FRC Increases During Bronchoscopy
Functional Residual Capacity (FRC) increases significantly during bronchoscopy, with elevations of approximately 30% when performed through an endotracheal tube and 17% when performed transnasally in spontaneously breathing patients. 1
Mechanism of FRC Increase
The elevation in FRC during bronchoscopy occurs through mechanical obstruction of the airways:
Placement of the bronchoscope in the airway causes dynamic hyperinflation by creating expiratory flow limitation, which traps air and prevents complete exhalation to the normal resting lung volume 1
The bronchoscope acts as a physical obstruction that increases airways resistance, particularly during expiration, leading to incomplete emptying of the lungs and progressive air trapping 1
FRC returns toward baseline values after removal of the bronchoscope, confirming that the increase is directly related to the mechanical presence of the instrument in the airway 1
Clinical Implications by Patient Population
Patients with COPD
COPD patients already have elevated baseline FRC due to chronic air trapping and loss of elastic recoil, making them particularly vulnerable to further increases during bronchoscopy 2
The FRC increase during bronchoscopy is more pronounced in COPD patients compared to those with normal lung function, as they have less respiratory reserve to accommodate additional air trapping 1
Severe COPD (FEV₁ <40% predicted and/or SaO₂ <93%) carries a 5% complication rate during bronchoscopy compared to 0.6% in patients with normal lung function, largely related to worsening hyperinflation and gas exchange 2, 3
Arterial blood gas tensions should be measured before bronchoscopy in patients with severe COPD to identify baseline CO₂ retention, as further FRC elevation can worsen ventilation-perfusion mismatch and hypercapnia 2
Patients with Asthma
Asthmatic patients experience similar FRC increases during bronchoscopy, but the primary concern is bronchospasm rather than hyperinflation 2
Premedication with a bronchodilator is mandatory in asthmatic patients before bronchoscopy to prevent procedure-related bronchospasm, which occurs in up to 8% of cases 2, 4
Short-acting β₂-agonists (SABAs) such as albuterol should be administered 15-20 minutes before the procedure to provide rapid bronchodilation and minimize airway reactivity 4
Impact on Gas Exchange
Despite the FRC increase, PaO₂ typically does not change substantially during bronchoscope insertion, though significant decreases occur following removal of the instrument in transnasally intubated patients 1
The elevated FRC creates or worsens ventilation-perfusion mismatch by reducing ventilation to dependent lung zones that remain well perfused, contributing to hypoxemia 5
Topical lignocaine (lidocaine) causes the major deterioration in lung function during bronchoscopy, producing significant falls in FEV₁, FVC, and peak flows independent of the bronchoscope's mechanical effects 6
Common Pitfalls to Avoid
Do not assume the bronchoscope itself is the primary cause of airflow obstruction—topical anesthetic agents like lignocaine produce the most significant decreases in spirometric values 6
Avoid sedation in patients with severe COPD and baseline hypercapnia, as oxygen supplementation and sedatives may further increase arterial CO₂ levels in the setting of already elevated FRC 2
In patients with moderate airway obstruction, the mean FRC increase of 30% with endotracheal intubation plus bronchoscopy represents a substantial physiologic burden that must be anticipated 1