Anesthetic Considerations in Congenital Diaphragmatic Hernia

CONGENITAL DIAPHRAGMATIC HERNIA

Pathophysiology

During fetal development, the gut can herniate into the thorax through one of three possible dia-phragmatic defects: the left or right posterolateral foramen of Bochdalek or the anterior foramen of Morgagni. The reported incidence of diaphrag-matic hernia is 1 in 3000–5000 live births. Left-sided herniation is the most common type (90%). Hallmarks of diaphragmatic herniation include hypoxia, a scaphoid abdomen, and evidence of bowel in the thorax by auscultation or radiogra-phy. Congenital diaphragmatic hernia is often diagnosed antenatally during a routine obstetric ultrasound examination. A reduction in alveoli and bronchioli (pulmonary hypoplasia) and mal-rotation of the intestines are almost always pres-ent. The ipsilateral lung is particularly impaired and the herniated gut can compress and retard the maturation of both lungs. Diaphragmatic hernia is often accompanied by marked pulmonary hyper-tension and is associated with 40–50% mortality. Cardiopulmonary compromise is primarily due to pulmonary hypoplasia and pulmonary hyperten-sion rather than to the mass effect of the herniated viscera.

Treatment is aimed at immediate stabilization with sedation, paralysis, and moderate hyperven-tilation. Pressure-limited ventilation is used. Some centers employ permissive hypercapnia (postductal Paco₂< 65 mm Hg) and accept mild hypoxemia (preductal Spo₂> 85%) in an effort to reduce pul-monary barotrauma. High-frequency oscillatory ventilation (HFOV) can improve ventilation and oxygenation with less barotrauma. Inhaled nitric oxide may be used to lower pulmonary artery pres-sures but does not appear to improve survival. If the pulmonary hypertension stabilizes and there is little right-to-left shunting, early surgical repair may be undertaken. If the patient fails to stabilize, extracorporeal membrane oxygenation (ECMO) may be undertaken. When initiated in the critical care unit in a neonate, venoarterial ECMO usu-ally involves pumping blood from the jugular vein through a membrane oxygenator and countercur-rent heat exchanger before returning it to ipsilat-eral carotid artery. Timing of the repair following ECMO is controversial. Treatment with prena-tal intrauterine surgery has not been shown to improve outcomes.

Anesthetic Considerations

Gastric distention must be minimized by placement of a nasogastric tube and avoidance of high levels of positive-pressure ventilation. The neonate is preoxy-genated and intubated awake, or without the aid of muscle relaxants. Anesthesia is maintained with low concentrations of volatile agents or opioids, muscle relaxants, and air as tolerated. Hypoxia and expan-sion of air in the bowel contraindicate the use of nitrous oxide. If possible, peak inspiratory airway pressures should be less than 30 cm H2O. A sud-den fall in lung compliance, blood pressure, or oxygenation may signal a contralateral (usually right-sided) pneumothorax and necessitate place-ment of a chest tube. Arterial blood gases are pref-erably monitored by sampling a preductal artery if an umbilical artery catheter is not already in place. Surgical repair is performed via a subcostal incision of the affected side; the bowel is reduced into the abdomen and the diaphragm is closed. Aggressive attempts at expansion of the ipsilateral lung fol-lowing surgical decompression are detrimental. Postoperative prognosis parallels the extent of pul-monary hypoplasia and the presence of other con-genital defects.