Board Simulation: Airway and Pulmonary Disorders

Samiya Razvi

QUESTIONS

1. An infant is born at 32 weeks gestation by cesarean section to a 19-year-old primigravida mother who had no antenatal care and whose Group B Streptococcal (GBS) status is unknown. He weighs 1100 g at birth; Apgar scores are 6 and 9 at 1 and 5 minutes. He is placed on continuous positive airway pressure (CPAP) with supplemental oxygen (FiO₂ = 0.5).

At 12 hours of age, he is noted to have increased retractions, grunting, and mild cyanosis. His heart rate is 170/minute, pulses are well felt, respiratory rate is 54/minute, and blood pressure is 70/40. Breath sounds are diminished on auscultation but heard equally over both lung fields. No murmur is heard on cardiac examination.

A portable chest radiograph (CXR) shows ground glass opacities and diffuse haziness of both lung fields. The most likely diagnosis is:

a) Transient tachypnea of the newborn

b) Meconium aspiration syndrome

c) Congenital pneumonia with neonatal sepsis

d) Respiratory distress syndrome with surfactant deficiency

e) Congenital diaphragmatic hernia with cardiorespiratory compromise

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Answer

The answer is d. The primary cause of respiratory distress in the newborn is inadequate surfactant, which serves to decrease alveolar surface tension. Inadequate surfactant results in diffuse alveolar atelectasis, decreased aeration, reduced lung compliance, edema, and cell injury. Clinically this is manifested as tachypnea, increased work of breathing with retractions, grunting, and cyanosis because of hypoxemia. Radiologically, the classic appearance is of low lung volumes, diffuse reticulogranular patterns, and air bronchograms on CXR. Management is aimed to prevent hypoxia and acidosis and includes surfactant replacement, optimizing fluid balance, reducing metabolic demands, and limiting lung injury because of barotrauma and oxygen while providing ventilatory support.

Transient tachypnea of the newborn is a self-limited disorder seen more often in near term or term infants, particularly those born by cesarean section. It represents transient pulmonary edema as a result of delayed absorption of pulmonary lung fluid by the pulmonary lymphatics. Infants are tachypneic with retractions, grunting within a few hours of delivery, and have a mild to moderate oxygen requirement. Symptoms typically last for 12 to 24 hours and rarely persist longer than 72 hours in severe cases.

Meconium aspiration syndrome (MAS) occurs because of acute or chronic hypoxia of the fetus with passage of meconium in utero. Gasping or initial breathing efforts of the fetus or newborn infant can result in aspiration of amniotic fluid contaminated by meconium. Meconium obstructs the airways and interferes with gas exchange resulting in severe respiratory distress. MAS occurs in about 8% to 15% of live births, rarely occurs prior to 37 weeks gestation but may occur in more than one third of post-term pregnancies. Prevention is by clearing the nose and oropharynx before the infant’s chest is delivered. Next, the trachea should be intubated under direct vision before inspiratory efforts begin and meconium suctioned to clear the trachea as possible.

2. A 6-month-old term infant born without complications is seen at a routine visit for immunization. She is alert, interactive, pink, and well appearing. Her weight is at the 50th and length at the 25th percentile for age. She has audible inspiratory stridor without retractions or distress. Her lungs are clear on auscultation.

She is feeding well with occasional spit ups and is gaining weight. Her mother has noted this noisy breathing, which she calls “wheezing” since 2 weeks of age. The “wheezing” was louder a week ago when she had a cold and upper respiratory symptoms for a few days. There is family history of asthma in both parents and two older siblings. The investigation you would consider at this point is:

a) CXR to evaluate for hyperinflation, asthma

b) Upper GI study to screen for structural anomalies

c) Chest computed tomography (CT) scan for structural abnormalities

d) Bronchoscopy to evaluate the airways

e) No investigations now, continue to observe and monitor clinically

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Answer

The answer is b. Stridor is an audible, coarse, grating sound with a classic crowing quality, caused by turbulent air flow during respiration as a direct result of narrowing of the airway. Factors that lead to increased airflow turbulence such as agitation, crying, and exertion result in an increase in stridor. Stridor may be decreased or even absent when the patient is breathing calmly at rest, or when asleep. The timing of stridor in the respiratory cycle can broadly help localize the site of location of airflow obstruction as shown in Table 31.1. Causes of stridor in infancy include:

Laryngomalacia
Tracheomalacia
Subglottic stenosis
Airway lesions such as webs, cysts, and hemangioma
Vascular malformations such as “ring/sling” anomalies
Vocal cord paralysis
Infection: croup, epiglottitis, bacterial tracheitis
Foreign body aspiration

The key/discerning features of these causes of noisy breathing in infants and children are summarized in Table 31.2.

The word malacia denotes an abnormal “softness of the tissues.” The most common cause of stridor in infants is laryngomalacia; there is softness of the laryngeal cartilages and increased collapsibility of the larynx and supralaryngeal tissues into the glottis during inspiration leading to airway obstruction. Symptoms classically appear soon after birth, and increase in intensity as the infant grows and becomes increasingly active.

