RESPIRATORY DISTRESS IN THE TERM NEWBORN INFANT
Saturday, August 16, 2008
Essentials of Diagnosis & Typical Features
Respiratory distress is among the most common symptom complexes seen in the newborn infant. It may result from both noncardiopulmonary and cardiopulmonary causes (Table 1–14). Chest radiography, arterial blood gases, and pulse oximetry are useful in assessing both the cause and the severity of the problem. It is important to consider the noncardiopulmonary causes listed in Table 1–14 because the natural tendency is to focus on the heart and lungs. Most of the noncardiopulmonary causes can be ruled out by the history, physical examination, and a few simple laboratory tests. The evaluation of cardiovascular disorders is discussed in a subsequent section.
The most common pulmonary causes of respiratory distress in the term infant are transient tachypnea, aspiration syndromes, congenital pneumonia, and air leaks.
A. Transient Tachypnea (Retained Fetal Lung Fluid): Respiratory distress is typically present from birth, usually associated with a mild to moderate oxygen requirement (25–50% O2). The infant may be term or near-term, nonasphyxiated, and born following a short labor or cesarean section without labor. Chest x-ray shows perihilar streaking and fluid in interlobar fissures. Resolution usually occurs within 12–24 hours.
B. Aspiration Syndromes: The infant is typically term or near-term, frequently with some fetal distress prior to delivery or depression at delivery. Blood or meconium is usually present in the amniotic fluid, but occasionally the fluid is clear. Respiratory distress is present from birth, in many cases manifested by a barrel chest appearance and coarse breath sounds. An increasing O2 need from pneumonitis may require intubation and ventilation. Chest x-ray shows coarse irregular infiltrates, hyperexpansion, and, in the worst cases, lobar consolidation.
When the amniotic fluid contains meconium or blood, suctioning of the infant’s mouth and nose as the head is delivered and before delivery of the chest is recommended to prevent aspiration of these secretions with the onset of breathing. If the infant is depressed or shows signs of respiratory distress at birth, suctioning of the trachea under direct vision is recommended, especially before commencing resuscitation with positive-pressure ventilation. Although these procedures are recommended, they will not prevent all cases of meconium or blood aspiration. Aspiration often occurs in utero as the stressed infant gasps. Babies with aspirations are at risk of air leak (pneumothorax) because of uneven aeration with segmental overdistention and are at risk for persistent pulmonary hypertension (see Cardiac Problems section, below). Standard treatment includes ventilatory support, antibiotics, and pressor support of systemic blood pressure.
C. Congenital Pneumonia: Infants may be of any gestational age, with or without a maternal history of prolonged rupture of the membranes, chorioamnionitis, or maternal antibiotic administration. Onset of respiratory distress may be at birth or may be delayed for several hours. Chest x-ray may resemble that of retained lung fluid or hyaline membrane disease; rarely, there may be a lobar infiltrate.
The lungs are the most common site of infection in the neonate. Most commonly, infections ascend from the genital tract before or during labor, with the vaginal or rectal flora the most likely infectious agents (group B streptococci, Escherichia coli, Klebsiella). Shock, poor perfusion, and absolute neutropenia (< 2000/mL) provide corroborating evidence for pneumonia. Gram stain of tracheal aspirate may be helpful. Because no signs or laboratory findings can confirm the presence or absence of pneumonia with certainty, all infants with respiratory distress should receive a blood culture and broad-spectrum antibiotic therapy (ampicillin 100 mg/kg in two divided doses and gentamicin 4 mg/kg every 24 hours or 2.5 mg/kg every 12 hours) until the diagnosis of a bacterial infection can be ruled out.
D. Spontaneous Pneumothorax: Respiratory distress (primarily tachypnea) is present from birth, typically not severe, and requires mild to moderate supplemental O2. Breath sounds may be decreased on the affected side; heart tones may be shifted toward the opposite side and may be distant. Chest x-ray will show pneumothorax or pneumomediastinum.
This entity occurs in 1% of all deliveries. The risk is increased by manipulations such as positive-pressure ventilation in the delivery room. Treatment usually consists of supplemental O2 and watchful waiting. Breathing 100% O2 for a few hours may accelerate reabsorption of the extrapulmonary gas by creating a diffusion gradient for nitrogen across the surface of the lung (nitrogen washout technique). This is effective only if the infant was breathing room air or O2 at low concentration at the time of the pneumothorax. Drainage by needle thoracentesis or tube thoracostomy is occasionally required. There is a small increased risk of renal abnormalities associated with spontaneous pneumothorax. Therefore, a careful physical examination of the kidneys and observation of urine output are indicated. If pulmonary hypoplasia with pneumothorax is suspected, renal ultrasound would also be indicated.
E. Other Pulmonary Causes: The other pulmonary causes of respiratory distress are fairly rare. Bilateral choanal atresia should be suspected if there is no air movement when the infant breathes through the nose. These infants present in the delivery room with good color and heart rate while crying but become cyanotic and bradycardiac when they quiet down and resume normal breathing. Other causes of upper airway obstruction are usually characterized by some degree of stridor or poor air movement despite good respiratory effort. Pleural effusions can be suspected in hydropic infants (eg, those with erythroblastosis fetalis). Space-occupying lesions cause a shift of the mediastinum and asymmetric breath sounds and would be apparent on chest x-ray.
