Transient tachypnea of the newborn

Transient tachypnea of the newborn (TTN) is a medical term for a mild self-limited respiratory problem of babies that begins after birth and lasts about three days. Other terms for TTN are “wet lungs” or type 2 respiratory distress syndrome. “Transient” means means temporary or it doesn’t last long, usually, less than 24 hours. “Tachypnea” means to breathe quickly or fast breathing rate.

Some newborns have very fast or labored breathing in the first few hours of life because of a lung condition called transient tachypnea of the newborn (TTN). About 1 to 2 percent of all newborns develop TTN ¹⁾. Although premature babies can have TTN, most babies with this problem are full-term. The incidence of transient tachypnea of the newborn is inversely proportional to gestation age and affects approximately 10% of infants delivered between 33 and 34 weeks, approximately 5% between 35 and 36 weeks, and less than 1% in term infants ²⁾.

Transient tachypnea of the newborn may be more likely to develop in babies delivered by cesarean section because the fluid in the lungs doesn’t get squeezed out as in a vaginal birth.

Babies with transient tachypnea are closely watched in the hospital, and some might need extra oxygen for a few days. Most babies make a full recovery. TTN usually does not have any lasting effects on a child’s growth or development.

TTN usually goes away by the time a baby is 3 days old. Until that happens, doctors can help the baby get enough oxygen and nutrition if he or she needs it. Treatments might include:

• Extra oxygen
• An intravenous (IV) feeding tube
• Antibiotics

Transient tachypnea of the newborn causes

It is thought that slow absorption of the fluid in the fetal lungs causes TTN ³⁾. This extra fluid in their lungs makes taking in oxygen harder and your baby breathes faster to compensate.

Before birth, a developing fetus does not use the lungs to breathe — all oxygen comes from the blood vessels of the placenta. During this time, the baby’s lungs are filled with fluid.

As the baby’s due date nears, the lungs begin to absorb the fluid. Some fluid also may be squeezed out during birth as the baby passes through the birth canal. After delivery, as a baby breathes for the first time, the lungs fill with air and more fluid is pushed out. Any remaining fluid is then coughed out or slowly absorbed through the bloodstream and lymphatic system.

Transient tachypnea of the newborn is more common in:

• Premature babies because their lungs are not fully developed
• Babies born by rapid vaginal deliveries or C-sections without labor. They don’t go through the usual hormonal changes of labor, so don’t have time to absorb much fluid.
• Babies whose mothers have asthma or diabetes.

Risk factors for developing transient tachypnea of the newborn

• Maternal risk factors include delivery before completion of 39 weeks gestation, a cesarean section without labor, gestational diabetes, and maternal asthma ⁴⁾.
• Fetal risk factors include male gender, perinatal asphyxia, prematurity, small for gestational age, and large for gestational age infants ⁵⁾.

Transient tachypnea of the newborn pathophysiology

Fetal Lung

• The fetal pulmonary epithelium secretes alveolar fluid at around 6 weeks of gestation ⁶⁾.
• Chloride ions in the interstitium enter the pulmonary epithelial cell through the active transport of sodium, potassium, and chloride into cells (Na-K-2Cl transporter) which, in turn, are secreted into the alveolus through various chloride channels.
• Sodium follows the chloride ions through para-cellular pathways, and water is transported across the cells via aquaporin ⁷⁾.
• Volume of fetal lung is maintained by the larynx, which acts as a one-way valve, allowing only outflow of fluid.

Neonatal Lung

• Passive movement of sodium through epithelial sodium channels (ENaC) is believed to be the principle mechanism of reabsorption of fetal lung fluid with starling forces and thoracic squeeze playing a minor role in clearance.
• With the onset of labor, maternal epinephrine ⁸⁾ and glucocorticoids activate the epithelial sodium channels on the apical membranes of type II pneumocytes.
• Sodium in the alveolus is transported passively across the ENaC proteins which in turn is actively transported back to the interstitium by the Na+/K+-ATPase pump ⁹⁾.
• An osmotic gradient is created which allows chloride and water to follow and be absorbed into pulmonary circulation and lymphatics.

