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  1113 74 Neonatal Respiratory Disorders MOIRA A. CROWLEY Multiple pathophysiologic mechanisms can present with pulmonary manifestations in term and preterm infants.  The clinical picture is most commonly dominated by respiratory distress, which presents as tachypnea, grunting, flaring, retractions, cyanosis, and hypoxemia. However, apnea and hypoventilation are also common. In preterm infants, these manifestations are commonly associated with respiratory distress syndrome (RDS) as discussed in Chapter 72. Nonpulmonary etiologies of respiratory distress include thermal instability, circula-tory problems, cardiac disease, neuromuscular disorders, sepsis, anemia or polycythemia, and methemoglobin-emia (Box 74-1). This section presents an overview of the many other respiratory disorders that can affect preterm and term infants. Developmental Diseases PULMONARY UNDERDEVELOPMENT: PULMONARY AGENESIS, APLASIA, AND HYPOPLASIA  Abnormal lung development varies from mild hypopla-sia, which can either be a primary or secondary defect, to agenesis of a single lobe or whole lung. Agenesis of the lung is a rare congenital anomaly defined as the total absence of pulmonary parenchyma, its supporting vascu-lature, and bronchi after the bifurcation. 18,78  Complete agenesis of the lung is usually unilateral (90%), although dysgenesis of the other lung has been reported. 32  Pulmo-nary aplasia can be classified as a subset of pulmonary agenesis defined by the presence of a blind-ending, rudi-mentary bronchus without associated lung parenchyma or pulmonary vasculature. 16  It has been hypothesized that pulmonary agenesis is vascular in srcin, most likely resulting from a disruption of the dorsal aortic arch blood flow during the fourth week of gestation. Although lung agenesis can be an isolated finding, it is commonly asso-ciated with other congenital malformations, including urogenital, vertebral, cardiac, and gastrointestinal, as well as malformations of the first and second branchial arch derivatives and radial ray defects. 18,32  As a result, pulmo-nary agenesis has been considered a subset of the  VACTERL ( v ertebral, a nal atresia; c ardiac defect; t  racheo- e sophageal fistula; r  enal anomalies; l imb anomalies) sequence or Goldenhar syndrome. Malformations of the first and second branchial arches and/or radial ray mal-formations are the most common malformations associ-ated with pulmonary agenesis, and all cases are ipsilateral to the pulmonary malformation. Those who do not have facial or radial ray anomalies appear to fit the VACTERL association. 32 Diagnosis is confirmed on antenatal ultrasound by the presence of mediastinal shift in the absence of a diaphragmatic hernia. Antenatal echocardiogram reveals total absence of the pulmonary artery or one of its branches on the affected side. Magnetic resonance imaging (MRI) examination can confirm the diagnosis, evaluate the size of the remaining lung, and evaluate the presence of other congenital malformations. After delivery, diag-nosis of infants with unilateral pulmonary agenesis can be suspected by decreased breath sounds and displace-ment of the mediastinum to the affected side. Some breath sounds, however, may be audible over the affected side if a portion of normal lung, which usually has under-gone compensatory hypertrophy, has herniated across the midline into the affected hemithorax. The radio-graphic appearance of a radiopaque hemithorax helps confirm the diagnosis, and accompanying vertebral defects are not uncommon (Figure 74-1). Treatment is largely supportive, and the prognosis depends on the presence or absence of other anomalies.Pulmonary hypoplasia is the result of deficient or incomplete development of the lung parenchyma leading to decreased number of distal airways, alveoli, and associ-ated pulmonary vessels. It can be classified as either primary  , caused by intrinsic failure of normal lung devel-opment, or  secondary  , caused by a multitude of different pathologic processes that interfere with normal lung development. The pathophysiology of secondary pulmo-nary hypoplasia includes (1) oligohydramnios secondary to renal malformations, prolonged early amniotic fluid