Pneumonia is an infection of the lungs, usually caused by a bacteria or virus. Some babies get pneumonia while they are still in the womb and must be treated at birth. Babies may also develop pneumonia at several weeks of age, often as a complication of being on a ventilator for respiratory problems, such as respiratory distress syndrome or bronchopulmonary dysplasia (described below). Babies with pneumonia often need to be treated with an increased amount of oxygen or even mechanical ventilation (a breathing machine) in addition to antibiotics.
The most common lung problem in a premature baby is respiratory distress syndrome (RDS), also known as hyaline membrane disease (HMD).
A baby develops HMD when the lungs do not produce sufficient amounts of surfactant, a substance that keeps the tiny air sacs in the lung open. As a result, a premature baby often has difficulty expanding her lungs, taking in oxygen, and getting rid of carbon dioxide. On a chest x-ray, the lungs of a baby with HMD look like ground glass.
HMD is common in premature babies because the lungs do not usually begin producing surfactant until about the 37th week of pregnancy. Other factors that increase a baby's risk of developing HMD include Caucasian race, male sex, family history, and maternal diabetes. HMD tends to be less severe in babies whose mothers received steroid treatment before delivery.
Fortunately, surfactant is now artificially produced and can be given to babies if doctors suspect they are not yet making surfactant on their own. Most of these babies also need extra oxygen and support from a ventilator, either through continuous positive airway pressure (CPAP) or an endotracheal tube.
Babies with RDS occasionally develop a complication known as a pneumothorax. A pneumothorax can also develop in the absence of RDS. This condition develops when a small air sac in the lung ruptures and air escapes from the lung into a space between the lung and the chest wall. If a large amount of air accumulates, the lungs cannot expand adequately. The pneumothorax can be drained by inserting a small needle into the chest. If the pneumothorax re-accumulates after being drained with a needle, a chest tube can be inserted between the ribs. The chest tube is connected to a suction device and continuously removes any air that has accumulated until the small hole in the lung heals.
Another complication of RDS is bronchopulmonary dysplasia (BPD), a chronic lung disease caused by injury to the lungs. BPD occurs in about 25 to 30% of babies who are born before 28 weeks and weigh less than 1.000 grams (2.2 pounds). It is most common in very premature babies born between 24 and 26 weeks.
The underlying cause of BPD is not well understood. However, because it occurs in babies who are on ventilators and/or receiving oxygen, doctors think that these treatments, while necessary, may injure a baby's immature lung tissue. Unfortunately, BPD, in turn, can cause a baby to require continued oxygen therapy and ventilator support. Sometimes, doctors use diuretic medications and inhaled medications, beginning when the baby is three to four weeks old, to help wean a baby from the ventilator and reduce the need for oxygen. In the past, doctors frequently used steroid medications to treat BPD. However, because the use of steroids has been linked to later developmental problems including cerebral palsy, doctors now use steroids in only the most severe cases of BPD. While BPD tends to improve as babies grow, it's not unusual for babies with BPD to continue to receive diuretic therapy and/or oxygen at home for several months.
Another common respiratory problem of premature babies is called apnea of prematurity. This is a condition in which the baby stops breathing, often causing the heart rate and oxygen level in the blood to drop. Apnea occurs in almost 100% of babies who are born before 28 weeks gestation. It is much less common in older premature babies, especially those born at 34 weeks or later. Apnea usually does not happen immediately after birth; it occurs more commonly at one to two days of age and sometimes is not evident until after a baby has been weaned from a ventilator.
There are two main causes of apnea in premature infants:
- The baby "forgets" to breathe, simply because the nervous system is immature. This is called central apnea.
- The baby tries to breathe, but the airway collapses and air cannot flow in and out of the lungs. This is called obstructive apnea.
Premature babies frequently have "mixed" apnea, which is a combination of central and obstructive apnea. A baby who is at risk for apnea needs to be connected to a monitor that records the heart rate, the breathing rate, and the oxygen level in the blood. If any of these fall below normal levels, an alarm sounds, alerting the staff that the baby is having an episode of apnea. The staff then stimulates the baby, usually by gently rubbing the baby's chest or back, and the baby begins to breathe again. Occasionally, a baby requires assistance with a bag and mask to begin breathing again. Central apnea can be treated with a medication called aminophylline or with caffeine. Both of these drugs stimulate the baby's immature respiratory system and reduce the number of episodes of apnea. If they don't or if the episodes are severe enough to require the staff to frequently stimulate the baby's breathing with a bag and mask, the baby may need to be put on a ventilator until the nervous system matures. Babies with purely obstructive apnea often need to be connected to a ventilator through an endotracheal tube to keep the airways open.
Apnea of prematurity usually resolves by the time a baby is 40 to 44 weeks of age (including the number of weeks of pregnancy and the number of weeks since the baby's birth) and, sometimes, as early as 34 to 35 weeks. However, occasionally apnea persists and the baby requires long-term therapy with aminophylline or caffeine and an apnea monitor at home. In that case, parents are trained to use the monitor and to give cardiopulmonary resuscitation (CPR) to stimulate breathing. Babies are not sent home on a monitor unless they are otherwise stable and are having only rare episodes of apnea in a 24-hour period.