Pulmonary vascular abnormalities in congenital diaphragmatic hernia.

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.