[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Clinical skills](https://durgical.com/en/clinical-skills/) › [Airway and cardiac procedures](https://durgical.com/en/clinical-skills/areas/airway-cardiac/) › Peak flow and inhaler technique

# Peak flow and inhaler technique

- Procedure

A small meter measures how fast a person can blow air out, and good inhaler technique gets the medicine into the lungs.

Updated Nov 13, 2026

## Key points

- PEF: best of three blows, standing or sitting upright, compared with personal best or predicted.
- Acute asthma severity by PEF (% of best or predicted): 50–75% moderate, 33–50% acute severe, under 33% life-threatening.
- Metered-dose inhaler: slow deep breath while pressing the canister, then hold the breath; a spacer improves delivery.
- Dry powder inhaler: fast, forceful breath in; do not shake it or breathe out into it.
- Check technique and adherence before stepping up treatment; rinse the mouth after inhaled corticosteroids.

On this page

- The basics Key points
- What it is
- Indications
- Equipment
- Step by step (and why)
- Next step
- Memory aid
- Elsewhere in DurgiPedia

- Clinical Acute asthma in adults: PEF as a percentage of best or predicted (with clinical features).
- Complications

- Safety Contraindications and precautions

- Study Test yourself

- Connections Connections

## What it is

Peak expiratory flow (PEF) is the fastest flow a person can produce in a short, forceful blow out after a full breath in. It falls when the large airways narrow, so it is a cheap, portable way to measure obstruction in asthma. A reading is compared with the predicted value for the person's age, height and sex or, better, with their own best reading. Variability between readings across the day or over weeks supports a diagnosis of asthma, serial readings at and away from work point to occupational asthma, and a single reading as a percentage of best or predicted helps grade an acute attack. PEF depends heavily on effort and technique and is less accurate than spirometry, which remains the test for diagnosis. Inhaler technique is checked at every visit, because most patients make at least one error and poor technique is a common reason for poor control. A pressurised metered-dose inhaler needs a slow, deep breath started just as the canister is pressed, ideally through a spacer; a dry powder inhaler needs a fast, forceful breath in, because the patient's own airflow disperses the powder. Checking technique, adherence and triggers comes before stepping up treatment.

## Indications

- Supporting the diagnosis of asthma by showing variable airflow obstruction (diurnal variation or response to treatment).
- Grading the severity of an acute asthma attack and following the response to treatment.
- Home monitoring with a written action plan based on personal best (green, yellow and red zones).
- Investigating occupational asthma with serial readings at and away from work.
- Inhaler technique: at diagnosis, every review, every change of device and before any step-up in treatment.

## Contraindications and precautions

- Effort-dependent: a poor effort or a cough gives a falsely low reading; it does not replace spirometry.
- Avoid forced blows after recent eye, chest or abdominal surgery, with pneumothorax, haemoptysis or unstable cardiac disease.
- In a patient too breathless to speak or with life-threatening features, treat first; do not insist on a reading.
- Use the same meter each time where possible, because meters differ from each other.
- Dry powder inhalers need a strong inspiratory flow; young children and very breathless patients may manage only a metered-dose inhaler with a spacer.

## Equipment

- Peak flow meter with a disposable one-way mouthpiece and a filter.
- Predicted value chart (age, height, sex) and the patient's diary or action plan.
- Placebo (demonstration) inhalers of the patient's device types.
- Spacer, with a face mask for young children.
- Gloves and cleaning material for shared equipment.

## Step by step (and why)

- Explain the test, set the pointer to zero and fit a new mouthpiece — a pointer left high gives a false reading.
- Ask the patient to stand or sit upright and hold the meter level without blocking the scale — posture changes the result.
- Breathe in fully, seal the lips round the mouthpiece and blow out as hard and fast as possible in a short blast — PEF is the first fraction of a second.
- Repeat three times and record the best, with time and treatment — the best of three reduces effort errors.
- Inhaler: watch the patient use their own device first — this shows their real errors.
- Metered-dose inhaler: shake, breathe out away from it, seal, press at the start of a slow deep breath — timing gets the drug to the lungs.
- Hold the breath for about 10 seconds, then wait before a second puff — holding lets the particles settle in the airways.
- With a spacer, one puff at a time into the spacer, then breathe in slowly or take several normal breaths — the spacer removes the timing problem.
- Dry powder inhaler: load it, breathe out away from it, then breathe in fast and deep — the patient's own flow disperses the powder.
- Rinse the mouth after an inhaled corticosteroid and have the patient show back the technique — this prevents thrush and checks learning.