Transient tachypnea of the newborn symptoms

Transient tachypnea of the newborn presents within the first few minutes to hours after birth.

The following are the most common symptoms of transient tachypnea of the newborn. However, each baby may experience symptoms differently.

TTN symptoms may include:

• very fast, labored breathing of more than 60 breaths/minute
• grunting sounds when the baby breathes out (exhales) ¹⁰⁾
• flaring of the nostrils or head bobbing
• skin pulling in between the ribs or under the ribcage with each breath also known as retractions
• bluish skin around the mouth and nose called cyanosis.

Other occasional exam findings:

• Crackles, diminished or normal breath sounds on auscultation
• Tachycardia
• Cyanosis
• Barrel-shaped chest because of hyperinflation

Transient tachypnea of the newborn complications

Air leaks and pneumothoraces are other rare complications.

Longitudinal studies have shown an association between TTN and subsequent development of asthma ¹¹⁾. Epidemiological studies showed that there is a relationship between TTN and the development of asthma in children ¹²⁾. This means that TTN alone is not only a condition itself but also a risk factor for future asthma in later childhood. Despite this, pinpointing a relationship between them is rather complicated due to cause or risk factors ¹³⁾.

Transient tachypnea of the newborn diagnosis

Doctors usually diagnose transient tachypnea of the newborn in the first few hours after a baby is born. Often, TTN is diagnosed when symptoms suddenly resolve by the third day of life.

Duration of respiratory distress is the principal determinant for diagnosis of TTN. If distress resolves within the first few hours of birth, it can be labeled as “delayed transition.” Six hours is an arbitrary cutoff between “delayed transition” and TTN because by this time baby might develop issues with feeding and might require further interventions ¹⁴⁾. TTN is usually a diagnosis of exclusion and hence any tachypnea lasting over 6 hours requires workup to rule out other causes of respiratory distress.

A doctor will examine the baby and also might order one or all of these tests:

• Chest X-ray. This safe and painless test uses a small amount of radiation to take a picture of the chest. Doctors can see if the lungs have fluid in them. On the chest x-ray, the lungs show a streaked appearance (prominent perihilar vascular markings, edema of interlobar septae or fluid in the fissures) and appear over-inflated ¹⁵⁾. However, it may be difficult to tell whether the problem is TTN or another kind of respiratory problem such as hyaline membrane disease.
• Pulse oximetry. This painless test measures how much oxygen is in the blood. A small piece of tape with an oxygen sensor is placed around a baby’s foot or hand, then connected to a monitor.
• Complete blood count (CBC), blood culture, C-reactive protein (CRP) and lactate. This blood tests check for signs of infection (neonatal sepsis).
• Preductal and postductal saturations: to rule out differential cyanosis
• ABG (arterial blood gas) analysis may show hypoxemia and hypocapnia due to tachypnea; hypercapnia is a sign of fatigue or air leak.

Other workups to consider:

• Ammonia level in the setting of lethargy and metabolic acidosis to rule out inborn errors of metabolism
• Echocardiography to rule out congenital cardiac defects in patients with differential cyanosis or persistent tachypnea for over 4 to 5 days.

Transient tachypnea of the newborn differential diagnosis

• Pneumonia
• Respiratory distress syndrome
• Aspiration syndromes: meconium, blood or amniotic fluid
• Pneumothorax
• Left-to-right cardiac shunt defects with failure
• Persistent pulmonary hypertension
• Central nervous system (CNS) irritation or disease: Subarachnoid hemorrhage, hypoxic-ischemic encephalopathy
• Inborn errors of metabolism
• Congenital malformations: Congenital diaphragmatic hernia, cystic adenomatoid malformations

Transient tachypnea of the newborn treatment

Given TTN is a self-limited condition, supportive care is the mainstay of treatment.

• Rule of 2 hours: Two hours after onset of respiratory distress, if an infant’s condition has not improved or has worsened or if fraction of inspired oxygen (concentration of oxygen that a person inhales or FiO2) required is more than 0.4 or chest x-ray is abnormal, consider transferring infant to a center with a higher level of neonatal care ¹⁶⁾.
• Routine NICU care including continuous cardiopulmonary monitoring, maintenance of neutral thermal environment, securing intravenous (IV) access, blood glucose checks, and observation for sepsis should be provided.

