Podcast Episode 8
Introduction
In podcast episode 8, we take a deeper look at respiratory distress syndrome. Respiratory distress syndrome is the most common lung disease in premature infants. But, not a disease that is exclusive to premature infants. Many infants in the NICU are affected by respiratory distress syndrome.
After listening to this episode, you will have a much better understanding of respiratory distress syndrome, or RDS – from your baby’s lung development in utero to which infants are most likely to develop respiratory distress syndrome. We also discuss what exactly RDS is, why it occurs, and how it is officially diagnosed. Finally, we conclude the discussion with the typical prevention and management approaches used by most NICUs for infants with RDS, so you will be able to better anticipate what the expectant treatment plan may be for your baby.
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I am a visual learner, so especially for difficult topics, I develop a better understanding if I can follow along with a visual image, so just for this episode, I put together a graphic that will take what can be a bit confusing and make it much easier to understand. Grab your RDS Graphic Now!
Respiratory Distress Syndrome
A common topic in the NICU is RDS or respiratory distress syndrome. Although it does not affect EVERY baby in the NICU, it is quite common.
In preterm infants, it is the dominant clinical problem they face. The incidence of respiratory distress syndrome decreases with advancing gestational age, with more severe disease in the smaller, more premature infants. So although it can occur in term neonates, it is much less common. It occurs in 60-80% of infants born at 26-28 weeks compared to only 15-30% for infants born at 32-36 weeks.
Respiratory distress syndrome is due to a deficiency of surfactant, either due to inadequate surfactant production, or surfactant inactivation.
One key part to remember, is that in utero, as your baby’s lungs are developing, the placenta is the main organ where gas exchange occurs for your baby. Your baby’s lungs are also filled with fluid when they are growing inside. It is the hormones from labor as well as the baby’s initial cries once they are born that transition the fluid out of the lungs.
Fetal Lung Development
Now, to fully understand how respiratory distress affects premature infants, and possibly your infant, I think it is helpful to do a very brief review of fetal lung growth and development.
Normal fetal lung development occurs in 5 different stages. First is the embryonic stage, from 0 up to 5 weeks. In this stage, as early as 26 days, the airways begin to differentiate with the beginning formations of the trachea, right and left main bronchi.
Next is the pseudoglanular stage from 5-16 weeks where there is progressive branching of the airways and vessels. The airways actually branch 15 to 20 times by the 18th week of gestation.
The canalicular stage starts around 13 weeks through 25 weeks gestation, and alot of important changes occur, especially towards the end. In this stage, there is further development of the distal airways and the capillary barrier is formed around the alveoli or tiny air sacs.
Specifically at 22-24 weeks, there is rapid growth of the capillary bed in the lungs which allows for sufficient gas exchange to support independent life and it is also during this time that surfactant production begins. So it makes sense that the edge of viability for babies is around 22-23 weeks since this is when they can actually begin to have sufficient gas exchange to sustain their life – with support of course.
The saccular stage occurs between 26 weeks and 36 weeks, and there is further maturation of the surfactant system and an increase in the gas exchange areas.
The final stage is the alveolar stage which occurs around 36 weeks and extends through 2 years of age. In this stage, the alveoli continue to form and mature which results in an increase of gas exchange.
Did you know that your baby’s lungs continue to grow and the amount of alveoli rapidly increases in your baby’s first 6 months of life? Lung growth and the volume continues to increase a large amount in the first 2 years. And, just as the rest of their body grows over time, so do their lungs, but at a slower rate after the first 2-3 years.
So how does all of this apply to your baby? As we said, Respiratory Distress Syndrome is due to a deficiency in surfactant. We just reviewed that it is during the canicular stage around 16-25 weeks when a fetus begins to have the early stages of gas exchange, but it is also just the beginning of surfactant production. Therefore, if your baby was born anywhere between 22 to 25 or 26 weeks, their lungs will be significantly deficient of surfactant.
The normal alveolar pool size of surfactant phospholipids in a full-term baby has been estimated around 100 gm/kg which is about 10 times greater than the amount found in the lungs of a newborn infant with respiratory distress syndrome.
