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Diaphragmatic Hernias
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breathing. The two lateral leaves of the central tendon relate to the parietal pleura above and
the peritoneum below, whereas the middle leaf is fused to the pericardium above and relates
to the triangular ligament of the liver in the abdomen.
Arterial supply to the diaphragm is largely via the right and left phrenic arteries, the
intercostal arteries and musculophrenic branches of the internal thoracic artery. There are
minor contributions from the pericardiophrenic arteries that run with the phrenic nerves,
entering the diaphragm where the nerves penetrate. Venous drainage is via the inferior
phrenic veins which drain into the inferior vena cava. In the thorax the venous drainage is via
the azygos and hemiazygos system.
The diaphragm has three major apertures: the aortic, the esophageal and the inferior vena
cava orifices. The esophageal hiatus is an oval aperture located behind the central tendon. It is
located at the level of D10 just left of the midline and anterior to the aortic hiatus. The caval
orifice is located in the right portion of the central tendon at the level of D8. This orifice is
stretched during diaphragmatic contraction, thus facilitating the flow of venous blood into the
thorax during inspiration. Also traversing this orifice are small branches of the right phrenic
nerve and few lymphatic vessels. The aortic opening is anterior to the lower body of D12,
between the crura and behind the median arcuate ligament. It also transmits the azygos vein,
the thoracic duct and the lymphatic vessels that descend from the thorax to the cisterna chyli.
Other structures that pass between the abdomen and the thorax, thorough the diaphragm
posterior to it, are the superior epigastric vessels passing between the sternal and costal
origins of the diaphragm, the musculophrenic vessels between the diaphragmatic origins at
seventh and eighth cartilages, the lower five intercostals nerves from the seventh cartilage
inferiorly, the sympathetic trunk, the splanchnic nerves, and the inferior hemiazygos vein.
There may be a triangular gap between the sternal and costal origins of the diaphragm
bilaterally, where the pleura and peritoneum are separated merely by loose areolar tissue.
Similarly, the muscular fibers of the diaphragm may be deficient between the costal portion
of the diaphragm and the portion arising from the lateral arcuate ligament bilaterally. These
potential spaces are not as common as the parasternal spaces just described, and when they
exist, the superior surface of the kidney is separated from the pleura only by areolar tissue. It
is thought that these potential spaces that characterize congenital diaphragmatic hernias may
occur in adults.
The Phrenic Nerve
The phrenic nerve arises chiefly from the fourth cervical nerve root with contributions
from the third and fifth cervical nerve roots. It originates on the scalenus medius, at the lateral
margin of the scalenus anterior under the sternomastoid muscle, at the level of the upper
border of the thyroid cartilage. It crosses to the scalenus anterior muscle and descends on this
muscle beneath tough fascial tissue, crossing the muscle from the lateral to the medial border
to the root of the neck. At the root of the neck, the right phrenic nerve is crossed by the
transverse cervical and suprascapular arteries; the left phrenic nerve is crossed also by the
thoracic duct. At the apex of the thorax, the right nerve, lying behind the innominate vein,
crosses the internal mammary artery from the lateral to medial, usually in the front of the
artery. The left phrenic nerve descends on the front of the first portion of the subclavian artery
to enter the thorax.
Ivan Martinez Serna and Antonio Pablo Gamez Garcia
182
The fifth cervical nerve root usually joins the phrenic trunk on the surface of the scalenus
anterior, but it may descend into the thorax before it joins the nerve.
In the thorax, the right phrenic nerve descends along the right side of the right innominate
vein and the superior vena cava, then along the side of the pericardium anterior to the root of
the lung. It then descends along the upper part of the interior vena cava to just above the
diaphragm where it branches. The left phrenic nerve descends between the left common
carotid and subclavian arteries, crossing in front of the left vagus. It passes lateral to the arch
of the aorta and continues down along the side of the pericardium to just above the diaphragm
where it branches. Merendino et al. [1956] are credited with defining the anatomic course of
the phrenic nerve in relationship to the diaphragm and the related strategy for diaphragm
incisions.
