Hyaline Membrane Disease / Respiratory Distress Syndrome
Hyaline membrane disease (HMD), also called respiratory distress syndrome (RDS), is one of the most common problems of premature babies. It can cause babies to need extra oxygen and help breathing. The course of illness with hyaline membrane disease depends on the size and gestational age of the baby, the severity of the disease, the presence of infection, whether or not a baby has a patent ductus arteriosus (a heart condition), and whether or not the baby needs mechanical help to breathe. HMD typically worsens over the first 48 to 72 hours, then improves with treatment.
HMD occurs when there is not enough of a substance in the lungs called surfactant. Surfactant is made by the cells in the airways and consists of phospholipids and protein. It begins to be produced in the fetus at about 24 to 28 weeks of pregnancy. Surfactant is found in amniotic fluid between 28 and 32 weeks. By about 35 weeks gestation, most babies have developed adequate amounts of surfactant.
Surfactant is normally released into the lung tissues where it helps lower surface tension in the airways. This helps keep the lung alveoli (air sacs) open. When there is not enough surfactant, the tiny alveoli collapse with each breath. As the alveoli collapse, damaged cells collect in the airways and further affect breathing ability. These cells are called hyaline membranes. The baby works harder and harder at breathing, trying to re-inflate the collapsed airways.
As the baby's lung function decreases, less oxygen is taken in and more carbon dioxide builds up in the blood. This can lead to increased acid in the blood called acidosis, a condition that can affect other body organs. Without treatment, the baby becomes exhausted trying to breathe and eventually gives up. A mechanical ventilator (breathing machine) must do the work of breathing instead.
HMD occurs in over half of babies born before 28 weeks gestation, but only in less than one-third of those born between 32 and 36 weeks. Some premature babies develop HMD severe enough to need a mechanical ventilator (breathing machine). The more premature the baby, the higher the risk and the more severe the HMD.
Although most babies with HMD are premature, other factors can influence the chances of developing the disease. These include the following:
- Caucasian or male babies
- previous birth of baby with HMD
- cesarean delivery
- perinatal asphyxia
- cold stress (a condition that suppresses surfactant production)
- perinatal infection
- multiple births (multiple birth babies are often premature)
- infants of diabetic mothers (too much insulin in a baby's system due to maternal diabetes can delay surfactant production)
- babies with patent ductus arteriosus
The following are the most common symptoms of HMD. However, each baby may experience symptoms differently. Symptoms may include:
- respiratory difficulty at birth that gets progressively worse
- cyanosis (blue coloring)
- flaring of the nostrils
- tachypnea (rapid breathing)
- grunting sounds with breathing
- chest retractions (pulling in at the ribs and sternum during breathing)
The symptoms of HMD usually peak by the third day, and may resolve quickly when the baby begins to diurese (excrete excess water in urine) and begins to need less oxygen and mechanical help to breathe.
The symptoms of HMD may resemble other conditions or medical problems. Always consult your baby's physician for a diagnosis.
HMD is usually diagnosed by a combination of assessments, including the following:
- appearance, color, and breathing efforts (indicate a baby's need for oxygen).
- chest x-rays of lungs - often show a unique "ground glass" appearance called a reticulogranular pattern. X-rays are electromagnetic energy used to produce images of bones and internal organs onto film.
- blood gases (tests for oxygen, carbon dioxide and acid in arterial blood) - often show lowered amounts of oxygen and increased carbon dioxide.
- echocardiography (EKG) - sometimes used to rule out heart problems that might cause symptoms similar to HMD. An electrocardiogram is a test that records the electrical activity of the heart, shows abnormal rhythms (arrhythmias or dysrhythmias), and detects heart muscle damage.
Specific treatment for HMD will be determined by your baby's physician based on:
- your baby's gestational age, overall health, and medical history
- extent of the condition
- your baby's tolerance for specific medications, procedures, or therapies
- expectations for the course of the condition
- your opinion or preference
Treatment for HMD may include:
- placing an endotracheal (ET) tube into the baby's windpipe
- mechanical breathing machine (to do the work of breathing for the baby)
- supplemental oxygen (extra amounts of oxygen)
- continuous positive airway pressure (CPAP) - a mechanical breathing machine that pushes a continuous flow of air or oxygen to the airways to help keep tiny air passages in the lungs open
- surfactant replacement with artificial surfactant - most effective if started in the first six hours of birth. Surfactant replacement has been shown to reduce the severity of HMD. Surfactant is given as prophylactic (preventive) treatment for some babies at very high risk for HMD. For others it is used as a "rescue" method. The drug comes as a powder to be mixed with sterile water and then is given through the ET tube (breathing tube). Surfactant is usually given in several doses.
- medications (to help sedate and ease pain in babies during treatment)
Babies with HMD sometimes develop complications of the disease or problems as side effects of treatment. As with any disease, more severe cases often have greater risks for complications. Some complications associated with HMD include the following:
- air leaks of the lung tissues such as:
- pneumomediastinum - air leaks into the mediastinum (the space in the thoracic cavity behind the sternum and between the two pleural sacs containing the lungs).
- pneumothorax - air leaks into the space between the chest wall and the outer tissues of the lungs.
- pneumopericardium - air leaks into the sac surrounding the heart.
- pulmonary interstitial emphysema (PIE) - air leaks and becomes trapped between the alveoli, the tiny air sacs of the lungs.
- chronic lung disease, sometimes called bronchopulmonary dysplasia
Preventing a preterm birth is the primary means of preventing HMD. When a preterm birth cannot be prevented, giving the mother medications called corticosteroids before delivery has been shown to dramatically lower the risk and severity of HMD in the baby. These steroids are often given to women between 24 and 34 weeks gestation who are at risk of early delivery.
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