Radiologic demonstration of postnatal liquid in the lungs of newborn lambs

The liquid which occupies the potential air spaces of the fetal lung is, at birth, displaced by air and removed by the pulmonary blood and lymphatic circulations. Delayed resorption of this liquid from the interstitial spaces may be associated with decreased lung compliance and be the cause of the syndrome "transient tachypnea of the newborn." Chest roentgenograms of these infants have shown the presence of alveolar and interstitial edema and pleural effusions which cleared during the first few days of life. We chose to test the possibility that a delay in clearance of lung liquid might occur and be associated with tachypnea and radiologic evidence of pulmonary edema in newborn lambs. Serial chest radiographs were obtained in 18 newborn lambs delivered at term by Caesarean section. The radiographs demonstrated the presence of lung liquid which gradually cleared in an average time of 2 hours following onset of breathing. Lung weight—body weight ratios obtained following sacrifice at various stages of clearing—decreased as pulmonary aeration increased. Microscopic examination of the lungs showed no evidence of inflammatory exudate or squamous debris but distension of perivascular tissues with liquid was demonstrated. An association between increasing lung aeration and decreasing respiratory rates was found.