Embryology: Congenital diaphragmatic hernia (CDH) is the result of a failure of the diaphragm (the muscle of respiration) to form normally in utero between the 8th and 10th week of gestation. The diaphragm is not only the muscle of respiration but it also separates the chest cavity (lungs and heart) from the abdominal cavity (stomach, intestines, liver, spleen). With this defect in the diaphragm, the abdominal contents can make their way (herniate) into the chest cavity at the critical time when the lungs are developing. The resultant “lung hypoplasia” can cause severe respiratory compromise.
Epidemiology
CDH occurs once in about every 2000-3000 live births. It occurs equally in boys and girls.
Pathophysiology
Congenital diaphragmatic hernia can occur on either the left side of the chest or the right side. Approximately 85% are left sided, 13% are right sided and 2% are bilateral. 50%-60% of the cases are isolated, meaning that there are no other associated abnormalities. The remaining 40%- 50% can occur along with chromosomal abnormalities, as well as abnormalities in the heart, kidneys, GI tract and/or brain and spinal cord. The presence of other defects is associated with worse outcomes.
Babies born with isolated CDH (e.g. not associated with other defects) have a survival rate between 50% -80%, with the best chance of survival occurring when the baby is born in a major hospital with a Level 3 NICU.
When the abdominal contents herniate into the chest cavity early in gestation, the lungs cannot develop normally and are smaller than normal at birth -- this is known as pulmonary hypoplasia. Even though the abdominal contents may only herniate into one side of the chest (usually the left side), the resultant displacement of the left lung and heart to the right side can cause both lungs to be smaller than normal at birth – too small to work adequately. This can then lead to severe respiratory failure at birth
The pulmonary blood vessels can also develop abnormally in utero contributing to a sometimes fatal condition called “pulmonary hypertension”, or high blood pressure in the lungs.
Diagnosis
Approximately 50% of cases can be diagnosed prenatally with a prenatal ultrasound. Prenatally a CDH may be suspected because of polyhydramnios (increased amount of amniotic fluid).
At birth, CDH may be suspected if the baby has acute respiratory distress in the delivery room and especially if also associated with a “scaphoid abdomen.” In other words, the abdomen appears sunken in rather than slightly rounded due to the absence of intestines and other organs. The diagnosis can be confirmed with a chest x-ray.
Management
Acute management should include the A, B, C’s of resuscitation i.e. securing the airway, making sure the baby is breathing, and providing adequate blood circulation. To keep the intestines from filling up with air and further compromising respiratory function, an endotracheal tube should be inserted and the baby put on a ventilator. Bag and mask ventilation – or especially CPAP -- is not recommended because air can get into and dilate the intestine with the bag and mask ventilation squeezing the lungs even smaller and worsening the respiratory distress. An oral or nasogastric tube is an essential part of the management of CDH to evacuate air from the intestines that are in the chest cavity so as to not impinge upon the lung.
The baby may require conventional mechanical ventilation, high frequency oscillatory ventilation (HFOV) or extracorporeal membrane oxygenation (ECMO) to maintain adequate respiratory function until a definitive surgical repair is done. Modern protocols also call for the use of inhaled nitric oxide to decrease the blood pressure in the lungs and improve oxgenation. Up to date management now usually include preoperative medical stabilization and delaying repair for up to 7-10 days or longer.
Long Term Prognosis
The gastrointestinal tract is also abnormal in CDH and even after definitive surgical repair patients are at risk for feeding problems (e.g. reflux, and failure to thrive). Hearing impairment, developmental delays, reactive airway disease and pulmonary hypertension have also been described as long term problems in patients with CDH(5).
Recommendations for Pregnant Women
Since most CDH defects can be identified on prenatal ultrasound, ask your obstetrician to perform an ultrasound after 20 weeks to assess your baby’s anatomy. This is especially true if you have more amniotic fluid than normal, or you are measuring big-for-dates. If your baby is diagnosed with CDH, make plans to deliver in a major hospital with a Level IV NICU (offers ECMO), with neonatologists and pediatric surgeons on staff and readily available. Meet with the neonatologists and pediatric surgeons prior to delivery to make a delivery plan. Ask for a tour of the NICU. No one can tell if your baby will be born with enough lung tissue to breathe, and unfortunately, some babies undergo months of surgical and NICU care, and still don’t survive. As difficult as it is, think about what you want for your baby, and if there are limits to what you want to put your baby through. This may help prepare you to make hard decisions, should that day come.
The best way to give your baby with a known CDH the highest possible chance of survival is to deliver him/her in a hospital with lots of experience with neonatal ECMO – even if that hospital is far away from where you live.