Bronchopulmonary Dysplasia

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Chapter 410 Bronchopulmonary Dysplasia

Steven Lestrud

Bronchopulmonary dysplasia (BPD) is a syndrome characterized by signs and symptoms of chronic lung disease that originates in the neonatal period (Chapter 95). The pathogenesis of the lung disease was originally thought to arise from mechanical and oxidant injury to the airways and interstitium leading to edema, inflammation, and fibrosis with characteristic radiographic and pathologic stages. The pathogenesis of lung disease in the population of neonates <1000 g also includes the contribution of immature development of airway and vascular structures of the lung. This fact has led to a change in recognized radiographic, pathologic, and clinical findings in BPD and an evolution in its definition. An accepted definition includes an oxygen requirement for 28 days postnatally, and the disorder is graded as mild, moderate or severe on the basis of supplemental oxygen requirement and gestational age (see Table 410-1 on the Nelson Textbook of Pediatrics website at www.expertconsult.com image).

Table 410-1 FORMS OF BRONCHOPULMONARY DYSPLASIA (BPD)

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Clinical Manifestations

Physical findings of the pulmonary exam vary with the severity of disease. Tachypnea is a common finding. Mouth breathing due to narrowed nasal passages and high arched palate is noted on upper airway exam. The chest demonstrates an increased anteroposterior diameter that suggests air trapping. Intercostal retractions are frequently present. Although breath sounds are frequently clear when the patient is well and abnormal only during an acute exacerbation, many patients have baseline wheeze or coarse crackles. A persistent fixed wheeze or stridor suggests subglottic stenosis or large airway malacia. Fine crackles may be present in patients prone to fluid overload.

The most severely affected patients require prolonged mechanical ventilation to achieve acceptable gas exchange. Supplemental oxygen may be required to maintain oxygen saturation values >90% and often is needed to minimize the work of breathing. Infants with significant lung disease exhibit growth failure from the elevated energy expenditure essential to maintain the increased metabolic demands of respiration. Chronic respiratory insufficiency may be evident as elevation of serum bicarbonate, elevation of PCO2 on blood gas analysis, or polycythemia.

Patients must be monitored for the development of cor pulmonale, especially if they require supplemental oxygen and have chronic respiratory insufficiency.

Gastroesophageal reflux disease (GERD) (Chapter 315) and pulmonary aspiration complicate pulmonary status, particularly during an exacerbation when the infant is most tachypneic and when pulmonary mechanics increase the risk of GERD. Other conditions due to premature birth complicating BPD include upper airway obstruction leading to hypoxia, neurodevelopmental delay with increased risk of aspiration, systemic hypertension with left ventricular hypertrophy, poor growth, and electrolyte disturbances.

In severely affected patients and patients with disease out of proportion to their risk for development of chronic lung disease, other pulmonary disease must be suspected, such as asthma, cystic fibrosis, and chronic aspiration pneumonitis. Recurrent episodes of respiratory distress are common, but anatomic airway abnormalities such as subglottic stenosis and airway malacia must also be considered.

A pulmonary exacerbation of BPD is typically triggered during viral upper respiratory infections. Other frequent triggers include viral lower respiratory infections, sinusitis, otitis media, weather changes, exposure to cigarette smoke, and exacerbations of gastroesophageal reflux. During an exacerbation, the infant exhibits increased work of breathing, with tachypnea and retractions becoming more prominent. Chest wall configuration may change, with an increased anteroposterior diameter. If wheezing is a prominent baseline finding, poor air entry during an exacerbation may result in less wheezing, signifying a significant deterioration of respiratory status.

Treatment

Treatment is aimed at decreasing the work of breathing and normalizing gas exchange, to allow for optimal growth and neurodevelopment. Infants requiring supplemental oxygen past 35 wk postmenstrual age have a higher incidence of lower airway obstruction and bronchodilator responsiveness and are more likely to be hospitalized during the toddler years than their peers. The etiology of wheezing in BPD may be lower airway inflammation, bronchial smooth muscle irritation, bronchial smooth muscle hypertrophy, and airway malacia. The administration of an inhaled bronchodilator is frequently undertaken to evaluate an individual’s response. Most commonly, inhaled β-agonists initially increase air movement and improve comfort of breathing, resulting in short-term improvement in pulmonary function values. For patients whose disease responds, the medication should be continued, especially during high-risk periods when triggers are present, such as an upper respiratory infection or hot humid days.

