While in the womb, a fetus’s oxygen needs are met by the mother. Blood is pumped by the baby’s heart through the umbilical cord arteries to the placenta where oxygen is extracted from the mother’s blood as it passes by the placenta. The maternal and fetal blood systems are separate. It is only oxygen that passes from maternal blood vessels to placental blood vessels by a process called diffusion. The umbilical cord vein delivers oxygenated blood to the fetus’s heart, where it is then pumped to the rest of the body.
Lung development
In the womb, the fetus’s lungs are filled with fluid. They are not used for breathing, but are developing and getting ready for baby’s first breath after birth. Compared to other organs such as the heart and kidneys, which are already functional in the womb, the lungs will not start working until after birth and are slower to develop to maturity. By the 24th week of pregnancy or so, most of the basic parts of the lung have developed, but it is not until the 37th week that the lung could be considered fully mature and ready to function on its own.
A baby’s first breath is dramatic, and sets off rapid changes: the lungs inflate for the first time and fill air sacs within the lungs, which help keep them from completely deflating when the baby breathes out. Blood flow, no longer needed to carry oxygen from the placenta, is redirected to the lungs and gas exchange begins. The process is quick and probably the most dramatic change for the baby. Think of how much more effort it takes to blow up a brand new balloon compared to one that has been previously inflated. A baby’s first breath will be their most difficult for the rest of their life.
The immature lung
Given the incomplete development of the lungs in the womb, premature babies often have some trouble breathing after birth. The level of difficulty a baby has is usually related to their gestational age: the more premature they are, the more likely they are to need assistance. In some cases, the effort required to breathe is still too much for a baby, or the lungs may not have had time to develop enough to prevent lung collapse with each breath out, or both. An immature lung has also yet to fully develop alveoli, the tiny air sacs that allow for gas exchange within the lungs, to oxygenate their blood properly. A lack of alveoli makes breathing very difficult and highly inefficient.
Fortunately, methods have been developed to help babies with immature lungs. In fact, the vast majority of premature babies with lung complications survive, most without severe lasting effects. Many premature babies, however, will need oxygen or the help of a mechanical ventilator or a dose of surfactant before they can breathe on their own.
In addition to problems associated with immaturity, lung complications can occur because of fluid in the lung, infection, abnormal development, or poor gas exchange, which result in lower levels of oxygen in the blood than is desirable. Oxygen and the physical forces of mechanical ventilation can injure the lungs of the premature baby.
How are breathing problems diagnosed in premature babies?
As a fetus grows and develops in the womb, the lungs are among the last organs to become fully functional. For this reason, lung problems are some of the most common complications of prematurity. In many cases, a premature baby may have trouble breathing normally not because there is something wrong, but rather because the lungs are immature and have not had time to fully develop.
As with all complications of prematurity, the more immature a baby is, the more likely they are to develop complications and the more severe those complications are likely to be.
All premature babies with breathing problems are carefully monitored to assess the severity of the breathing problem, to detect changes in the severity of the problem, and to follow progress. The blood gas test measures the amount of oxygen, carbon dioxide, and acid in the blood. These three measures indicate the severity of the baby’s respiratory distress. The blood gas specimen is obtained from an artery or by heel prick. It is also possible to estimate the oxygen and carbon dioxide in the blood by using “transcutaneous” devices that make these measurements through the skin. Transcutaneous measurements may be inaccurate if the skin is too thick, contains too much fluid, or has a reduced blood flow.
Pulse oximetry, or the transcutaneous measurement of oxygen saturation, is another non-invasive approach to monitoring. A small light is attached to one of the baby’s extremities, usually finger or toe. As the light passes through the body, the light is measured to indicate how much oxygen is in the blood. Oximetry can confirm that a baby is breathing the appropriate amount of oxygen.
How are breathing problems treated in premature babies?
In general terms, lung complications interfere with breathing, resulting in respiratory distress. Frequently, there is a lower oxygen level and higher carbon dioxide level in the blood. Lung complications may also interfere with the heart. The lungs and heart are dependent upon each other: the lungs providing the mechanism for gas exchange and the heart providing the mechanism by which oxygen is delivered to all regions of the body. Since the heart and lungs are interdependent in this way, problems with the function of the lungs can interfere with the physical action of the heart and vice versa.
That being said, the management or treatment of lung problems involves trying to achieve the correct amount of oxygen in the blood by improving the gas exchange that occurs within the lungs. Unfortunately, weakened, immature, or damaged lungs can only be pushed so far; at a certain point, the effort to improve the amount of oxygen in the blood by treating the lung can cause injury that may result in lung damage or make it worse. Treatment of the lungs must take into consideration the balance between the benefit of improving oxygen levels and the risk of creating lung damage, which may be permanent, in the process.
Monitoring and assessment of treatment effectiveness
The effect of treatments is assessed at frequent intervals. Since the goal is to improve the delivery of oxygen and remove carbon dioxide from the blood, which are the prime functions of the lungs, measurement of these blood gases will be frequent and more or less continuous.