The right phrenic nerve reaches the diaphragm just lateral to the inferior vena cava,
whereas the left phrenic nerve joins the diaphragm just lateral to the left border of the heart in
a slightly more anterior plane than the right phrenic nerve. The nerves divide at the level of
the diaphragm, or just above it, into several terminal branches, with the right nerve being the
mirror image of the left nerve. Aside from small branches innervating the serosa of the
diaphragm, three muscular rami arise: one is directed anteromedially toward the sternum,
another is directed anterolaterally, and the third is directed posteriorly. This latter ramus
divides into a posterolateral branch and a branch that runs posteriorly and medially to the
region of the crus. These branches are named the sternal or anterior branch, the anterolateral
branch, the posterolateral branch and the crural or posterior branch. They are usually deep
within the muscle rather than lying exposed on the under surface of the diaphragm. Because
of the rapid diminution in the size of the branches of the phrenic nerve it, is often impractical
to delineate areas where incisions in the diaphragm can be safely made. Further, incisions in
presumed safe areas are generally of little practical value to the thoracic surgeon; however,
circumferential incisions anywhere in the periphery of the diaphragm result in little, if any,
loss of diaphragmatic function. Thoracoabdominal incisions associated with circumferential
incisions in the diaphragm do not interfere significantly with function. Similarly, incisions in
the central tendon do not interrupt any major branch of the phrenic nerve. Radial incisions in
the diaphragm from the costal margin to the esophageal hiatus result in almost total
diaphragmatic paralysis.
PHYSIOLOGY OF RESPIRATION
The diaphragm is the most important muscle of inspiration. It separates the thoracic and
abdominal cavities and most of its function can be inferred from this anatomical arrangement
[Epstein, 1994]. It has a non-contractile tendon from which muscle fibers radiate downwards
and outwards. The costal portion of the diaphragm consists of those fibers that insert
anteriorly on the posterior portion of the xyphoid process and laterally on the lower ribcage,
whereas the crural portion is composed of those fibers that arise from the central tendon and
insert posteriorly in the first three lumbar vertebral bodies on the left and the first two on the
right. During contraction the diaphragm assists lung inflation thought three mechanisms.
First, it uses the abdomen as a fulcrum against which it leans, thereby expanding the rib cage
Diaphragmatic Hernias
183
[Loring and Mead, 1982; Rochester 1985]. Second, during contraction, the diaphragm also
helps inflation because of the cephalocaudal orientation of his fibers and the curvature of his
shape [Rochester, 1985]. This anatomic arrangement expands the rib cage as the fibers
shorten. The curvature of the diaphragm approximates the shape of a hemisphere with a
radius, r. Laplace´s law for a sphere states that P=2T/r, where P is the pressure inside the
sphere and T is the tension of the wall. If T is constant and the diaphragm flattens, its
curvature will decrease, r will increase, and, by definition, P must decrease. Finally, the
diaphragm transmits the increase in abdominal pressure during contraction to the rib cage,
through its zone of apposition which also has an expansive action directed to the rib
cage[Mead, 1979].
During inspiration, the central portion of the diaphragm descends, lowering the
diaphragmatic domes and causing costal elevation. The thorax increases in diameter and
intrathoracic pressure decreases, allowing alveolar air filling. Abdominal organs are pressed
downward by the action of the diaphragm, with an increase in abdominal pressure. During
relaxed breathing with the sole intervention of the diaphragm, the cupule descends around 1
cm, creating a pressure gradient of 1 to 3 mm Hg and inhalation of approximately 500 ml of
air. In forced breathing, which occurs in association with the accessory muscles, the
diaphragm cupule descending down to 10cm, there is a significant increase of the pressure
gradient of up to 100 mmHg which generates an inspiratory capacity of 2 to 3 litres of air.
During inspiration, the pressure also changes at the interpleural level, from being
approximately 756 mm Hg before inspiration, to 754 mm Hg during inspiration, with an
accompanying decrease in alveolar pressure from 760 to 758mm Hg. This gradient of
pressure is responsible for the inspiratory airflow. The accessory respiratory muscles are
responsible for the duration and increase in thoracic volume. The external intercostals elevate
the ribs, the sternocleidomastoid muscle on the sternum, the scalene muscles on the 1st and
2nd ribs, and the pectoralis minor muscle on the 3rd to 5th ribs.
Expiration is a passive process, caused by muscle relaxation, without active contractile
action. The diaphragm rises, reducing the anteroposterior diameter of the chest and its vertical
dimension, thus reducing the intrathoracic volume and allowing the flow of air from the lung
(762 mm Hg pressure in alveolar expiration) to the outside (760 mm Hg) and decreasing the
abdominal pressure.
