine fetal blood transfusions in severe (<9 g/dL)
fetal anaemia are red cell alloimmunization, fetomaternal haemorrhage and parvovirus B19 infection with fetal hydrops. The volume of blood to be transfused (V)
depends upon several factors:
V = Vf(H2−H1)/Ht
where H1 = preoperative fetal Hb concentration (g/dL), H2 = fetal Hb concentration expected at the end of the procedure, Ht = Hb concentration in the donor
blood, optimally around 70–80% and Vf = fetal blood volume (80 mL/kg). The
final haemoglobin concentration should roughly be 14 g/dL in the presence of
hydrops and 16 g/dL in the absence of hydrops.
In severe fetal anaemia before 18–19 weeks, intraperitoneal blood transfusion
is an alternative which can be life saving. Very rarely, in cases of fetal terminal
Ultrasound in obstetrics and gynaecology
anaemia with bradycardia, intracardiac blood transfusion can be given in the left
ventricle of the heart.
23
In severe fetal alloimmune thrombocytopenia (<50,000 platelets/dL), intravascular platelet transfusion may be indicated and should be repeated weekly if gestational age is still remote from term. One platelet unit of 10 mL usually brings fetal
platelet count up to 100,000 platelets/dL. However, this is usually a second-line
treatment given only when maternal administration of corticosteroids and nonspecific immunoglobulins has failed to improve fetal platelet count in 6–8 weeks.
238
Complications
The complications are similar to those of FBS. However, cord haematoma/tamponade is more frequent in transfusions, especially with fetal movements and
needle displacements in the absence of curarization. Fetal bradycardia is more
frequent in arterial transfusion.
Specific complications due to administration of blood products can be overcome by selection of blood negative for CMV, hepatitis and HIV. Twenty-fiveGy
irradiation of the blood will prevent graft vs host immunization, and separation of
blood cells will allow for concentrated blood or platelet units to be prepared.
Prevention and early recognition of these complications involve checking the
fetal heart rate and contractility during the procedure as well as the direct flow of
the blood transfused in the umbilical vessel. The procedure should be discontinued
when bradycardia or a decrease in ventricular contraction arises or when the needle
placement is uncertain or when an echogenic area develops within the cord.
FETAL SHUNTS
Recognition of fetal obstructive diseases by prenatal ultrasound examination has
made it possible to envisage in utero derivation of the obstructed cavity/organ
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into the amniotic cavity. Fetal shunting should be contemplated only for conditions frequently associated with significant mortality and morbidity since there is
sufficient evidence from both animal and human data that the natural development can be altered by the procedure.
Fetal shunting has been performed for a variety of conditions including obstructive uropathies, hydrocephalus, pleural effusion, pulmonary cysts and ascites.
To date, however, only three diseases still leave some scope for antenatal shunting
in carefully evaluated cases: obstructive uropathy, macrocystic congenital cystic
malformations (CCAM) of the lungs or compressive pleural effusions when complicated by fetal hydrops.
Permanent irreversible renal damage can only arise from bilateral urethral
obstruction or low obstruction such as in posterior urethral valves or urethral
atresia. The only condition whereby unilateral obstruction could indicate invasive
renal assessment including drainage is in severe pyeloureteral junction obstruction with contralateral renal agenesis. In these situations, an ultrasound assessment alone has a low sensitivity which can be increased by the analysis of urine
concentrations of calcium and sodium which have the best sensitivity and specificity, respectively. β2-microglobulin concentration in the fetal plasma is another
useful marker in obstructive uropathies. Urine biochemistry cannot be assessed
by a single evaluation and this should be repeated at 1–2 week intervals.17 This
should precede indications for bladder shunting. Fetuses with persistent megacystis who have ultrasound-based and biochemical evidence of adequate renal function are the most likely group to benefit from shunting. However, close follow-up
of this group should be done in order to redefine indications for shunting fetuses
with obstructive uropathy, mainly when the obstruction is severe and biochemically assessed renal function is normal at a gestation still remote from term.
Complete drainage of the fetal bladder might be unsuccessful at obtaining
resolution of hydronephrosis or ureteral dilation; this is usually due to a bladder
wall hypertrophy responsible for subsequent low bilateral ureteral obstruction,
massive reflux, ureterocele or a combination of these.
