Should nebulizers be run with air in both asthma and Chronic Obstructive Pulmonary Disease (COPD) or just COPD?

Nebulizer Driving Gas Selection in Asthma and COPD

For patients with asthma, nebulizers should be driven by oxygen, while for patients with COPD or at risk of hypercapnic respiratory failure, nebulizers should be driven by compressed air with supplemental oxygen if needed. 1

Driving Gas Selection Algorithm

For Asthma Patients:

• Use oxygen as the driving gas at a flow rate of 6-8 L/min 1
• This is because asthma patients are at risk of hypoxemia during acute exacerbations
• If oxygen cylinders cannot produce adequate flow rates (6-8 L/min), use an air-driven nebulizer with electrical compressor and provide supplemental oxygen via nasal cannulae at 2-6 L/min 1

For COPD Patients:

• Use compressed air to drive nebulizers 1
• This is because oxygen-driven nebulization can cause hypercapnia and respiratory acidosis within 15 minutes in COPD patients 1, 2
• If supplemental oxygen is required, provide it concurrently via nasal cannulae to maintain oxygen saturation of 88-92% 1
• Monitor oxygen saturation continuously during treatment 1

Evidence Supporting These Recommendations

The British Thoracic Society (BTS) guidelines provide clear recommendations on this issue. For patients with asthma, oxygen should be used as the driving gas whenever possible because these patients are at risk of hypoxemia during acute exacerbations 1. High-flow oxygen (6-8 L/min) ensures effective nebulization of bronchodilator medications.

In contrast, for patients with COPD, oxygen-driven nebulization can cause significant increases in arterial carbon dioxide tension (PaCO2). A randomized controlled trial showed that oxygen-driven nebulization led to a mean increase in transcutaneous PCO2 of 3.4 mmHg compared to only 0.1 mmHg with air-driven nebulization (p<0.001) 2. This increase in CO2 can worsen hypercapnic respiratory failure, which is already a risk in COPD patients.

Special Considerations

Emergency Settings:

• In ambulance settings where air-driven compressors may not be available, oxygen-driven nebulizers may be used for COPD patients, but limit use to 6 minutes to deliver most of the drug while minimizing hypercapnia risk 1
• Ambulance services should consider introducing battery-powered air-driven or portable ultrasonic nebulizers 1

Patients with Hypercapnic Acidosis:

• Use ultrasonic nebulizers or jet nebulizers driven by compressed air 1
• Provide supplemental oxygen via nasal cannulae if needed to maintain SpO2 88-92% 1
• Apply the same precautions to patients at risk of hypercapnic respiratory failure before blood gas results are available 1

Flow Rate Requirements:

• Maintain a gas flow rate of 6-8 L/min to ensure proper nebulization of particles to 2-5 μm diameter for effective airway deposition 1
• If oxygen cylinders cannot produce this flow rate, use an electrical compressor with supplemental oxygen 1

Common Pitfalls to Avoid

1. Using oxygen-driven nebulizers for all patients regardless of diagnosis: This can lead to dangerous hypercapnia in COPD patients 2, 3

2. Failing to monitor oxygen saturation during nebulization: Continuous monitoring is essential, especially in patients at risk of hypercapnic respiratory failure 1

3. Not returning patients to their usual oxygen delivery method after nebulization: After completing nebulizer therapy, patients should be returned to their previous targeted oxygen therapy 1

4. Using water as a diluent in nebulizers: This can cause bronchoconstriction when nebulized; 0.9% sodium chloride should be used instead 1

5. Inadequate flow rates: Using flow rates below 6 L/min may result in suboptimal particle size generation and poor drug delivery 1

By following these evidence-based recommendations, clinicians can optimize nebulizer therapy while minimizing the risks of hypoxemia in asthma patients and hypercapnia in COPD patients.