## Acute asthma in adults: PEF as a percentage of best or predicted (with clinical features).

| Severity | PEF | Other features |
| --- | --- | --- |
| Moderate | 50–75% | Speaks in sentences; no features of severe asthma |
| Acute severe | 33–50% | Cannot finish sentences, fast breathing, fast heart rate |
| Life-threatening | Under 33% | Silent chest, cyanosis, exhaustion, confusion, low saturation |

## Complications

- Coughing, bronchospasm or light-headedness from repeated forced blows.
- Falsely low readings from poor effort, coughing, a tongue over the mouthpiece or a partly blocked meter.
- Falsely high readings from spitting or a «trumpet» blow using the cheeks.
- Oral candidiasis and hoarse voice from inhaled corticosteroids, reduced by a spacer and rinsing the mouth.
- Tremor and palpitations from short-acting bronchodilators, especially with overuse.

## Next step

- Confirm a suspected diagnosis with spirometry and a bronchodilator reversibility test where available.
- In an acute attack with a PEF of 50% or less, or any life-threatening feature, treat as severe and call a senior at once.
- Give the patient a written action plan with zones based on personal best and what to do in each.
- Review technique, adherence and triggers at every visit, and change the device or add a spacer if technique stays poor.
- Arrange follow-up after any attack, and frequent reliever use calls for a review of controller treatment.

## Memory aid

Metered-dose: «slow and steady». Dry powder: «fast and forceful».

## Test yourself

Think of the answer, then tap the question to see it.

## How is a peak expiratory flow reading performed and recorded?

Pointer at zero, patient upright, full breath in, lips sealed, then a short, maximal, fast blow; repeated three times and the best value recorded with the time.

## What is the key difference in inhalation between a metered-dose and a dry powder inhaler?

A metered-dose inhaler needs a slow, deep breath started as the canister is pressed; a dry powder inhaler needs a fast, forceful breath, because the patient's airflow disperses the powder.

## Which PEF values mark acute severe and life-threatening asthma in adults?

Acute severe asthma: PEF 33–50% of best or predicted; life-threatening asthma: PEF under 33%, together with the clinical features of each.

## Why is a spacer recommended with a metered-dose inhaler?

It removes the need to coordinate pressing and breathing, slows the particles so fewer hit the throat, increases lung delivery and reduces oral thrush from inhaled steroids.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/clinical-skills/peak-flow-and-inhaler-technique/)

## Elsewhere in DurgiPedia

- [Lung volumes, capacities and spirometry](https://durgical.com/en/physiology/lung-volumes-capacities-and-spirometry/)
- [Airway resistance](https://durgical.com/en/physiology/airway-resistance/)
- [Respiratory symptoms: cough, sputum, hemoptysis and dyspnea](https://durgical.com/en/clinical-exam/respiratory-symptoms-cough-sputum-hemoptysis-and-dyspnea/)

## Connections

## Related 3

- [Reading spirometry: obstructive or restrictive?](https://durgical.com/en/clinical-skills/reading-spirometry-obstructive-or-restrictive/)
- [The counselling and explanation station](https://durgical.com/en/clinical-skills/the-counselling-and-explanation-station/)
- [Starting non-invasive ventilation](https://durgical.com/en/clinical-skills/starting-non-invasive-ventilation/)

## Related conditions 2

- [Asthma](https://durgical.com/en/conditions/asthma/)
- [Chronic obstructive pulmonary disease (COPD)](https://durgical.com/en/conditions/chronic-obstructive-pulmonary-disease/)

## In Pharmacology 4

- [Salbutamol](https://durgical.com/en/pharmacology/salbutamol/)
- [Beta-2 adrenergic agonists](https://durgical.com/en/pharmacology/classes/beta-2-adrenergic-agonists/)
- [Inhaled corticosteroids](https://durgical.com/en/pharmacology/classes/inhaled-corticosteroids/)
- [Budesonide + formoterol](https://durgical.com/en/pharmacology/budesonide-formoterol/)

[← All clinical skills](https://durgical.com/en/clinical-skills/)

Educational content; it does not replace supervised hands-on training, your institution's protocols or a prescriber's order. A procedure is learnt with a teacher and done only once you are trained to do it.

Sources: [Peak Flow Rate Measurement](https://www.ncbi.nlm.nih.gov/books/NBK459325/) (StatPearls (NCBI Bookshelf), 2024).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/clinical-skills/peak-flow-and-inhaler-technique/