leak, placental abnormalities, or intrauterine growth restriction; (2) space-occupying lesions compressing the lungs and preventing normal growth as seen with con-genital diaphragmatic hernia (which is thought to have some evidence of primary pulmonary hypoplasia as  well), cystic lung disease, or cardiac malformations with extreme cardiomegaly (e.g., tricuspid atresia or Ebstein anomaly); and (3) absence or abnormal diaphragmatic activity (which is essential for lung development) result-ing from a central or peripheral nervous system disorder or musculoskeletal disease, which can prevent chest wall expansion and breathing movements.Diagnosis of pulmonary hypoplasia is made patho-logically by measuring the lung-to-body ratio; however, this truly only captures those with lethal pulmonary hypoplasia. Methods to diagnose pulmonary hypoplasia antenatally in those fetuses at risk for developing pulmo-nary hypoplasia because of associated findings, have Descargado para Anonymous User (n/a) en Universidad Nacional Autonoma de Mexico de por Elsevier en enero 29, 2019.Para uso personal exclusivamente. No se permiten otros usos sin autorización. Copyright ©2019. Elsevier Inc. Todos los derechos reservados.  1114 PART 12  ã THE RESPIRATORY SYSTEM Figure 74-1  Unilateral left lung agenesis. (From Greenough A, Ahmed J, Broughton S. Unilateral pulmonary agenesis.  J Perinat Med  . 2006;34:80, with permission.) NEUROMUSCULAR DISORDERS (see Chapter 63) ã Central nervous system: asphyxia, hemorrhage, malfor-mations, drugs, infectionã Spinal cord: cord injury, spinal muscular atrophy ã Nerves: phrenic nerve injury, cranial nerve palsy ã Neuromuscular plate: myasthenia gravisã Muscular: dystrophies OBSTRUCTIVE-RESTRICTIVE DISORDERS ã Airway obstruction (see Chapter 76)ã Intrinsic: choanal atresia, floppy epiglottis, laryngeal  web, cord paralysis, laryngospasm, malacia, tracheal stenosisã Extrinsic: tubes, secretions, Pierre Robin syndrome, macroglossia, goiter, vascular ring, cystic hygroma, mediastinal and cervical massesã Rib cage abnormalitiesã Thoracic dystrophiesã Rickets and bone diseaseã Fracturesã Pectus excavatum DIAPHRAGMATIC DISORDERS ã Congenital eventrationã Abdominal distention HEMATOLOGIC DISORDERS (see Chapter 88) ã Anemiaã Polycythemiaã Methemoglobinemia METABOLIC DISORDERS (see Part 16) ã Metabolic acidosisã Hypoglycemiaã Hypocalcemia CARDIOVASCULAR DISORDERS (see Part 13) ã Increased pulmonary flow ã Patent ductus arteriosusã Ventricular septal defect ã Transposition of the great arteriesã Truncus arteriosusã Decreased pulmonary flow ã Persistent pulmonary hypertensionã Pulmonary atresiaã Tetralogy of Fallot ã Tricuspid atresiaã Cardiomegaly ã Tricuspid atresiaã Ebstein anomaly ã Left heart obstruction (e.g., coarctation, mitral atresia, total anomalous pulmonary venous return)ã Hypotension MISCELLANEOUS (see Parts 6 and 10) ã Sepsisã Painã Hypothermiaã Hyperthermia BOX 74-1  CLASSIFICATION OF EXTRAPULMONARY CAUSES OF RESPIRATORY DISTRESS been reported and include the use of prenatal ultrasound techniques, both two- and three-dimensional, as well as fetal MRI. Ultrasound measurement techniques include thoracic circumference (TC) corrected for gestational age or femur length, TC : abdominal circumference ratio, and thoracic : heart area. These techniques, however, measure the thoracic wall rather than lung parenchyma itself. More recently, measurement of lung volume using three-dimensional ultrasound has been reported, but methodologic standards and definitions are not yet ready for this tool to be used for predicting lethality. 21  Pathologic examination of the hypoplastic lung can show a low ratio of lung to body weight, low DNA content, or decreased radial alveolar count. Peripheral bronchioles are decreased in number, as are the pulmo-nary arterioles, which often exhibit hypertrophy of medial smooth muscle, a predisposition to persistent pulmonary hypertension.Secondary pulmonary hypoplasia is most commonly encountered in oligohydramnios and congenital dia-phragmatic hernia (CDH). Survival of infants with pul-monary hypoplasia depends on the degree to which lung growth is restricted and the underlying cause of hypopla-sia. It is not uncommon for these patients to present  with severe respiratory