RESPIRATORY DISTRESS SYNDROME (HYALINE MEMBRANE DISEASE)

RESPIRATORY DISTRESS SYNDROME (HYALINE MEMBRANE DISEASE)

Respiratory distress syndrome (RDS), formerly known as hyaline membrane disease, is a syndrome of premature neonates that is characterized by progressive and usually fatal respiratory failure resulting from atelectasis and immaturity of the lungs. RDS occurs most commonly in premature neonates (primarily weighing between 1,000 and 1,500 g) and between 28 and 37 weeks' gestation. In neonates 28 to 30 weeks' gestation, the incidence is 50% to 70% and increases with degree of prematurity.

RDS can be fatal; those who survive are at risk for chronic respiratory and neurologic complications.

Pathophysiology and Etiology

• Adequate pulmonary function at birth depends on:
• An adequate amount of surfactant (a lipoprotein mixture) lining the alveolar cells, which allows for alveolar stability and prevents alveolar collapse at the end of expiration.
• An adequate surface area in air spaces to allow for gas exchange       (ie, sufficient pulmonary capillary bed in contact with this alveolar surface area).
• RDS is ultimately the result of decreased pulmonary surfactant, incomplete structural development of lung, and a highly compliant chest wall.
• Contributing factors are any factor that decreases surfactant, such as:
• Prematurity and immature alveolar lining cells.
• Acidosis.
• Hypothermia.
• Hypoxia.
• Hypovolemia.
• Diabetes.
• Elective cesarean delivery.
• Fetal or intrapartum stress that compromises blood supply to fetal lungs: vaginal bleeding, maternal hypertension, difficult resuscitation associated with birth asphyxia. (Some situations, such as steroid therapy or a heroin-addicted mother, result in the acceleration of surfactant.)
• RDS due to non-pulmonary factors such as: cardiac defects, sepsis, airway obstruction, intraventricular hemorrhage, hypoglycemia, and acute blood loss.
• Surfactant production is deficient by type II alveolar cells. (Although some surfactant may be present at birth, it may not be regenerated at an adequate rate.) Surfactant production may be reduced due to:
• Extreme immaturity of alveolar lining cells.
• Diminished or impaired production rate resulting from fetal or early neonatal stress.
• Impairment of release mechanism for phospholipid from type II alveolar cells.
• Death of many of these cells responsible for decreased surfactant production.
• Intra-alveolar surface tension is increased, and alveoli are unstable and collapse at the end of expiration. Functional reserve capacity—the amount of air left in the lungs after expiration—is decreased; thus, the next breath requires almost as much effort as the first breath after birth.
• More oxygen and energy are required to expand the alveoli with each breath, causing fatigue.
• The number of alveoli that expand progressively decreases, leading to alveolar instability and atelectasis.
• Pulmonary vascular resistance increases, causing hypoperfusion of lung.
• Persistence of fetal circulation right-to-left shunt results, leading to hypoxemia and hypercapnia, which lead to respiratory and metabolic acidosis.
• Hypoxemia and pulmonary vascular pressure cause ischemia in the alveoli, leading to transudate in the alveoli and formation of a membranous layer.
• Gas exchange becomes inhibited. Lungs become stiff (decreased compliance), requiring more pressure to expand them.
• Airway obstruction leads to increased hypoxia and vasoconstriction, and the cycle continues.
• RDS is usually a self-limiting disease, and symptoms peak in about 3 to 4 days, at which time surfactant synthesis begins to accelerate, and pulmonary function and clinical appearance begin to improve.
• Moderately ill infants or those who do not require assisted ventilation usually show slow improvement by about 48 hours and rapid recovery over 3 to 4 days with few complications.
• Severely ill and very immature infants who require some ventilatory assistance usually demonstrate rapid deterioration, such as decreased cardiac inflow, decreased arterial pressure, apneic episodes, cyanosis, pallor, and flaccid, unresponsive shocklike state. Ventilatory assistance may be required for several days, and chronic lung disease and other complications are common.

Clinical Manifestations

Symptoms are usually observed soon after birth and may include those listed here and increase in severity over the first 2 days of life.

Primary Signs and Symptoms

• Expiratory grunting or whining (when the infant is not crying).
• Sternal, suprasternal, substernal, and intercostal retractions progressing to paradoxical seesaw respirations.
• Inspiratory nasal flaring.
• Tachypnea less than 60 breaths per minute.
• Hypothermia.
• Cyanosis when child is in room air (infants with severe disease may be cyanotic even when given oxygen), increasing need for oxygen.
• Decreased breath sounds and dry “sandpaper” breath sounds.
• Pulmonary edema.
• As the disease progresses:
• Seesaw retractions become marked with marked abdominal protrusion on expiration.
• Peripheral edema increases.
• Muscle tone decreases.
• Cyanosis increases.
• Body temperature drops.
• Short periods of apnea occur.
• Bradycardia may occur.
• Changes in distribution of blood throughout the body result in pale gray skin color.
• Diminished breath sounds.