β-agonists may worsen the air exchange, particularly in infants with BPD and concomitant airway malacia. Bronchial smooth muscle may maintain airway caliber in the affected airway; smooth muscle relaxation after administration of a β-agonist results in increased small airway collapse. Patients in whom β-agonists have these effects may benefit from alternative bronchodilators, such as inhaled ipratropium and oral methylxanthines. The administration of preventive anti-inflammatory medications such as inhaled glucocorticoids and leukotriene-modifying agents may be considered in patients with frequent inflammatory triggers.

Targeted goals for supplemental oxygen therapy after discharge from the nursery are to improve oxygen saturation values and decrease likelihood of desaturation, reduce the risk of cor pulmonale, diminish the work of breathing, and improve growth. This therapy likely improves neurodevelopmental outcome and may decrease exacerbations caused by hypoxia. Oxygen saturation values should exceed 90%, but the optimal goal above this level is unknown. The addition of diuretic therapy with furosemide or thiazides may improve pulmonary mechanics by decreasing lung water and allow tapering of supplemental oxygen. Therapy beyond several weeks, however, is not known to improve outcome and places the child at risk for electrolyte disorders.

Adequate caloric intake can be difficult for many reasons, including oral aversion, discoordinate suck and swallow, GERD, aspiration, and aspiration with GERD. In addition, tachypnea, episodic respiratory distress, increased work of breathing, and requirement for supplement oxygen place the infant at risk for growth failure. A high caloric intake is necessary, with ranges of 120-160 kcal/kg/day required, frequently in combination with fluid restriction. To provide such high caloric intake in the compromised infant, supplemental feedings through a nasogastric or gastrostomy tube may be considered. Careful attention is necessary to maintain fluid balance.

Gastroesophageal reflux is common and must be suspected in patients not showing response to therapy and in patients with frequent exacerbations, especially exacerbations without clear triggers. Definitive diagnosis is necessary because these patients will be subject to prolonged promotility and antacid medications. Appropriate antireflux therapy in infants with GERD decreases respiratory complications. Gastroesophageal reflux with pulmonary aspiration or aspiration alone may manifest as chronic chest congestion, wheezing, and episodic hypoxic spells. Fundoplication with a gastrostomy tube is performed in patients showing no response to medical therapy. Evaluation and treatment by a speech therapist, pediatric pulmonologist, or otolaryngologist may decrease the risk for development of chronic lung disease associated with aspiration.

Prevention of respiratory viral illness is vitally important; frequent handwashing by caregivers, especially before they handle the baby, and avoidance of contact with children and adults with current respiratory symptoms are essential. Respiratory syncytial virus (RSV) immunoprophylaxis should be considered on the basis of the severity of lung disease as well as the patient’s gestational age, and current age.

The prognosis for infants with BPD is generally good. Through school age, the family can expect frequent medical interactions for episodes of respiratory distress, commonly triggered by simple upper respiratory tract infections and weather changes. Pulmonary function in severely affected patients remains decreased, and exercise limitation may be present because of dyspnea. The most severely affected patients benefit from care administered by a multidisciplinary team of caregivers, including the pediatrician, pulmonologist, speech therapist, nutritionist, and developmental specialists.

Bibliography

American Thoracic Society. Statement on the care of the child with chronic lung disease of infancy and childhood. Am J Respir Crit Care Med. 2003;168:356-396.

Baraldi E, Filippone M. Chronic lung disease after premature birth. N Engl J Med. 2007;357:1946-1955.

Bott L, Beghin L, Devos P, et al. Nutritional status at 2 years in former infants with bronchopulmonary dysplasia influences nutrition and pulmonary outcomes during childhood. Pediatr Res. 2006;60:340-344.

Jobe AJ. The new BPD: an arrest of lung development. Pediatr Res. 1999;46:641-643.

Kinsella JP, Greenough A, Abman SH. Bronchopulmonary dysplasia. Lancet. 2006;367:1421-1430.

Stocks J, Coates A, Bush A. Lung function in infants and young children with chronic lung disease of infancy: the next steps? Pediatr Pulmonol. 2007;42:3-9.

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