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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5817_Библиотеки_им_академика_М_И_Перельмана.pdf
Doppler Ultrasound Diagnosis in Preeclampsia, Eclampsia, and HELLP Syndrome
2
Hypertension
Brain
Generalizedvasospasm
Fig. 10.1 The effects of vasospasm on various organs and
development of symptoms.
viscosity, resulting in reduced perfusion. At the same
time colloid osmotic pressure and the plasticity of the
erythrocytes decrease.
Our own research showed that in women with preeclampsia uterine and renal vascular resistance was increased. In order to determine if this increase in resistance also affected other maternal vessels, we additionally examined the thyroid vessels. In these vessels
there was no difference in perfusion between women
whose pregnancy was normal, and those who suffered
from preeclampsia, suggesting that the increase in resistance in the uterine and renal vascular beds must be
of local origin. The reduction in perfusion in our preeclamptic population was more marked in the kidneys
than in the uterus.
Another attempt to explain the pathogenesis of
preeclampsia was by abnormal immune processes.
However, despite an increase in antibody formation in
preeclamptic women so far no unequivocal evidence
has shown this process to be causative in the clinical
Placenta
Kidney
Liver
Retina
Headache,
seizures
Placental abruption,
high infantile mortality
Oliguria,
acute renal failure
Jaundice,
acute hepatic failure
Double vision,
amaurosis
picture of preeclampsia.
The primary symptom of preeclampsia is a rise in
blood pressure in the course of pregnancy. The course
of preeclampsia is monitored by following blood pressure and edema, as well as total protein and uric acid.
Other available options include quantitative monitoring of albuminuria, ultrasonic monitoring of the fetus,
and cardiotocography. Doppler ultrasound can provide
important information concerning fetal condition in
clinical picture.
Changes in the placental vascular bed can be demonstrated by tissue examination in patients with preeclampsia and are relatively common. In such cases
changes in the maternal vessels supplying the placenta
may be demonstrated by Doppler ultrasound. Such
Doppler sonographic changes can at times be demonstrated long before clinical symptoms appear, making
Doppler ultrasound a future screening tool for preeclampsia (cf.
placental bed on the maternal side do not necessarily
signify anomalies on the fetal side. In this respect the
placenta has an enormous compensatory capacity.
As is to be expected, elevated blood pressures in the
mother without placental changes are accompanied by
normal flow profiles in the fetal and fetoplacental vessels.
There are altogether three indications for using Doppler ultrasound in diagnosis:
1. To anticipate or screen for the risk of preeclampsia
by examining the uteroplacental vessels in the first
or second trimester.
2. To confirm a diagnosis of preeclampsia in the second half of pregnancy by finding changes characteristic of preeclampsia in the uteroplacental bed,
such as a notch or corresponding increases in resistance, correlating with a poorly developed
placental vascular bed.
3. Evaluation of the fetal or fetoplacental vessels to exclude any risk to the fetus. The examination determines how the fetus is coping with the changes resulting from the preeclampsia.
Chapter
9, p.쏝). However, changes in the
104
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Evaluating the Risk of Preeclampsia in the First and Second Trimesters
Evaluating the Risk of Preeclampsia in the First and Second Trimesters—Examining the Uteroplacental Arteries
A significantly increased pregnancy risk results from
failure of the adaptations needed to cope with the increased perfusion demand of the uteroplacentofetal
unit.
At the onset of the second trimester a physiological
vasodilatation—probably the result of NO—leads to a
demonstrable rise in diastolic flow rates in the uteroplacentalaa. At theend of the26th week ofpregnancy at
the latest this leads to the disappearance of the late systolicnotch in the waveformof these aa. (Campbell 1993,
Fleischer et al. 1986). These physiological changes are
designed to provide an adequate blood supply to the
placenta in the third trimester and, if they fail to occur,
the result is often preeclampsia, gestational hypertension, or fetal growthrestriction (Brosens 1977, Campbell
et al.1983, 1986, Cohen-Overbeek etal. 1985, Hackettet
al. 1986). Vascular occlusion leads to the same result
(Sheppard and Bonnar 1980). By means of placental biopsies Voigt and Becker (1992) were able to demonstrate a correspondingly close correlation between
morphological changes in the placental vascular bed
and the uteroplacental waveform.