Thoracoamniotic shunting in CCAM or in pleural effusions should only
be attempted in severely compressive conditions. The fetus would therefore be
hydropic and signs of thoracic compression should be present with at least one
of the following: polyhydramnios, severe mediastinal shift, eversion of the diaphragm and venous and cardiac compression as documented by a reverse flow in
the ductus venosus Doppler waveform during atrial contraction.
Shunting should result in immediate and nearly complete drainage. Incomplete
drainage with failure of the lungs to expand and fill the chest following pleuroamniotic shunting, although technically satisfactory, should raise the suspicion of
pulmonary hypoplasia.
Invasive procedures in obstetrics
Techniques
Extensive counselling by an experienced operator and consultation with a neonatologist and most often a paediatric surgeon are essential prerequisites for
shunting.
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A
B
C
The shunting can be performed as an outpatient procedure with a mild maternal sedation (diazepam or Rohypnol 10 mg) given orally as well as prophylactic
tocolysis with indometacin (50 mg suppository) and antibiotics can be recommended for maternal and operator comfort although there is no strong evidence
that they have a significant impact on the outcome. Fetal analgesia may be given
(sufentanyl 0.5 μg/kg) in the umbilical circulation and pancuronium may also be
administered for fetal paralysis (10 μg/kg). This involves performing a cordocen-
tesis as described above.
The most widely used catheter in Europe is the Rocket (Rocket of London
Ltd, Watford, UK) developed by Rodeck et al in 1982.18 It is a double-pigtail
silastic catheter with an external diameter of 2.1 mm, with radio-opaque stainless steel inserts at each end and lateral holes around the coils which are preformed at right angles to each other. This makes dislodgement less likely. The
catheter is introduced through a cannula loaded with a sharp triangular-shaped
trocar mounted on a handle. The external diameter of the 18 cm long trocar is
2.5 mm (Fig. 12.5).
Ultrasound in obstetrics and gynaecology
The best transverse section of the fetal target is obtained without magnification
and the expected site of entry in the fetus is placed in the centre of the screen.
Local anaesthetic is administered as previously described. If there is oligohydramnios, a 20 gauge needle is first passed into the amniotic cavity and an amnioinfusion given with 150–200 mL of warmed normal saline. This may improve the
image and allow the anomaly scan to be completed, but its main purpose is to
facilitate the deposition of the intra-amniotic end of the catheter.
240
Fig. 12.5 Shunting instruments. (A) Cannula. (B) Trocar. (C) Double-pigtail catheter.
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The trocar and cannula are introduced into the amniotic cavity and then
inserted through the fetal cavity to be drained. After checking that the cannula
is in the correct position, the trocar is removed and the end of the catheter is
blocked with the operator's finger. The fetal catheter is straightened out on its
wire and inserted into the cannula. The guidewire is removed and the shorter
obturator pushes half the catheter out and this coils up inside the fetus in the
fluid. The cannula is carefully drawn back into the amniotic cavity where the
other half of the catheter is deposited by the longer obturator. This requires fluid
in the amniotic cavity.
In bladder shunting, the shunt should be inserted suprapubicly and away
from the midline. In thoracic shunting, the shunt should be inserted in the
midthoracic region below the scapula and posterior to the axillary midline in
order to minimize the risk of catheter dislodgement by the fetus. If drainage
from the contralateral region is also needed, fetal curarization will usually allow
rotation of the fetal body with the tip of the cannula once the trocar has been
removed.
Complications
The fetal loss or premature delivery rate can be roughly estimated to range
between 5% and 15%, often preceded by rupture of the membranes and/or chorioamnionitis, depending on the operator’s experience and the gestational age at
which this is performed. Other complications are more frequent, such as inadequate drainage (20%) or shunt dislodgement. Dislodgement can happen either
spontaneously or by the fetus itself in up to 25% of cases. Most dislodgements
will cause externalization of the catheter in the amniotic fluid which must be
checked at the time of delivery; however, some catheters are occasionally displaced into the cavity they were meant to drain and they should be surgically
removed postnatally.
Some complications are rare but could cause technical and clinical management dilemmas. Urinary ascites is usually associated with vesicoamniotic shunt
dislodgement and can indicate peritoneo-amniotic drainage. Amniotic fluid leakage to the maternal peritoneal cavity can occur through the path of the trocar, causing painful maternal chemical peritonitis; this often requires morphine
administration but will resolve spontaneously within hours.