Other infants at an increased risk of developing RDS
Although a deficiency of surfactant production occurs most commonly in premature infants, there are term infants who are also at an increased risk of developing RDS. Male infants are more prone to developing RDS, with a male to female ratio around 1.3~1 as well as Caucasian infants and the second twin in twin pregnancies have a greater risk of developing RDS. There is also a genetic predisposition that places infants at an increased risk of developing RDS.
Infants delivered via cesarean section, especially those without established labor are at an increased risk of developing RDS due to the combination of delayed removal of lung fluid, but most importantly, the lack of cortisol response associated with spontaneous labor.
Infants of diabetic mothers are also more likely to develop RDS. The elevated insulin levels in the baby is exposed to in utero causing a suppression of surfactant production and immature lungs.
Infants may also develop secondary surfactant deficiency due to intrapartum complications like intrapartum asphyxia, infections, especially Group B streptococcal pneumonia, pulmonary hemorrhages, meconium aspiration syndrome, congenital diaphragmatic hernia, or pulmonary hypoplasia.
Additionally, it is important to point out that respiratory distress syndrome is different than just the term respiratory distress. Many infants may develop respiratory distress due to other underlying conditions, but for it to be diagnosed at RDS, the distress is due to a deficiency of surfactant in the lungs supported by specific XR findings which we will discuss later in the episode.
What is Surfactant and Why is it so Important?
Surfactant is predominantly lipid-dense liquid. It is compromised with phospholipids, proteins, and neutral lipids and is produced in the lungs.
Once produced, surfactant spreads like a thin layer over the alveoli in the lungs and ultimately helps to keep them open. It acts like a lubricant in between the air sacs so they do not stick together. For effective breathing, the alveoli must be open to allow oxygen to enter the blood from the lungs and carbon dioxide to be released from the blood into the lungs.
Surfactant also lowers the surface tension and prevents the alveoli or air sacs from collapsing in the lungs with each breath. It also decreases the amount of pressure required for each subsequent inflation or breath.
Over time, when there is an insufficient amount of surfactant, more and more alveoli will collapse and result in what is called atelectasis or a complete or partial collapse of the lungs. With atelectasis, the baby has to work harder to breathe trying to re-inflate the collapsed airways.
And since oxygen enters the bloodstream through the alveoli, once too many collapse, the lungs are unable to get oxygen to the rest of their body resulting in hypoxemia or an abnormally low level of oxygen in the blood. Once hypoxemia occurs, carbon dioxide begins to build up in the blood which is called hypercarbia. With an increase of carbon dioxide in the blood, it leads to an increased amount of acid in the blood or acidosis. And with acidosis, it will begin to affect more of your baby’s organs. The hypoxemia and acidosis further impair the oxygenation by causing pulmonary vasoconstriction that results in poor perfusion throughout the baby’s body.
What are the common symptoms of RDS?
A baby with RDS may breathe fast, greater than 60 times per minute which is called tachypnea. He or she may have retractions or pulling between the ribs or under the rib cage due to their attempt to generate a higher pressure to expand their non-compliant lungs. Babies with RDS will often grunt – or “sigh” at the end of expiration. This sign of distress results from the baby’s effort to maintain the volume of air in their lungs. Baby’s may also have nasal flaring, cyanosis, and upon auscultation, decreased air movement in their lungs.
How is RDS diagnosed?
Your infant would be taken into the special care nursery or neonatal intensive care nursery if they present with signs or symptoms of respiratory distress syndrome.
The care team will continue to assess the baby’s clinical appearance, but would also order a chest X-Ray. An infant with RDS would typically have low lung volumes, and a reticular granular pattern on a chest X-Ray. If the atelectasis becomes worse, the lungs will show what is called a “white out” due to severe collapse of the lung tissue.
A blood gas will also be collected and may show hypoxemia and respiratory acidosis or an increase in carbon dioxide. And with worsening respiratory distress, it can also lead to metabolic acidosis and lactic acidemia.
Additional labs will be drawn to diagnose and to also assist with treatment including but not limited to a CBC, a blood culture, and an electrolyte panel at some point.
At times, an echocardiogram or an ultrasound of your baby’s heart may be performed. An echo may be done to rule out any heart conditions that may cause symptoms similar to RDS.
How to prevent and treat RDS
The treatment for RDS is based on your baby’s gestational age, cause of the surfactant deficiency, extent of the condition, and how your baby responds to the procedures, medications, and treatment methods.