In most cases, the amount of oxygen in the blood, called oxygen saturation, can be measured with a test called pulse oximetry, avoiding the repeated drawing of blood to determine levels of blood gases. In pulse oximetry, a long, thin wire is attached to a monitor. This wire connects to a sensor that is usually put over the baby’s finger or toe. The probe has a small red light on one side and a detector on the other side. The red light shines through the baby’s finger or toe and is “seen” by the detector on the other side. In this way, the detector can measure the amount of oxygen in the blood.
Carbon dioxide levels can also be monitored using a non-invasive monitor which has a special probe that sits on the surface of the skin. This probe can estimate the amount of carbon dioxide in the blood stream.
Surfactant replacement therapy
Surfactant, a naturally produced substance, is a kind of foamy, fatty liquid that acts like grease within the lungs. Without it, the air sacs open but have difficulty remaining open because they stick together. Surfactant allows the sacs to remain open.
Surfactant usually appears in the fetus’s lungs at about the 24th week of pregnancy and gradually builds up to its full level by the 37th week. If a premature baby is lacking surfactant, artificial surfactant may be given.
Surfactant is delivered using an artificial airway or breathing tube that is inserted into the trachea, or windpipe, either immediately at birth for extremely premature babies, or later once respiratory problems have revealed themselves. Surfactant is administered through the windpipe over the course of a few minutes. During this time, the baby will be turned and moved in an effort to distribute the surfactant to all parts of the lung. Depending on the severity of the lung condition, surfactant may be administered more than once.
Surfactant replacement therapy cannot begin until breathing has been stabilized, perhaps with mechanical ventilation, and the proper monitoring equipment has been set up.
Treatment of the immature lung
Extremely premature babies who have respiratory distress but show no specific reason for that distress may have an immature lung. If the baby does not respond to surfactant replacement therapy, this can be another indication of an immature lung. Although immature lungs may appear normal on X-ray, the alveoli, which are the small sacs lining the lung where gas exchange takes place, may not have developed or may not have developed enough. For this reason, surfactant may not improve breathing or not improve it by much. Babies suspected of having an immature lung may be given:
- surfactant replacement therapy
- oxygen
- continuous positive airway pressure (CPAP) or
- mechanical ventilation
Treatment of respiratory distress syndrome
Respiratory distress syndrome (RDS) is characterized by surfactant deficiency in the premature baby’s lung. The condition is generally progressive in that the breathing difficulties experienced by the baby begin immediately at birth and worsen over time. The severity of RDS and its progression have to do with the maturity of the lung. As with most conditions affecting premature babies, the more premature the baby, the more likely RDS is to be severe. Treatment of RDS may include surfactant replacement therapy and supplemental oxygen delivered by one of these ventilation methods:
- continuous positive airway pressure (CPAP)
- conventional mechanical ventilation (CMV)
- high frequency oscillation (HFO)
- high frequency jet ventilation (HFJV)
Treatment of chronic lung disease
Chronic lung disease (CLD) comes as a result of lung injury. The likelihood of CLD occurring is influenced by events during pregnancy or birth, the degree of immaturity, the underlying lung condition, exposure of the lung to supplemental oxygen, the use of mechanical ventilation, and the presence of infection. The longer a baby needs supplemental oxygen and mechanical ventilation, the more likely it is that they will develop CLD.
About 50% of extremely premature babies who have respiratory distress syndrome (RDS) will have CLD to some degree. In many ways, CLD is the price to pay for surviving respiratory distress and other lung complications. Luckily, severe cases are rare and most babies grow to maturity without major long-term complications. As the lungs attempt to repair the damage associated with the RDS treatment, the force of the ventilator and the extra oxygen can interfere with the healing process.
The treatment goal with CLD is to maintain an acceptable oxygen level in the blood without causing further lung damage.
Babies with CLD may not be mechanically ventilated. If a baby with CLD is ventilated, because ventilation is partly to blame for the lung injury, babies with CLD will be weaned off mechanical ventilation as quickly as possible. In some cases, this may mean tolerating a higher level of carbon dioxide than normal. Called permissive hypercapnea, this approach is used to prevent further lung damage and encourage spontaneous breathing.
Babies with CLD may also be managed with one or more of the following approaches:
- diuretics, which are medications that encourage urination and therefore help maintain a proper fluid balance
- bronchodilators, which may encourage the airways to stay open
- steroids, which may decrease inflammation in the airways
- mechanical ventilation
- antibiotics, if there is suspected or proven infection in the lung
CLD and bronchopulmonary dysplasia
The terms CLD and bronchopulmonary dysplasia (BPD) are at times used to describe the same lung condition, although there are differences.
Although in both conditions scar tissue has formed in the lungs, with BPD the fibrosis created by the scarring will generally not heal normally; this will cause the lung to become quite stiff. Additionally, babies with BPD are at a higher risk for heart problems, specifically cor pulmonale or a failure of the right ventricle of the heart. Thankfully, BPD is rare.