Doppler Ultrasound Findings
A late systolic notch in the waveform af ter the 26th
week of pregnancy reflects pathological changes in the
placenta. This notch is an expression of the increased
peripheral resistance opposing the pulse wave
generated by the ejection phase of the cardiac cycle.
Such an increase in resistance, which is the result of vasoconstriction, canonly be generated because too many
blood vessels, for this gestational age, are still surrounded by a muscular layer. By contrast, in a normal
pregnancy blood vessels without muscle fibers are the
preponderant vessels at the end of the 26th week of gestation at the latest. This reduces the peripheral resistance and leads to the disappearance of the notch.
CalculatingDoppler indices such as the pulsatility index
(PI), resistance index (RI), or ratio of systolic peak to
end-diastole(A/B ratio) is of no great value indetermining pathological changes in the first half of pregnancy.
Thus, a postsystolic notch in the uteroplacental vessels is abnormal in the second half of pregnancy. As
notedabove, it probablyrepresents theresult of a defective trophoblast invasion during placentation in the
first half of pregnancy. Campbell et al. (1983) considered the notch to be the characteristicDoppler sono-
graphiccorrelate of preeclampsia. Fleischeret al. (1986)
considered the notch, when accompanied by hypertension, highly associated with dystocia and prematurity,
with a sensitivity of 83% and a specificity of 95%. Thus,
according to Gonser and Vetter (1995) this characteristic dual-phase notch is a better indicator of hypertensive complications of pregnancy than, for instance,
creatinineclearance or plasma uric acid level.Kofinas et
al. (1989) were able to demonstrate that the incidence
of preeclampsia or intrauterine growth restriction
(IUGR) was greater with unilateral implantation of the
placenta than with central implantation. Gonser et al.
(1993) made the complementary discovery that in the
case of a unilateral placenta the findings from the
uterine aa. on the contralateral side correlated significantly with the clinical and metabolic condition of the
newborn:Where a notchis found, theoutcome is significantly worse than when this is absent. According to
Thaler et al. (1992),when a notchis found, theincidence
of cesarean section for abnormal cardiotocogram (CTG)
is also increased. The subjects in all the studies cited so
far were from a high-risk population. Steel et al. (1990),
on the other hand, studied the possibility of including
Doppler sonography of the uteroplacental vessels in a
screening protocol for preeclampsia, by examining the
uterine aa. of a population of healthy pregnant women
during the 18th and 24th weeks of pregnancy. In cases
where the Doppler findings were abnormal in both examinations (i. e., they showed a notch), the risk for subsequent hypertensive complications of pregnancy increased significantly. Steel et al. found the risk for hypertension increased from 5% to 25 %, for preeclampsia
from 1 % to 10%, and for fetal hypotrophy from 7 % to
27%. Harrington et al. (1991) in a comparable screening
study calculated a sensitivity of 76% at a specificity of
96% for the subsequent development of preeclampsia
after corresponding changes in the uterine vessels. It
follows from these studies that a Doppler screening examination of the uteroplacental vessels may detect an
impending preeclampsia.
Since it is possible to determine the risk of a gestational hypertensive disorder, the question naturally
arises of how to prevent its development. The administration of low-dose acetylsalicylic acid (ASA) has been
hypothesized to have a positive influence on the course
of the disease. McParland et al. (1990) administered
prophylactic aspirin to pregnant subjects (excluding
nulliparae) with abnormal Doppler findings on screening during the 18th week of pregnancy and a controlexamination at 24th weeks. The dosage was 75 mg ASA a
day vs. placebo. The results showed that administering
ASA reduced the frequency of hypertensive complications of pregnancy and of preeclampsia significantly.