Babies with TTN are watched closely and may go to a neonatal intensive care unit (NICU) or special care nursery. There, doctors check babies’ heart rates, breathing rates, and oxygen levels to make sure breathing slows down and oxygen levels are normal.

Specific treatment for transient tachypnea of your newborn may include:

• Supplemental oxygen given by mask on your baby’s face or by placing your baby under an oxygen hood
• Blood tests to measure blood oxygen levels
• Continuous positive airway pressure (CPAP) – a mechanical breathing machine that pushes a continuous flow of air or oxygen to the airways to help keep tiny air passages in the lungs open

Tube feedings may also be necessary if your baby’s breathing rate is too high, because of the risk of aspiration of the food.

Once TTN goes away, your baby usually recovers quickly and has no increased risk for additional respiratory problems.

Breathing help

Some babies with TTN need extra oxygen. They get this through a small tube under the nose called a nasal cannula .

A baby who gets extra oxygen but still struggles to breathe might need continuous positive airway pressure (CPAP) to keep the lungs from collapsing. With CPAP, a machine pushes a steady stream of pressurized air or oxygen through a nasal cannula or mask. This helps keep the lungs open during breathing.

• Oxygen support may be required if pulse oximetry or ABG suggest hypoxemia.
• An oxygen hood is the preferred initial method; however, nasal cannula, CPAP can also be used.
• Concentration should be adjusted to maintain oxygen saturation in low 90s.
• Endotracheal intubation and requirement of extracorporeal membrane oxygenation (ECMO) support is usually uncommon but should always be considered in patients with declining respiratory status.
• Arterial blood gas (ABG) analysis should be repeated, and pulse oximetry monitoring should be continued until signs of respiratory distress have resolved.

Nutrition

• Neonates’ respiratory status is the usual determinant for the degree of nutritional support required.
• Tachypnea of over 80 breaths per minute with associated increased work of breathing often makes it unsafe for the infant to receive oral feeds.
• Such infants should be kept nil per oral (NPO), and intravenous (IV) fluids should be started at 60 to 80 ml per kg per day.
• If respiratory distress is resolving, diagnosis is certain and respiratory rate is less than 80 breaths per minute; enteral feeds can be started.
• Enteral feeds should always be started slowly with progressive increments in volume of feeds until tachypnea has completely resolved

Good nutrition can be a problem when a baby is breathing so fast that he or she can’t suck, swallow, and breathe at the same time. If so, intravenous (IV) fluids can keep the baby hydrated while preventing blood sugar from dipping too low.

If your baby has TTN and you want to breastfeed, talk to your doctor or nurse about pumping and storing breast milk until your baby is ready to feed. Sometimes babies can get breast milk or formula through a:

• nasogastric (NG) tube: a small tube placed through the baby’s nose that carries food right to the stomach
• orogastric (OG) tube: a small tube placed through the baby’s mouth that carries food right to the stomach

If your baby has one of these tubes, ask the doctor about providing breast milk for your baby.

Symptoms of transient tachypnea usually get better within 24–72 hours. A baby can go home when breathing is normal and he or she has been feeding well for at least 24 hours.

Infectious

Since TTN may be difficult to distinguish from early neonatal sepsis and pneumonia, empiric antibiotic therapy with ampicillin and gentamicin should always be considered.

Medications

• Randomized control trials studying the efficacy of furosemide ¹⁷⁾ or racemic epinephrine ¹⁸⁾ in TTN showed no significant difference in duration of tachypnea or length of hospital stay compared with controls
• Salbutamol (inhaled beta2-agonist) has been shown to decrease the duration of symptoms and hospital stay; however, more evidence-based studies are needed to confirm its efficacy and safety ¹⁹⁾.

Transient tachypnea of the newborn prognosis

Overall prognosis is excellent with most of the symptoms resolving within 48 hours of onset.

In some case reports, malignant TTN has been reported in which affected newborns develop persistent pulmonary hypertension due to a possible elevation of pulmonary vascular resistance due to retained lung fluid ²⁰⁾.