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)
Particle size | Site of deposition |
>10 μm | Oropharynx |
5–10 μm | Large bronchi |
2–5 μm | Small airways |
1–2 μm | Alveoli |
<1 μm | Exhaled |
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
Feature | MDI(Meter dose inhaler) | DPI(Dry powder inhaler ) | Nebuliser |
Drug form | Aerosol | Dry powder | Aerosol mist |
Propellant | Yes | No | No |
Coordination needed | Yes | No | No |
Inspiratory effort needed | Low | High | Minimal |
Acute severe asthma | No | No | Yes |
ICU/ventilator | Limited | No | Yes |
Portability | High | High | Low |
Cost | Low | Moderate | High |
How MDI CAN be used with a ventilator
Requirements (ALL must be met)
- Special MDI adaptor / spacer inserted into ventilator circuit
- Usually placed between Y-piece and ETT
- Synchronisation with inspiration
- Temporary ventilator adjustments
- Closed circuit maintained (no disconnection)
—> Without these → lung deposition is extremely poor.
Ventilator adjustments for MDI
Parameter | Recommendation | Reason |
Mode | Volume control preferred | Predictable tidal volume |
Inspiratory flow | Low–moderate | ↓ impaction |
Inspiratory time | Prolonged | ↑ deposition |
Humidification | OFF briefly | Humidity reduces aerosol |
Actuation timing | At start of inspiration | Max lung entry |
Drug delivery efficiency
Method | Lung deposition |
Nebuliser (mesh) | 10–20% |
MDI + spacer + ventilator | 2–6% |
MDI without spacer | <1% |
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)
- Explain procedure
- Sit patient upright (or 30–45° head-up)
- Load correct drug + diluent
- Attach mask or mouthpiece
- Flow rate 6–8 L/min
- Encourage slow deep breaths
- Continue until sputtering stops (8–10 min)
- 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
- Example:
📌 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
Mode | Flow Control |
Volume Control | Best (flow can be set) |
Pressure Control | Flow is variable |
PSV | Poor control |
APRV | Poor for nebulisation |
## 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