The rate of cesarean sections for these conditions was
alsoreduced. There wasno changein bleeding tendency
due to the medication, and no other side effects due to
the low-dose ASA were listed.
Obstetric Applications of Doppler Ultrasound
105
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Doppler Ultrasound Diagnosis in Preeclampsia, Eclampsia, and HELLP Syndrome
Confirming a Diagnosis of Preeclampsia in the Second Half of Pregnancy—Demonstrating Characteristic Doppler Sonographic Changes of Preeclampsia in the Utero-
placental Vessels
2
Doppler examination of the uteroplacental aa. during
the first half of pregnancy is used to determine the risk
for the subsequent development of preeclampsia. The
question in the second half of pregnancy is whether
examining the uteroplacental vessels when clinical
symptoms of preeclampsia are already present would
be of any use. In this case Doppler examination will
most often show a notch, since the above-mentioned
changes in the uterine aa. are presumably present.
However, the finding is not as significant as in the first
half of pregnancy. If a notch can be demonstrated, it is
likely that the gestational hypertension or preeclampsia was caused by the sequence of events following a
defective trophoblast invasion. If the notch is absent,
such a causal connection is not confirmed for the individual case, but there is no change in clinical management: As soon as clinical signs of preeclampsia are
present, management depends on the maternal and
fetal condition, not on the Doppler findings in the
uterine aa.
Finding a notch therefore allows a pathophysiological sequence to be postulated, perhaps satisfying diagnostic curiosity. However, such a finding does not
change the obstetric management. It follows that this
diagnostic procedure is of secondary importance in the
second half of pregnancy.
Doppler Sonographic Findings
The finding to be noted in the second half of pregnancy
is the notch described above. To be significant we recommend a threshold value of the 90th to 95th percentile of the Doppler indices.
Evidence for or Exclusion of Fetal Risk—Evaluating the Fetal or Fetoplacental Vessels
The task is to distinguish between chronic changes
caused by preeclampsia, or acute problems occurring
without warning. The former can be demonstrated by
Doppler ultrasound in the fetal vessels when they lead
to poor blood supply in the fetus; however, an acute
rise in maternal blood pressure can lead to fetal distress, which may elicit changes in the CTG, but does not
appear in the Doppler sonogram. In rapid changes of
this kind with placental insufficiency, fetal flow patterns may be unchanged, because the infant has had no
time to respond.
By contrast, when a long-term deficiency in the
placental supply—caused by the deficient trophoblast
invasion noted above—results in fetal growth restriction, decompensation of the placental supply may result in abnormal Doppler findings in the umbilical aa.
or fetal vessels.
The prime consideration is that abnormal flow patterns on the maternal side do not necessarily cause ab-
Fig.
normal flow patterns on the fetal side (
instance, the experience in our clinical practice is that
not all infants born to women showing symptoms of
preeclampsia are delivered growth restricted or prematurely.
10.2). For
Doppler Sonographic Findings
While vascular changes specific to preeclampsia such
as a notch may be found in the uteroplacental vessels
on the maternal side, no changes in the waveforms of
the fetus are characteristic of preeclampsia. Risk to the
fetus is shown by an increased resistance, i. e., in the
first instance by reduction in diastole in the umbilical
aa. and the fetal aorta.
Reductions in diastolic flow (e.g., RI above the 90th
to 95th percentile) in the fetal aorta or the umbilical aa.
are considered to be abnormal Doppler patterns.
Absent or reversed end-diastolic flow (ARED) in
these vessels is the most important alarm signal. The
centralization of the fetal circulation, i. e., increase in
the peripheral resistance and decrease in the resistance of the central vessels is a sign of increased risk
F
igure
to the fetus.
normal and abnormal flow profiles in the fetal and maternal vessels.
There is some promise for the future that examination of fetal v.’s (ductus venosus, vena cava, hepatic v.’s,
and umbilical v.) may provide additional parameters
for the detection of fetal risk (cf. Chapter18, p. 161).