distress associated with bilateral pneumothorax as well as hypoxia from both fixed and reactive pulmonary hypertension. Pulmonary hypoplasia is present in up to 33% of patients with oligohydramnios and can be associated with a high mortality rate (55%-100%) depending on the severity of hypoplasia 72  (see Chapter 25). Patients with pulmonary hypoplasia sec-ondary to prolonged premature rupture of membranes (PPROM) starting in the second trimester have been shown to have a better prognosis than initially expected. In a review of 98 deliveries with PPROM starting at 20 weeks’ gestation, survival using modern neonatal Descargado para Anonymous User (n/a) en Universidad Nacional Autonoma de Mexico de por Elsevier en enero 29, 2019.Para uso personal exclusivamente. No se permiten otros usos sin autorización. Copyright ©2019. Elsevier Inc. Todos los derechos reservados.  1115 74  ã NEONATAL RESPIRATORY DISORDERS most predictive), and estimated fetal lung volume by MRI. 20,50,54,56,79  Because it has been reported that the LHR increases exponentially with gestational age, some experts have advocated that the LHR should be corrected for gestational age and have used an observed : expected LHR (O/E LHR) based on the LHR in the CDH patient com-pared with what is considered normal for that gestational age. 55  When using the corrected LHR, the CDH registry has quoted the following numbers based on 184 fetuses  with isolated left-sided CDH evaluated between 22 and 28 weeks’ gestation: 37 ã Fetuses with O/E LHR less than 15% have extreme pulmonary hypoplasia, with virtually no survivors.ã Fetuses with O/E LHR between 15% and 25% have severe pulmonary hypoplasia, with a predicted survival of 20%. (Those with liver completely down in the abdomen fare better than those with liver herniated up into the chest.)ã Fetuses with O/E LHR between 26% and 35% and those with O/E LHR between 36% and 45%, but liver in the chest, have moderate pulmonary hypoplasia,  with expected survival between 30% and 60%.ã Fetuses with O/E LHR between 36% and 45% with liver down and those with an O/E LHR greater than 45% have mild hypoplasia and are likely to survive ( > 75%). The ability of these parameters to predict survival has not been consistent. This is mostly secondary to the small number of patients in each series, challenges in measure-ment consistency, absence of standardized measurement and lack of correlation with actual lung volume, incon-sistent measures for survival or morbidity, and differ-ences in postnatal management and survival. Nevertheless, these tools give clinicians some data to use when counsel-ing families faced with the diagnosis of CDH. The clinical presentation of patients with CDH can  vary from asymptomatic in mild cases to severe respira-tory failure at birth. Diagnosis should be suspected in previously undiagnosed patients by the presence of severe respiratory distress, cyanosis, scaphoid abdomen, and failure to improve with ventilation. Physical examination reveals absence of breath sounds on the affected side with displacement of heart sounds to the contralateral side, and occasionally bowel sounds can be heard over the thorax. Once the diagnosis is made or suspected, patients should be immediately intubated and an orogastric tube placed to evacuate the stomach. Aggressive ventilatory strategies should be avoided (see later). Chest radiograph shows the presence of bowel loops in the affected chest cavity with shifting of the heart to the contralateral side (Figure 74-2). If the stomach is included in the hernia, the tip of orogastric tube will be seen within the thorax.  The presence of liver in the chest is suspected by deviation of the umbilical venous line. Late presentation of Boch-dalek hernia occurs in less than 3% of cases. 64  These patients can be asymptomatic at birth and usually present later in life with respiratory or gastrointestinal symptoms. High index of suspicion is needed in these cases to prevent unwarranted and potentially dangerous interven-tions such as the insertion of a chest tube for suspected pleural effusion or pneumothorax. Diagnosis can be therapies was 70%, and medical history was not helpful in predicting survival. 