Treatment
Whatever the cause, the cornerstone of treatment of neonatal respiratory distress is provision of adequate supplemental oxygen to maintain a PaO2 of 60–70 mm Hg and a saturation by pulse oximetry (SpO2) of 92–96%. PaO2 levels less than 50 mm Hg are associated with pulmonary vasoconstriction, which can exacerbate hypoxemia, whereas those greater than 100 mm Hg may increase the risk of oxygen toxicity without additional benefit. Oxygen should be warmed, humidified, and delivered through an air blender. Concentration should be measured with a calibrated oxygen analyzer. An umbilical or peripheral arterial line should be placed in any infant requiring more than 45% FIO2 by 4–6 hours of life to allow frequent blood gas determinations. Noninvasive monitoring with a pulse oximeter should be used.
Other supportive treatment includes intravenous provision of glucose and water. Unless infection can be unequivocally ruled out, blood cultures should be obtained and broad-spectrum antibiotics started. Volume expansion (normal saline; 5% albumin) can be given in infusions of 10 mL/kg over 30 minutes for low blood pressure, poor perfusion, and metabolic acidosis. Sodium bicarbonate (1–2 mEq/kg) is indicated for treatment of documented metabolic acidosis that has not responded to oxygen, ventilation, and volume. Specific workup should be pursued as indicated by the history and physical findings. In most cases, a chest x-ray study, blood gas measurements, complete blood count, and blood glucose allow a diagnosis.
Intubation and ventilation should be undertaken for signs of respiratory failure (PaO2 <> 60 mm Hg). Peak pressures should be adequate to produce chest wall expansion and audible breath sounds (usually 18–24 cm H2O). Positive end-expiratory pressure (4–6 cm H2O) should also be used. Ventilation rates of 20–50 breaths per minute are usually required. The goal is to maintain a PaO2 of 60–70 mm Hg and a PaCO2 of 40–50 mm Hg.
Prognosis
Most of the respiratory conditions affecting the term infant are acute and resolve in the first several days. Meconium aspiration syndrome and congenital pneumonia are associated with significant long-term pulmonary morbidity (chronic lung disease) and mortality (approximately 10–20%). Mortality rates in these disorders have been reduced by use of high-frequency ventilation, inhaled nitric oxide to treat pulmonary hypertension, and extracorporeal membrane oxygenation (ECMO).
- Tachypnea, respiratory rate > 60 breaths/min.
- Retractions (intercostal, sternal).
- Expiratory grunting.
- Cyanosis on room air.
Respiratory distress is among the most common symptom complexes seen in the newborn infant. It may result from both noncardiopulmonary and cardiopulmonary causes (Table 1–14). Chest radiography, arterial blood gases, and pulse oximetry are useful in assessing both the cause and the severity of the problem. It is important to consider the noncardiopulmonary causes listed in Table 1–14 because the natural tendency is to focus on the heart and lungs. Most of the noncardiopulmonary causes can be ruled out by the history, physical examination, and a few simple laboratory tests. The evaluation of cardiovascular disorders is discussed in a subsequent section.
The most common pulmonary causes of respiratory distress in the term infant are transient tachypnea, aspiration syndromes, congenital pneumonia, and air leaks.
A. Transient Tachypnea (Retained Fetal Lung Fluid): Respiratory distress is typically present from birth, usually associated with a mild to moderate oxygen requirement (25–50% O2). The infant may be term or near-term, nonasphyxiated, and born following a short labor or cesarean section without labor. Chest x-ray shows perihilar streaking and fluid in interlobar fissures. Resolution usually occurs within 12–24 hours.
B. Aspiration Syndromes: The infant is typically term or near-term, frequently with some fetal distress prior to delivery or depression at delivery. Blood or meconium is usually present in the amniotic fluid, but occasionally the fluid is clear. Respiratory distress is present from birth, in many cases manifested by a barrel chest appearance and coarse breath sounds. An increasing O2 need from pneumonitis may require intubation and ventilation. Chest x-ray shows coarse irregular infiltrates, hyperexpansion, and, in the worst cases, lobar consolidation.
When the amniotic fluid contains meconium or blood, suctioning of the infant’s mouth and nose as the head is delivered and before delivery of the chest is recommended to prevent aspiration of these secretions with the onset of breathing. If the infant is depressed or shows signs of respiratory distress at birth, suctioning of the trachea under direct vision is recommended, especially before commencing resuscitation with positive-pressure ventilation. Although these procedures are recommended, they will not prevent all cases of meconium or blood aspiration. Aspiration often occurs in utero as the stressed infant gasps. Babies with aspirations are at risk of air leak (pneumothorax) because of uneven aeration with segmental overdistention and are at risk for persistent pulmonary hypertension (see Cardiac Problems section, below). Standard treatment includes ventilatory support, antibiotics, and pressor support of systemic blood pressure.