CONGENITAL DIAPHRAGMATIC HERNIA
Congenital diaphragmatic hernia (CDH) can be defined as a developmental defect of the
diaphragm that allows abdominal viscera to herniate into the chest through the diaphragm.
There are two basic types of congenital hernia: 1.) Bochdaleck hernia, due to a defect in
fusion of the septum trasversum and the chest wall. It is principally located on the
posterolateral left side and usually lacks a hernia sac; and 2.) Morgagni hernia, due to
maldevelopment of the embryologic septum transversum, with failure of the sternal and costal
fibrotendinous elements of the diaphragm to fuse. It is most frequently located on the anterior
midline and has in most cases a hernia sac is present.
Ivan Martinez Serna and Antonio Pablo Gamez Garcia
184
Historical Perspective
CDH was first described by Riverius in 1679, and the first pediatric case was described
by Holt in 1701 [Irish et al., 1996]. The first surgical repair in a child was reported by
O´Dwyer in 1890 [Koehler and Smith, 1994], and the first neonatal repair was done by Gross
in 1946 [Greenholz, 1996]. In the 1980s, prenatal diagnosis of CDH became possible owing
to the advent of high resolution ultrasound, allowing maternal transport to a perinatal center
prior to delivery in many cases. With the advent of antenatal diagnosis and improvement of
neonatal care, survival has improved, but there still remain significant risk of death and
complications in infants with CDH.
Incidence
According to Graham et al. [1990], incidence of CDH is estimated to be 1 out of every
2200 live births. Distribution among males and females is equal, and there is no known racial
predisposition [Morin et al., 1994; Mullins et al., 2001]. Familial cases have been estimated at
less than 5%, and most cases are sporadic [Mead, 1979; Norio et al., 1984; Gelman et al.,
1991]. The most common CDH is Bochdaleck hernia accounting for 95% of congenital
hernias. Approximately 80% of defects are on the left side, 20% are on the right and rarely
both sides of the diaphragm are affected.
Etiology
CDH may involve a defect on the diaphragmatic muscle which can be partial or
complete, but the morphology of the musculature is normal [Dietz and Pongratz, 1991].
Salacin et al. [1994] suggest that hernias diagnosed in young adults could be caused from
birth defects that manifest with age, due to rising intra-abdominal pressure during growth. In
the case of fetuses or newborns, specific causes have not been established but several studies
have found an association between diaphragmatic hernia and trisomy 13 and 18, as well as
relationship with exposure to various chemicals such as zinc, cadmium or thalidomide.
Pathophysiology
Mortality of children with CDH usually arises from associated anomalies, pulmonary
hypoplasia and pulmonary hypertension. Population-based studies have shown that
potentially lethal structural and chromosomal anomalies are present in 30% to 40% of infants
with CDH [Wenstrom et al., 1991; Torfs et al., 1992]. Other authors, using both prenatal and
postnatal data, report the occurrence of such potentially lethal anomalies to be in excess of
50% [Puri and Gorman, 1984]. The most common chromosomal anomalies are trisomies 13,
18 and 21; and the most common structural anomalies involve the cardiovascular (23%),
genitourinary (15%) and central nervous systems (10%) [Benjamin et al., 1988].
Diaphragmatic Hernias
185
Pulmonary Hypoplasia
Because herniation occurs during the critical period of lung development when bronchial
and pulmonary artery branching occurs, lung compression by the herniated bowel can result
in pulmonary hypoplasia. With increasing severity of lung compression, there is a
corresponding decrease in bronchial branching resulting in a reduction of bronchi and lung
tissue. In some cases, lung hypoplasia is so severe as to be incompatible with life. Prenatally,
the degree of lung hypoplasia can be estimated using ultrasound by determining if the
herniated contents include the liver, and by evaluating the lung area to head circumference
ratio. Postnatally, there is no single test to determine the degree of hypoplasia. The severity of
respiratory distress and the response of the infant to treatment are the best postnatal measures
of lung hypoplasia.