10.3 provides an overview of the
106
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Evidence for or Exclusion of Fetal Risk—Evaluating the Fetal or Fetoplacental Vessels
Uterine a.
(normal finding)
Umbilical a.
(normal finding)
Fig. 10.2 An abnormal flow profile in the uterine a. should not
automatically lead to the conclusion that the flow profile of the
Uterine a.
(abnormal finding)
Obstetric Applications of Doppler Ultrasound
Umbilical a.
(abnormal finding)
umbilical a. is abnormal. All combinations of abnormal and
physiological flow profiles can occur.
Redistribution of Blood (Brain Sparing)
The concept of “brain sparing” ties the redistribution of
cardiac output to the essential organs heart, adrenals,
and brain at the expense of the rest of the body, such as
the intestines, the skin, or the kidneys. The term “redistribution” is more appropriate, since it carries fewer
implications than “brain sparing.”
Redistribution is considered to be a fetal emergency
adaptation, especially for respiratory function. In animal experiments the effect can be elicited at will. Similarly, in human gestation an association can be found
between an abnormal intrauterine blood gas analysis
and redistribution.
blubber
The term redistribution is generally used when Doppler sonography shows a change in the systolic/diastolic variability in the indicator vessels. The Doppler
ultrasound indices used include the PI, RI, or the S/D
ratio. With increased diastolic flow velocities the indices are lower in the favored organs, while in the remaining vascular regions flows may slow or stop entirely or, in some cases, even reverse. With quantitative
analysis, for example, when taking readings of absolute flow rates from specific vessels, an increase in flow
rates in the selectively perfused organs can be clearly
demonstrated.
Certain vessels are more accessible. Among these,
the middle cerebral a., the descending aorta, and the
107
Doppler Ultrasound Diagnosis in Preeclampsia, Eclampsia, and HELLP Syndrome
2
a
c
b
d
108
e
g
Fig. 10.3 Compilation of physiological and pathological flow
profiles in fetal and maternal vessels, especially in the third
trimester.
a Uterine a., normal finding.
b Uterine a., abnormal finding.
c Aorta, normal finding.
blubber
f
h
d Aorta, abnormal finding.
e Umbilical a., normal finding.
f Umbilical a., abnormal finding.
g Middle cerebral a., normal finding.
h Middle cerebral a., abnormal finding.
Summary
umbilical aa. are most often selected. The activity of
the fetus must be taken into account, as it can influence the Doppler readings from the middle cerebral
a. When the fetus is active, diastolic flow velocities increase in relation to the systolic peak velocity, and absolute velocities also increase.
The slogan “heart sparing” has been used in corresponding examinations of the coronary aa.. In addition
to the heart and the brain, the same effect could also be
found in a third selectively perfused organ, the adrenal
gland. Whether examination of still other organs
would expand our understanding is not clear.
The development of Doppler sonographic changes in
opposite directions of the umbilical a. and the middle
cerebral a., i. e., reduced diastolic flow rates in the
umbilical a. and increased flow rates in the middle
cerebral a., is of great practical importance in daily
practice, independent of more refined pathophysiological measurements.
Summary
By examining the maternal vessels using Doppler ultrasound it is possible to determine the risk of complications developing in the course of a pregnancy long
before clinical signs of preeclampsia appear, so that
therapeutic measures may be undertaken early.
Moreover, clinical symptoms arising in the third
trimester can be shown by examination of the utero-
Redistribution is not a static process, but rather a
compensation mechanism that changes with increasing disruption in the supply. With continuing decompensation the initially increased flow velocity in the
middle cerebral a. decreases—a pseudonormalization
of blood flow. For this reason the interpretation of Doppler readings without knowledge of their development
over time or of related findings is insufficient. Ultimately diastolic flow may be absent or even reverse.
This state has been associated among other pathology
with cerebral edema.
It should be noted that the same effect may be elicited by increased pressure on the fetal head by the
transducer. For this reason it is essential to check the
stability and consistency of the findings and to relate
them to other results before evaluating their clinical
impact.
