When is pulmonary function testing (PFT) indicated in children, and which specific tests should be used based on age and developmental level?

Pulmonary Function Testing in Pediatrics

Direct Answer

Pulmonary function testing in children should be selected based on age and developmental capability: tidal breathing techniques (forced oscillation, interrupter resistance, multiple-breath washout) for ages 3-5 years, and standard spirometry for ages 6-7 years and older. 1

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Age-Specific Test Selection Algorithm

Ages 3-5 Years (Preschool): Tidal Breathing Techniques Only

Prioritize these tests that require minimal cooperation: 1

• Forced oscillation technique (FOT) - measures respiratory system resistance during normal breathing 2, 1
• Interrupter resistance (Rint) - easily implemented, suitable for field studies and epidemiological work 2
• Specific airway resistance (sRaw) - measured in plethysmograph 2, 1
• Functional residual capacity (FRC) - using gas dilution techniques 2, 1
• Multiple-breath washout (MBW) - detects peripheral lung disease, particularly useful for cystic fibrosis 2, 1

Critical sequencing: If attempting forced expiratory maneuvers in this age group, perform them AFTER tidal breathing measurements, because it is easier to "wind up" young children than to calm them down afterward. 2, 1

Ages 6-7 Years and Older: Standard Spirometry

Children at this age can reliably perform: 1

• Standard spirometry (FVC, FEV₁, FEV₁/FVC ratio) - now feasible as children can follow instructions and maintain effort throughout the maneuver 1, 3
• Peak expiratory flow measurements - accurate from age 6-7 years when children can execute forceful "blast" exhalation 3
• Comprehensive PFT battery - including lung volumes (TLC, RV, FRC) and diffusing capacity (DLCO) when clinically indicated 4

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Clinical Indications by Disease Category

Asthma and Wheezing Disorders

Use objective PFT to confirm diagnosis and prevent overdiagnosis that occurs in 33% of patients diagnosed without PFTs. 4

• Ages 3-5: FOT or Rint for baseline assessment and bronchodilator response 2, 1
• Ages 6+: Spirometry with bronchodilator response testing is the gold standard 4
• Avoid peak flow variability as primary diagnostic test in children 5-16 years (only consider when spirometry unavailable) 3

Cystic Fibrosis

Multiple-breath washout is particularly valuable as CF starts in lung periphery and requires tests capable of detecting peripheral lung changes. 2, 1

• Begin monitoring from preschool age using tidal breathing techniques 2
• Progress to comprehensive PFT including spirometry and DLCO as child matures 4

Chronic Neonatal Lung Disease

Longitudinal assessments from early childhood are essential to understand disease evolution and guide management. 2

• Start with tidal breathing techniques at age 3 1
• Serial monitoring every 3-6 months initially, then 6-12 months once stable 4

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Critical Technical Requirements

Equipment Specifications

Pediatric-specific adaptations are mandatory - adult equipment produces inaccurate results in young children. 1

• Minimize total apparatus dead space 2
• Use equipment specifically designed or validated for pediatric use 2, 1
• Operators must have access to raw data to allow age-appropriate algorithm investigation 1

Personnel Requirements

Trained staff experienced in pediatric testing is non-negotiable to engage preschool children who have short attention spans. 2, 1

• Create child-friendly environment with bright, pleasant atmosphere and age-appropriate materials 1, 3
• Staff must provide encouragement and detailed but simple instructions 3
• Testing in adult laboratories without pediatric accommodations significantly reduces success rates 1, 3

Quality Control

Express results as z-scores (multiples of standard deviation), NOT percentages of predicted values. 2, 1

• Never extrapolate reference data from older subjects to children under 6 years 1
• Validate reference data by testing at least 30-50 healthy preschool children using identical techniques 2, 1

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Physiological Developmental Considerations

Preschool-Specific Limitations

Young children lack chest wall muscle strength to maintain flow limitation to lung volumes as low as 90% of exhaled vital capacity. 2, 1

• FEV₁/FVC ratio in healthy 5-6 year olds is 90-95% (even higher in younger children), substantially different from adults 2, 1
• Use FEV₀.₅ or FEV₀.₇₅ instead of FEV₁ as more appropriate outcome measures in preschoolers 2, 1
• Children can blow either "hard" or "long" but frequently cannot do both simultaneously 2, 1

Bronchial Tone Considerations

Avoid deep inhalation maneuvers in children with asthma during initial testing as deep inhalation may change bronchial tone. 2, 1

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Common Pitfalls and How to Avoid Them

Timing Issues

Do not test during or within 3 weeks of respiratory infection - produces invalid baseline measurements. 1

• Ensure oxygen saturation above 95% before testing 1
• Have bronchodilator and resuscitation equipment immediately available 1

Sedation Misconception

Never use sedation for preschool children - they are too old for infant sedation approaches, and testing under anesthesia is neither ethically acceptable nor physiologically relevant. 2, 1

Quality Standards

Do not apply adult quality-control requirements to preschool children. 2

• Only 58% of preschool children can produce acceptable forced expiration lasting 1 second, though 73% can manage FEV₀.₅ 2
• Alternative criteria are needed for this age group 2

Interpretation Errors

Variability measurements from healthy children cannot be extrapolated to those with disease. 2

• Within-subject variability assessments need at least 30 subjects of similar age and diagnostic category 2
• Reproducibility must be established at intervals relevant to intended test uses 2

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Test Selection by Clinical Question

For Epidemiological Studies

Interrupter technique (Rint) is most suitable - easily implemented and appropriate for field measurements. 2

For Early Peripheral Lung Disease Detection

Gas washout techniques and forced oscillation are preferred - capable of reflecting parenchymal changes that start in lung periphery (e.g., cystic fibrosis). 2

For Monitoring Treatment Response

Choose test based on age: 2, 1

• Ages 3-5: FOT or Rint with bronchodilator response
• Ages 6+: Standard spirometry with bronchodilator response