Is it acceptable to administer 6 puffs of medication back to back without waiting a minute between each puff to a mechanically ventilated patient with Chronic Obstructive Pulmonary Disease (COPD) or asthma?

Administration of Multiple MDI Puffs in Mechanically Ventilated Patients

In mechanically ventilated patients, you should deliver only one puff per ventilator breath into the spacer device, allowing each breath to carry that single actuation into the lungs before actuating again. 1

Why One Puff Per Breath Maximizes Drug Delivery

The critical principle underlying this recommendation relates to how aerosol particles behave in the ventilator circuit and airways through three key mechanisms:

Impaction

• When multiple puffs are actuated into a spacer before inhalation, drug particles collide with each other and the spacer walls at high velocity, causing them to aggregate and deposit in the device rather than reaching the lungs 1
• Single actuation per breath minimizes particle collision and wall impaction, allowing more drug to remain airborne for inhalation 1

Sedimentation

• Aerosol particles begin settling due to gravity immediately after actuation 1
• By coordinating one puff with the onset of each inspiratory cycle, particles are swept into the airways before significant gravitational settling occurs in the spacer 1
• Multiple actuations create a saturated aerosol cloud where particles settle onto each other, dramatically reducing available drug 1

Diffusion

• Fine particles (1.5-6 μm) that reach the lower airways deposit through Brownian motion and diffusion into the alveolar surface 1
• The one-puff-per-breath technique ensures optimal particle size distribution reaches the distal airways where diffusion-mediated deposition occurs 1

The Critical Technical Error to Avoid

Never actuate multiple times into the spacer before allowing inhalation, as this dramatically reduces lung deposition 1. This is the single most important pitfall in MDI administration during mechanical ventilation. Multiple actuations cause:

• Particle aggregation reducing respirable fraction 1
• Spacer wall deposition of 40-50% of the dose 1
• Reduced fine particle fraction available for alveolar deposition 1

Optimal Administration Protocol for 6 Puffs

When administering 6 puffs to a ventilated patient:

1. Position the spacer in the inspiratory limb within 30 cm of the Y-piece 1
2. Temporarily disconnect humidification (reduces delivery by ~50% if left on) 1
3. Actuate one puff precisely at the onset of the ventilator's inspiratory cycle 1
4. Allow one complete ventilator breath cycle to pass 1
5. Repeat steps 3-4 for each of the remaining 5 puffs 1
6. Reconnect humidification after completing all actuations 1

Why This Differs from Spontaneously Breathing Patients

The ventilator circuit creates unique challenges:

• Lung deposition in ventilated patients is only 1.5-6% compared to 10-15% in spontaneously breathing patients 1
• The artificial airway, circuit dead space, and humidification all reduce drug delivery 1
• Precise timing with mechanical breaths is essential because the patient cannot coordinate their own inspiratory effort 1

Clinical Context for Dosing

For acute exacerbations requiring 6 puffs (600 μg of albuterol):

• Standard maintenance dosing is 2 puffs every 2-4 hours 1
• Acute exacerbations may require 4-8 puffs every 20 minutes for 3 doses, then every 1-4 hours 2
• The one-puff-per-breath technique remains essential regardless of total dose to maximize the limited 1.5-6% lung deposition achievable in ventilated patients 1