Although there are several possible causes of stridor, a careful history and physical examination help to differentiate those who need further evaluation and intervention from those who may safely be monitored clinically and observed. A barium swallow and upper gastrointestinal study is useful to screen for vascular (ring/sling) anomalies that can cause airway compromise seen as a filling defect in the barium column or indentation of the esophagus. Symptoms resolve with increasing age in the majority by
12 to 18 months of age and infants may be followed closely without intervention if feeding, growth, and development are normal. Severe cases of laryngomalacia may interfere with feeding and surgical interventions to trim the redundant supralaryngeal tissues may be indicated.

TABLE 31.1 TIMING OF STRIDOR AND ITS RELATION TO AIRWAY OBSTRUCTION

Phase of Respiration When Stridor Occurs	Location of Airway Obstruction	Features
Inspiration	Extrathoracic airway: Larynx, extrathoracic trachea	Extrathoracic airway subject to negative intrapleural pressures generated in inspiration and collapses
Expiration	Intrathoracic airway: Trachea, large bronchi	Intrathoracic airways subject to extramural positive pressures that compress airways during expiration
Biphasic: both inspiration and expiration	Suggestive of fixed airway obstruction at any site in trachea	Fixed obstruction causes constant airflow obstruction in both phases of respiration
Variable: changing	Suggestive of dynamic, changing airway obstruction	Lesions that cause varying obstruction of airway, e.g., airway polyps, hemangiomas

Asthma is associated with wheezing, an expiratory high pitched whistling sound indicative of small airways obstruction, and not stridor. Chest CT scan is not indicated here as there are no symptoms or signs of lower airway or parenchymal lung disease. Bronchoscopy is a definitive, diagnostic tool to examine the airways and airway dynamics but is invasive and requires sedation. It is not indicated at this point in an otherwise well, thriving infant with inspiratory stridor and typical presentation of laryngomalacia.

3. A healthy 10-year-old boy is active in sport and plays soccer. He has a history of wheezing with respiratory infections, especially in winter and fewer symptoms in summer. He has frequent sneezing, nasal congestion, and watering of eyes in spring and fall. He uses inhaled bronchodilators (Albuterol) with good symptom relief. His father notes that he coughs while running and playing soccer and is visibly short of breath. He coughs at night, but this does not awaken him from sleep. You decide to evaluate his symptoms with spirometry (preand postbronchodilator), which assesses:

a) Oxygenation and desaturation pre- and post-exercise

b) Diffusing capacity of the lungs for oxygen

c) Expiratory flow rates and volumes

d) Maximal minute ventilation and exercise capacity

e) Total lung capacity, vital capacity, residual volume and air trapping secondary to small airway obstruction

TABLE 31.2 KEY DISCERNING FEATURES OF COMMON CAUSES OF “NOISY BREATHING” IN INFANTS AND CHILDREN

	Timing	Feature	Bronchoscopy	Diagnosis
Laryngomalacia	Inspiratory “Crowing”	Improves with age, ↑with exertion ↑ supine, ↓ prone	Curled epiglottis (“omega”) Prolapse of arytenoids	Clinical features Natural course Bronchoscopy
Tracheomalacia	Wheezing biphasic	Prematurity, Postsurgical inflammation ↑ agitation ↑ exertion	Anteroposterior dynamic collapse of trachea	Flexible bronchoscopy Airway fluoroscopy
Subglottic stenosis	Biphasic High-pitched	History of intubation, trauma	Narrowing of subglottis	Radiograph of airway Bronchoscopy
Vascular ring or sling	Inspiratory stridor Wheeze	Indentation of esophagus on barium swallow	May have dysphagia, reflux	Upper GI study (indentation of esophagus) CT imaging
Vocal cord palsy	Dysphonia Aphonia	Trauma CNS lesions Cardiac surgery	Immobile cords Unilateral or bilateral	Direct visualization by endoscopy

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Answer

The answer is c. Asthma is characterized by expiratory airflow obstruction with wheezing, a high-pitched whistling sound in expiration, cough indicative of airway inflammation, and often exercise-induced symptoms. A careful history of symptom pattern and recurrence and treatment response to inhaled β-agonists (which cause bronchodilatation) and/or anti-inflammatory medications (corticosteroids, leukotriene inhibitors) is consistent with the clinical diagnosis of asthma. Spirometry is an objective test for asthma and measures expiratory airflow rates and volumes on a forced expiratory maneuver that requires patient cooperation. Measurements are compared with population based norms for airflow rates, forced vital capacity (FVC), and forced expiratory volume in one second (FEV1) and are expressed as a percentage of predicted measures.

Typical patterns in the configuration of the flow volume loop and airflow indices on spirometry are seen in obstructive diseases (e.g., asthma, airway malacia or narrowing) and restrictive diseases (e.g., respiratory muscle weakness in muscular dystrophy, neuromuscular disease, and thoracic cage abnormalities such as kyphoscoliosis). Classic spirometry patterns shown in Figure 31.1 are summarized in Table 31.3. Body plethysmography measures lung volumes including total lung capacity and residual volumes. The diffusing capacity of the lungs for oxygen uptake is measured utilizing carbon monoxide, an inert gas. An exercise test assesses the cardiopulmonary responses to graded exercise in the laboratory, including the anaerobic threshold and whether there is ventilation limitation in an individual’s response to the physiologic demands of exercise.

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