Chronic lung disease in premature babies can develop due to factors that affect lung development before and after birth. Chronic lung disease in very premature babies is sometimes referred to as bronchopulmonary dysplasia (BPD).
What is chronic lung disease of prematurity?
A baby is considered to have chronic lung disease if:
- They are born before 32 weeks' gestation and need supplemental oxygen (or mechanical ventilation) by the time they reach the 36 weeks post-menstrual age.
- They are born after 32 weeks' gestation and still require supplemental oxygen (or mechanical ventilation) after 28 days of age.
What causes chronic lung disease of prematurity
The causes of chronic lung disease of prematurity can be grouped into antenatal (before birth) factors and postnatal (after birth) factors.
Before birth
Prematurity, poor fetal growth and smoking during pregnancy are all known to affect lung development in the fetus. Premature babies’ lungs are immature and may also lack surfactant, a substance that helps the lungs inflate. Very preterm babies have a higher risk of developing chronic lung disease. Babies who have had restricted or poor growth before birth may have lungs that are more prone to injury. Smoking during pregnancy also increases the risk of chronic lung disease in premature babies.
After birth
Some babies with respiratory distress syndrome (RDS) need a ventilator to help them breathe. In many cases, this is a life-saving intervention. However, both oxygen and mechanical ventilation can have a bad effect on a lung that is still developing or a lung that is damaged and in the process of repairing itself. A premature baby’s lungs are often weak and may be inflamed. This is a common effect of RDS. The baby needs a ventilator to help them breathe; however, their fragile lungs can be damaged by the pressures and size of the ventilator breaths.
Oxygen in high concentrations is also known to cause lung injury in premature babies because they cannot easily clear the by-products of oxygen that are left behind after oxygen is used in the body. These by-products can then damage the cells of the lung.
As the lungs attempt to repair the damage, the force of the ventilator and the extra oxygen can interfere with the healing process, and the new tissues may not form normally. The health-care team will always attempt to use the lowest effective pressure and size of breath from the ventilator and transition babies to other forms of respiratory support as soon as possible to avoid any ongoing damage to lung tissues. In order to reduce the effects of oxygen on the lung, the health-care team will use the lowest concentration (amount) of oxygen that a baby needs.
The longer a child needs mechanical ventilation, the more likely it is that they will develop chronic lung disease. About 50 per cent of extremely premature babies who have RDS will have chronic lung disease to some degree.
Infections such as pneumonia or sepsis in premature babies can also cause lung injury and increase the risk of developing chronic lung disease.
How is chronic lung disease of prematurity diagnosed?
Babies with chronic lung disease require help with their breathing based on the definitions previously described. They often have an increased respiratory rate (fast breathing) and use their rib muscles and abdominal muscles to breathe. They may have difficulty gaining weight because they need more calories to keep up with the energy needed for their fast breathing. In babies with chronic lung disease, X-rays can show typical patterns depending on the severity of the lung injury. Some babies may have a hazy pattern or excess fluid in the lungs, and others may develop areas of the lung that are overinflated and some areas that are more collapsed.
Blood gases may show a lowered level of oxygen and an elevated level of carbon dioxide in the blood. This indicates the lungs are having difficulty exchanging oxygen and carbon dioxide.
How is chronic lung disease of prematurity treated?
Since babies with chronic lung disease require more calories to meet the energy needs due to their faster breathing, they benefit from close monitoring of weight gain and growth to ensure that their nutrition is optimized.
Some babies with chronic lung disease of prematurity are treated with diuretics to help reduce the extra fluid that may build up in their lungs. Steroids may be prescribed for some babies felt to be at risk for developing severe chronic lung disease. If babies are ready for discharge from hospital but still require ongoing oxygen, they may be discharged with home oxygen. The majority of babies discharged on home oxygen for chronic lung disease of prematurity will improve in the first year of life and often outgrow the need for home oxygen.
Babies with chronic lung disease of prematurity will improve over time as their lungs grow and they grow. After discharge, they will be monitored by a paediatric specialist.
How can chronic lung disease of prematurity be prevented?
The following measures can all help promote lung development in babies born prematurely and reduce the risk of developing chronic lung disease of prematurity:
- smoking cessation in pregnancy
- regular prenatal visits to monitor the growth of the fetus
- administering steroids to pregnant people in premature labour or at risk of preterm labour
- avoiding mechanical ventilation or early extubation to non-invasive support if deemed appropriate
- optimal post-natal nutrition to support linear growth
- reducing the frequency of hospital-acquired infections via good hand hygiene and central line practices
Preventing further lung damage
Babies with chronic lung disease of prematurity who are discharged from hospital are at risk of further lung damage if they develop respiratory infections from viruses or bacteria. The best way to reduce that risk is with immunization. Regular childhood immunization, as well as immunization to protect against RSV, influenza and SARS-COV-2, are strongly recommended.
What are the complications of chronic lung disease of prematurity?
The most common complication of chronic lung disease of prematurity is poor weight gain because babies are using a lot of energy breathing quickly and need more calories to grow.
If babies with chronic lung disease of prematurity are exposed to viruses, they are at higher risk of developing more severe respiratory infections compared to babies without chronic lung disease.
Some babies with chronic lung disease of prematurity can develop high pressure in the blood vessels that go to the lungs. This condition is called pulmonary hypertension. Pulmonary hypertension is diagnosed with an echocardiogram and requires ongoing management by a cardiologist.