“One of the most common reasons babies end up in the NICU is due to respiratory distress...”

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Respiratory Disorders in the NICU

One of the most common reasons babies end up in the NICU is due to respiratory distress. Let's get back to basics and review some of the respiratory disorders that we see in the NICU.

In part 1 of this respiratory disorder series, let's review Transient Tachypnea of the Newborn and Respiratory Distress Syndrome

Transient Tachypnea of the Newborn

Before a baby is born their lungs are filled with fetal lung fluid. This fluid is different from amniotic fluid and is important for pulmonary development. The fluid creates a distending pressure in the developing lungs to help it resist the natural recoil of the chest wall.

When the mother goes into labor, a surge of catecholamines triggers the epithelial cells within the lung to switch from secreting fluid, to start absorbing fluid. This is done by the passive absorption of Na+ through the epithelial Na+ channels (ENaC) and excretion into the interstitial space where it is absorbed. During labor up to 60% of fetal lung fluid may be absorbed, with the remaining becoming absorbed during breathing. We previously believed that the "vaginal squeeze" was a major contributor to clearance of fetal lung fluid. However, now it it thought to only have minor contribution.

Transient tachypnea of the newborn (TTN) is a common disorder in the newborn caused by inadequate or delayed clearance of fetal lung fluid. Some of the infants who are at risk of TTN are those who are born premature, to a mother who did not labor (elective cesarean section or precipitous delivery), and twins. Understandbly if a mother did not experience labor prior to delivery, the catecholamine release did not trigger the absorption of the fetal lung fluid and the baby is born with retained fetal lung fluid.

One big challenge with neonatal respiratory distress is differentiating the different disorders because the symptoms are all the same. Signs of TTN include tachypnea, expiratory grunting, retractions, nasal flaring and mild respiratory acidosis. The most characteristic finding of TTN is the fact that it is transient and symptoms resolve by 48-72 hours.

One characteristic diagnostic factor in TTN are perihilar markings and fluid in the fissure that are resolved within 48 hours. Treatment of these babies is supportive. I have seen many many babies who have transitioned from CPAP to room air within 12 to 24 hours.

Respiratory Distress Syndrome

Surfactant is critical to normal pulmonary function and it is first seen at the end of the "canalicular" phase of embryonic development. That is around 22-24 weeks gestation. Surfactant is composed of phospholipids, proteins, and fats and has multiple functions for normal pulmonary function including maintaining stability of alveolar membrane, contributing to the innate immune response, and reducing surface tension. Premature babies have slow synthesis, secretion, metabolism, and recycling of surfactant because they have less alveoli and type II pneumocytes.

When there is no, or insufficient, surfactant a baby has Respiratory Distress Syndrome (RDS). Prematurity is the most common contributor to RDS. A baby who is born between 22 to 25 weeks gestation has the canalicular development interrupted, and their alveoli do not function like mature alveoli. The immature alveoli and lack of surfactant leaves the baby with alveolar collapse and with a ventilation to perfusion mismatch causing cyanosis, impaired gas exchange, acidosis, and increased pulmonary pressures.

Signs of RDS include increased work of breathing (retractions, grunting, tachypnea, nasal flaring), cyanosis, and apnea. The baby requires ventilatory support to stabilize their alveoli. On chest X-Ray we often see a "ground glass" appearance, air bronchograms, and low lung volumes. This is due to the collapsed alveoli and interstitial edema.

The American Academy of Pediatrics recommends early initiation of CPAP at birth in babies born preterm with selective surfactant administration. Surfactant replacement therapy can dramatically improve gas exchange, reduce surface tension, decrease the need for high ventilator pressures, improve findings on the chest x-ray, and improve survival. There are several methods of administering surfactant replacement therapies and researchers are actively working on less invasive approaches. How do you give surfactant in your NICU?

Ventilatory Support for Respiratory Distress

There are many modes of ventilation we can use to support babies who are experiencing respiratory distress. Have you ever wondered why we try to extubate early? Any why we would use CPAP vs NIPPV vs High Flow Nasal Cannula? What is the difference? The incubator podcast did a great series a few weeks ago that tackled many of those questions and more. I really enjoyed it and hope you will too! Click on the button below to listen 🎧

Check out the incubator podcast here

In our next blog we will review some more disorders that cause respiratory distress. See you there!

Wishing you all the best!

Amanda xoxo

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References:

Crowley, M. Neonatal Respiratory Disorders in Fanaroff, et al., Klaus & Fanaroff's Care of the High-Risk Neonate, Elsevier-Saunders, 2020

Wilson, J., & Fitzgerald, J. The Respiratory System in Jnah & Trembath's Fetal & Neonatal Physiology for the Advanced Practice Nurse. Springer 2018

Committee on Fetus and Newborn; American Academy of Pediatrics. Respiratory support in preterm infants at birth. Pediatrics. 2014;133(1):171-174. doi:10.1542/peds.2013-3442