Consistently, in all of the research, there are currently 3 important advances in prevention and treatment of respiratory distress syndrome coupled with supportive treatment.
The first line of prevention is Antenatal Steroids. If there is a risk of preterm delivery, research has shown that a course of steroids given to the mother prior to delivery reduces the risk of neonatal death, RDS, intraventricular hemorrhage, and additional neonatal morbidities. Antenatal steroids accelerate lung growth and the release of surfactant in the baby. Antenatal steroids can be given to women as early as 22 weeks typically up through 34 weeks gestation. The goal for timing of the steroids is at least 24 to 48 hours before the preterm delivery.
Once the infant is born and if they develop respiratory distress, they will be supported with respiratory support. The second common management approach for RDS, is continuous positive airway pressure or CPAP. CPAP pushes a continuous flow of air with or without additional oxygen into the airways to keep the tiny air sacs in the lungs open. By keeping the alveoli open, the infant does not have to work so hard to manually keep them open and it ultimately reduces atelectasis.
In most institutions, non-invasive modes of ventilation are preferred over invasive ventilation or with an endotracheal tube. But the decision will ultimately be up to the care team and based on your infant’s clinical condition which mode is preferred or needed. Infants with RDS, may need to be intubated and placed on a standard ventilator or a high-frequency jet ventilator, or a high-frequency oscillating ventilator. If they do not require a breathing tube, the non-invasive forms of ventilation can be delivered via a nasal cannula or a face mask and include nIMV or non-invasive mechanical ventilation, CPAP or continuous positive airway pressure, or High Flow nasal cannula.
The length of time that each baby needs respiratory support and/or supplemental oxygen depends on their gestational age, severity of respiratory distress syndrome, other clinical complications, and their response to the support. The care team will monitor the baby’s response to the respiratory support and adjust it based on the blood gas results, metrics on the ventilator, percentage of oxygen required, and the baby’s clinical appearance. Some severely premature infants or micropreemies may take weeks to months to be weaned from the ventilator. And regardless of even the most recent advancements in medicine, some infants may not be able to be weaned and will need a tracheostomy or at the very least home oxygen.
The final main treatment management used in infants with respiratory distress syndrome is with exogenous or artificial surfactant. Surfactant replacement therapy has been shown to reduce the severity of RDS, it improves oxygenation, decreases the risk of air leaks, and decreases overall mortality.
Previously, surfactant was only able to be given to babies after intubation with an endotracheal or breathing tube. But with recent advancements, some NICUs are able to administer it in a less invasive way either through the LISA method, less invasive surfactant administration, or through a laryngeal mask or the aerosolized method.
The amount of surfactant given is based on the baby’s weight and manufacturer’s recommendations. Up to 3 doses can be given and the recommendation is at 12 hour intervals.
Administration of surfactant improves the baby’s lung compliance and reduces the surface tension. It dramatically improves gas exchange and decreases the baby’s need for higher levels of supplemental oxygen and respiratory support. Surfactant assists with their oxygenation by decreasing the atelectasis and increasing the volume of air present in the lungs at the end of exhalation. With lower levels of ventilatory support needed, it also reduces the associated risk of a pneumothorax and additional complications.
Infants with RDS also need supportive therapy in addition to the aforementioned treatments including but not limited to, thermoregulation or helping the infant maintain a stable temperature, nutritional support with either IV nutrition or enteral nutrition, fluid and electrolyte management, and consideration of antibiotic therapy.
How Will RDS Affect By Baby in the Future?
Respiratory distress syndrome can affect infants for weeks, months, and sometimes even years. I do not say this to scare you, but to remind you that depending on your infant and their degree of RDS, they may possibly require home oxygen. We brought our son William home on oxygen and monitors. And I understand how scary that thought may be, but if that is the case, the hospital will ensure that you are fully supported before sending you home.
Closing
Remember, if you are the parent, be sure to ask the care team questions and for clarification if you do not understand something. My goal is to provide you with knowledge so you understand some of the NICU concepts and management strategies better, but as I’ve said it before, every NICU and how they manage their patients can be quite varied. As you gain more NICU knowledge, you will feel more comfortable and empowered to ask questions.
If you have not done so already, go and grab your free graphic that correlates with this post. It will make it all come together and you will walk away with a much better understanding of RDS in the NICU and for your own baby. Plus, it will help you with future episodes as well!
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