Invasive procedures in obstetrics
Delivery and shunt removal
Mode of delivery should not be influenced by the presence of the shunt. However,
an experienced neonatologist should be present at delivery. A vesical shunt should
be left in situ and be used for postnatal drainage until surgical correction of the
problem. There is no consensus with regard to pleural shunts; however, immediate clamping is a reasonable option, followed by gentle ablation once respiratory assistance has been started. The main risk is for a pneumothorax to develop.
When the shunt cannot be found at birth, both the neonate and the mother
should undergo x-ray to locate the radio-opaque steel tips of the shunts.
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Outcome
Selection of cases of obstructive uropathies is a difficult process and there are
no randomized trials or detailed long-term studies that assess the benefit of
vesicoamniotic shunting. A major worry is the transformation of a group of neonates who would have died without a shunt into a group of severely chronically
ill survivors. There seems to be a strong incentive to drain early in the obstructive process which could be picked up in the late first trimester. However, such
a policy would require the creation of adapted instruments; it would also be
necessary to randomize the cases for future evaluation.
Shunting for thoracic fluid is less controversial when the cases are selected
on the presence of hydrops due to thoracic compression and the benefit can be
assessed in utero and soon after birth.
DIAGNOSTIC AND OPERATIVE FETOSCOPY
Embryo-fetoscopy is a relatively old technique that allows the direct endoscopic
visualization of the embryo or the fetus by introducing an endoscope through the
Ultrasound in obstetrics and gynaecology
cervix or through the maternal abdomen and the uterine wall. This was also the
first manner of guidance for performing fetal blood sampling through an operative channel of the scope. The development of high-resolution ultrasonography
made the technique obsolete in the late 1980s. However, technical development
has also enabled the construction of new endoscopes with a diameter less than
3 mm. The field of view in these endoscopes is rather limited and all of them must
be introduced and moved inside the amniotic cavity under ultrasound guidance.
At present there are hardly any indications for embryoscopy between 11 and
14 weeks. With high-resolution transvaginal ultrasound, one can do a thorough
work-up of the fetal anatomy.
The only established indication for operative fetoscopy to date is for fetoplacental surgery in the severe complications affecting monochorionic multiple
pregnancies. Such complications mainly represent the severe twin-to-twin transfusion syndrome (TTTS), acardiac twinning and discordant anomalies in monochorionic twins when the abnormality is not lethal and/or has a threatening effect
on the whole pregnancy, i.e. polyhydramnios in the sac of an anencephalic fetus.
The target of the fetoscopically assisted procedure is then either the placental
surface such as in TTTS or the umbilical cord of a monochorionic twin to be
selectively coagulated.
The technique involves percutaneous introduction of a trocar which will carry
the fetoscope, as well as a 400–600 μm Nd:YAG or diode laser fibre, under ultrasound guidance after local analgesia has been given, as previously described.
One should avoid penetrating the placenta. When the placental surface must be
explored, the trocar is introduced away from the stuck donor twin and at right
angles to it, in order to maximize the chances of being able to follow the insertion of the intertwin membrane which usually runs close and parallel to the long
axis of the donor twin in an oligohydramniotic sac. Identification of the vessels to
242
coagulate and the technique of coagulation are described elsewhere.
19
19
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PREGNANCY REDUCTION IN MULTIFETAL PREGNANCIES
In the absence of fetal abnormalities, embryo reduction is medically justified in
quadruplet and higher-order pregnancies resulting in a significantly better outcome for the reduced pregnancies.24 In twins, very few indications would be
accepted by most operators beyond selective fetocide for fetal abnormality.
The optimal number of fetuses to be left alive is now widely accepted to be
two as an ideal compromise to allow for a good neonatal outcome of the survivors and an acceptable procedure-related fetal loss rate. Indeed, the neonatal
outcome improves as the number of live fetuses decreases, but the fetal loss
rate increases inversely. Preoperative counselling should discuss the 6–15% fetal
loss rate before 24 weeks of gestation, mainly between 2 and 8 weeks after the
procedure.
