Nebulisers and Peak Flow: Correct Technique, Oxygen vs Air, and What the Numbers Mean

Nebulisers and peak flow meters are everyday equipment on medical wards, emergency departments, children’s units and asthma clinics. Both look simple, yet both are often used incorrectly. A poorly given nebuliser may deliver little medicine, and a badly performed peak flow can make a patient look better or worse than they really are. This guide covers the essentials.

Part 1: Nebulisers

What does a nebuliser do?

A nebuliser turns liquid medicine into a fine mist that the patient breathes in through a mask or mouthpiece. It’s used when a patient is too breathless to use an inhaler effectively, or when a medicine is only available as a nebuliser solution.

For mild to moderate asthma attacks, a pressurised metered-dose inhaler (pMDI) with a spacer is often as effective as a nebuliser, and is quicker, cheaper and spreads fewer aerosols. Many guidelines recommend inhaler and spacer as first-line in children and adults with non-severe attacks. Nebulisers are generally kept for severe or life-threatening attacks or when a patient cannot use a spacer.

Common nebulised medicines

• Salbutamol (short-acting beta-2 agonist) for bronchospasm in asthma and COPD
• Ipratropium bromide (anticholinergic), often added in severe asthma or COPD exacerbations
• Adrenaline for croup or airway swelling, as prescribed
• Budesonide for croup in some settings
• Hypertonic saline to loosen secretions in conditions such as bronchiectasis or cystic fibrosis

Oxygen or air?

This is a key safety decision:

• Asthma: nebulisers are usually driven by oxygen (6 to 8 L/min), because acute asthma causes hypoxaemia.
• COPD with a risk of hypercapnic respiratory failure: nebulisers should usually be driven by compressed air, with supplemental oxygen given separately by nasal cannulae if needed to keep saturation in the target range (often 88 to 92%). Driving a nebuliser with high-flow oxygen for a long period can cause carbon dioxide retention and drowsiness. Limit oxygen-driven nebulisers to about 6 minutes if air isn’t available, per British Thoracic Society guidance.

Always check the prescription and the patient’s target oxygen saturation.

Giving a nebuliser step by step

1. Check the prescription, patient identity and allergies.
2. Explain the procedure and sit the patient upright.
3. Record baseline observations: respiratory rate, oxygen saturation, heart rate, and peak flow if the patient can do it.
4. Wash your hands and assemble the nebuliser chamber, tubing and mask or mouthpiece.
5. Add the medicine (and diluent if prescribed) to the chamber.
6. Connect to oxygen or air at the correct flow rate (usually 6 to 8 L/min) to produce a fine mist.
7. Ask the patient to breathe normally through the mouth. A mouthpiece is better for adults who can manage it, because it reduces deposition on the face and eyes.
8. Continue until the chamber is empty or begins to splutter (usually 5 to 10 minutes). Tapping the chamber can help.
9. Monitor the patient during treatment. Salbutamol commonly causes tremor and a fast heart rate.
10. Repeat observations after treatment to assess response.
11. Rinse the mouth after steroids; clean, dry and store the equipment as per policy. Nebuliser kits are usually single-patient use.
12. Document medicine, time, gas used and response.

Infection control

Nebulisers can disperse aerosols. In patients with suspected airborne infections (for example TB or some respiratory viruses), follow local infection prevention guidance on PPE and room choice, and consider inhaler with spacer as an alternative.

Part 2: Peak expiratory flow (PEF)

What is peak flow?

Peak expiratory flow is the fastest speed at which a person can blow air out after taking a full breath. It’s measured in litres per minute (L/min) with a simple handheld meter. It’s used to:

• Assess the severity of an asthma attack
• Monitor response to treatment
• Help diagnose asthma (looking for variability over time)
• Support self-management through personal asthma action plans

How to measure peak flow correctly

1. Set the marker on the meter to zero.
2. Ask the patient to stand or sit upright (record the position and use the same position each time).
3. Hold the meter horizontally, keeping fingers away from the scale and the vent.
4. Ask the patient to take the deepest breath possible.
5. Seal the lips tightly around the mouthpiece.
6. Blow out as hard and fast as possible in a short, sharp “huff”, like blowing out candles. It doesn’t need to be a long breath.
7. Read and record the number.
8. Repeat three times and record the highest reading.

Common errors include not taking a full breath, coughing or spitting into the meter, blocking the scale with fingers, and recording the average instead of the best value.

Interpreting the result

Compare the reading with the patient’s personal best (the best they achieve when well) or, if unknown, a predicted value based on age, sex and height.

In acute asthma in adults, the British Thoracic Society/SIGN asthma guideline uses PEF to classify severity:

• Moderate: PEF more than 50 to 75% of best or predicted
• Acute severe: PEF 33 to 50%, or respiratory rate 25 or more, heart rate 110 or more, or unable to complete sentences
• Life-threatening: PEF below 33%, or SpO2 below 92%, silent chest, cyanosis, poor respiratory effort, exhaustion, confusion, arrhythmia or hypotension

A patient too breathless to do a peak flow is likely to have a severe attack. Don’t force a peak flow in a patient with life-threatening features; treat and call for help immediately.

Peak flow in children

Most children over about 5 years can perform peak flow with coaching. Use child-appropriate predicted charts and focus on technique. In younger children, assess severity using clinical signs instead.

Peak flow diaries and action plans

Teaching patients to record peak flow at home helps them recognise when asthma is getting worse. A personal asthma action plan usually has zones, for example:

• Green: more than 80% of best. Continue usual treatment.
• Amber: 50 to 80%. Increase reliever use and follow the plan; seek advice.
• Red: below 50%. Emergency. Take reliever and seek urgent medical help.

Key points

• For mild to moderate asthma, an inhaler with spacer works as well as a nebuliser.
• Drive nebulisers with oxygen in asthma, but with air in COPD patients at risk of CO2 retention.
• Monitor observations before and after every nebuliser.
• Peak flow: best of three short, sharp blows, compared with personal best or predicted.
• Life-threatening asthma is a clinical diagnosis. Don’t delay treatment for a peak flow.

References

• BTS/SIGN/NICE: Asthma guidelines
• British Thoracic Society: Emergency oxygen guideline
• Global Initiative for Asthma (GINA)