2.6 Pulmonary Function, Bronchoscopy & Specimen Diagnostics

2.6 Pulmonary Function, Bronchoscopy & Specimen Diagnostics

Pediatric Pulmonary Function Testing (PFT)

Pulmonary function testing objectively evaluates respiratory mechanics, airway resistance, and response to therapeutic interventions in cooperative children aged ≥ 5 to 6 years.

Spirometry Indices & Diagnostic Criteria

• Forced Vital Capacity (FVC): Total volume of gas exhaled forcefully and rapidly from maximal inspiration.
• Forced Expiratory Volume in 1 Second (FEV1): Volume exhaled during the first second of forced exhalation. Reflects large and medium airway caliber.
• FEV1 / FVC Ratio: Fraction of total capacity exhaled in the first second.
  • Reference interpretation: Compare FEV1, FVC, and FEV1/FVC with age-, sex-, height-, and population-appropriate reference equations and z-scores. Children do not have one fixed normal ratio.
  • Obstructive pattern: FEV1/FVC below the statistically defined lower limit of normal (approximately a z-score below -1.645) supports airflow obstruction.
  • Possible restriction: A low FVC with a normal or high FEV1/FVC suggests restriction but does not prove it. Confirm restriction when total lung capacity is below its reference lower limit; obstruction with air trapping, effort, and test quality can also lower FVC.

Bronchodilator Reversibility Protocol

To assess bronchodilator responsiveness as one component of evaluating suspected pediatric asthma:

1. Perform baseline spirometry using current ATS/ERS acceptability and age-appropriate repeatability criteria; document test quality rather than applying one adult volume threshold to every child.
2. Administer 4 puffs of albuterol sulfate (90 mcg/puff) via metered-dose inhaler (MDI) with a valved holding chamber.
3. Wait 10 to 15 minutes; repeat spirometry.
4. Positive Reversibility:
   • Current ATS/ERS interpretation expresses the change in FEV1 or FVC as a percentage of the predicted value; a change greater than 10% of predicted supports a bronchodilator response.
   • Some asthma guidelines use a pediatric threshold greater than 12% of predicted. State the reference used; a fixed 200 mL requirement is not appropriate for every child.

% Reversibility = [(Post-FEV1 - Pre-FEV1) / Pre-FEV1] × 100

Lung Volume Subdivisions & Plethysmography

• Body plethysmography: Measures thoracic gas volume and can capture trapped gas; gas-dilution or washout methods can also measure lung volumes but may underestimate poorly communicating regions.
• Air trapping: An RV or RV/TLC above the appropriate upper limit of normal supports air trapping; fixed percentage cutoffs can misclassify growing children.
• Hyperinflation: TLC above its reference upper limit supports hyperinflation. Interpret all volumes with quality checks and suitable reference equations.

Peak Expiratory Flow (PEF) Asthma Action Plan Zones

Home monitoring utilizes the child's personal best PEF:

• Green Zone (80% to 100% of personal best): Good control; continue maintenance controller medications.
• Yellow Zone (50% to 79% of personal best): Caution; acute exacerbation or poor baseline control. Administer inhaled short-acting beta-2 agonist (SABA) and intensify controller therapy as directed.
• Red Zone (< 50% of personal best): Medical Alert; severe airway obstruction. Inhale rescue SABA immediately and seek emergency medical evaluation.

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Worked Clinical Calculation: Bronchodilator Reversibility

Clinical Scenario

A 9-year-old child with exercise-induced wheezing undergoes spirometry. Baseline results show:

• FEV1 = 1.50 L
• FVC = 2.40 L
• FEV1 / FVC = 62.5%

Following administration of 4 puffs of albuterol via MDI with a spacer, repeat testing reveals:

• FEV1 = 1.80 L
• FVC = 2.50 L

Step-by-Step Calculation

1. Calculate absolute volume change in FEV1: ΔFEV1 = Post-FEV1 - Pre-FEV1 = 1.80 L - 1.50 L = 0.30 L = 300 mL
2. Calculate percentage improvement: % ΔFEV1 = [(1.80 - 1.50) / 1.50] × 100 = (0.30 / 1.50) × 100 = 20.0%
3. Evaluation: The child demonstrated a 20% increase from baseline and a 300 mL absolute increase. To apply current ATS/ERS criteria, divide the change by the predicted FEV1; the response supports variable airflow obstruction. Spirometry supports but does not alone diagnose asthma without compatible symptoms and clinical context.

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NPS Exam Traps

NPS Exam Trap 1: Neck Position Changing ETT Tip Depth

If an exam question describes an ETT tip resting at the carina on a film where the child's chin is touching the sternum, do not immediately withdraw the tube 3 cm. Recognize that neck flexion advances the tube toward the carina. Re-evaluate the patient's head position in a neutral posture before adjusting depth.

NPS Exam Trap 2: 'Steeple Sign' vs. 'Thumbprint Sign'

Confusing the radiographic signatures of croup and epiglottitis is a classic NBRC pitfall. Remember: Croup = Steeple Sign on AP neck (subglottic tapered narrowing). Epiglottitis = Thumbprint Sign on Lateral neck (supraglottic rounded enlargement of the epiglottis).

NPS Exam Trap 3: Diagnosing Restriction by FVC Alone

A low FVC on spirometry does not establish restriction. Poor effort or airflow obstruction with air trapping can reduce FVC. Confirm a restrictive ventilatory defect with TLC below the appropriate lower limit of normal, measured with a validated lung-volume method, and interpret it with test quality and the clinical picture.

Bronchoscopy, Microbiology & Diagnostic Specimens

Flexible bronchoscopy evaluates airway anatomy, dynamic collapse, obstruction, bleeding, and persistent lobar disease; it can also obtain bronchoalveolar lavage. Before the procedure, verify indication, airway plan, equipment size, oxygen reserve, sedation responsibilities, specimen containers, and emergency support. The bronchoscope narrows the airway and raises resistance, so monitor ventilation, oxygenation, hemodynamics, and airway pressures continuously.

Collect blood, tracheal aspirate, sputum, viral, and lavage specimens with correct labeling and transport. Interpret a tracheal culture in the clinical context because colonization does not prove pneumonia. Pair microbiology with symptoms, imaging, inflammatory trends, and specimen quality. Document volume and appearance of secretions and any response to lavage or airway clearance.