42  Both human and animal studies have shown that some of these infants who present with early severe respiratory failure consistent with pulmonary hypoplasia may benefit from inhaled nitric oxide (iNO). Supportive therapy with gentle ventilation is the main-stay of therapy. CONGENITAL DIAPHRAGMATIC HERNIA Congenital diaphragmatic hernia (CDH) results from a developmental defect during the formation of the dia-phragm that allows for the herniation of abdominal con-tents into the thoracic cavity (see Chapter 78). Defects of the diaphragm are classified according to the anatomic region of the diaphragm that is defective. The most common defect involves the posterolateral diaphragm (Bochdalek) and accounts for 70% of diaphragmatic hernias. Anterior diaphragm defects (Morgagni) account for 25% to 30% of diaphragmatic hernias, and central diaphragmatic defects are rare, occurring in 2% to 5%. 60   The incidence of CDH is 1 in 2000 to 3000 newborns, and it occurs most commonly on the left side (85%),  whereas bilateral hernias are rare (1%) and usually fatal.Congenital diaphragmatic hernia is either an isolated defect or can be associated with other congenital anoma-lies, including cardiac, urogenital, chromosomal, and musculoskeletal. Most reports estimate that 40% to 60% of patients with CDH have non–hernia-related anoma-lies. 118  In a review of 3062 patients with CDH, the Con-genital Diaphragmatic Hernia Study Group reported a 28% incidence of severe malformations (major cardiac, syndromal, and chromosomal disorders) in patients who did not undergo surgical repair secondary to unsalvage-able hernia compared with 7% in repaired patients. 25  This emphasizes the importance of adequate evaluation of associated malformations in patients with CDH. The underlying pathophysiology of CDH is that of pulmonary insufficiency and persistent pulmonary hyper-tension of the newborn (PPHN) secondary to pulmonary hypoplasia, lower number of alveoli, and airway and vas-cular muscular hypertrophy associated with compression by abdominal contents. Pulmonary hypoplasia may also have a primary developmental component, as animal models have confirmed that developmental regulation of the lung and diaphragm are controlled by some of the same genes. The severity of CDH is related mostly to the degree of lung hypoplasia, which depends on the size of the defect, the presence of the liver in the chest, and how early in gestation the abdominal contents were displaced. 25 In a review of reports from 13 tertiary centers, 56% of CDH cases were diagnosed antenatally. Antenatal diagno-sis is associated with a poor prognosis, and the data suggest that infants with a prenatal diagnosis have a better chance of survival if they are born in a tertiary center. 75  Several antenatal parameters have been evalu-ated for their ability to predict survival and morbidity in cases of isolated CDH. Most of these predictors rely on the indirect assessment of the size of the contralateral lung as a proxy for pulmonary hypoplasia. Methods used include lung area to head circumference ratio (LHR) between 22 and 28 weeks’ gestation, the presence of the liver in the chest (which has been thought to be Descargado para Anonymous User (n/a) en Universidad Nacional Autonoma de Mexico de por Elsevier en enero 29, 2019.Para uso personal exclusivamente. No se permiten otros usos sin autorización. Copyright ©2019. Elsevier Inc. Todos los derechos reservados.  1116 PART 12  ã THE RESPIRATORY SYSTEM 5. Using ECMO as rescue therapy with variable indica-tions in different centers, including persistent oxygen-ation index (OI) greater than 40, persistent hypoxemia, or failure of ventilatory management to support oxy-genation, ventilation, or tissue perfusion.6. Delaying surgical repair until physiologic stabilization and improvement of PPHN.Questions regarding the use of chest tubes, repair on or off ECMO, and benefits of various options for surgical reconstruction of large defects remain to be answered.Postnatal survival rate at tertiary centers has improved  with reported rates of 70% to 92%. 