Secondary Signs and Symptoms

• Hypotension.
• Edema of the hands and feet.
• Absent bowel sounds early in the illness.
• Decreased urine output.

Diagnostic Evaluation

• Prenatal diagnosis: Evaluation of amniotic fluids to assess fetal lung maturity.
• Lecithin/sphingomyelin ratio—tests of surfactant phospholipids in amniotic fluid.
• Phosphatidylcholine and phosphatidylglycerol (PG)—phospholipids that stabilize surfactant.
• TDX fetal maturity assay—determines PG levels in amniotic fluid or neonatal tracheal aspirates.
• Lamellar bodies test—measures a storage form of surfactant in amniotic fluids.
• Laboratory tests:
• PaCO₂—elevated.
• Partial pressure of arterial oxygen (PaO₂)—low.
• Blood pH—low due to metabolic acidosis.
• Calcium—low.
• Serum glucose—low.
• Chest X-ray—diffuse, fine granularity; “whiteout,” very heavy, uniform granularity reflecting fluid-filled alveoli and atelectasis of some alveoli, surrounded by hyperdistended bronchioles; “ground glass” appearance with prominent air bronchogram extending into periphery of lung fields.  Pulmonary interstitial emphysema (PIE) is observed in premature neonates with RDS due to overdistention of distal airways.
• Pulmonary function studies—stiff lung with a reduced effective pulmonary blood flow.

Management

Early recognition is imperative so that treatment may be initiated to halt the progression of RDS. In fact, treatment should begin prior to birth if the mother is at risk for delivering the baby pre-term. Transportation to a facility providing specialized care is desirable when possible.

Supportive

• Maintenance of oxygenation—PaO₂ at 60 to 80 mm Hg to prevent hypoxia; frequent arterial pH and blood gas measurements, and use of a pulse oximeter.
• Maintenance of respiration with ventilatory support, if necessary.
• Maintenance of normal body temperature.
• Maintenance of fluid, electrolyte, and acid-base balance—metabolic acidosis buffered with sodium bicarbonate.
• Maintenance of nutrition—I.V. dextrose 10% in water usually required.
• Antibiotics as needed to treat infection.
• Constant observation for complications—pneumothorax, disseminated intravascular coagulation (DIC), patent ductus arteriosus (PDA) with heart failure, chronic lung disease.
• Care appropriate for a small, premature neonate.
• Prevent hypotension.
• Maintain a hematocrit of 40% to 45%.

Aggressive (Offered in Tertiary Care Centers)

• Administration of exogenous surfactant into lungs early in the disease.
• Surfactant replacement therapy.
• High-frequency ventilation—mechanical ventilation that uses rapid rates    (can be greater than 900 breaths per minute) and tidal volumes near and, commonly, less than anatomical dead spaces.
• Extracorporeal membrane oxygenation (ECMO)—indicated in infants with reversible cardiac or respiratory failure. ECMO is a modified heart-lung bypass machine used to allow gas exchange outside the body.

Complications

• Complications related to respiratory therapy:
• Air leak: pneumothorax, pneumomediastinum, pneumopericardium, and pneumoperitoneum.
• Pneumonia, especially gram-negative organisms.
• Pulmonary interstitial emphysema.
• PDA or heart failure.
• Hypotension.
• Intraventricular hemorrhage—typically seen in infants weighing less than 1,500 g.
• DIC.
• Chronic problems associated with long-term use of oxygen:
• Bronchopulmonary dysplasia (BPD)—cystic-appearing lungs with hyperinfiltration, obstructive bronchiolitis, dysplastic changes, and pulmonary fibrosis.
• Chronic respiratory infections.
• Necrotizing enterocolitis.
• Tracheal stenosis.
• Retinopathy of prematurity (retrolental fibroplasia).
• Other complications related to prematurity.

Nursing Assessment

• Review the birth history.
• Apgar scores 1 and 5 minutes after birth.
• Type of resuscitation required.
• Treatments or medications administered.
• Medications or anesthesia administered to the mother during labor.
• Estimated gestational age.
• Maternal history—contributing factors or complications.
• Carefully assess the infant's respiratory status to determine the degree of respiratory distress.
• Determine the degree and severity of retractions.
• Count the respiratory rate for 1 full minute, note level of activity, and determine if they are regular or irregular.
• Identify periods of apnea, length, and type of stimulation necessary.
• Listen for expiratory grunting or whining sounds from the infant when quiet. This indicates an attempt to maintain PEEP and prevent alveoli from collapse.
• Note nasal flaring.
• Note cyanosis—location, improvement with oxygen.
• Auscultate chest for diminished breath sounds and presence of crackles.
• Determine the infant's cardiac rate and rhythm.
• Count the apical pulse for 1 full minute.
• Note irregularities in the rate or bounding pulses.
• Observe the infant's general activity.
• Lethargic or listless.
• Active and responds to stimuli.
• Infant's cry.
• Assess the skin for cyanosis, jaundice, mottling, paleness or grayness, and edema.