PEFR % Predicted
Calculates peak expiratory flow rate as percentage of predicted to classify asthma severity. PEF is one feature: BTS/SIGN severity also uses respiratory rate, heart rate, ability to complete sentences, SpO₂ and other signs.
Score interpretation
PEF > 75% of best or predicted.
→ Adults: salbutamol 2.5–5 mg nebulised (or 2–4 puffs via spacer). Reassess in 1 hour. Children: use a children's formulary.
PEF > 50–75% of best or predicted: moderate exacerbation.
→ Oxygen. Adults: salbutamol 5 mg neb; ipratropium 500 mcg neb; prednisolone 40–50 mg PO or hydrocortisone 100 mg IV. Children: use a children's formulary.
PEF 33–50% of best or predicted: acute severe asthma.
→ Oxygen target SpO₂ 94–98%. Back-to-back salbutamol nebs. IV/PO steroids. Senior review. Consider IV MgSO₄ (adults: 1.2–2g). Children: use a children's formulary.
PEF < 33% of best or predicted: life-threatening asthma.
→ CALL FOR HELP. Anaesthetics. Continuous salbutamol neb. IV MgSO₄ (adults: 2g over 20 min). IV aminophylline if refractory. Prepare for intubation. Children: use a children's formulary.
Interpretation bands for the PEFR %. Apply clinical judgement and local guidance.
References
- BTS/SIGN British Guideline on the Management of Asthma. 2019 (Updated 2022).
Related
Curated clinical cross-links plus same-class fallbacks.
- Salbutamol (Paediatric — Asthma/Wheeze) · Short-Acting Beta-2 Agonist (SABA)
- Prednisolone (Paediatric) · Corticosteroid — Asthma Exacerbation / Croup / Nephrotic Syndrome / IBD
- Tezepelumab (CRSwNP / Severe Asthma) · Anti-TSLP (Thymic Stromal Lymphopoietin) Monoclonal Antibody
- Montelukast (Paediatric) · Leukotriene Receptor Antagonist — Asthma Prophylaxis / Allergic Rhinitis
- Magnesium Sulphate IV (Acute Asthma) · Bronchodilator / Smooth muscle relaxant
- Dupilumab (Moderate-Severe Asthma) · Anti-IL-4/IL-13 receptor alpha monoclonal antibody (type 2 inflammation biologic)
- Acute Asthma in Adults · BTS/SIGN British Guideline on Asthma 2019; NICE NG80
- Pulmonary Embolism Assessment · NICE NG158; ESC 2019 PE Guidelines
- Acute Exacerbation of COPD (AECOPD) · NICE NG115; GOLD 2024
- Spontaneous Pneumothorax (Adult) · BTS Pleural Disease 2023
- Atypical Pneumonia (Legionella / Mycoplasma / Chlamydophila) · BTS 2023; IDSA
- COPD Exacerbation Management · NICE NG115 / GOLD 2024
Decision support only — verify against a current formulary, NICE, or your local guideline before clinical use.