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What
is it?
Congenital diaphragmatic hernia (CDH)
is a major congenital anomaly that results from abdominal organs
moving into the chest through a defect in the diaphragm which
alters the development of the lungs at a very vulnerable time.
CDH occurs in about 1/4000 births. The incidence in stillborn
children is probably higher. The causes are unknown. The genetic
sources of CDH are not clear. It does not reliably run in families
nor is it inherited in the same manner as better known conditions
such as hemophilia, cystic fibrosis, or metabolic errors. Although
CDH is sometimes associated with congenital abnormalities of the
heart or central nervous system, it is usually a single isolated
malformation. CDH is much more common on the left side of the
chest and is much more common in boys.
How
does it happen?
The embryologic events leading to CDH
are somewhat speculative but are thought to begin in about the
12-14th week of gestation. At this point three things relevant
events are occurring in the human fetus. First, the torso is one
cavity. The diaphragm has not yet formed to separate the chest
from the abdomen. Second, most of the intestinal tract, having
undergone very rapid growth beyond the space available in the
abdomen, is temporarily residing in the umbilical cord. Third,
the lungs are present but in a very primitive primordial, undeveloped
state. Ordinarily, the diaphragm forms to separate the chest from
the abdomen, the intestine then migrates into its proper abdominal
cavity, and the lungs go on to develop into a fully formed organs.
Discoordination of these events leads to CDH. In other words,
if the diaphragm forms too late or the intestine returns to the
abdomen too soon, there is nothing to prevent the intestine from
taking up the space needed by the developing lungs. This affects
both lungs. The abdominal organs become a "space-occupying-mass"
on the side of the hernia. Pressure on the structures in the middle
of the chest push the heart towards the opposite side and become
a "space occupying-mass" on the opposite side. This compromise
of lung growth and function occurs very early in gestation and
is not thought to become more pronounced as gestation proceeds.
It is more of a growth/development arrest rather than an on-going
process.
What are the
consequences?
Two general categories of problems
result. One is called pulmonary hypoplasia. The lungs are smaller
than normal. Both lungs are affected, the side of the hernia more
so than the other. The primitive lung, at the time CDH occurs,
has the normal number of lobes and each lobe has the normal number
of segments. However, the number of "grape clusters", or acini,
per segment is less than normal. Ironically, the number of grapes
per cluster may actually be increased, perhaps in an effort to
compensate. The artery coming from the heart to bring unoxygenated
blood to the lung is the pulmonary artery. The development and
branching of the pulmonary artery exactly parallels the branching
of the airway and is compromised in a similar way.
The other
problem is called pulmonary hypertension. In the fetus, there
is no need for blood to pass through the lungs because the fetus
receives all its oxygen from the placenta. Once the fetus comes
up for air as a newborn baby, the placenta is no longer available.
The short time between birth and the newborn's first cry, when
he/she goes from blue to pink, is the time when the lungs are
unfurling like a sail, relaxing, and allowing the heart to send
blood through them and become the source of oxygen. This is called
a transitional circulation. The infants with CDH, however, have
some degree of pulmonary hypertension. They gave have high blood
pressure in their lungs. Their lungs have a more difficult time
relaxing and allowing the heart to send blood through them. These
lungs are more nervous about coming out of the water and making
the usual changes that accompany the transitional circulation.
Which of these
two variable, pulmonary hypertension and pulmonary hypoplasia,
predominates to a large degree determines whether the baby will
or will not survive. The other variable that affects outcomes
is how the baby is cared for in the first vulnerable days of life.
What
is the pre-natal treatment for CDH?
The treatment of CDH begins when the
diagnosis is made. Increasingly, high-resolution prenatal ultrasound
examinations make the diagnosis between 20 and 25 weeks gestation.
The ultrasound diagnosis is generally made by finding the fetal
stomach in the chest at the same level as the heart, sometimes
accompanied by a portion of liver in the chest. The most important
element of the prenatal treatment is parent education as to the
meaning of the diagnosis, particularly the treatment decisions
that may need to be made once the baby is born. In the event of
a prenatal diagnosis, pediatric surgeons, neonatologists, and
obstetricians are always asked to estimate prognosis for the baby.
