NEBULISATION 

1. Definition

Nebulisation is a drug delivery technique in which a liquid medication is converted into an aerosol (fine mist) and inhaled into the lower respiratory tract, allowing direct local action with minimal systemic effects.

 Drug reaches:

• Upper airway
• Tracheobronchial tree
• Alveoli (depending on particle size)

2. Particle Size (MMAD – Mass Median Aerodynamic Diameter)

 Ideal nebulisation target: 2–5 μm

3. Types of Nebulisers

A. Jet (Pneumatic) Nebuliser – Most Common

Mechanism

• Compressed gas (oxygen or air) passes through narrow orifice
• Creates negative pressure → draws liquid up
• Breaks liquid into aerosol (Venturi effect)

Advantages

• Cheap
• Widely available
• Can nebulise most drugs

Disadvantages

• Bulky
• Noisy
• Drug wastage
• Long nebulisation time

📌 Flow rate: 6–8 L/min
📌 Residual volume: 0.5–1 mL

B. Ultrasonic Nebuliser

Mechanism

• High-frequency vibrations via piezoelectric crystal
• Produces aerosol

Advantages

• Silent
• High output

Disadvantages

• Heats solution → denatures proteins
• Not suitable for:
  • Antibiotics
  • Steroids
  • Protein drugs

📌 Used rarely in ICU now

C. Mesh Nebuliser (Preferred in ICU & Ventilated Patients)

Mechanism

• Vibrating mesh with microscopic pores
• Forces liquid through → uniform aerosol

Advantages

• Small particle size
• Minimal drug wastage
• Silent
• Works in ventilator circuits
• No heating

Disadvantages

• Expensive
• Mesh blockage possible

## Best for ICU, NIV, ventilated patients

4. Nebulisation vs MDI vs DPI

How MDI CAN be used with a ventilator

Requirements (ALL must be met)

1. Special MDI adaptor / spacer inserted into ventilator circuit
   • Usually placed between Y-piece and ETT

2. Synchronisation with inspiration
3. Temporary ventilator adjustments
4. Closed circuit maintained (no disconnection)

—> Without these → lung deposition is extremely poor.

Ventilator adjustments for MDI 

Drug delivery efficiency 

 Hence MDI = less reliable

Which drugs are used via MDI on ventilator

Mostly bronchodilators:

• Salbutamol
• Ipratropium
• Combination inhalers

## Steroids and antibiotics → not preferred via MDI

5. Indications of Nebulisation

• Acute asthma exacerbation
• COPD exacerbation
• Bronchospasm
• Bronchiolitis (selected cases)
• Post-extubation stridor
• Laryngotracheobronchitis (croup)
• Pneumonia with bronchospasm
• ARDS (selected drugs)
• Inhalation injury
• Thick secretions
• Nebulised antibiotics
• ARDS adjunct therapy
• Post-operative atelectasis

7. Nebulisation in Mechanically Ventilated Patients

Key Principles

• Place nebuliser close to ventilator Y-piece(Placing the nebuliser close to the ventilator Y-piece maximises aerosol delivery to the patient by minimising drug loss due to deposition in the ventilator tubing and humidifier.)

Best location depends on nebuliser type

—>Jet nebuliser-Place close to Y-piece on inspiratory limb

 Needs driving gas → positioning is critical

—>Mesh nebuliser —Place between Y-piece and ETT

• Adjust ventilator:
  • Low flow(Low inspiratory flow improves aerosol lung deposition by reducing turbulent flow and inertial impaction of particles in the airway and ventilator circuit.)
  • Longer inspiratory time
• Humidification OFF temporarily (jet nebuliser especially)

8. Technique of Nebulisation (Step-by-Step)

1. Explain procedure
2. Sit patient upright (or 30–45° head-up)
3. Load correct drug + diluent
4. Attach mask or mouthpiece
5. Flow rate 6–8 L/min
6. Encourage slow deep breaths
7. Continue until sputtering stops (8–10 min)
8. Rinse mouth after steroid nebulisation

9. Complications of Nebulisation

Drug-Related

• Tachycardia
• Tremor
• Hypokalemia
• Arrhythmias
• Bronchospasm (NAC)

Technique-Related

• Infection transmission
• Drug wastage
• Poor lung deposition

ICU-Specific

• Ventilator circuit contamination
• Increased airway resistance

How to DECREASE inspiratory flow during nebulisation on a ventilator?

Core Principle

Inspiratory flow = Tidal volume ÷ Inspiratory time

So you decrease flow by:

• Increasing inspiratory time
• Reducing peak inspiratory flow settings
• Choosing appropriate ventilator mode

1. Increase Inspiratory Time (MOST IMPORTANT)

How?

• Change I:E ratio
  • From 1:2 → 1:1 or 1:1.5

Effect

• Same tidal volume delivered over longer time
• ↓ inspiratory flow
• ↑ aerosol deposition

2. Reduce Set Inspiratory Flow (Volume Control Mode)

In Volume Control Ventilation (VCV)

• Manually set lower inspiratory flow
  • Example:
    • From 60 L/min → 30–40 L/min

📌 This is the most direct method

3. Change Flow Pattern

Prefer

• Decelerating flow (if available)

4. Reduce Tidal Volume (If Clinically Safe)

Since:

Flow ∝ Tidal volume

Lower VT → lower required flow

5. Switch Mode if Needed

## VCV preferred during nebulisation

6. Adjust Respiratory Rate

• Slightly ↓ RR
• Allows longer inspiratory time

## Avoid hypercapnia

7. NIV / Non-invasive ventilation

• Reduce:
  • Pressure support
  • Rise time (slower rise)
• Minimise leaks