It is believed that the severity of pulmonary hypoplasia is related to both the timing of
herniation and volume of herniated viscera. This theory is supported by the observation that
smaller hernias and those developing later in gestation are associated with lower mortality
[Adzick et al., 1985] and by animal experiments in which creation of an intrathoracic mass or
a diaphragmatic defect resulted in pulmonary hypoplasia [Harrison et al., 1980; de Luca et al.,
1987]. Another theory proposes that the diaphragmatic defect and pulmonary hypoplasia are
concurrent phenomena, and visceral herniation does not interfere with lung growth [Kluth et
al., 1996]. This theory is also supported by the observation that children with Fryns
syndrome, which is characterized by familial CDH, may present with pulmonary hypoplasia
in the presence or absence of CDH [Willems et al., 1991]. Pulmonary hypoplasia is most
severe on the ipsilateral side of the hernia but may also occur on the contralateral side if the
mediastinum shifts and compresses the contralateral lung. In addition, arterial branching is
reduced and there is muscular hyperplasia of the pulmonary arterial tree [Bloss et al., 1981].
Biochemical analysis indicates there is a secondary surfactant deficiency [Wilcox et al., 1994;
Wilcox et al., 1995].
Pulmonary Hypertension
Hypoxemia, acidosis, and hypotension increase the risk of pulmonary hypertension by
inducing a reactive vasoconstrictive element to the pre-existing fixed arterial muscular
hyperplasia component. The degree of respiratory distress is dependent on the severity of lung
hypoplasia and pulmonary hypertension. Many infants with CDH demonstrate adequate gas
exchange immediately after birth, suggesting that they do not have critical pulmonary
hypoplasia. However, after a “honeymoon” period of 12 to 24 hours they develop severe
pulmonary hypertension, which results in left-to-right shunting through the foramen ovale and
ductus arteriosus (persistent fetal circulation) and a vicious cycle ensues resulting in death.
These physiologic changes are accompanied by microscopic evidence of medial hypertrophy
in the preacinar arterioles [Geggel et al., 1985]. Several mechanisms have been postulated for
these physiologic changes, including the actions of nitric oxide, prostanoids, and endothelin,
and activation of collagen synthesis [Nakayama et al., 1992; Kobayashi and Puri, 1994;
Nobuhara and Wilson, 1996; Yatamaka and Puri, 1997]. A decrease of phospholipids leading
to a reduction in surfactant has also been postulated as a factor in disease, though this is not
universally accepted [Blackburn et al., 1977].
Generally, 45 to 50% of infants with CDH have other associated congenital
abnormalities that worsen the prognosis. Pittinger and Sawin [2000] suggest the presence of
Ivan Martinez Serna and Antonio Pablo Gamez Garcia
186
adrenal insufficiency in a possible association with an inadequate response to stress and
related low concentration of cortisol that could contribute to inadequate lung development.
Alterations in the pulmonary vasculature are the greatest prognostic factor for newborns
affected with diaphragmatic hernia.
Clinical Manifestations
Infants with CDH most often develop respiratory distress in the first few hours or days of
life. The spectrum of presentation can vary widely from acute, severe respiratory distress at
birth, which is common, to minimal or no symptoms, with occasional serendipitous discovery
in asymptomatic patients. In neonates, the most common clinical feature is respiration
insufficiency. The typical affected newborn develops respiratory distress, cyanosis or
cardiorespiratory collapse within the first minutes to hours after birth. Physical examination
reveals a barrel-shaped chest, a scaphoid-appearing abdomen related to loss of the abdominal
contents into the chest, and absence of respiratory sounds on the ipsilateral side. Because the
lesion is on the left side in most CDH patients, the heartbeat is displaced to the right due to a
shift in the mediastinum. Abdominal symptoms may appear if the herniated viscera become
incarcerated. Associated anomalies are seen in approximately 50% of CDH cases and include
chromosomal abnormalities, congenital heart disease, and neural tube defects. In stillborn
infants, associated anomalies are more common. These anomalies are often diagnosed
prenatally and are discussed in greater detail separately. Adrenal insufficiency is reported to
be a common finding in infants with CDH. In one retrospective study of 58 CDH patients,
adrenal insufficiency was demonstrated in two-thirds of the group who were assessed for
adrenal function [Kamath et al., 2010]. Infants with adrenal insufficiency were more likely to
have herniation of the liver, and had more severe illness requiring epinephrine for vasopressor
support, high-frequency ventilation, and inhaled nitric oxide for a longer duration of time.