The short response is that we are unable to make a reliable prediction
of outcome. (See last section) To be sure, CDH infants with an
additional associated anomaly such as congenital heart disease
have a poor prognosis. However, efforts to associate findings
such as diagnosis before 25 weeks gestation, excessive amniotic
fluid, the stomach in the chest, estimation of fetal breathing,
and finding the liver in the chest with poor prognosis have been
inconsistent. The most we can say with confidence from a prenatal
ultrasound is that the baby almost certainly has CDH. This frustration
has vexed those centers that have developed considerable expertise
in direct intervention in the fetus with CDH. The fetal interventions
consist of direct operative repair of the CDH in the fetus (now
largely abandoned) and obstruction of the fetal trachea in an
effort to provoke compensatory lung growth. Despite truly
commendable advances in surgical approaches to structural abnormalities
of the human fetus, identifying the fetus whom, at some risk to
the mother, will clearly benefit from intervention remains uncertain
and highly experimental. Centers practicing prenatal surgical
intervention have tried to identify the highest risk CDH fetuses
based on a ratio between the head and chest circumference. Although
this ratio may identify a potentially challenging infant, the
values are untested in other major neonatal centers. The number
of fetus treated prenataly is very small. The outcomes highly
variable and often accompanied by complications of prematurity.
Other experimental approaches to the
fetus with CDH involve medical efforts to enhance maturation and
growth of the lungs. It has been established that the steroid
prednisone will accelerate maturation of fetal lungs threatened
with preterm labor. Laboratory and early clinical evidence are
suggesting that prednisone may do likewise for CDH lungs.
What
is the post-natal treatment for CDH?
Most CDH fetuses are delivered as close
to term as possible. Unless obstetric concerns intervene, there
is no reason, just because of the CDH, to have anything other
than a vaginal delivery. Caesarian section is not indicated, everything
else being equal. At birth the infant's abdomen will appear empty
and the chest over expanded because of the abdominal organs that
are in the chest instead of the abdomen. The infant is usually
in some degree of respiratory distress. They are intubated (a
tube passed into the airway) and placed on assisted ventilation.
An intravenous catheter is placed for administering fluids and
medicines and an umbilical artery catheter placed for blood sampling
and pressure monitoring. Devices for monitoring the oxygen saturation
in the blood are applied to the skin of the right hand and either
foot. Another tube is passed from the nose to the stomach to keep
it empty and from getting distended. A chest x-ray is obtained
to confirm the diagnosis. The x-ray will show bubbles of gas in
the intestine in one side of the chest or the other and the heart
will be shifted away from the side of the hernia.
The goal of
the management is to support the baby while the pulmonary hypertension
improves in a way that minimizes the injury to the lungs that
can occur from excessive ventilator pressure and extra oxygen.
It is important to remember that the infant with CDH has a physiologic
emergency because of the congenital lung abnormalities, not a
surgical emergency because of the organs in the chest. An unstable
infant will become even unstable with an emergency operation and
have a smaller chance of survival than one that is stabilized
and brought to the operating room electively.
The manner in which the infant ventilator
is used is beyond to scope of this document but, again, strategies
that compromise the infant's inherent protective mechanisms and
create more problems than they are intended to help are to be
avoided.
A variety of medicines, in addition
to the oxygen being administered by the ventilator, are used to
control the pulmonary hypertension. Some are other inhaled gases
(nitric oxide) or inhaled medicines (surfactant) and others are
administered intravenously (priscolene, dolbutamine). The effect
of these medicines in the setting of CDH is unpredictable. If
they help, their effect may not be lasting. The most important
tools for the treatment of CDH infants are patience, attention
to detail, and time.
What
is ECMO?
Extracorporeal membrane oxygenation
(ECMO) is a form of extracorporeal life support that can be a
very potent tool in selected infants with CDH. Treating an infant
with ECMO involves draining the blood from the right side of the
heart, passing it through a mechanical heart, a mechanical lung,
rewarming it, and returning it to the left side of the heart.
This is done continuously for up to 3 weeks via special catheters
placed into the heart by an operation on blood vessels in the
neck. In order to do this the clotting system must be suppressed.
This is important since CDH is a surgical problem. While
being treated with ECMO, the extensive ventilator and pharmacologic
support that precedes ECMO can be weaned to vary safe levels.
During this period of "rest" on ECMO, it is anticipated that the
pulmonary hypertension will resolve and whatever lung injury caused
by previous treatments will heal. As the infant improves, he/she
is weaned from ECMO back to conventional ventilator support but
at much less aggressive levels. ECMO is a treatment for
pulmonary hypertension that is refractory to less invasive treatments.
About 10-15% of ECMO treated infants may have a neurologic complication
while on ECMO. This is one of the important reasons ECMO is reserved
for infants judged to have in excess of 90% mortality likelihood
with continued conventional treatment. ECMO may be indicated as
part of the pre-operative resuscitation to stabilize an infant
for the operating room or after the surgery in the event of a
serious decompensation.
