43 Pediatric Pulmonary Diseases 1

Question 1

Airway diseases

Answer 1

• Among the most common reasons for doctor visits during the winter months
• Asthma and bronchiolitis
• The single most common cause of hospitalization among children
• The major reason for loss of school days
• Comprise the vast majority of the kinds of problems seen by the pediatric pulmonologist

Question 2

History

• Always take a birth history
• Did the problem arise within the 1st 6 months of life?
• What triggers the cough or wheeze?

Answer 2

• Always take a birth history
  
  • ​Gravity, parity, prematurity, intubation, and meconium are all important to ask about.
• Did the problem arise within the 1st 6 months of life?
  
  • Congenital airway malformations are fairly common and always become symptomatic within the first 6 months of life
  • This is not to say that all wheezing that occurs in the first 6 months is due to airway malformations, but persistent wheezing within the first 6 months should raise your index of suspicion for congenital airway malformations
• What triggers the cough or wheeze?
  
  • “Triggers” are extremely important
  • Unlike children over age 4 to 5 and adults, allergy is only a rare cause of or trigger for asthma in infants and toddlers
  • The single most common trigger for pediatric wheezing is viral respiratory tract infection (VRI)
    
    • This is one reason there is such a seasonal predisposition for asthma hospitalizations in this country
  • When the wheezing is not associated with a VRI you should consider other triggers, like gastro-esophageal reflux (more on this later) or, in the older child (>5), allergy to house dust mite

Question 3

History

• Response or lack of response to therapy
• What is the nature of the cough?
• Does the cough awaken the infant from sleep?

Answer 3

• Response or lack of response to therapy
  
  • Just as a good response to a bronchodilator is useful in establishing a diagnosis of asthma, a lack of response to a bronchodilator should make you question that diagnosis
• What is the nature of the cough?
  
  • Is it wet or dry?
    
    • Unlike adult asthmatics, most infants and young children with asthma have a dry, hacking cough
    • A wet sounding cough implies that there is purulence in the airways and is worrisome for bacterial disease
  • Just the same, viral respiratory infections can on occasion induce production of a great deal of mucus and secretions, so a wet-sounding cough is not specific for bacterial lower airway disease
  • A chronic wet cough in a child is typical of cystic fibrosis and can be seen in another disease of impaired mucociliary clearance: primary ciliary dyskinesia (PCD)
    
    • Kartagener’s syndrome is one form of PCD: it is the original description with complete situs inversus, sinusitis, and bronchiectasis
  • Children of smokers may get a bronchitis from passive smoking and get a wet cough from this
    
    • Cigarette smoke poisons the cilia and can lead functionally to a pattern similar to that of PCD with recurrent OM, sinusitis, and bronchitis
• Does the cough awaken the infant from sleep?
  
  • A cough that awakens a child from sleep is not specific to one diagnosis or another but is a RED FLAG
  • The cough that awakens a child from a sound sleep is generally reflective of significant pathology and requires medical attention
  • Most simple colds, by comparison, don’t awaken one from sleep

Question 4

History

• Family medical history
• Environmental history

Answer 4

• Family medical history
  
  • Ask about the “atopic triad:” asthma, eczema, allergies
  • Most new CF diagnoses have negative FMH (typical of autosomal recessive diseases)
  • When you hear “emphysema, CAD, CVA, lung Ca, think cigarette
• Environmental history
  
  • Cigarette smoke exposure is the most common environmental evil
    
    • Ask about exposure in the home and in the car and remember that “a home with a smoking area is like a swimming pool with a peeing area”
  • Also ask about animal danders, house dust mite, occupational dusts, wood burning stoves, cockroaches, etc

Question 5

Review of systems

• Gastro-esophageal reflux (GER)
• Recurrent otitis media (OM), sinusitis, and pneumonia/bronchitis/bronchiolitis
• Stool history

Answer 5

• Gastro-esophageal reflux (GER)
  
  • Symptoms of GERD include arching/pain behaviors – especially at night – spitting, hoarseness/stridor, recurrent croup, and occasionally apnea
  • The presence of dried vomitus in the crib in the morning is NEVER normal and should be considered a sign of pathological reflux
• Recurrent otitis media (OM), sinusitis, and pneumonia/bronchitis/bronchiolitis
  
  • Suggests humoral immunodeficiency
  • Most commonly this is an IgA and/or IgG subclass deficiency
  • Primiary ciliary dyskinesia (PCD) or Kartagener’s syndrome is associated with recurrent OM, sinusitis, and bronchitis/bronchiectasis
    
    • It is much less common, 1:20,000
  • Cystic fibrosis is associated with recurrent bronchitis and with sinusitis but NOT with otitis media
    
    • Its incidence is 1:3,000, so it’s fairly common
• Stool history
  
  • ​Oil or grease in the stool (steatorrhea) is suggestive of CF
    
    • Half of newborns with CF do NOT malabsorb
  • Failure to thrive is a red flag and should suggest a diagnosis of CF
    