Obstetric Applications of Doppler Ultrasound
placental vessels to be caused by a defective trophoblast invasion. However, the decisive use of Doppler
sonographic findings in the third trimester is that it
has a bearing on the timing of labor, thus reducing perinatal mortality, i.e., it allows the obstetric attendant to
select the optimal management.
blubber
109
2
110
blubber
11 Doppler Ultrasound in the Diagnosis of Fetal Anomalies
It is axiomatic that the initial diagnosis of fetal anomalies is made by conventional gray-scale B-mode sono-
graphy. However, Doppler ultrasound—especially
color-coded blood flow diagnosis—increasingly allows
the diagnosis to b e refined and more precisely delineated. Thus, whereas the detection of an anomaly
depends on the experience of the examiner and the
resolution of the B-mode image, the use of color Doppler ultrasound is highly advantageous in further exploring organ function and differential diagnosis. This
is accepted unanimously for fetal echocardiography.
However, even a simple example will demonstrate the
importance of color Doppler ultrasound in the diagnosis of malformations: The differential diagnosis between an intracerebral cyst and an aneurysm can be
made with certainty only using color-coded Doppler
ultrasound, since an aneurysm will be outlined in
color, while a cyst remains colorless.
But even the demonstration of a normal vascular
tree or pathological changes in it can clarify fetal
anomalies. For instance, the demonstration by color
Doppler of the absence of a renal a. can prove renal
agenesis.
However, the precondition for the diagnosis of fetal
anomalies is the correct setting of the instrument. For
the display of venous flows, the setting must be
adapted to their slow range of flow velocities, i.e., a
low pulse repetition frequency (PRF) must be selected.
By contrast, the faster arterial flow rates can only be
displayed accurately with higher PRFs.
Since, as stated above, the diagnosis of fetal anomalies depends primarily on a high-resolution B-mode
image, only those fetal anomalies in various organ systems are described in the following for which diagnosis is facilitated by using color Doppler sonography.
They are listed in Table
Tabelle 11.1 Diagnoses and further differentiation of fetal
malformations that can be markedly facilitated by color Doppler ultrasound.
Region of body Fetal malformationKörperregion
Central nervous
system, head, neck
Lung Hypoplasia of the lung (?),
Heart All cardiac anomalies
Gastrointestinal tract Omphalocele, gastroschisis
Urogenital system Renal malformations
Skeleton Sacrococcygeal teratomata
Other anomalies Placenta, hydrops fetalis,
11.1.
Arachnoid cysts, porencephalic
cysts, intracranial neoplasms,
hydrocephalus, tumors of the
neck, fetal goiters, hemangiomata
diaphragmatic herniae, hemangiomata
anhydramnios, anomalies of the
umbilical cord
Obstetric Applications of Doppler Ultrasound
Anomalies in the Region of the Head and Neck
Examination of this region of the body by color Doppler is most profitable for anomalies of the fetal brain
and soft-tissue tumors of the neck.
A normal color Doppler display of the blood supply
at the base of the skull is shown in
display showing intracerebral cysts might be of an
A
actual cystic space such as an arachnoidal cyst, a
ventricular hydrocephalic dilatation, cystic brain
anomalies as in holoprosencephaly, choroid plexus
cysts, or aneurysms of the vein of Galen. Naturally only
aneurysms will show blood flow inside the cyst, while
other anomalies by their nature do not (
Additionally, the spectral Doppler feature of Doppler
ultrasound examination of the intracerebral aa., espe-
Figure 11.1.
Fig. 11.2a−c).
blubber
111
Fig. 11.1 Display of the normal vascular supply at the base of
the skull. Circle of Willis with middle cerebral a.
Doppler Ultrasound in the Diagnosis of Fetal Anomalies
2
a
c
cially the middle cerebral a., permits conclusions to be
drawn about intracerebral pressure.
The thickness of the cerebral cortical mantle in hy-
Fig.
drocephalus (
nosis for cognitive development. Perhaps in the future
the degree of intracranial pressure, measured by Doppler sonography, may provide such an indication
(Fig. 11.3b).