Although CLD cannot always be avoided through careful use of ventilation technologies, the damage caused, though similar to that of BPD, is not necessarily permanent. Babies with established CLD are often treated with supplemental oxygen and may sometimes go home needing oxygen for a few weeks or months.
Ongoing care of chronic lung disease
Chronic lung disease (CLD) is the most common reason for re-hospitalization during the first year of a premature baby’s life. Babies who have had lung conditions and needed mechanical ventilation in the NICU will need follow-up care, preferably at a lung clinic if one exists in the area. In the least, parents should have all the baby’s medical documents including X-rays and try to find a paediatrician to provide medical care after discharge. Usually, it is best that one health care professional does the follow-up. That professional will have a more detailed understanding of the baby and their condition, making it less likely that an assessment such as an X-ray or a lung function test will be misinterpreted.
CLD and infection
Although all babies are at risk, premature babies who have CLD are at higher risk for common lung infections in infancy. Several things can be done to reduce the risk. First, parents may wish to take steps to lower the chances that the baby will be exposed to an infectious agent. This might involve restricting visitors to the home especially during the winter months when viral infections are common. Second, parents should make sure that the baby is immunized against whooping cough, diphtheria, and other serious infections.
Respiratory syncytial virus (RSV) is a common respiratory tract infection in all age groups. The infection occurs most often and is most severe in young babies aged three to six months. Babies with weakened lungs are more at risk for severe effects of the virus. Nearly 60% of babies are infected in the first year of life.
RSV protection is recommended for all high-risk babies during the winter months. Babies considered at high risk for RSV infection include premature babies born before 35 weeks of pregnancy and babies with a major congenital heart condition. Passive immunization with an antibody against RSV is injected intramuscularly every month during the winter season. A drug called palivizumab is the current approach to preventing RSV infection.
Ventilation and supplemental oxygen
Babies rarely go home while still requiring ventilation. However, some premature babies will go home with supplemental oxygen. Supplemental oxygen is delivered through nasal prongs and simply increases the amount of oxygen in the air that a baby breathes without interfering with the baby’s spontaneous breaths.
If a baby is going home with supplemental oxygen, parents will have to learn how to use the equipment. They will have to prepare for it to be available at all times, starting with the baby’s initial arrival at the family home. Additionally, parents will have to consider how the equipment and service will be paid for. A discharge nurse or staff at the lung clinic should be able to help out.
It is not difficult to learn how to use supplemental oxygen, however, it does take some effort. Additionally, babies on supplemental oxygen will likely need some form of home care. This, coupled with the need to have people come by to replace oxygen tanks and perhaps service the machine, means there will be less privacy for the family.
Babies using supplemental oxygen are also monitored to ensure that the oxygen levels in the body remains appropriate. This is usually accomplished with pulse oximetry, a small, non-invasive monitor that is attached to a baby’s finger or toe. A light shines through the finger and measures the amount of oxygen in the blood. An alarm goes off if the oxygen level falls below the desired level.
Oxygen in concentrated amounts is potentially dangerous and open flames in the house should be avoided.
Generally speaking, babies are slowly weaned off supplemental oxygen. This process can take a few months, to the best part of a year or sometimes even longer. At follow up-visits, health care providers will slowly decrease the amount flow of oxygen while monitoring the baby’s oxygen level in the body, and see what happens. As time goes by, babies will be able to go longer and longer periods without supplemental oxygen until they reach a point where they no longer need it at all.
When to worry about breathing problems
Parents of premature babies with weakened lungs should learn the signs of respiratory distress. Usually, these include:
- indrawing, which is a retraction of the skin between the ribs or over the windpipe during breathing
- increased respirations
- nostril flaring
- change in baby’s colour or level of awareness
Respiratory distress is an emergency and requires immediate medical attention. Respiratory distress can occur as a result of common respiratory infections.
Apnea
Apnea, or a brief pause in breathing, is common and is often not a concern. However, if a baby suffers apnea associated with changes in colour, parents should seek medical attention. Home apnea monitors are available; however, their utility in decreasing the risk of the life-threatening consequences of apnea is still in question. Therefore, home apnea monitors are not routinely recommended.
Apnea can occur because of mixed signals from the brain, which is called central apnea, or it may be caused by an obstruction. If a baby is trying to breath but air is not reaching the lungs, this is probably a sign of an obstruction which must be removed immediately. Additionally, if a baby is taking quick shallow breaths, this may be a sign of obstruction since this behaviour compensates for a lack of oxygen reaching the lungs.
Medication
Some premature babies may be prescribed inhaled medications such as Ventolin (albuterol or salbutamol) or steroids, which must continue as a treatment when the baby goes home. Parents must learn how to use a baby inhaler and make sure that the supply of the inhaled medications is maintained. These inhaled medications work to reduce inflammation of the lung tissues and dilate the airways and therefore improve breathing. Because a baby is undergoing this type of treatment, it does not mean that they will have to continue on the inhalers for the rest of their life. Most children eventually become healthy enough that they no longer require the inhaled medications.