Respiratory Disorders of the Newborn
I Persistent Pulmonary Hypertension in the Newborn (PPHN)
1. Pulmonary hypertension impairs the transition from fetal to neonatal circulation.
2. Right-to-left shunting occurs when the ductus arteriosus and foramen ovale remain open or reopen after closure.
B Pathophysiology (Figure 27-1)
1. Pulmonary hypertension and high pulmonary vascular resistance (PVR) impede blood flow to the lungs.
2. The pulmonary arterioles react to the resulting hypoxemia, hypercapnia, and acidemia with vasoconstriction, further impeding pulmonary blood flow.
3. High PVR results in right heart pressures greater than systemic blood pressure, causing right-to-left shunting through the ductus arteriosus and foramen ovale.
4. This combination of responses leads to a cyclic pattern of decreased cardiac output, decreased pulmonary blood flow, and vasoconstriction.
1. Near-term, term, and postterm neonates
2. Majority present within the first 72 hours after birth
4. Signs and symptoms of respiratory distress to varying degrees
1. Contrast or “bubble” echocardiography
a. Demonstrates the presence of right-to-left shunt through the foramen or ductus.
b. Used to evaluate cardiac structures and rule out cyanotic cardiac anomalies.
a. Place infant in 100% oxygen for 5 to 10 minutes and obtain arterial blood gas.
b. If Pao2 does not increase, right-to-left shunting is present.
c. Does not differentiate between PPHN and congenital heart disease.
3. Comparison of preductal and postductal arterial Pao2
a. Obtain simultaneous arterial blood gases from a preductal artery (right radial or brachial) and postductal artery (left radial or umbilical).
b. A difference of ≥15 mm Hg in preductal and postductal Pao2 indicates ductal shunting.
c. A difference of <15 mm Hg indicates no ductal shunting but does not rule out PPHN or congenital heart disease.
d. Pulse oximetry sensors can be placed at preductal and postductal sites to assess the presence of shunting and allow continuous monitoring for recurrent shunting.
4. Hypoxemia-hyperventilation test
a. Most definitive test to detect PPHN.
b. The patient is hyperventilated at a high rate using a manual resuscitator and 100% oxygen.
c. Hyperventilation results in a decrease in Paco2, causing pulmonary vasodilation.
d. PPHN is confirmed when Pao2 is <50 mm Hg before hyperventilation and increases to ≥100 mm Hg during hyperventilation.
e. For most congenital heart diseases, Pao2 will not increase significantly during this test.
a. Stop the cyclic pattern of deterioration.
b. Increase pulmonary blood flow by decreasing PVR or increasing systemic vascular resistance (SVR).
2. Minimize handling and stimulation of the infant to avoid transient hypoxemia.
a. A selective pulmonary vasodilator approved for management of PPHN in neonates of gestational age ≥34 weeks.
b. Initial dose is 20 parts per million (ppm).
c. If there is no response at 20 ppm, increasing to 40 to 80 ppm will not improve oxygenation.
4. Mechanical ventilation and oxygen
a. Conventional mechanical ventilation (CMV) and high frequency oscillatory ventilation (HFOV) have been used with success.
b. Hyperventilation and induced alkalosis have been widely used but are controversial.
(1) Effects of hyperventilation and alkalosis
(a) Acute pulmonary vasodilation
(c) Cerebral vasoconstriction, which may lead to neurodevelopmental problems.
(2) Because of the higher level of ventilator support necessary, hyperventilation carries an increased risk of lung injury.
c. A widely practiced approach is to set the ventilator to produce mild hypocapnia and respiratory alkalosis.
d. Success has been reported using lung protective ventilator strategies without inducing alkalinization.
(3) Manage metabolic acidosis with sodium bicarbonate.
(4) Use low positive end-expiratory pressure (PEEP) in the absence of parenchymal lung disease.
e. Muscle relaxants and sedatives to prevent patient-ventilator dysynchrony and resulting fluctuations of Pao2.
5. Administer surfactant if the infant has respiratory distress syndrome (RDS).
a. Increase SVR with vasopressors such as dopamine and dobutamine.
b. Decrease PVR and hypertension with vasodilators (e.g., prostaglandin I, tolazoline, or nitroprusside).
c. Correct hypotension using volume expanders and dopamine.
d. PPHN is reversed when the pulmonary artery pressure is less than the arterial pressure.