Diagnosis
With increased use of ultrasound (US), many cases of CDH are diagnosed prenatally,
visualizing stomach or intestinal loops in the fetal chest. Other US findings may include
polyhydramnios, shift of the mediastinum, and presence of other anomalies. If
polyhydramnios is detected, an exhaustive evaluation of the patient should be performed,
since CDH may present in up to 76% of such patients. In general, the diagnosis can be made
from the 11th week of gestation until birth, but it is not simple because the echogenicity of the
abdominal viscera may be similar to the lung in the newborn. US is diagnostic in up to 90%
of cases. CDH should be suspected in any full term infants with respiratory distress,
especially in the absence of respiratory sounds.
Diagnosis is aided by chest radiography showing herniation of abdominal contents
(usually air or fluid containing bowel) into the thoracic cavity. Typically, there is little or no
visible air-filled lung on the side of the herniation. Other findings include contralateral
displacement of the heart and other mediastinal structures, compression of the contralateral
lung, and reduced size of the abdomen with decreased or absent air-containing intra-
Diaphragmatic Hernias
187
abdominal bowel. Placement of a nasogastric tube into the stomach may facilitate the
diagnosis if the chest radiograph demonstrates the nasogastric tube within the thoracic cavity
or deviation from its expected anatomic course [Sakurai et al., 2000]. If the CDH is right
sided, the liver may be the only herniated organ and will appear as a large thoracic soft tissue
mass with absence of an intra-abdominal liver shadow on chest radiograph.
Imaging: Bochdalek Hernia
The initial chest radiography typically reveals opacity of the hemithorax on the affected
side and contralateral shift of the mediastinum, owing to the herniation of the abdominal
contents into the chest. As air is swallowed, bowel loops in the chest become filled with gas
and produce multiple lucencies.
In the adult, a Bochdalek hernia is seen on the chest radiography as a soft tissue mass of
variable size bulging upward through the posterior aspect of hemidiaphragm. The hernia
contents usually can be defined without difficulty on CT scan, which can also demonstrate the
diaphragm defect. Barium studies may reveal herniated bowel loops. Small, focal diaphragm
defects or discontinuities, with or without, herniated fat or viscera are seen in more than 10%
of adults on CT scans [Gale, 1985]. Increased incidence with age, obesity and emphysema
strongly suggest that the vast majority of such abnormalities are simply acquired defects and
not true Bochdalek hernias.
Imaging: Morgagni Hernia
Foramen Morgagni hernias are related to maldevelopment of the embryologic septum
transversum with failure of fusion of the sternal and costal fibrotendinous elements of the
diaphragm. In contrast to the Bochdalek hernia, a hernia sac of peritoneum and pleura
surrounds the contents of a Morgagni hernia. Morgagni hernias are most often right-sided,
probably because left-sided defects are covered by the heart and pericardium, and they are
often associated with obesity. The hernia sac usually contains omentum but may contain
transverse colon or, rarely, stomach, small bowel or liver [Tayer et al., 1989]. Most Morgagni
hernias are asymptomatic although some produce epigastric pressure or discomfort and rarely
strangulation of contained portions of gastrointestinal tract. Morgagni hernias usually come to
clinical attention as asymptomatic right cardiophrenic angle masses detected on chest
radiographs. Gas-filled intestinal loops may be present, facilitating diagnosis. CT scans
permit distinction from other causes of cardiophrenic angle masses, such as pericardical cysts,
pericardial fat pads, lymphadenopathy, and pleural or parenchymal masses by presence of
omental fat, omental vessels and abdominal viscera peripheral to the diaphragm in the lower
anterior chest.
Differential Diagnosis
Thoracic lesions that should also be considered when a diagnosis of CDH is made
prenatally by ultrasound include diaphragmatic eventration, congenital cystic adenomatoid
malformation, bronchopulmonary sequestration, bronchogenic cysts, bronchial atresia, enteric
cysts, and teratomas
Ivan Martinez Serna and Antonio Pablo Gamez Garcia
188
Prognostic Factors
The identification of prognostic factors predictive of survival has been a priority in the
treatment of CDH. Prognosis is worse in cases with abnormal karyotypes associated with
severe anomalies, and in cases with right-sided defects, liver herniation, and low fetal lung
volume [Downard and Wilson, 2003]. The lung area to head circumference ratio (LHR) is
more predictive of morbidity than mortality. A large defect is more likely to result in
pulmonary hypoplasia and death than a small defect. The size of the defect is not measurable
prenatally, so the presence of liver herniation and fetal lung volume measurements serve as
proxies for defect size.
