Incidence and classification

CDH occurs in about 1 in every 2500 live births. Classification is based on location of the defect, with the most common and significant being the posterior lateral aspect of the diaphragm, through the foramen of Bochdalek (80%). Left-sided hernias occur five times more often than right-sided ones. Hernias through the esophageal hiatus are generally small, with no compromise of pulmonary function, and do not usually present in the neonatal period. Figure 201-1 illustrates other sites in which hernias may be evidenced. Incomplete muscularization of the diaphragm (eventration) may occur, resulting in the development of a hernia sac. Many cases are asymptomatic, but severe cases may present identically to CDH.

Embryology

In the fetus, the pleuroperitoneal cavity begins as a single compartment. The development and closure of the diaphragm are usually complete by the ninth fetal week, with return of the gut to the peritoneal cavity in the tenth week. Gut return from the yolk stalk occurring early or diaphragmatic formation occurring late produces the potential for a diaphragmatic hernia. Anatomic defects of the lung occur because bronchial development can be impeded by the herniated abdominal contents.

Clinical presentation

CDH may be suspected in utero because about 30% of cases are associated with polyhydramnios. Severe CDH is usually discovered by ultrasound prenatally, immediately after birth, or within the first 6 h of life. Some visceral herniations can act as an evolving lesion and may present at birth, even though the diaphragmatic defect occurs in gestation. The infant presents with cyanosis and respiratory distress. Physical findings include shifted cardiac sounds, scaphoid abdomen, and diminished breath sounds on the affected side. The primary cause of death is progressive hypoxemia and acidosis. Radiographs are usually confirmatory. The immediate therapy is tracheal intubation and mechanical ventilation along with placement of a nasogastric tube to decompress the gut. Significant degrees of postsurgical hypoxemia and acidosis may result in persistent fetal circulation, with right-to-left shunting of desaturated blood. Progressive deterioration and death can result from the subsequent high pulmonary pressures. Ligation of a patent ductus arteriosus in infants with severe persistent fetal circulation is controversial because acute right ventricular failure and death can occur. Prior to delivery, parturients who are anticipated to deliver an infant with CDH should be transferred to a facility that is equipped to provide specialized therapies (e.g., extracorporeal membrane oxygenation [ECMO]) and drugs (e.g., inhaled nitric oxide).

Anesthetic management

Most infants with CDH are urgently intubated in the delivery room. If the infant is not intubated before coming to the operating room, the tracheal tube can be placed while the infant is awake, or a rapid sequence intravenous induction can be planned. The neonate is preoxygenated, cricoid pressure is applied, and precautions are taken to prevent aspiration of stomach contents. Positive-pressure ventilation with bag and mask prior to intubation should be avoided because it may cause further distention of the gut. The use of standard monitors, along with arterial and central venous pressure catheters, is recommended. Because heat loss is rapid, the operating room should be warmed, and a source of radiant heat provided.

Selection of anesthetic agent and technique depends on the infant’s condition. The usual technique is O₂/opioid/neuromuscular blocking agent. The use of N₂O is contraindicated. Any sudden deterioration in heart rate, blood pressure, SpO₂, or lung compliance suggests a contralateral pneumothorax, which should be promptly treated by inserting a chest tube. Some practitioners advocate the prophylactic insertion of a contralateral chest tube. A peak inspiratory pressure of less than 30 cm H₂O is recommended.

Two factors that affect pulmonary vascular resistance are PO₂ and PCO₂. The PaO₂ should be maintained in the 90- to 100-mm Hg range. The lungs should be hyperventilated to achieve a PaCO₂ of 25 to 30 mm Hg (to decrease pulmonary vascular resistance). After repair of the diaphragmatic defect, the infant’s abdomen may be primarily closed, or a staged closure may be performed with a Silastic pouch. After surgery, the infant should be transferred to an intensive care unit and remain intubated, mechanically ventilated, and paralyzed in a warmed incubator unit. Attempts to expand the ipsilateral lung may lead to excessive airway pressure and pneumothorax.

Postoperative care

The postoperative care of infants with CDH is critical. ECMO may be required. Infants with relatively normal lungs usually do well, but those with varying degrees of pulmonary hypoplasia have difficulty maintaining adequate oxygenation because of persistent fetal circulation. The postoperative use of positive-pressure ventilation usually will be necessary. Bilateral chest tubes are also frequently needed. Gastric suction should be continued. Pain management is important and may include epidural or caudal analgesia.

The use of extracorporeal membrane oxygenation

Criteria have been established to identify infants with CHD who do not respond to pharmacologic and ventilatory therapy, a group that might benefit from a period of ECMO to provide time for pulmonary growth and remodeling. Selection criteria for ECMO include hemodynamic instability, persistent acidosis, and pneumothoraces, as well as severe pulmonary hypertension unresponsive to pharmacologic intervention. However, the use of ECMO is associated with significant risks, and contraindications do exist (Box 201-1). ECMO is discontinued if irreversible brain damage or lethal organ failure occurs or when lung function improves. The overall survival rate of infants with CDH treated with ECMO is reported to be between 50% and 87%.

The prenatal diagnosis of CDH is important, but unfortunately, ultrasound diagnosis of CDH is, in most cases, an incidental finding. The possible association with chromosomal anomalies or syndromes is an important prognostic factor. Fetal liver herniation into the chest can also be prognostic. The lung-to-head circumference ratio is a measurement of the contralateral lung taken by ultrasound at the four-chamber heart view and compared with the head circumference. A value less than 1.0 is associated with increased morbidity and an increased need for ECMO.

Mortality rate

Overall mortality rate in patients with CDH remains high (20% to 80%, average 50%). The survivors lead fairly normal lives, despite having some residual hypoplastic lung disease. Long-term sequelae include bronchopulmonary dysplasia, pulmonary hypoperfusion, and abnormal findings on pulmonary function tests (i.e., decreased forced expiratory volume in 1 sec and decreased maximum voluntary ventilation) but normal functional residual capacity.