Diagnostic Procedures in Respiratory Disease¶

Chapter 297 | Part 7: Disorders of the Respiratory System · Part 7 – Respiratory Disorders · Chapter 297

Key Clinical Points¶

DLCO decreases with increased membrane thickness (fibrosis) or reduced capillary volume (anemia, pulmonary hypertension).
FEV1/FVC ratio is a key indicator of airflow obstruction; however, high RV can make this ratio appear artifactually normal.
Flow-volume loops distinguish lower airway obstruction (scooping in asthma/emphysema) from fixed upper-airway obstruction (plateaus).
Respiratory muscle strength is assessed via pressure at FRC (>±60 cmH2O) or supine spirometry (10% to >25% drop indicates weakness).
Thoracentesis should ideally be guided by point-of-care ultrasound to reduce risks of dry tap and pneumothorax.
Light's criteria remain the standard for distinguishing exudates from transudates in pleural fluid analysis.
EBUS-TBNA has high sensitivity (~90%) for epithelial malignancies and ~70% for lymphoma.
Robotic navigation and radial EBUS enhance the detection of small, peripheral lung nodules.
MRI is preferred in pediatric populations or when repeated imaging is required due to the absence of ionizing radiation.
Complication rates for invasive procedures include hemorrhage (1/4 to 1/3) and pneumothorax (17–28%).

DEFINITION & OVERVIEW¶

• Scope: Includes a wide array of invasive and noninvasive modalities for obtaining diagnostic specimens and imaging. • Reference: Pulmonary function tests and gas exchange measurements are detailed in Chap. 295.

ETIOLOGY & PATHOPHYSIOLOGY¶

Spirometry and Flow-Volume Loops¶

• Spirometry: Used for lung volume determination and measuring airflow (dynamic properties). • FVC Maneuver: Patient inhales to TLC → exhales rapidly/forcefully to RV; ensures flow limitation is reached. • FEV1: Volume change per time in the first second of exhalation. • FEV1/FVC Ratio: ◦ Typically reduced in airflow obstruction. ◦ Note: Obstruction can increase RV → potentially making FEV1/FVC ratio appear artifactually normal. • Flow-Volume Loops: Plot of flow vs. volume to identify site of obstruction. ◦ Lower airway obstruction (asthma, emphysema) → rapid decrease in flow with declining lung volumes → characteristic "scooping" of the loop. ◦ Fixed upper-airway obstruction → inspiratory and/or expiratory flow plateaus.

Respiratory Muscle Strength¶

• Measurement: Patient exhales/inhales with maximal effort against a closed shutter while pressure is monitored. • Threshold: Pressure > ± 60 cmH2O at FRC → indicates adequate muscle strength; unlikely to cause resting ventilatory dysfunction. • Supine Spirometry: More sensitive for inspiratory muscle weakness. ◦ Normal subjects: FVC decreases ~3–8% from upright to supine. ◦ Weakness/Paralysis: FVC decreases 10 to >25%.

DIFFERENTIAL DIAGNOSIS¶

• Imaging Findings: ◦ Kerley B lines (engorged lymphatics), cephalization (prominent nondependent vasculature), and bronchial cuffing (blurred borders) → suggest congestive heart failure. ◦ Thickened interstitium → may indicate hydrostatic pulmonary edema, interstitial lung disease, or carcinomatosis. • CXR Utility: Excellent initial diagnostic to distinguish pulmonary vs. extrapulmonary disease.

INVESTIGATIONS & DIAGNOSIS¶

Bedside Pleural Procedures¶

• Thoracentesis: Percutaneous aspiration of fluid from the pleural space. ◦ Standard of care: Use point-of-care ultrasonography to mark site → reduces risk of dry tap and pneumothorax. • Pleural Fluid Analysis: ◦ Includes hematologic, biochemical, microbiologic, and cytologic studies. ◦ Light's criteria: Used to distinguish exudates from transudates. ◦ Mesothelin-1 testing: Newer assay for neoplastic diseases (e.g., mesothelioma).

Closed Pleural Biopsy¶

• Methods: Performed blindly (Abrams needle) or with imaging guidance (CT or ultrasound). ◦ Ultrasound is performed in real-time. • Clinical Utility: ◦ No ultrasound: Highly sensitive for pleural tuberculosis (due to diffuse involvement). ◦ Image-guided: Most helpful for focal abnormalities like nodules (highly suggestive of malignancy). ◦ Yield: ~80–90% when specific abnormalities are visualized.

Thoracic Surgical Procedures¶

• Pleuroscopy: Single port access; used for parietal biopsy, minor lysis of adhesions, pleurodesis, or catheter placement. Usually performed under conscious sedation. • VATS/RATS: More invasive; requires general anesthesia and single-lung ventilation. Allows lung biopsy, lymph node sampling, lobectomy, decortication, and pericardial window creation. • Open Thoracotomy: Large incision for complex tasks like creating a Clagett window for chronic bronchopleural fistula with empyema.

Bronchoscopy¶

• Flexible Bronchoscopy: Most common; allows access to distal parts of the respiratory tract. • Rigid Bronchoscopy: Limited to central airways; provides secure airway for ventilation and a conduit for instruments. Used primarily when severe bleeding is anticipated (e.g., transbronchial cryobiopsy).

Guided Peripheral Bronchoscopy¶

• Step 1: Navigation: ◦ Electromagnetic navigational bronchoscopy (GPS-like feedback). ◦ Virtual bronchoscopy (overlay of live images on CT map). ◦ Shape-sensing technology. • Step 2: Localization: ◦ Radial EBUS: Thin ultrasound-tipped catheter; concentric image of target → high yield. ◦ Cone-beam CT: Intraprocedural confirmation of tool-in-lesion. • Step 3: Sampling: ◦ Tools: Biopsy forceps, brushes, aspiration needles (TBNA has highest sensitivity for malignant nodules). ◦ Cryobiopsy: Emerging use for sampling discrete peripheral lesions.

Medical Imaging¶

• Modalities: X-ray, CT, MRI, and PET. ◦ Applications: Assess alveolar perfusion, metabolic activity of nodules, bronchovascular source of hemoptysis, or early parenchymal changes. • MRI Specifics: No ionizing radiation; preferred for pediatric patients or repeated assessments.

Miscellaneous Testing¶

• Sputum Analysis: Microscopy and culture to identify pathogens. ◦ Sputum induction: Use provocative nebulization with saline for non-expectorating patients; safe even in those with airflow limitation.

PROGNOSIS & COMPLICATIONS¶

• Hemorrhage: Occurs in 1/4 to 1/3 of cases. • Pneumothorax: Occurs in 17–28% of cases (most do not require chest tube).

SPECIAL CONSIDERATIONS¶

Pediatric Considerations¶

• MRI: Preferred due to lack of ionizing radiation.

KEY PEARLS & HIGH-YIELD POINTS¶

• DLCO Factors (Table 1): ◦ \uparrow Surface area or \uparrow Hemoglobin → \uparrow DLCO. ◦ \uparrow Membrane thickness, Pulmonary HTN, or Anemia → \downarrow DLCO. ◦ Asthma, polycythemia, or pulmonary hemorrhage → \uparrow DLCO. • Oxygen Content (Table 2): ◦ Formula: $CaO_2 = 1.39 imes [ ext{hemoglobin}] imes \%SaO_2 + 0.003 imes PaO_2$. • Spirometry Logic: Flow-volume loops distinguish lower airway (scooping) from upper airway (plateaus).