The term “wet lung” commonly describes Transient Tachypnea of the Newborn (TTN), a temporary, non-infectious breathing condition in newborns. TTN causes babies to breathe rapidly, usually starting within the first few hours after birth. It occurs because the lungs retain excess fluid that should have been cleared during and immediately after delivery. This condition is self-limiting, resolving on its own as the baby’s body gradually absorbs the fluid. This article explores the underlying mechanism, risk factors, symptoms, and supportive care used for management.
The Mechanism of Transient Tachypnea of the Newborn
During gestation, a fetus’s lungs are filled with specialized fluid necessary for normal development. The transition from fluid-filled to air-filled lungs requires the rapid clearance of this fluid from the air sacs (alveoli) for effective oxygen intake.
Fluid clearance is triggered by hormonal changes in the mother and baby just before and during labor. These hormones activate specialized channels in the lung cells, such as the epithelial sodium channels (ENaC). These channels actively transport sodium out of the air spaces, and water follows by osmosis, moving the fluid into the bloodstream and lymphatic system for removal.
In a vaginal delivery, the mechanical squeeze of the birth canal aids this process by physically pushing some fluid out of the chest. TTN occurs when this fluid clearance mechanism is incomplete or significantly delayed. The retained fluid acts as a barrier, preventing the alveoli from fully opening and filling with air.
To compensate for reduced oxygen exchange, the baby breathes much faster and harder. This rapid, shallow breathing is known as tachypnea. Since the underlying issue is delayed absorption, the condition is referred to as “transient” because the body eventually completes the necessary fluid clearance.
Key Risk Factors and Causes
The primary factor contributing to TTN is any event that interrupts the normal sequence of labor-induced hormonal changes and mechanical compression. Delivery via elective Cesarean section, especially if performed before the onset of labor, is a well-established risk factor. Without the natural signals of labor, the hormonal surge that initiates the fluid-clearing process does not occur as effectively.
A rapid or precipitous vaginal delivery can also be a cause, as it limits the amount of time the baby spends in the birth canal. This reduced time means less mechanical compression to squeeze the fluid out of the chest. Babies born late preterm, between 34 and 36 weeks of gestation, are also at higher risk compared to full-term infants.
Their lung cells may be less mature and therefore less efficient at activating the sodium channels required for rapid fluid absorption. Certain maternal health conditions can also predispose a newborn to TTN. Babies born to mothers with diabetes, particularly if the condition was not well-controlled during pregnancy, have an elevated risk. Similarly, a mother having asthma may also increase the likelihood of her baby developing this temporary respiratory condition.
Identifying the Clinical Symptoms
Symptoms of TTN typically appear quickly, often within the first one to two hours following birth. The most noticeable sign is tachypnea, or rapid breathing, which often exceeds 60 breaths per minute and can reach 80 to 100.
The effort required to breathe with fluid-filled lungs leads to several observable signs of respiratory distress. Babies may make a soft grunting sound on exhalation, which attempts to keep the air sacs open against the retained fluid. Other signs include nasal flaring, where the nostrils widen with each breath to take in more air.
Retractions are also a common symptom, involving the visible pulling in of the skin and muscles between or below the ribs. This indicates the baby is using accessory muscles to force air into the lungs. These symptoms are generally mild to moderate and usually begin to resolve within 24 to 72 hours as the fluid is absorbed.
Diagnostic Process and Treatment Protocols
Diagnosis is initially clinical, based on the rapid onset of symptoms and the baby’s overall appearance. However, because TTN symptoms mimic those of more serious conditions like neonatal sepsis or pneumonia, diagnostic tests are required to rule out these other possibilities.
A chest X-ray is a standard tool, often revealing characteristic signs of TTN. The X-ray typically shows hyperinflated lungs due to trapped air, and streaks of fluid visible in the fissures between the lung lobes. Blood tests, including blood cultures, may also be performed to ensure the respiratory distress is not caused by a bacterial infection.
Management focuses entirely on supportive care until the fluid naturally clears. Supplemental oxygen, delivered through a nasal cannula or an oxygen hood, is the mainstay of treatment to maintain adequate blood oxygen saturation levels. Continuous Positive Airway Pressure (CPAP) may be used to gently push air into the airways, helping to keep the air sacs open and facilitate fluid clearance.
Monitoring vital signs, including heart rate, respiratory rate, and oxygen levels, is continuous. Feeding is often temporarily restricted, and nutrition and hydration are provided through intravenous (IV) fluids if the baby’s breathing rate remains too high. This temporary measure prevents the risk of aspiration while the baby struggles to coordinate sucking and rapid breathing. The prognosis is excellent, with complete recovery expected in nearly all cases.