Humidification, nebulisers and inhalers

1Definitions (3 marks in S21)

• Humidification: adding water vapour (a gas) to inspired air or oxygen, to warm and moisten it.
• Nebulisation: turning a liquid (usually a drug solution) into an aerosol of fine droplets that can be breathed into the airways.
• Aerosol: tiny liquid or solid particles suspended in a gas.

2Humidification (3 marks in S17 and W17)

Normal airway conditioning

The nose and upper airway warm and humidify inspired air so that, a few centimetres below the carina, it is at body temperature (37 °C) and fully saturated (100% relative humidity, about 44 mg of water per litre). This point is called the isothermic saturation boundary.

Why intubated patients need it (W17)

An endotracheal tube or tracheostomy bypasses the nose and throat, so dry, cold gas reaches the trachea. This causes thick, sticky secretions, slows the cilia, damages the airway lining, blocks the tube, causes collapse and loses body heat and water. The AARC (2012) strongly recommends humidification for every invasively ventilated patient.

Uses (S17): intubated and tracheostomy patients; high-flow oxygen used for long periods; thick secretions; NIV comfort; dry upper airway.

Hazards: overheating and airway burns (heated systems); water collecting in the tubing (can be washed into the patient, spreads infection, triggers false breaths); infection from contaminated water; extra resistance and dead space with an HME, which can block with secretions.

3Nebulisation (7 marks in S20 and S24)

Particle size decides where the drug lands

Types of nebuliser

Indications (S24) and three conditions with purpose (S19)

• Acute severe asthma or COPD exacerbation: bronchodilators (salbutamol, ipratropium) to relieve bronchospasm.
• Cystic fibrosis and bronchiectasis: hypertonic saline or dornase alfa to loosen sputum before airway clearance; inhaled antibiotics to control infection.
• Ventilated patients: bronchodilators given in-line.
• Children with croup: nebulised adrenaline or steroid as prescribed.
• Sputum induction for TB and other tests (hypertonic saline).
• Anyone who cannot use an inhaler: very young, very old, confused or very breathless patients.

Contraindications and precautions

• Known allergy to the drug.
• Hypertonic saline can cause bronchospasm: give a bronchodilator first and check peak flow or spirometry with the first dose.
• Patients at risk of high CO₂ (COPD): drive the nebuliser with compressed air, not oxygen, and give oxygen separately by nasal cannula (BTS).
• Side effects: fast heart rate and tremor (salbutamol), low potassium with frequent high doses.
• Infection control: nebulising can spread infection (aerosol-generating); clean, dry and do not share equipment.

Technique

1. Sit upright; fill the cup (usually 2–5 mL).
2. Use a mouthpiece where possible (less drug lost to the face and eyes); a mask for children and very breathless patients.
3. Breathe normally through the mouth, with an occasional slow deep breath.
4. Continue until the nebuliser starts to splutter.
5. Rinse the mouth after steroids; wash and dry the parts.

4Inhalers (3 marks in W25)

Metered-dose inhaler (MDI)

A pressurised canister holds the drug with a propellant; a metering valve releases a fixed dose with each press (for example 100 µg of salbutamol per puff).

1. Remove the cap and shake the inhaler.
2. Breathe out gently, away from the inhaler.
3. Seal the lips around the mouthpiece.
4. Start a slow, deep breath in (about 3–5 seconds) and press the canister once at the start.
5. Hold the breath for up to 10 seconds, then breathe out slowly.
6. Wait about 30–60 seconds before a second puff; rinse the mouth after a steroid inhaler.

• Advantages: small, quick, cheap, many drugs available.
• Disadvantages: needs hand–breath coordination; much of the dose hits the throat; cold spray can stop the breath.
• Spacer (holding chamber): the puff goes into the chamber and is breathed in over a few breaths, so coordination matters less and less drug lands in the throat. With a face mask for young children. In acute asthma an MDI with a spacer works as well as a nebuliser (Cochrane, 2013).

Dry powder inhaler (DPI)

Drug powder released by the patient's own fast, deep breath in (for example Rotahaler with capsules, Accuhaler, Turbuhaler). No propellant and no coordination needed, but the patient must breathe in quickly and strongly, so it does not suit young children or a severe attack. Do not breathe out into it (moisture spoils the powder).

5Exam corner

Past questions (MUHS, 2016–2026)

• 7-mark questionsPrinciple of working of jet and ultrasonic nebulisers (S20). Indications and contraindications of nebulisation and types of nebulisation systems (S24).
• 3-mark questionsHumidification and its uses (S17). Need for humidification in an intubated patient (W17). Three conditions in which nebulisers are used, with purpose (S19). Define humidification and nebulisation (S21). Metered-dose inhalers (W25).