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  1. Definition. Transient tachypnea of the newborn (TTN) is also known as wet lung or type II respiratory distress syndrome (RDS). It is a benign disease of near-term, term, or large premature infants who have respiratory distress shortly after delivery that usually resolves within 3–5 days.

  2. Incidence. The incidence of TTN is ~1–2% of all newborns.

  3. Pathophysiology. Its true cause is unknown, but three factors are involved.

      1. Delayed resorption of fetal lung fluid. TTN is thought to occur because of delayed resorption of fetal lung fluid from the pulmonary lymphatic system. The increased fluid volume causes a reduction in lung compliance and increased airway resistance. This results in tachypnea and retractions. Infants delivered by elective cesarean delivery are at risk because of lack of the normal vaginal thoracic squeeze, which forces lung fluid out.

      1. Pulmonary immaturity. One study noted that a mild degree of pulmonary immaturity is a central factor in the cause of TTN. The authors found a mature L-S ratio but negative phosphatidylglycerol (the presence of phosphatidylglycerol indicates completed lung maturation) in infants with TTN. Infants who were closer to 36 weeks' gestation than to 38 weeks had an increased risk of TTN.

      1. Mild surfactant deficiency. One hypothesis is that TTN may represent a mild surfactant deficiency in these infants.

  4. Risk factors

      1. Elective cesarean delivery without preceding labor (especially with gestational age <38 weeks).

      1. Male sex.

      1. Macrosomia.

      1. Excessive maternal sedation.

      1. Prolonged labor.

      1. Negative amniotic fluid phosphatidylglycerol.

      1. Birth asphyxia.

      1. Fluid overload to the mother, especially with oxytocin infusion.

      1. Maternal asthma.

      1. Delayed clamping of the umbilical cord. Optimal time is 45 s.

      1. Breech delivery.

      1. Fetal polycythemia.

      1. Infant of a diabetic mother.

      1. Prematurity (can occur but is less frequent).

      1. Infant of drug-dependent mother (narcotics).

      1. Very low birthweight neonates.

      1. Exposure to B-mimetic agents.

      1. Precipitous delivery.

      1. Multiple gestations.

  5. Clinical presentation. The infant is usually near term, term, or large and premature and shortly after delivery has tachypnea (>60 breaths/min and can be up to 100–120 breaths/min). The infant may also have grunting, nasal flaring, rib retraction, and varying degrees of cyanosis. The infant often appears to have the classic "barrel chest" secondary to the increased anteroposterior diameter. There are usually no signs of sepsis. Some infants may have edema and a mild ileus on physical examination. One can also see tachycardia with usually a normal blood pressure.

  6. Diagnosis

      1. Laboratory studies

          1. Prenatal testing. A mature L-S ratio with the presence of phosphatidylglycerol in the amniotic fluid may help rule out HMD.

          1. Postnatal testing

              1. Arterial blood gas on room air shows some degree of mild hypoxia. Hypocarbia is usually present. Hypercarbia, if it exists, is usually mild (PCO2 >55 mm Hg). Extreme hypercarbia is rare and, if present, another diagnosis should be considered.

              1. Complete blood cell count with differential is normal in TTN but should be obtained if one is considering an infectious process. The hematocrit will also rule out polycythemia.

              1. Urine and serum antigen test may help rule out certain bacterial infections.

              1. Plasma endothelin-1 levels (ET-1). One study revealed that plasma ET-1 ...

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