Several other clinical features initially thought to be related to low likelihood of survival
have not been confirmed as consistently reliable prognostic indicators. These features include
early gestational age at diagnosis, severe mediastinal shift, polyhydramnios, a small lung-
thorax transverse area ratio, left ventricle/right ventricle index, left heart hypoplasia, and the
presence of stomach in the chest [Breaux et al., 1992; Ryan et al., 1994; Lally, 1996;
Seetharamaiah et al., 2009].
Factors that have prognostic value for CDH include:
Liver herniation; the most reliable prenatal predictor of postnatal survival is absence
of liver herniation. [Mullassery et al., 2010].
Fetal lung volume [Mahieu-Caputo et al., 2001, Paek et al. 2001; Gorincour et al.,
2005; Bonfils et al., 2006; Büsing et al., 2008]. Several studies have suggested that
postnatal survival is poor when fetal lung volume measured by MRI is less than
about 30% of expected lung volume.
Right versus left-sided lesion [Hedrick et al., 2004; Fisher et al., 2008]. Disease in
patients with right-sided lesions appears to be as, or more, severe than those with
left-sided lesions. infants with right-sided CDH had a lower survival rate than those
with left-sided lesions. Further, a greater proportion of infants with right-sided
lesions required extracorporeal membrane oxygenation (ECMO) treatment.
Lung area to head circumference ratio (LHR) [Metkus et al., 1996; Harrison et al.,
2003; Jani et al., 2007]. The LHR is an estimate of contralateral lung size and
mediastinal shift at the level of the atria as found on transverse scan of the fetal
thorax. Although there is a significant correlation between LHR and survival, the
lower limit of LHR compatible with survival appears to be dropping, so the test is
less predictive than in the past.
Treatment
Management of the Critically Ill Neonate with CDH
Preoperative care is directed towards stabilizing the infant's oxygenation, blood pressure,
and acid-base status. Although there are no randomized clinical trials, aggressive medical
management with decompression of the lung tissue (or at least minimization of any increase
in compression), cardiovascular support with fluids and inotropic agents, and ventilatory
support including high frequency ventilation and ECMO all help to minimize lung injury, and
Diaphragmatic Hernias
189
when combined with surgical correction appear to be associated with improved survival rates
[Reickert et al., 1996; Frenckner et al., 1997; Downard et al., 2003].
Initial Resuscitation
Initial management involves intubation and ventilation, usually before a definitive
diagnosis is made. Any delay in obtaining an airway can intensify the resultant acidosis and
hypoxia, which can increase the risk of pulmonary hypertension. The downward spiral of
hypoxia, hypercarbia, and acidosis is difficult to reverse in this population. Ventilation using
a mask and a bag should be avoided, because this may fill the intrathoracic bowel and
stomach with air. A nasogastric tube should be placed immediately. As with any critically ill
neonate, control of temperature and adequate intravenous hydratation are extremely important
[Langer et al., 1987]. Once stabilized, the infant should be transferred to a neonatal center.
Blood pressure support should be given to maintain arterial mean blood pressure levels ≥50
mm Hg to minimize any right to left shunting. Such support includes the use of isotonic fluids
and inotropic agents such as dopamine and/or dobutamine.
Ventilator Management
The goals of ventilator management of the infant with CDH are to maintain adequate
oxygenation and ventilation, and to minimize the severity of pulmonary hypertension. The
mode of ventilation is aimed at administering only enough pressure to maintain preductal
oxygen saturations above 80% or preductal partial pressure of oxygen (PaO
2
) above 60 mm
Hg. Barotrauma to the hypoplastic lungs may be largely responsible for the instability of the
infant and contributes to 25% of CDH deaths [Kolobow et al.,1987; Dreyfuss et al., 1988].
Initiation of conventional ventilator management includes pressure-limited ventilation at rates
of 30 to 100 breaths per minute at peak inspiratory pressures of 20 to 25 cm H
2
O [Wung et
al., 1995]. Peak inspiratory pressures that exceed 28 cm H
2
O are used transiently as a bridge
to ECMO. Positive end-expiratory pressure (PEEP) should be maintained at physiologic
levels (3 to 5 cm H
2
O) whenever possible. Hyperventilation, hypocarbia, and alkalosis may
decrease ductal shunting and control pulmonary hypertension in CDH [Drummond et al.,
1981; Reynolds et al., 1984], but at the expense of increased risk of barotrauma.
