Acute severe asthma

Acute asthma is covered by BTS/SIGN 158 — the 2024 BTS/NICE/SIGN guideline (NG245) does not cover attacks.

Act now

1
Oxygen to SpO₂ 94–98%.
2
Nebulised salbutamol (oxygen-driven), repeat or back-to-back if poor response.
3
Add nebulised ipratropium in severe or life-threatening attacks or poor response.
4
Steroids in all attacks: oral prednisolone, or IV hydrocortisone if unable to swallow.

Acute severe (any one): PEF 33–50% best/predicted, RR ≥25, HR ≥110, cannot complete sentences.
Life-threatening (any one): PEF <33%, SpO₂ <92%, PaO₂ <8 kPa, normal PaCO₂ (4.6–6.0 kPa), silent chest, cyanosis, poor effort, arrhythmia, exhaustion, altered consciousness, hypotension.
Near-fatal: raised PaCO₂ and/or needing ventilation.

PEF before and after treatment, arterial gas if SpO₂ <92% or life-threatening features, CXR if suspected pneumothorax/consolidation or not improving.
U&E — beta-agonists and steroids lower potassium.

Severe attack not responding to initial bronchodilators: single dose of IV magnesium sulfate.
Do not give routine antibiotics.
Before discharge: check inhaler technique, steroid course, personalised asthma action plan, follow-up.

Life-threatening or near-fatal features, deteriorating PEF, persistent or worsening hypoxia, rising PaCO₂, exhaustion, drowsiness: senior and critical care immediately.

Salbutamol

5 mg nebulised.

Ipratropium bromide

500 micrograms nebulised 4–6-hourly.

Prednisolone

40–50 mg orally daily for at least 5 days; or hydrocortisone 100 mg IV 6-hourly.

Magnesium sulfate

1.2–2 g IV over 20 minutes (single dose).

Check the BNF and your local formulary before prescribing.

Written to current guidance · sources checked 14 Nov 2026. We watch NICE for updates weekly.

Sources (3)

Reviewed by Aboodee Alhasso, MPharm MRCPharm IP on 14 Nov 2026

For healthcare professionals, as an aid to clinical judgement — not a substitute for it. Follow your local policy and ask a senior when in doubt.