Recent Advances in Pathophysiology and Management of Transient Tachypnea of Newborn

Abstract

Transient tachypnea of newborn (TTN) results from failure of the newborn to effectively clear the fetal lung fluid soon after birth. TTN represents the most common etiology of respiratory distress in term gestation newborns and sometimes requires admission to the neonatal intensive care unit. TTN can lead to maternal-infant separation, the need for respiratory support, extended unnecessary exposure to antibiotics and prolonged hospital stays. Recent evidence also suggests that TTN may be associated with wheezing syndromes later in childhood. New imaging modalities such as lung ultrasound can help in the diagnosis of TTN and early management with distending pressure using continuous positive airway pressure may prevent exacerbation of respiratory distress.

Fig. 1. Illustration detailing mechanisms of lung fluid secretion and clearance during fetal gestation and after birth.

During fetal gestation, type 2 alveolar pneumocytes actively secrete chloride (Cl⁻) into the alveolar space. Sodium (Na⁺) and water passively accompany Cl⁻. The fluid secretion peaks at 5 ml/kg/h at a maximum volume of 25–30 ml/kg in late gestation. During labor, epithelial sodium channels (ENaC) become activated by adrenergic stimulation. Basolateral Na⁺/K⁺ ATPase helps move Na⁺ into the interstitium along with Cl⁻ and water. Most interstitial lung liquid moves into the pulmonary circulation; some drains via the lung lymphatics. The darker blue hue represents normal vaginal delivery and the lighter hue represents delayed fluid resorption in TTN. Modified from Pathophysiology of fetal lung development by Mathew et al. in Essentials of Neonatal Edition (Elsevier); Copyright Satyan Lakshminrusimha.

Fig. 2. Airway liquid retention and role of respiration.

The fetal fluid-filled lungs do not participate in gas exchange but the lung volume approximates the functional residual capacity (FRC) of the airfilled lung after birth. Following delivery of the head and air breathing, the pressure from inspiration creates a pressure differential that promotes airway liquid to move into the lung tissue, which can raise interstitial pressure. A high interstitial pressure at end-expiration may shift fluid back into the alveoli. Copyright Satyan Lakshminrusimha.

Fig. 3. Risk factors, symptoms and signs, management of transient tachypnea of the newborn and associated childhood respiratory complications.

List of prenatal, maternal and infant risk factors of transient tachypnea of the newborn (TTN). Genetic polymorphisms and maternal asthma may increase risk of childhood asthma in newborns who have TTN.

Fig. 4. Differential diagnosis of transient tachypnea of the newborn with associated roentgenograms.

Differential diagnosis of tachypnea in the newborn can be remembered by using the mnemonic “TACHYPNEA” T: transient tachypnea of the newborn, A: Aspiration C: Congential anomalies, HY: Hyaline membrane disease, P: Pneumonia, Primary Ciliary Dyskinesia, E: Effusion, and A: Air-leak syndromes.

Fig. 5. X-ray findings of transient tachypnea of the newborn.

Retained lung fluid may result in diffuse streaky pulmonary interstitial opacities, and fluid in the minor fissures. Prominent perihilar pulmonary vascular markings observed are sometimes referred to as a “sunburst” pattern. There may be a degree of hyperinflation and pleural effusions that are usually small. Occasionally mild cardiomegaly can be seen.

Fig. 6. Lung ultrasound as a diagnostic tool for newborn lung pathology.

a Normal lung showing horizontal A-lines (reverberation artifact from pleural line). b In TTN, A-lines are obscured and B-lines are separated giving the appearance of comet tails. c Patient with respiratory distress syndrome (RDS) showing an irregular and thickened pleural line, consolidation, and so-called “coalesced B-lines:” referring to the inability to distinguish B-lines, absence of A-lines, making a “white lung” appearance. Ultrasound pictures provided by J. Lauren Ruoss, MD and colleagues I. Prelipcean and D. Rajderkar, University of Florida.