38,45,46,59,77,83  However, the survival data might underestimate hidden mortality secondary to termination, stillborn, and referral pattern for outborn patients. With improvement in survival, there has been a focus on improving long-term morbidity of survivors. Infants born with CDH have multiple long-term morbidities affecting the pulmonary, gastroin-testinal, neurologic, and skeletal systems. Respiratory complications include pulmonary vascular abnormalities presumably causing pulmonary hypertension, a higher incidence of obstructive airway disease, and a restrictive lung function pattern that continues into adulthood. 100  Gastroesophageal reflux disease (GERD), sometimes in made after nasogastric tube insertion, contrast upper gas-trointestinal study, or chest computed tomography (CT) scan. Prognosis for cases with late presentation is excel-lent once the correct diagnosis is made.Improved survival has been reported using a consistent approach in the management of CDH that can be facilitated by the development of multidisciplinary stan-dardized treatment guidelines, including input from neonatology, pediatric surgery, extracorporeal membrane oxygenation (ECMO) specialists, and respiratory therapy (Box 74-2). Predetermined criteria for the use of ECMO and an underlying “protect the lung” strategy are essential components in the care of these infants and can be as important as the specific medical interventions chosen.  Whereas animal studies have suggested lung immaturity and surfactant deficiency in models of CDH, the use of antenatal steroids and surfactant replacement has not been shown to be beneficial. 112  A systematic review of strategies associated with improved survival among infants with CDH in 13 centers that cared for at least 20 patients and reported a survival rate of 75% or more has described multiple successful treatment strategies associated with this improved survival. 75  Although these centers used different mechanical ventilation strategies, most of these targeted the use of gentle ventilation or permissive hypercapnia. The basic elements of this treat-ment strategy are:1. Ventilation of the patient with low peak inspiratory pressures (PIP) to minimize lung injury. The goal of PIP is usually less than 25 cm H 2 O.2. Accepting preductal saturations of greater than or equal to 85%, regardless of postductal saturation, and higher Pa CO 2  levels of less than or equal to 65 with a pH of at least 7.25 as long as there is evidence of adequate tissue perfusion and oxygenation.3. Instituting high-frequency oscillatory ventilation (HFOV) or high-frequency positive pressure ventila-tion once the preset limit failed to achieve adequate  ventilation, although HFOV was used by some as the primary mode of ventilation.4. Even though iNO might produce short-term benefits, the routine use of iNO is not supported by current data and might actually be associated with a worse outcome. RESOLVED ISSUES ã There is a high incidence of associated malformations.ã Delivery at a tertiary center improves survival for ante-natally diagnosed patients.ã Agenesis of the diaphragm and herniation of the liver are poor prognostic signs.ã Multidisciplinary approach using gentle ventilation improves outcome.ã Survivors need long-term follow-up and management of associated complications. UNRESOLVED ISSUES ã The utility of antenatal ultrasound and magnetic reso-nance imaging markers to predict survivalã The role of antenatal steroids, surfactant, and inhaled nitric oxide in management ã Surgical approachã Benefit of extracorporeal membrane oxygenation (ECMO) and use of chest tube RECOMMENDATIONS ã Accept preductal saturations greater than or equal to 85%, Pa CO 2  less than or equal to 65 mm Hg, and pH greater than or equal to 7.25.ã Identify preset ventilatory limits that are not to be exceeded.ã Use high-frequency oscillatory ventilation if, conven-tional mechanical ventilation, fails.ã Use ECMO per preset criteria.ã Delay surgery until persistent pulmonary hyperten-sion improves. BOX 74-2  MANAGEMENT OF CONGENITAL DIAPHRAGMATIC HERNIA  Figure 74-2  Left-sided diaphragmatic hernia in a 1-day-old term infant. Descargado para Anonymous User (n/a) en Universidad Nacional Autonoma de Mexico de por Elsevier en enero 29, 2019.Para uso personal exclusivamente. No se permiten otros usos sin autorización. Copyright ©2019. Elsevier Inc. Todos los derechos reservados.
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