Infant respiratory distress syndrome
From Wikipedia, the free encyclopedia
| ICD-10 | P22. |
|---|---|
| ICD-9 | 769 |
| OMIM | 267450 |
| DiseasesDB | 6087 |
| MedlinePlus | 001563 |
| eMedicine | emerg/15 |
Infant respiratory distress syndrome ("RDS", also called "Respiratory distress syndrome of newborn", previously called hyaline membrane disease), is a syndrome caused by developmental lack of surfactant and structural immaturity in the lungs of premature infants. RDS affects about 1% of newborn infants. The incidence decreases with advancing gestational age (length of pregnancy), from about 50% in babies born at 26-28 weeks, to about 25% at 30-31 weeks. The syndrome is more frequent in infants of diabetic mothers and in the second born of premature twins.
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[edit] Clinical course
Respiratory distress syndrome begins shortly after birth, and is manifest by tachypnea and "sucking in" (retractions) of the chest wall during breathing efforts (respiratory distress). In addition grunting respirations, flaring of the nostrils and cyanosis (a blue discoloration of the skin due to low oxygen content in the blood) are frequent. As the disease progresses, the baby may develop ventilatory failure (climbing carbon dioxide concentrations in the blood), and prolonged cessations of breathing ("apnea"). Whether treated or not, the clinical course for the acute disease lasts about 2 to 3 days. During the first, the patient worsens and requires more support. During the second the baby may be remarkably stable on adequate support and resolution is noted during the third day, heralded by a prompt diuresis. Despite huge advances in care, RDS remains the most common single cause of death in the first month of life. Complications include metabolic disorders (acidosis, low blood sugar), patent ductus arteriosus, low blood pressure, chronic lung changes, and intracranial hemorrhage. The disease is frequently complicated by prematurity and its additional defects in other organ function.
[edit] Pathology
The characteristic pathology seen in babies who die from RDS was the source of the name "hyaline membrane disease". These waxy-appearing layers line the collapsed tiny air sacs ("alveoli") of the lung. In addition, the lungs show bleeding, over-distention of airways and damage to the lining cells.
[edit] Pathophysiology
The lungs are developmentally deficient in a material called surfactant, which allows the alveoli to remain open throughout the normal cycle of inhalation and exhalation. Surfactant is a complex system of lipids, proteins and glycoproteins which are produced in specialized lung cells called Type II cell or Type II pneumocyte. The surfactant is packaged by the cell in structures called lamellar bodies, and extruded into the alveoli. The lamellar bodies then unfold into a complex lining of the alveoli. This layer serves the purpose of reducing the surface tension which would tend to cause the alveoli to collapse in the presence of gas. Without adequate amounts of surfactant, the alveoli collapse and are very difficult to expand. Microscopically, it is characterized by collapsed alveoli alternating with hyperaerated alveoli, vascular congestion and, in time, hyaline membranes (resulted from fibrin, cellular debris, red blood cells, rare neutrophils and macrophages). Hyaline membranes appear like an eosinophilic (pink), amorphous material, lining or filling the alveolar spaces and blocking the gases exchange [1]. The blood (which normally receives oxygen from the alveolar gas and unloads carbon dioxide into the alveoli) passes through the lungs without this vital exchange. Blood oxygen levels fall, and carbon dioxide rises, resulting in rising blood acid levels. Structural immaturity, as manifest by low numbers of alveoli, also contributes to the disease process. It is also clear that the oxygen and breathing treatments used, while life-saving, can also damage the lung. The diagnosis is made by the clinical picture and the chest xray, which demostrates decreased lung volumes (bell-shaped chest), absence of the thymus (after about 6 hours), a small (0.5-1 mm), discrete, uniform infiltrate involving all lobes of the lung and air-bronchograms (ie the infiltrate will outline the larger breathing tubes which remain air-filled). In severe cases, this becomes exaggerated until the cardiac borders become inapparent ('white-out' or 'ground-glass').
[edit] Prevention
Most cases of hyaline membrane disease can be ameliorated or prevented if mothers who are about to deliver prematurely can be given one of a group of hormones glucocorticoids. This speeds the production of surfactant. For very premature deliveries, a glucocorticoid is given without testing the fetal lung maturity. In pregnancies of greater than 30 weeks, the fetal lung maturity may be tested by sampling the amount of surfactant in the amniotic fluid, obtained by inserting a needle through the mother's abdomen and uterus. The 'maturity level' is expressed as the lecithin-sphingomyelin (or "L/S") ratio. If this ratio is less than 2, the fetal lungs may be surfactant deficient, and a glucocorticoid is given.
[edit] Treatment
Oxygen is given with a small amount of continuous positive airway pressure ("CPAP"), and intravenous fluids are administered to stabilize the blood sugar, blood salts, and blood pressure. If the baby's condition worsens, an endotracheal tube (breathing tube) is inserted into the trachea and intermittent breaths are given by a mechanical device. An exogenous preparation of surfactant, either synthetic or extracted from animal's lungs, is given through the breathing tube into the lungs. Smaller premature infants may remain ventilated for months. Chronic lung disease including bronchopulmonary dysplasia are common in severe RDS. The etiology of BPD is problematic and may be due to oxygen, overventilation or underventilation. The mortality rate for babies greater than 27 weeks gestation is less than 10%.
[edit] Related disorders
Acute respiratory distress syndrome (ARDS) has some similarities to IRDS.
[edit] Famous victims
Patrick Bouvier Kennedy, son of President John F. Kennedy and First Lady Jacqueline Kennedy, died of RDS two days after his premature birth in 1963. He was never attended by a pediatrician. It is very likely that he would have lived, had current medical practices been known and available then.
[edit] Further reading
Wyman ML. "Neonatal Respiratory Distress" in Essentials of Pediatric Intensive Care (2 volume set) by Levin and Morriss, 1997.