For many years it was thought that the pulmonary vasculature was extremely sensitive to
hypoxemia, hypercapnea and acidosis and that infants should be aggressively hyperventilated
to achieve a pO2 above 100 mm Hg and pCO2 below 40 mm Hg [Fong and Pemberton,
1985]. The ability to bring pCO2 down to less than 40 mm Hg without excessive ventilation
was a significant predictor of survival [Bohn et al., 1984; Bohn et al., 1987]. However, this
type of ventilation resulted in barotrauma in many infants, with significant associated
morbidity and mortality [Gibson and Fonkalsrud, 1983; Hansen et al., 1984]. More recently, a
strategy of “gentle ventilation” has been proposed, allowing the pCO2 to rise to levels
previously thought to be unsafe. Gentle ventilation with permissive hypercapnea may result in
significant improvement in survival rates presumably owing to avoidance of barotrauma
[Walsh-Sukys et al., 1994; Wung et al., 1995], with reports of increased survival compared to
cases treated with hyperventilation and alkalization [Boloker et al., 2002; Chiu et al., 2006].
Another ventilatory approach that has been used is high frequency ventilation (HFV).
This technique permits gas exchange without significant flow in the airway. The theoretic
advantage of HFV in infants is the ability to ventilate at lower airway pressures, thus avoiding
Ivan Martinez Serna and Antonio Pablo Gamez Garcia
190
barotrauma [Kohelet et al., 1998]. HFV is generally reserved for neonates that continue to
have hypoxia and hypercarbia refractory to conventional ventilation. Although the indications
for HFV are not clearly defined, there are retrospective reports of effective pCO
2
reduction
and increased survival in neonates with CDH [Datin-Dorriere et al., 2008; Somaschini et al.,
1999]; however, the overall survival rate is comparable to other reports that utilize
conventional ventilation. [Karl et al., 1983; Boynton et al., 1984; Tamura et al., 1988; Fujino
et al., 1989; Carter et al., 1990; Miguet et al., 1994]. In infants with CDH, there are no
randomized trials comparing HFV to other modes of ventilation. Further data are needed to
determine whether HFV has a role in managing neonates with CDH.
Intratracheal pulmonary ventilation (ITPV) is another technique which has been used to
accomplish gas exchange with less barotrauma. However, there is little experience with this
technique in infants having CDH [Wilson et al., 1993]
Pulmonary Vasodilators
Because infants with CDH often die from pulmonary hypertension, there is great focus on
the pharmacologic treatment of this condition. Nitric oxide is a potent vasodilator, and
because of its short half-life is selective for the pulmonary vasculature when inhaled. In the
past few years, inhaled nitric oxide has been used extensively for management of pulmonary
hypertension in children [Kinsella and Abman, 1993], and many studies have shown this
approach to decrease the need for ECMO [Finner et al., 1994]. Experience in infants with
CDH has been more limited, and results have varied. In individual cases, nitric oxide may
significantly decrease vascular resistance, but an overall survival advantage has not been
clearly documented.
Surfactant Therapy
The use of surfactant therapy has been suggested for treatment of infants with CDH
[Glick et al., 1992]. However, some reports found that surfactant therapy did not improve
outcomes [Van Meurs, 2004], though this was not a prospective controlled trial and infants
who received surfactant may have had more severe disease. Still, the use of surfactant should
be considered for neonates ≤34 weeks of gestation with chest radiographic findings of
alveolar atelectasis suggestive of respiratory distress syndrome.
Extracorporeal Membrane Oxygenation (ECMO)
The use of ECMO for neonatal respiratory failure was first described by Bartlett in 1976.
The rationale for using ECMO in infants with CDH is to “rest” the lungs while pulmonary
hypertension resolves, without subjecting them to unnecessary barotrauma. The selection
criteria for ECMO are controversial. Since ECMO has been most effective in the group of
infants who have transient pulmonary hypertension without lethal pulmonary hypoplasia
[Stollar et al., 1988; Steimle et al., 1994], many institutions offer it only to infants who have
had a “honeymoon period” where they have demonstrated adequate pulmonary parenchyma,
as reflected by oxygenation and ventilation criteria. Several single institution series have
reported improved survival rates with the use of ECMO in infants having CDH [Langham et
al., 1987; Bailey et al., 1989; Van Meurs et al., 1990; Rothenbach et al., 2005]. Initially,
attempts were made to identify those neonates with a greater than 80% risk of death, and
ECMO offered only to this group. However, there are no absolute predictors of lethal