C. Congenital Pneumonia: Infants may be of any gestational age, with or without a maternal history of prolonged rupture of the membranes, chorioamnionitis, or maternal antibiotic administration. Onset of respiratory distress may be at birth or may be delayed for several hours. Chest x-ray may resemble that of retained lung fluid or hyaline membrane disease; rarely, there may be a lobar infiltrate.
The lungs are the most common site of infection in the neonate. Most commonly, infections ascend from the genital tract before or during labor, with the vaginal or rectal flora the most likely infectious agents (group B streptococci, Escherichia coli, Klebsiella). Shock, poor perfusion, and absolute neutropenia (< 2000/mL) provide corroborating evidence for pneumonia. Gram stain of tracheal aspirate may be helpful. Because no signs or laboratory findings can confirm the presence or absence of pneumonia with certainty, all infants with respiratory distress should receive a blood culture and broad-spectrum antibiotic therapy (ampicillin 100 mg/kg in two divided doses and gentamicin 4 mg/kg every 24 hours or 2.5 mg/kg every 12 hours) until the diagnosis of a bacterial infection can be ruled out.
D. Spontaneous Pneumothorax: Respiratory distress (primarily tachypnea) is present from birth, typically not severe, and requires mild to moderate supplemental O2. Breath sounds may be decreased on the affected side; heart tones may be shifted toward the opposite side and may be distant. Chest x-ray will show pneumothorax or pneumomediastinum.
This entity occurs in 1% of all deliveries. The risk is increased by manipulations such as positive-pressure ventilation in the delivery room. Treatment usually consists of supplemental O2 and watchful waiting. Breathing 100% O2 for a few hours may accelerate reabsorption of the extrapulmonary gas by creating a diffusion gradient for nitrogen across the surface of the lung (nitrogen washout technique). This is effective only if the infant was breathing room air or O2 at low concentration at the time of the pneumothorax. Drainage by needle thoracentesis or tube thoracostomy is occasionally required. There is a small increased risk of renal abnormalities associated with spontaneous pneumothorax. Therefore, a careful physical examination of the kidneys and observation of urine output are indicated. If pulmonary hypoplasia with pneumothorax is suspected, renal ultrasound would also be indicated.
E. Other Pulmonary Causes: The other pulmonary causes of respiratory distress are fairly rare. Bilateral choanal atresia should be suspected if there is no air movement when the infant breathes through the nose. These infants present in the delivery room with good color and heart rate while crying but become cyanotic and bradycardiac when they quiet down and resume normal breathing. Other causes of upper airway obstruction are usually characterized by some degree of stridor or poor air movement despite good respiratory effort. Pleural effusions can be suspected in hydropic infants (eg, those with erythroblastosis fetalis). Space-occupying lesions cause a shift of the mediastinum and asymmetric breath sounds and would be apparent on chest x-ray.
Treatment
Whatever the cause, the cornerstone of treatment of neonatal respiratory distress is provision of adequate supplemental oxygen to maintain a PaO2 of 60–70 mm Hg and a saturation by pulse oximetry (SpO2) of 92–96%. PaO2 levels less than 50 mm Hg are associated with pulmonary vasoconstriction, which can exacerbate hypoxemia, whereas those greater than 100 mm Hg may increase the risk of oxygen toxicity without additional benefit. Oxygen should be warmed, humidified, and delivered through an air blender. Concentration should be measured with a calibrated oxygen analyzer. An umbilical or peripheral arterial line should be placed in any infant requiring more than 45% FIO2 by 4–6 hours of life to allow frequent blood gas determinations. Noninvasive monitoring with a pulse oximeter should be used.
Other supportive treatment includes intravenous provision of glucose and water. Unless infection can be unequivocally ruled out, blood cultures should be obtained and broad-spectrum antibiotics started. Volume expansion (normal saline; 5% albumin) can be given in infusions of 10 mL/kg over 30 minutes for low blood pressure, poor perfusion, and metabolic acidosis. Sodium bicarbonate (1–2 mEq/kg) is indicated for treatment of documented metabolic acidosis that has not responded to oxygen, ventilation, and volume. Specific workup should be pursued as indicated by the history and physical findings. In most cases, a chest x-ray study, blood gas measurements, complete blood count, and blood glucose allow a diagnosis.
Intubation and ventilation should be undertaken for signs of respiratory failure (PaO2 <> 60 mm Hg). Peak pressures should be adequate to produce chest wall expansion and audible breath sounds (usually 18–24 cm H2O). Positive end-expiratory pressure (4–6 cm H2O) should also be used. Ventilation rates of 20–50 breaths per minute are usually required. The goal is to maintain a PaO2 of 60–70 mm Hg and a PaCO2 of 40–50 mm Hg.
Prognosis
Most of the respiratory conditions affecting the term infant are acute and resolve in the first several days. Meconium aspiration syndrome and congenital pneumonia are associated with significant long-term pulmonary morbidity (chronic lung disease) and mortality (approximately 10–20%). Mortality rates in these disorders have been reduced by use of high-frequency ventilation, inhaled nitric oxide to treat pulmonary hypertension, and extracorporeal membrane oxygenation (ECMO).
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