What are the management strategies for a patient with a history of respiratory conditions, such as asthma or chronic obstructive pulmonary disease (COPD), who experiences decreased tidal volume (VT) and loss of swivel adaptor reflex bronchoconstriction during bronchoscopy?

Management of Decreased Tidal Volume and Loss of Swivel Adaptor Function During Bronchoscopy

When performing bronchoscopy on mechanically ventilated patients, particularly those with asthma or COPD, you must use a special swivel connector with a perforated diaphragm to maintain ventilation and PEEP, adjust ventilator settings to mandatory mode with increased pressure limits, and accept reduced tidal volumes rather than risk hyperinflation. 1

Understanding the Physiologic Problem

The bronchoscope occupies significant cross-sectional area within the endotracheal tube, creating substantial airway resistance that threatens adequate ventilation. 1 A 5.7 mm bronchoscope occupies 40% of a 9 mm endotracheal tube and 66% of a 7 mm tube, dramatically increasing resistance to airflow. 1

Key Mechanism of Tidal Volume Loss

• The physical obstruction from the bronchoscope reduces effective tidal volume delivery, particularly when ventilator pressure limits are reached. 1
• In mechanically ventilated patients, inserting the bronchoscope decreases end-expiratory lung volume (EELV) in 64% of cases by an average of 325 mL. 2
• Suctioning maneuvers further decrease EELV in 76% of cases by approximately 120 mL. 2

Critical Ventilator Adjustments Required

Pre-Procedure Settings

Pre-oxygenate with 100% FiO2 and maintain this throughout the procedure and immediate recovery period. 1

• Switch ventilator to mandatory mode—triggered modes like pressure support or assist control will not reliably maintain ventilation during bronchoscopy. 1
• Increase the ventilator pressure limit to ensure adequate tidal volumes are delivered during each respiratory cycle. 1
• Increase the ventilator rate if necessary to compensate for reduced tidal volumes. 1

The Swivel Adaptor Solution

Use a special swivel connector (with perforated diaphragm) through which the bronchoscope can be inserted—this allows continued ventilation and maintenance of PEEP/CPAP. 1 This is particularly critical when performing bronchoscopy in hypoxic patients with ARDS. 1

Population-Specific Management Strategies

Patients with Asthma

Premedicate all asthmatic patients with a bronchodilator before bronchoscopy. 1

• Bronchospasm occurs in 8% of asthmatic patients during bronchoscopy, though the overall rate is only 0.02% in general populations. 1
• Lignocaine (topical anesthetic) may produce bronchoconstriction in asthmatics, which is attenuated by preoperative atropine. 1
• Asthmatic patients experience greater postoperative falls in FEV1 and FVC compared to normal subjects, inversely correlated with baseline methacholine PC20. 1
• Use sedation with particular care in asthmatics because the procedure may exacerbate bronchoconstriction. 1

Patients with Severe COPD

Check spirometry before bronchoscopy in suspected COPD patients, and if severe (FEV1 <40% predicted and/or SaO2 <93%), measure arterial blood gas tensions. 1

• Severe COPD carries a 5% complication rate during bronchoscopy compared to 0.6% in patients with normal lung function. 1, 3
• Avoid sedation when pre-bronchoscopy arterial CO2 is elevated—oxygen supplementation and sedatives may further increase CO2 levels. 1, 3
• Give oxygen supplementation only with extreme caution in hypercapnic COPD patients. 1
• COPD patients have elevated baseline FRC due to chronic air trapping and loss of elastic recoil, making them particularly vulnerable to further increases during bronchoscopy. 3

Monitoring Requirements During Procedure

Continuous multi-modal physiological monitoring must be continued during and after bronchoscopy. 1

Essential monitoring includes:

• ECG for heart rate and rhythm 1
• Continuous intra-arterial blood pressure or intermittent cuff measurements 1
• Pulse oximetry (SpO2) with appropriate alarm limits 1
• Tidal volume and minute ventilation monitoring (available on most modern microprocessor-controlled ventilators) 1
• Endotracheal CO2 monitoring in head-injured patients to detect falls in minute ventilation 1

Accepting Reduced Tidal Volumes: The Safe Strategy

Peak pressure limiting ventilation protects against hyperinflation with a consequent, well-tolerated reduction in tidal volume and hypercapnea. 2

• Allowing VT reduction during bronchoscopy prevents dangerous hyperinflation from expiratory flow limitation. 2
• Expect PaCO2 to increase by approximately 15 mmHg post-bronchoscopy—this is clinically acceptable. 2
• Expect PaO2 to decrease by approximately 61 mmHg—maintain 100% FiO2 to compensate. 2
• There is no clinically significant increase in EELV when using pressure-limited ventilation during bronchoscopy. 2

Critical Pitfalls to Avoid

• Never use triggered ventilator modes during bronchoscopy—they will not reliably maintain ventilation. 1
• Never proceed without a swivel adaptor in hypoxic patients—loss of PEEP can be catastrophic in ARDS. 1
• Never sedate severe COPD patients with baseline hypercapnia—this can precipitate respiratory failure. 1, 3
• Never forget bronchodilator premedication in asthmatics—8% will develop bronchospasm without it. 1
• Limit suctioning maneuvers—each suction decreases EELV and increases derecruitment risk. 2

When to Abort the Procedure

Adverse events require immediate withdrawal of the bronchoscope and resuscitation of the patient. 1 The clinician must then weigh benefits against risks before proceeding further. 1

Immediate withdrawal indications include:

• Severe hypoxemia despite 100% FiO2 1
• Hemodynamic instability 1
• Severe bronchospasm unresponsive to treatment 1
• Rising intracranial pressure in head-injured patients 1