    • It is neither sensitive nor specific for CF

Question 6

Physiology of pediatric airway disease

• The primary difference between the physiology of the infant chest and the adult chest
• 2 kinds of airway diseases

Answer 6

• The primary difference between the physiology of the infant chest and the adult chest
  
  • For the first six months of life the infant’s chest wall is excessively compliant
• 2 kinds of airway diseases
  
  • Those of the LARGE airways
    
    • Uncomplicated LARGE airway obstruction does NOT lead to hypoxemia
    • Ex. the infant born with a floppy trachea or bronchus (tracheomalacia or bronchomalacia) who is otherwise normal
      
      • That baby is the typical “happy wheezer” – he has chronic noisy breathing but NEVER has respiratory distress, and is always normoxemic (has normal oxygen levels and saturations)
  • Those of the SMALL airways

Question 7

Physiology of pediatric airway disease

• Hypoxemia in infants is almost always due to…
• Resistance and compliance (straw and balloon)

Answer 7

• Hypoxemia in infants is almost always due to…
  
  • Ventilation-perfusion (V/Q) mismatching due to SMALL airway disease
  • In this situation, the alveolus is well perfused but poorly ventilated
  • The low oxygen tension in the alveolus depresses the oxygen tension in the blood returning to the heart, and leads to a low saturation, detectable with a simple non-invasive test, the pulse oximeter
• Resistance and compliance (straw and balloon)
  
  • Imagine a straw tied to the mouth of an inflated balloon
  • The balloon has compliance, and the straw has resistance
  • The properties of both the balloon and the straw determine the emptying time of that unit
  • A thin straw will slow down deflation, and a stretched-out, baggy balloon will empty more slowly even through a normal straw

Question 8

Physiology of pediatric airway disease:
Resistance

• General
• Units
• Poiseuille’s equation
• Essential equation

Answer 8

• The difficulty inherent in pushing air through a tube
  
  • Smaller and longer tubes lead to greater resistance
• Defined in units of pressure/flow
• In areas of laminar flow, this is defined by Poiseuille’s equation:
  
  • R = 8nL/πr⁴
  • “n” is the viscosity constant of air
  • “L” is the length of the airway
  • “r” is the radius of the airway
• Since we cannot change n without Heliox, we don’t change L except with growth, and π is a constant, this equation is essentially…
  
  • R α 1/r⁴
  • Resistance is proportional to the inverse of the radius to the 4th power
  • Small changes in radius lead to large changes in resistance
  • Ex. If you decrease the radius by 2, resistance goes up by 16

Question 9

Physiology of pediatric airway disease:
Compliance

• Refers to…
• Units
• Think about blowing up that balloon
• Primary diseases characterized by compliance changes
  
  • Infants
  • Adults
• Increased compliance seen in emphysema might be seen in…

Answer 9

• Refers to the alveolus and lung parenchyma
  
  • Should be thought of as “stretchability”
• Defined in units of volume/pressure
• Think about blowing up that balloon
  
  • A non-compliant lung unit is STIFF
    
    • Not much volume resulting from a lot of pressure
  • An overly complaint lung unit (like in emphysema) is baggy
    
    • A lot of volume from not much pressure
• Primary diseases characterized by compliance changes
  
  • Rare in infants
    
    • Occasionally see decreased compliance in infants and children in the setting of interstitial lung disease
  • More typically seen in the adult population
    
    • (1) non-compliant, stiff lungs are typified by idiopathic pulmonary fibrosis
    • (2) overly compliant lungs are typified by emphysema
• Increased compliance seen in emphysema might be seen in…
  
  • Bronchopulmonary dysplasia (BPD)
  • In a focal manner in congenital lobar emphysema (CLE)

Question 10

Physiology of pediatric airway disease:
Time constant

• Equation
• Units
• Emptying is a logarithmic function
• Ex. an infant with RSV bronchiolitis
• ​Air trapping

Answer 10

• The mathematical product of resistance (R) and compliance (C)
  
  • τ (tau) = R • C
• The unit of the time constant is seconds
  
  • τ (tau) = (pressure/flow) x (volume/pressure) = volume / (volume/time) = liters / (liters/sec) = sec
• Emptying is a logarithmic function
  
  • Think of τ as a kind of half life, but one based on natural log, so it’s more like a third life (e is 2.7)
    
    • It takes roughly 3 times the time constant for that lung unit to empty
  • Small airway diseases in infants lead to longer time constants and thus longer emptying times for the lung units
• Ex. an infant with RSV bronchiolitis
  
  • Those little airways are narrowed from the edema and inflammation induced by the respiratory syncitial virus (decreased r for radius)
    
    • This makes for increased resistance (R) and consequently a longer time constant
  • Infants with respiratory problems NEVER breathe more slowly, regardless of whether it might be a better breathing strategy
    
    • This infant will breath more rapidly (tachypnea)
  • The more rapid pattern will mean that the lung units will not have time to fully deflate before they start reinflating
  • This leads to stacking of breaths, and air trapping
• ​Air trapping
  