ECMO is not
a treatment for overwhelming pulmonary hypoplasia to a degree
incompatible with life. While it is true that newborn lungs will
grow new air sacs (alveoli) over the first several years of life,
not much happens in the first two weeks. An infant dying from
overwhelming pulmonary hypoplasia can be placed on ECMO but this
creates an untenable situation. Such an infant is alive only because
of life support without a real end-point. It is unusual that a
CDH infant has overwhelming pulmonary hypoplasia but, if, based
on analysis of oxygen levels in the blood in the right arm, there
is overwhelming pulmonary hypoplasia, ECMO is not a reasonable
treatment.
What
is the surgery for CDH?
The operation for CDH has three components.
The incision parallels and is just beneath the rib margin on the
side of the hernia. The first component is to remove all of the
abdominal organs from the chest. The liver may be the most challenging.
The second component is to build a diaphragm. If, despite the
defect, there is enough native tissue to close the hole safely,
that is the first choice. If this cannot be done, a prosthetic
material such as Gortex is used to close the defect. If a prosthetic
is used, it is permanent. It will become encased in scar tissue
and the tissue around it will grow with the child, but not the
prosthetic. The third component is to close the abdomen. Because
the abdominal organs have been in the chest through much of gestation,
the abdomen will be smaller than normal. If all the abdominal
organs can be safely returned to the abdomen without closure causing
undue pressure, that is preferred. If not, Gortex is again used
to augment the abdominal wall. In contrast to using Gortex to
close the diaphragm defect, if Gortex is used to close the abdominal
wall, it is temporary. By several days post-operative, the abdomen
will have stretched sufficiently to make the abdominal wall Gortex
unnecessary. At this point the baby is returned to the operating
room, the Gortex removed, and the abdomen formally closed.
The baby is often more difficult to
manage first day or two after the operation. This is normal. After
any operation, a baby's body hold on to more water, looks a bit
swollen, and is "stiffer". This causes the ventilator to work
harder than preoperatively to provide adequate respiratory support.
As the baby recovers, the excess water is passed as urine, the
body becomes more supple, and the ventilator needs decrease.
What
happens when the respiratory crisis is over?
Once a CDH infant is weaned from ECMO
(if needed) and a ventilator the next major problem is getting
the baby to eat. Because the stomach is often kinked up into the
chest with CDH, the esophagus and stomach are poorly coordinated
in their ability to pass a muscular wave from one end to the other.
Often, food will make it into the stomach but when the stomach
try to pass it along it manages to send it back up the esophagus.
The term commonly used for this condition is gastro-esophageal
reflux (a better term is foregut dismotility). The diagnostic
evaluation for this consists of an upper gastrointestinal series,
where the baby swallow a x-ray contrast and pictures are taken,
and a 24-hour pH study. This is a study where a fine electrode
is passed through the baby's nose into the esophagus and attached
to a small recording device that measure how much and how often
acid comes up from the stomach into the esophagus. If these studies
confirm the diagnosis (they usually do) the baby will be initially
treated with a medicine to suppress the acid made in the stomach
(zantac or prilosec) and another medicine to improve the coordination
of the esophagus and stomach (reglan or cisapride). In addition
the baby will be fed initially with a continuous drip through
a small placed from the nose into the stomach. Prior to this time
the baby will have received all the needed nutrition intravenously.
The intravenous feedings are decreased and discontinued as the
stomach feedings are increased. Once all the nutrition is being
given continuously into the stomach, the volume is slowly condensed
to a bolus with the goal of transitioning the baby to bottle-feeding.
This process, once the infant no longer needs a ventilator, can
take 2 weeks to 2 months. Many mothers seek to feed their infants
breast milk. This is to be encouraged. However, with the uncertainty
of the surgery and the time it takes for the feedings to be worked
out, this may become frustrating. If breast-feeding does not work
it is not a failure. Infant formulas are excellent and yield growing
thriving children.
What
are the chances the baby with CDH will be well?
The honest answer is that no one really
knows because for any one infant survival is either 0% or 100%.
However, given a large group of CDH infants, current experience
in several major neonatal centers confirms that the vast majority
of CDH infants will survive and be sent home with their parents
(80-90%). At the time of discharge, it is the rare child that
needs continued respiratory support. After discharge the infants
are followed by a pediatric gastroenterologist for their reflux
and by a pediatric pulmonologist for their lung development. Additional
surgery for recurrent hernia and gastro-esophageal reflux is unusual.
With improved respiratory care strategies, the need for ECMO has
decreased from 45% to 15%. Neurologic consequences in ECMO treated
infants, the ones that would not survive without it, is about
15%. Those infants surviving without ECMO have rare neurologic
consequences. The grim mortality rates often quoted in some textbooks
and some medical literature are simply not correct. To be sure,
parents of infants with this problem need not be reminded that
this is a serious, life-threatening problem, but it is also one
that parents should view with cautious optimism.
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