Respiratory Emergency Medicine Strong — BTS/SIGN Guideline

PEFR % Predicted

Calculates peak expiratory flow rate as percentage of predicted to classify asthma severity.

Score interpretation

Mild ≥ 75

PEFR ≥75% predicted: Mild exacerbation.

→ Salbutamol 2.5–5 mg nebulised (or 2–4 puffs via spacer). Reassess in 1 hour.

Moderate 50–74.9

PEFR 50–74% predicted: Moderate exacerbation.

→ Oxygen. Salbutamol 5 mg neb. Ipratropium 500 mcg neb. Prednisolone 40–50 mg PO or hydrocortisone 100 mg IV.

Severe 33–49.9

PEFR 33–49% predicted: Severe exacerbation.

→ Oxygen target SpO₂ 94–98%. Back-to-back salbutamol nebs. IV/PO steroids. Senior review. Consider IV MgSO₄ 1.2–2g.

Life-Threatening 0–32.9

PEFR < 33% predicted: Life-threatening asthma.

→ CALL FOR HELP. Anaesthetics. Continuous salbutamol neb. IV MgSO₄ 2g over 20 min. IV aminophylline if refractory. Prepare for intubation.

Interpretation bands for the PEFR %. Apply clinical judgement and local guidance.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Drugs

Pathways

Decision support only — verify against a current formulary, NICE, or your local guideline before clinical use.