Clinical Manifestations Common with Newborn and Early Childhood Respiratory Disorders

Respiratory disorders are the leading causes of admission to the neonatal intensive care unit (NICU). Essential to the understanding of respiratory distress of the neonate is the axiom “Oxygen is the primary nutrient of the human body.” The clinical manifestations presented by a baby in early respiratory distress include lethargy, cyanosis, increased respiratory rate, nasal flaring, expiratory grunting, intercostal retractions, substernal retraction, tachycardia, increased blood pressure, and acute alveolar hyperventilation with hypoxemia. The late, ominous manifestations include a decreased respiratory rate, gasping respirations, apnea, bradycardia, decreased blood pressure, and acute ventilatory failure with both CO₂ retention and hypoxemia.

Although many of the pathophysiologic mechanisms and clinical manifestations presented by the newborn with a respiratory disorder are identical to those seen in the older child or adult, some of the pathophysiologic mechanisms and clinical manifestations are unique to the newborn. The more important clinical manifestations associated with neonatal respiratory disorders and the primary pathophysiologic mechanisms responsible for these clinical manifestations are outlined in this chapter.

Clinical Manifestations Associated with More Negative Intrapleural Pressures during Inspiration

The thorax of the newborn infant is quite flexible—that is, the compliance of the infant’s thorax is high. This flexibility is a result of the large amount of cartilage found in the skeletal structure of newborns. Because of the structural alterations associated with many newborn respiratory disorders, however, the compliance of the infant’s lungs is low. In an effort to offset the decreased lung compliance, the infant must generate more negative intrapleural pressures during inspiration. This condition causes the following (see Figure 31-1):

• The soft tissues between the ribs retract during inspiration.

• The substernal area retracts and the abdominal area protrudes in a seesaw fashion during inspiration. The substernal retraction is caused by high negative intrapleural pressure, and the abdominal distention is caused by the contraction (depression) of the diaphragm during inspiration.

• The blood vessels in the more dependent portions of the thoracic and abdominal areas dilate and pool blood, causing these areas to appear cyanotic.

Flaring Nostrils (or Nasal Flaring)

Flaring nostrils (or nasal flaring) frequently are observed in infants in respiratory distress. This clinical manifestation probably is a facial reflex to facilitate the movement of gas into the tracheobronchial tree. The dilator naris, which originates from the maxilla and inserts into the ala of the nose, is the muscle responsible for this movement. When activated, the dilator naris pulls the alae laterally and widens the nasal aperture, providing a larger orifice for gas to enter during inspiration (Figure 31-2).

Expiratory Grunting

An audible expiratory grunt frequently is heard in infants with respiratory problems. Depending on the listener’s auditory perception, the expiratory grunt may sound like an expiratory cry. It often is first detected on auscultation. The expiratory grunt is a natural physiologic mechanism that generates high positive pressures in the alveoli, which, at least in part, counteracts the hypoventilation associated with the disorder (e.g., infant respiratory distress syndrome [RDS]). In short, as the gas pressure in the alveoli increases, the infant’s Pao₂ increases. During exhalation the infant’s epiglottis covers the glottis, which causes the intrapulmonary air pressure to increase. When the epiglottis abruptly opens, gas rushes past the infant’s vocal cords and produces an expiratory grunt or cry.

Apnea of Prematurity

Periodic breathing frequently is seen in the newborn and is described as cycles of short pauses in respiration followed by an increased breathing rate. What is called apnea of prematurity also is a common form of apnea in the newborn. It is defined as a cessation of breathing effort that is longer than 20 seconds, or any respiratory pause that is long enough to cause bradycardia, cyanosis, or both to appear in a baby of less than 37 weeks’ gestation. About 75% of premature babies weighing less than 1250 g experience severe apnea. More than 25% of infants weighing more than 1500 g manifest severe apnea. In general, the younger the infant, the greater the number of apneic episodes that may occur.

Premature infants are believed to be susceptible to apneic episodes because of immature functioning of the chemoreceptors, receptors in the airways, and central nervous system. Rapid eye movement (REM) sleep also is thought to play an important role in causing sleep apnea. Box 31-1 lists factors that trigger apneic episodes.

Box 31-1   Factors That Trigger Apnea in the Premature Infant

Control of Ventilation

• REM sleep

• Decreased hypoxic and hypercapnic response

• Ondine’s curse (idiopathic alveolar hypoventilation)

Reflex Stimulation

• Suctioning of the nasopharynx and trachea

• Laryngeal stimulation

• Bowel movements (vagal response)

• Hiccups

Environmental Conditions

• Ambient temperature changes

Neurologic Disorders

• Seizures

• Intracranial hemorrhage

• Meningitis

Drug Depression

• Sedatives

• Analgesics

• Prostaglandins

Respiratory Diseases

• Respiratory distress syndrome (RDS)

• Pneumonia

• Transient tachypnea of the newborn (TTN)

• Meconium aspiration syndrome (MAS)

• Bronchopulmonary dysplasia (BPD)

• Diaphragmatic hernia

Cardiac Disorders

• Patent ductus arteriosus

• Congestive heart failure

• Right-to-left intracardiac shunting

Systemic Processes

• Hypothermia

• Hypoglycemia

• Hyponatremia

• Hypocalcemia

• Sepsis (group B Streptococcus)

Body Position

• Head flexion

Anatomic Abnormalities

• Micrognathia

• Choanal atresia

• Macroglossia

Persistent Pulmonary Hypertension of the Newborn

Persistent pulmonary hypertension of the newborn (PPHN) is commonly seen in infants with an underlying respiratory disorder such as pneumonia, meconium aspiration syndrome (MAS), or RDS. Box 31-2 lists disorders commonly associated with PPHN.

