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Cardiac evaluation is an important part of the investigation of a fetus with a diaphragmatic hernia. The heart is displaced by the physical presence of the abdominal contents in the chest, and the flow dynamics within the heart are altered. This can produce secondary diminution of chamber growth, particularly of the left heart. Structural heart malformation is also a frequently associated finding. Evaluation of cardiovascular flow profiles may give us further understanding of the pathophysiology of this lesion and may help to predict those fetuses that might benefit from intrauterine therapy.

Congenital diaphragmatic hernia results in abnormal lung development. There is a global hypoplasia with both lungs affected, the ipsilateral lung more severely. This results in a reduction in the number of bronchial divisions and a decrease in the quantity and maturity of the alveoli. The pneumocytes are dysfunctional, resulting in a total quantitative and qualitative reduction in surfactant and a decrease in antioxidant enzyme activity.

Congenital diaphragmatic hernia (CDH) has been described, studied, and treated for over 400 years. A historical perspective is given. Great strides have been made in the care of patients with CDH; however, the mortality rate remains 30% to 60%. Consideration of historical references, observations, and achievements in the study of CDH is important for the continued advancement and improvement in our understanding of and future success in treating infants and children with CDH.

Persistent pulmonary hypertension poses a significant problem to the surgeon managing an infant with congenital diaphragmatic hernia. It is likely that a number of abnormalities contribute to this pathophysiologic entity. These include: (1) in the hypoplastic lung the overall cross-sectional area of the pulmonary vascular bed is reduced, (2) the muscular arteries are hypertrophied and extend more peripherally than normal, (3) the pulmonary vessels are more labile than normal and are overly sensitive to the normal stimuli of vasoconstriction, and (4) the immature surfactant-deficient lung is predisposed to barotrauma and atelectasis, resulting in alveolar hypoxemia which contributes to pulmonary hypertension. All of these interfere with the ability of the lung to accept the increase in pulmonary blood flow required by the transitional circulation. If this impairment reaches a level such that the lung cannot accept the right ventricular output then pulmonary hypertension will ensue and a poor outcome can be anticipated.

The first animal model of congenital diaphragmatic hernia (CDH) was described in 1967. This was a late-gestational, surgically-created lamb model. Since then, animal modeling has become more sophisticated. Using a variety of techniques and laboratory species, animal models have been produced to investigate the pathophysiology of CDH, from whole animal physiology studies to lung molecular changes. To provide the animal tissue required, three different approaches have been used: (1) a surgically-created model which has been reported in lambs and rabbits, (2) a teratogen-induced model which to date has been described in rats and mice, and (3) a congenital model which is present in a specific pig herd. All animal models are discussed in this article.

Since the late 1970s, congenital diaphragmatic hernia (CDH) has been diagnosed antenatally by ultrasound. With improvements in ultrasound resolution, CDH is being diagnosed more frequently and at an earlier stage in gestation. This provides an opportunity to administer in utero therapy to the fetus. As 50% of babies born with CDH survive, it is imperative that accurate prognostic indicators are available to guide antenatal therapy. Antenatal diagnosis and prognostic indicators are discussed.

The emphasis in postnatal management has shifted from the neonatal surgical emergency approach to strategies designed to deal with pulmonary hypoplasia and the pulmonary vascular abnormalities. There has been extensive experience with alternative ventilation strategies such as ECMO and high frequency ventilation, without there being convincing evidence that these have had a major impact on mortality. Strategies that emphasize the importance of minimizing ongoing lung injury, such as pressure limited (permissive hypercapnia) ventilation and the use of surfactant replacement therapy, are beginning to show some encouraging results.