7. Extracorporeal membrane oxygenation (ECMO) is used for severe cases.
II Respiratory Distress Syndrome
1. RDS is a disease resulting from immature lung anatomy and physiology.
2. The primary abnormality is surfactant deficiency.
3. Without enough surfactant, alveoli collapse with each breath, and the lungs cannot maintain expansion.
4. Underdeveloped alveoli and pulmonary capillary beds further compromise gas exchange.
B Factors that increase the risk of developing RDS
4. Male infants have twice the risk of female infants.
5. Maternal hemorrhage during delivery
C Pathophysiology (Figure 27-2)
1. Surfactant deficiency causes atelectasis and reduced lung compliance.
2. Gas exchange is impaired, resulting in hypoxemia, hypercapnia, and acidemia.
3. Work of breathing increases, and the neonate begins to fatigue and hypoventilate.
4. Pulmonary vasoconstriction and increased PVR lead to hypoperfusion of the lung.
5. PPHN with shunting through the ductus arteriosus (right-to-left shunt).
6. Hypoxia causes damage to alveolar epithelium.
7. Pulmonary capillary permeability increases, and plasma leaks from the capillaries.
8. Fibrin present in plasma forms a hyaline membrane that lines the alveoli and bronchioles.
9. Alveolar ventilation decreases, and diffusion gradient increases.
10. High FIO2 and airway pressures during mechanical ventilation cause further tissue damage.
E Radiographic findings (Figure 27-3)
1. Classic appearance in the untreated newborn is reticulogranular infiltrates described as having a “ground glass” appearance.
2. Air bronchograms show collapsed alveoli surrounding air-filled bronchi.
3. Chest radiograph changes take place within 8 hours.
4. Severe RDS may progress to a “total whiteout,” in which the heart border and diaphragm are indistinct because of severe atelectasis.
1. Monitoring of vital signs and arterial blood gases.
2. Manage hypoxemia; maintain Pao2 of 60 to 80 mm Hg.
3. Continuous positive airway pressure (CPAP) may be used initially.
4. Mechanical ventilation is usually required to manage severe acidemia, hypercapnia, and hypoxemia.
5. High respiratory rate, FIO2, and airway pressures are often required.
6. HFOV may be used either initially or in cases in which CMV is unsuccessful.
7. Surfactant replacement therapy
a. Synthetic and animal-derived products are available (Table 27-1).
TABLE 27-1
Surfactant Replacement Therapy
| Generic Name | Brand Name | Source | Characteristics | Route | Dosage |
| Colfosceril | Exosurf | Synthetic surfactant | No surfactant associated proteins | Side port on endotracheal tube adaptor | Initial: Two 2.5-ml/kg half-doses; avoid endotracheal suctioning for 2 hr after treatment |
| Beractant | Survanta | Exogenous surfactant from bovine lung extract | Contains surfactant associated proteins | Intratracheal | Initial: 4 ml/kg; if needed, 4 doses in the first 48 hr of life; ≥ 6 hr between each dose |
| Poractant alfa | Curosurf | Derived from minced porcine lung extract | Contains surfactant associated proteins | Intratracheal | Initial: 2.5-ml/kg dose divided in 2 aliquots; up to 2 more doses of 1.25 ml/kg, 12 hr apart, if needed |
| Calfactant | Infasurf | Derived from lavage of calf lungs | Contains surfactant associated proteins | Intratracheal | Initial: 3-ml/kg dose divided into 2 aliquots; 3 doses of 3 ml/kg, 12 hr apart, if needed |
b. Method of administration depends on the drug used.
(1) Can be given through a side port adaptor on the endotracheal tube (ETT).
(2) Or through a small catheter inserted just past the tip of the ETT.
c. Results in rapid and dramatic improvement in lung compliance and gas exchange.
d. High levels of ventilatory support usually can be significantly reduced.
e. Widespread use of surfactant has markedly decreased mortality from RDS.
f. To avoid potential pneumothorax, it is important to decrease airway pressures and tidal volumes promptly when compliance improves during or immediately after surfactant administration.
g. The most common adverse effects are transient oxygen desaturation and bradycardia.
9. Maintain normal body temperature, and minimize stimulation of infant.
10. Provide appropriate fluid, electrolytes, glucose, and calories.
11. Maintain blood pressure and hematocrit.
III Meconium Aspiration Syndrome (MAS)
1. Ten percent to 22% of newborns have meconium-stained amniotic fluid.
1. Meconium is a viscous fluid consisting of undigested amniotic fluid and epithelial cells.
2. Meconium is present in the colon late in gestation.
3. Meconium staining of the amniotic fluid can be a sign of fetal distress and hypoxemia.
4. Fetal responses to intrauterine hypoxemia
a. Anal sphincter relaxes, and peristalsis increases.
b. Meconium passes into amniotic fluid.
c. Fetus makes gasping respiratory efforts, drawing meconium into the pharynx.
5. During the newborn’s initial breaths, meconium present in the pharynx is aspirated below the vocal cords.
1. The effects of meconium aspiration on the lower airways:
a. Creates an airway obstruction
(1) Meconium acts as a ball valve in the airways, allowing inspiration but obstructing effective expiration.