Box 31-2   Factors Associated with Persistent Pulmonary Hypertension of the Newborn (PPHN)

Maternal Factors

• Diabetes

• Cesarean section

• Hypoxia

Cardiovascular Factors

• Systemic hypotension

• Congenital heart disease

• Shock

Hematologic Factors

• Increased hematocrit

• Septicemia

• Maternal-fetal blood loss

• Abruptio placentae

• Placenta previa

• Acute blood loss

Respiratory Diseases

• Meconium aspiration syndrome (MAS)

• Respiratory distress syndrome (RDS)

• Pneumonia

Fetal Factors

• Intrauterine stress

• Hypoxia

• Decreased pH

• Placental vascular abnormalities

Other Factors

• Central nervous system disorders

• Hypoglycemia

• Hypocalcemia

• Neuromuscular disorders

PPHN is caused in part by reflex pulmonary vasoconstriction, which can be activated by myriad stimuli, including alveolar hypoxia, hypercapnia, and decreased pH. As a result of the high pulmonary vascular resistance (PVR), right-to-left shunting develops—that is, mixed venous blood bypasses the infant’s lungs via the ductus arteriosus and foramen ovale (see fetal circulation pathways, Figure 31-3).

After birth, approximately 80% of the PVR normally decreases within the first 24 hours in response to (1) increased Pao₂ and pH; (2) lung expansion; and (3) release of vasoactive substances, including prostaglandins, bradykinin, and endothelium-derived relaxing factor (ERF). In infants with PPHN, however, the PVR stays high because of pulmonary vascular hyperreactivity to irritating stimuli. Clinically, PPHN usually appears within the first 12 hours of life with cyanosis, tachypnea, intercostal retractions, nasal flaring, and grunting. Arterial blood gases typically show what is termed shunt physiology: a low Pao₂ that is refractory to oxygen therapy. Cardiomegaly may develop as a result of the increased right ventricular afterload caused by the increased PVR.

Arterial Blood Gases

Acute alveolar hyperventilation with hypoxemia and acute ventilatory failure with hypoxemia commonly are seen in newborn babies with pulmonary disorders. This is especially true for newborn infants who have MAS, transient tachypnea of the newborn (TTN), RDS, pulmonary air leak syndromes, respiratory syncytial virus infections, and/or diaphragmatic hernia.

There are three major mechanisms responsible for the decreased Pao₂ observed in the disorders of the newborn just mentioned: (1) pulmonary shunting and venous admixture, (2) PPHN, and (3) infant fatigue. During the early or mild stages of the disorder, the infant commonly hyperventilates, causing the Paco₂ to decrease and the pH to increase. During the advanced or late stages of the disorder, the infant often goes into acute ventilatory failure. When this occurs, there is a progressive increase in the Paco₂, a secondary increase in the , and a decrease in the pH. The decreased pH also may result from the decreased Pao₂ and the metabolic acidosis that results from anaerobic metabolism and lactic acid accumulation. If this is the case, the calculated reading and pH will be lower than expected for a particular Paco₂ level.

Assessment of the Newborn

As already discussed in Chapter 10, good assessment skills include (1) the systematic collection of clinical data, (2) the evaluation of the data, and (3) the formulation of an appropriate treatment plan. As with the older child or adult, the newborn with respiratory disease must be evaluated frequently. To enhance this process, Figure 31-4 illustrates objective data, assessments, and treatment plans commonly associated with newborn respiratory disorders. Another common assessment tool for the newborn is the Apgar score.

Apgar Score

The Apgar score is a rating system for the rapid identification of infants requiring immediate intervention or transfer to an NICU. The Apgar evaluation is performed 1 minute after birth and again 5 minutes later. It is based on a rating of five factors that reflect the infant’s ability to adjust to extrauterine life. As shown in Figure 31-5, the infant’s heart rate, respiratory effort, muscle tone, reflex irritability, and color are scored from a low value of 0 to a normal value of 2. The five scores are combined and the totals at 1 minute and 5 minutes are recorded. For example, Apgar 8/10 is a score of 8 at 1 minute and 10 at 5 minutes.

A score of 0 to 3 represents severe distress, a score of 4 to 6 indicates moderate distress, and a score of 7 to 10 represents an absence of difficulty in adjusting to extrauterine life. The 5-minute score is normally higher than the 1-minute score. A low 1-minute score requires immediate intervention, including the administration of oxygen and oral and nasal suctioning. A baby with a low score that remains low after 5 minutes requires expert care, which may include transfer to the NICU, continuous positive airway pressure (CPAP), umbilical catheterization, and mechanical ventilation.

In the newborn who is lethargic, apneic, pale, blue, and bradycardic at birth, assessments to verify that resuscitation efforts are being done correctly and effectively typically follow this order: First, the heart rate returns to normal. This is followed by spontaneous respiratory movements and improved color. The last assessment to be made is that of the baby’s tone and reflex irritability.