The optimal gestational age at which reduction should be performed is still
debated but is focused at around 11 weeks. Indeed, the spontaneous fetal loss rate
decreases from 15% to less than 2% between 5 and 11 weeks of gestation. The NT
measurement as well as an early examination of the fetal anatomy can therefore
be performed to help select the fetuses to be reduced. When the fetuses cannot be
selected on this basis, fetocide will be targeted to the fetuses which are most easily accessible, therefore closer to the fundus of the uterus when the procedure is
performed transabdominally. Multifetal pregnancy reduction can only be contemplated in dichorionic fetuses. If the multifetal pregnancy includes a set of monochorionic twins, both should preferentially be reduced, since reducing one fetus could
precipitate acute haemodynamic changes in its co-twin and lead to the development of severe sequelae. Monochorionic twins can also develop TTTS in up to 14%
of cases.
Careful and precise mapping of the fetuses and the trophoblasts should be
done prior to the procedure in cases where the heart would only stop temporarily, there would be a high risk of abnormal fetal development and the procedure
should therefore be completed.
24
Invasive procedures in obstetrics
Technique
Although transabdominal and transvaginal techniques are equally effective, a
transabdominal approach should be used whenever possible since it will preserve
fetuses closer to the cervix and therefore potentially decrease the risk of preterm
premature rupture of the membranes and/or infection.
Asepsis should be obtained as described for any invasive procedure. A transverse view of the thorax of the fetus(es) to be reduced is placed in the middle of
the screen and the needle should be introduced so that the sac of embryos which
are meant to remain alive is not perforated. Local anaesthetic is given down to
the myometrium. A 20 gauge needle is directed in the fetal thorax and 1–2 mL
of a mixture of fentanyl and potassium chloride is injected into the fetal heart/
thorax. The needle is left in place for 15–30 seconds after the heart has stopped
beating to confirm fetal death. When another embryo is to be reduced, the needle
is then pushed through the dividing membranes sharply to avoid tenting and the
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procedure is repeated on the second fetus. Amniocentesis/amniodrainage of the
sac of the reduced fetus is unnecessary and potentially deleterious.
SELECTIVE FETOCIDE FOR FETAL ABNORMALITY
This represents an indication for fetocide to be performed in a twin or higherorder multifetal pregnancy. The same technique applies to these cases. The risk
of miscarriage roughly doubles after 16 weeks. Therefore, in order to obtain
early information of the karyotype, first-trimester screening by NT measurement and CVS is advisable in multiple pregnancies when one fetus is at high
risk of fetal abnormality or aneuploidy. In late gestation (>20 weeks), sufentanyl
followed by KCl can be injected in the umbilical vein using the same technique
as that described for intrauterine transfusion. This avoids the potentially painful and often difficult intracardiac injection at this gestation. Abortions later
than weeks 22 or 24 are accepted in only a few countries. The same goes for
fetocide.
Ultrasound in obstetrics and gynaecology
In monochorionic multiple gestations, KCl injection cannot be used for selective fetocide. Indeed, this would precipitate an acute hypotensive episode in the
surviving twin through bleeding into the dead co-twin through the placental
anastomoses still present on the placental surface. This would occur irrespective of the histological nature of the vessels. The alternative is to coagulate the
umbilical cord. This can be achieved using Nd:YAG laser technology when the
cord is still small in diameter; however, the technique may not be used after
20 weeks of gestation. Alternatively, a bipolar forceps of 2–3 mm has been developed that can be passed down a cannula under ultrasound guidance and grasp
the cord to coagulate. This is done under continuous ultrasound/colour Doppler
control. This efficient technique is still under evaluation. The subsequent risk of
preterm premature rupture of the membranes is not precisely known, but could
be as high as 20–30%.
244
CONCLUSION
Ultrasound-guided invasive procedures represent the foundation for fetal
medicine. They can be learned as variations of the same technical approach,
implying the use of both hands of one operator which would shorten the
learning curve and improve the safety of the most frequently performed
procedures, such as amniocentesis and CVS. There is rarely such a thing as
a difficult procedure when done by a well-trained operator who performs
a high number of invasive procedures. In addition, it is important to plan
the procedure well by following the simple rules mentioned in this chapter.
Ultrasound examination prior to performing the procedure is therefore a key
element. Visualizing the target and the entry point on the maternal abdomen
ensures a straightforward path without interposition of any fetal structures
in the path of the needle.