(2) The results are air trapping, hypoventilation, and atelectasis.
b. Begins an inflammatory response in the lungs known as chemical pneumonitis
2. During the first few hours after aspiration, hypercapnia, hypoxemia, and metabolic acidosis develop.
3. As pulmonary vascular resistance increases, the infant often develops PPHN.
4. If mechanical ventilation is required, recovery may be complicated by barotrauma and pneumothorax.
1. Bilateral diffuse, coarse, patchy infiltrates
1. Meconium staining of the amniotic fluid.
2. Sign and symptoms of respiratory distress
3. Arterial blood gases show hypoxemia, hypercapnia, and respiratory and lactic acidosis.
4. Breath sounds are coarse with rhonchi and rales.
6. In severe cases the chest is hyperexpanded from air trapping.
1. If meconium-stained amniotic fluid is present, the mouth, nose, nasopharynx, and oropharynx are always suctioned when the newborn’s head presents during birth, before the first breath is taken.
2. If meconium is present in the oropharynx, the vocal cords are viewed under direct vision, and the airway is suctioned above the cords.
3. If meconium is suctioned above the vocal cords, the trachea is intubated with a meconium aspirator, and the airway below the cords is suctioned.
4. The airway must be cleared of meconium by suction before any positive pressure breaths are given.
5. Supplemental blow-by oxygen is usually necessary.
6. CPAP is often used to improve oxygenation.
7. Mechanical ventilation is initiated if the infant fails to respond to oxygen with CPAP and develops worsening hypoxemia, hypercapnia, and acidemia.
8. HFOV may be used as primary therapy or when ventilation with CMV is unsuccessful.
9. Term infants often require sedation and sometimes muscle relaxers to maintain synchrony with the ventilator.
10. Inhaled nitric oxide can be used if PPHN is present.
11. Secretion clearance techniques, such as frequent endotracheal suctioning and chest physical therapy, are often useful.
12. ECMO may be required to manage severe MAS (Table 27-2).
TABLE 27-2
ECMO/ECLS Use and Survival for Neonates
| Diagnosis | Number of Cases* | Percentage Survival |
| MAS | 6263 | 94 |
| CDH | 4101 | 53 |
| Sepsis | 2307 | 75 |
| PPHN | 2649 | 79 |
| RDS | 1357 | 84 |
| Others | 1411 | 65 |
*Includes all cases reported to the registry.
From ELSO registry data. January 2003.
1. Stiff lungs with low compliance (e.g., RDS)
2. Hyperinflated lungs (e.g., MAS)
3. Hypoplastic lungs (e.g., congenital diaphragmatic hernia)
a. Asymptomatic air leaks occur in 2% to 10% of term infants.
b. Caused by high pressures (40 to 80 cm H2O) that the infant generates to take its first breath.
c. Usually minor and resolve without treatment in 24 to 48 hours.
6. Surfactant replacement therapy has significantly reduced the incidence of pneumothorax.
1. Air trapping in obstructed airways.
2. Regional overdistention and rupture of alveoli can occur when more compliant alveoli are adjacent to atelectatic alveoli.
3. Ruptured alveoli can result in pulmonary interstitial emphysema (PIE).
1. Chest radiography is the gold standard.
2. Transillumination is useful for critically ill infants if there is a delay in obtaining the chest radiograph.
a. Transillumination is the passage of light through body tissues for the purpose of examining a structure.
b. A fiberoptic transilluminator is placed against both sides of the infant’s chest superior and inferior to the nipple.
c. If the lung is inflated the tissue will absorb most of the light.
d. A greater appearance of light through the chest suggests an abnormal amount of air in the thoracic cavity.
e. In full-term infants, pneumothorax may not be visible under transillumination.
1. Prompt decompression by chest tube placement
a. The tube is inserted at the second to third intercostal space lateral to the midclavicular line.
b. The tube is connected to an underwater seal drainage unit with −20 cm H2O of suction.
2. Chest tube placement usually results in immediate improvement.
3. Needle aspiration is sometimes performed in an emergency.
A Incidence of pneumonia during birth or after delivery
1. Bacteria usually cause the infection.
a. Group B Streptococcus is the most common pathogen.
b. Gram-negative organisms (e.g., Escherichia coli, Klebsiella, Pseudomonas, Serratia marcescens)
c. Less frequently caused by Staphylococcus aureus or Staphylococcus epidermis
2. Candida can cause fungal pneumonia.
1. The neonate can acquire infection via three routes.
a. Transplacental, when pathogens are transferred across the placenta in utero.
b. Perinatal, by aspiration of contaminated amniotic fluid during labor and delivery.
c. Postnatal, from the mother, caregivers, or environment during the hospital stay.
2. Rupture of placental membranes ≥12 hours before birth increases the chance that infectious agents will spread to the amniotic fluid and the fetus.
3. Bacterial pneumonia causes inflamed, fluid-filled alveoli more often than viral pneumonia, and in severe cases necrosis of lung tissue develops.
4. Sepsis can rapidly develop from gram-negative pulmonary infections.
5. Bacterial pneumonia acquired in utero leads to stillbirth and premature delivery in many cases.
6. Pneumonia caused by viruses and mycoplasmae involve the bronchi and interstitium, resulting in loss of ciliary function and mucus stasis.