Postpartum changes in blood flow velocity in relation to the degree of ventricular dilatation in hydrocephalus may be divided into three stages:
11.3a) is not an indicator of the prog-
b
Fig. 11.2a Fetal brain with several cysts, which on color Doppler are seen to be filled with blood, showing they are
aneurysms.
Fig. 11.2b, c Additional cuts display more aneurysms in the
brain.
Stage 1:
In the slowly developing so-called “low-pressure hydrocephalus,” in which the ventricles are only minimally dilated, no significant changes can be found by
Doppler ultrasound in the flow rates in the intracranial
vessels.
Stage 2:
In moderately dilated ventricles increased diastolic
blood flows may be found, and these may lead to a reduced pulsatility index (PI). This phenomenon is interpreted as increased perfusion and a protective mechanism for cerebral tissue (brain sparing).
112
Fig. 11.3a Fetal hydrocephalus in the 33rd week of gestation. Fig. 11.3b Physiologically there should be diastolic forward
flow in the 32nd week of gestation. The middle cerebral a. in
this infant exhibits zero diastolic flow, which may indicate increased intracranial pressure.
blubber
Anomalies of the Lung and Diaphragm
Stage 3:
Rapidly progressive ventricular dilatation is marked by
a significant reduction in diastolic amplitude. In especially severe cases blood flow may even be reversed
(Fig. 11.4).The result isa raised PI.Such a findingis an indicator of impending ischemic cerebral tissue damage.
A derivation of this postpartum procedure is the use
of Doppler ultrasound ante partum.
In a fairly large number of cases of hydrocephalus
Voigt and his co-workers (Voigt et al. 1995) demon-
Fig. 11.4 Display of reverse diastolic flow in the middle cerebral a., suggesting very high intracranial pressure.
strated that increasing ventricular dilatation led to increased resistance in cerebral blood flow, with consequentimpairment of perfusion. In this waythe reduction in the cortical mantle was associated with an increase in intracerebral pressure. The authors point out
that Doppler ultrasound is the ideal means of determining the correct time for delivery in order to prevent
damage to the fetal brain by excessive pressure.
Figure
11.5 shows the relationship betweenperfusion pressure
and increased intracerebral pressure.
P
(mmHg)
P
(mmHg)
V
BP
ICP
BP
ICP
cm/s
t (s) t (s)
V
cm/s
t (s)t (s)
Obstetric Applications of Doppler Ultrasound
Fig. 11.5 Association between perfusion pressure (PP) and
flow profile in the cerebral arteries (PP = BP−ICP). The left side
shows the relation between blood pressure (BP), which is considered constant, and increasing intracranial pressure (ICP). The
right shows the corresponding Doppler spectra that might be
expected theoretically. As ICP increases, PP decreases with a
consequent decrease in diastolic flow. Once ICP reaches end-diastolic pressure, no more forward flow can be detected. If ICP
exceeds BP during diastole, the result is end-diastolic flow reversal (after Voigt et al 1995).
Anomalies of the Lung and Diaphragm
Hypoplasia of the lung cannot be diagnosed or evaluated with absolute certainty by B-mode imaging.
There is some hope that in the future displaying the
perfusion of the lung may facilitate diagnosis by allowing conclusions about pulmonary function to be drawn
from the vascular tree.
Diaphragmatic hernia is always associated with an
anomaly and displacement of the lung, making the
evaluation of pulmonary function of great prognostic
P
(mmHg)
P
(mmHg)
V
BP
ICP
cm/s
t (s) t (s)
V
ICP
BP
cm/s
t (s)t (s)
importance. In this, color-coded Doppler ultrasound
could provide significant assistance.
Cystic areas in the fetal lungs that lie very close to
the heart may be delimited from the latter because
they are not fille d with blood.
Malformations of the lungs, like hemangiomata, may
be assigned to definite areas by their perfusion.
113
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