  • The affected lung units are not being ventilated with fresh air, so the alveolar PO2 drops
  • This leads to hypoxemia
  • The air trapping over-expands the lungs, pushing the diaphragm away from the chest wall, and leads to subcostal retractions, as the contracting diaphragm pulls inward on the compliant chest wall

Question 11

Physical examination:
Inspection

• (1)
• Respiratory rate
• The isolated presence of subcostal retractions (RTX)
• Cyanosis

Answer 11

• Look at the breathing pattern
• Measure the respiratory rate
  
  • Resting respiratory rate changes with age
  • Normal for a 2 week old is up to 50, for a 6 month old is up to 44, for a 1 year old is up to 32
• The isolated presence of subcostal retractions (RTX)
  
  • Almost always is a sign of the hyperinflation or air trapping that accompanies small airways disease (exception: severe UAO)
  • Intercostal and suprasternal RTX indicates a breathing pattern in which excessive negative pleural pressure is used, such as a severe pneumonia, RDS, or an interstitial lung disease
• Cyanosis is hard to detect
  
  • Don’t trust your eyes when it comes to oxygenation

Question 12

Physical examination:
Palpation

• Hand placement
• Palpable vibrations
• Unilateral vibrations
• Indrawing

Answer 12

• Rest your hands on the chest
• Palpable vibrations usually indicate partial obstruction of large airways
• Unilateral vibrations are typical of bronchomalacia, foreign body, or a mucus plug
• Feel the lower end of the ribcage for indrawing, which indicates loss of the zone of apposition
  
  • This is the result of a diaphragm that is out of position pulling inward on the overly compliantchest wall of the infant
  • It suggests a diagnosis of small airways disease

Question 13

Physical examination:
Percussion

• Determine the location of…
• Percussion note
• You might find…

Answer 13

• Determine the location of the domes of the diaphragms relative to tips of the scapulae
• The tone of what you hear is called the percussion note: hyperresonant vs. dull
• You might find an elevated hemidiaphragm with unilateral diaphragmatic paralysis or eventration
  
  • In the latter diagnosis, the diaphragm is replaced by a thin, non-contractile sheet of fibrous tissue

Question 14

Physical examination:
Auscultation

• Normal breath sounds vary with…
• If you listen over the large airways, inspiratory and expiratory…
• As you listen further out, the sounds become…
• Over the periphery, the breath sounds…
• The sounds are much louder on…
• ALL breath sounds…
• ​Most of what we hear with a stethoscope originates in…
• As you go more peripherally, the flow becomes…
• Infants have…

Answer 14

• Normal breath sounds vary with…
  
  • Location and timing in the respiratory cycle
• If you listen over the large airways, inspiratory and expiratory…
  
  • Times are similar
  • Sounds are tubular (bronchial)
• As you listen further out, the sounds become…
  
  • Bronchovesicular (mid 1/3) and then vesicular
• Over the periphery, the breath sounds…
  
  • Are called vesicular
  • Have a longer expiratory phase
• The sounds are much louder on…
  
  • Inspiration (sound is moving towards you) than on expiration (sound is moving away from you)
• ALL breath sounds…
  
  • Emanate from the airway
• ​Most of what we hear with a stethoscope originates in…
  
  • The central airways, where there is the most turbulence of flow
• As you go more peripherally, the flow becomes…
  
  • More laminar and is quieter
  • The air makes NO sound as it fills the alveolus, contrary to popular belief
• Infants have…
  
  • Fewer generations of airways
  • Coarser breath sounds

Question 15

Physical examination:
Auscultation

• The 2 main abnormal breath sounds
• The way to differentiate between them
• Either can be…

Answer 15

• The 2 main abnormal breath sounds
  
  • Crackle vs wheeze
• The way to differentiate between them
  
  • Crackle
    
    • A discontinuous sound
    • More prominent on inspiration
  • Wheeze
    
    • A continuous sound
    • More prominent on expiration
• Either can be…
  
  • Inspiratory or expiratory

Question 16

Physical examination:
Auscultation

• Monophonic
• Polyphonic

Answer 16

• Monophonic
  
  • No matter where you listen, it sounds the same; a single sound
  • Typical of tracheo- and bronchomalacia, vascular ring, and bronchial foreign body
  • All of these are characterized by a single location of partial obstruction in the large airway
• Polyphonic
  
  • Many different pitches
  • Characterize a diffuse airway lesion such as asthma or bronchiolitis
  • You hear vibrations coming from various-sized, partially obstructed airways

Question 17

Physical examination:
Auscultation

• Crackle
• Wheezes

Answer 17

• Crackle (or rale)
  
  • A popping sound produced by a fluid meniscus in an airway
  • Fine or coarse
    
    • Fine crackles emanate from smaller airways
    • Coarse crackles emanate from larger airways
  • Also found in interstitial lung disease (sound like Velcro)
• Wheezes
  
  • ​Result from the vibration of walls of narrowed airways as air flows through them
  • Monophonic or polyphonic