Neonatal wet lung is one of the causes of neonatal respiratory distress, characterized by increased respiratory rate due to excessive fluid in the lungs, hence also known as transient tachypnea of the newborn. The fetal lungs contain approximately 30–35 ml/kg of fluid. During childbirth, about 10–15 ml/kg of fluid is expelled due to compression through the birth canal and replaced by air. The remaining fluid in the lungs is absorbed into the interstitium and then transported to the bloodstream via lymphatic vessels and veins. This process is typically completed within the first 4 hours after birth. If the fetal chest is not compressed during cesarean delivery or if there is impaired fluid transport, fluid may accumulate in the lungs, leading to congestion in the lymphatic vessels and veins. Additionally, small amounts of fluid may collect in the interlobar spaces and pleural cavity, impairing respiration.

bubble_chart Diagnosis

(1) Medical History More common in full-term infants, especially those delivered by cesarean section.

(2) Clinical Manifestations Within 3 to 6 hours after birth, the infant exhibits increased respiratory rate and slight cyanosis around the lips, but generally appears well, with strong crying and normal feeding. A few severe cases may present with moaning and cyanosis. Pulmonary signs are usually limited to coarse or diminished breath sounds, occasionally moist rales, and sometimes no pulmonary signs at all.

(3) Pulmonary X-ray Findings The lung fields may show faint, uniformly distributed patchy shadows of varying sizes; the lung markings are thickened and radiate outward from the hilum; interstitial fluid accumulation may appear as short, thick linear shadows, sometimes accompanied by fluid in the right upper and middle lung lobes and a small amount of pleural effusion; the heart shadow may be slightly enlarged (grade I), predominantly on the right side. Although the X-ray changes are diverse, they resolve quickly and may disappear within 2 to 3 days.

﹝Treatment﹞

This condition is a self-limiting disease with a good prognosis. Symptoms in most affected children disappear within 1 to 2 days after birth. A small number of severe cases require intensive care and symptomatic treatment, but generally do not require antibiotic therapy, and recovery usually occurs in about 5 to 6 days.

bubble_chart Differentiation

In the early stages, this condition must be differentiated from hyaline membrane disease, which has a longer course, reduced lung aeration on X-ray, and is more common in premature infants. Infants with aspiration pneumonia often have a history of birth asphyxia, with rare interlobar and pleural effusions on X-ray. The lesions take longer to resolve, and clinical symptoms are more severe.