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Acute asthma
Grade it fast, treat it hard — and fear the quiet chest. Measure the PEF and SpO₂, grade the attack, start nebulisers and steroids, escalate through magnesium to ITU if needed, and only discharge when it is truly safe. Built for revision, not live patient decisions.
Settle them, and check the basics
grade itRed flags — what each should make you think
A "normal" PaCO₂ in an acute asthma attack is a bad sign. A breathless asthmatic should be blowing CO₂ off, so a normal level (4.6–6.0 kPa) means they are tiring. A rising CO₂ means near-fatal asthma, and they need ITU now.
Treatment ladder (BTS/SIGN)
- O₂Oxygen
- β₂Salbutamol 5 mg nebulised
- IpIpratropium 500 micrograms
- StSteroids
- MgIV magnesium sulfate
- ☎Senior + ITU
Understand the patient — grade the attack
BTS/SIGNSeverity
- Moderate — PEF 50–75% best/predicted, no severe features
- Acute severe — any of: PEF 33–50%, RR ≥25, HR ≥110, unable to complete sentences
- Life-threatening — any of: PEF below 33%, SpO₂ below 92%, PaO₂ below 8 kPa, "normal" PaCO₂, silent chest, cyanosis, poor effort, arrhythmia, exhaustion, altered consciousness, hypotension
- Near-fatal — raised PaCO₂ and/or needing ventilation with raised inflation pressures
Don't forget
- ABG if SpO₂ below 92% or any life-threatening features
- CXR only if pneumothorax, consolidation, life-threatening asthma, or failure to respond
- IV aminophylline only with senior/ITU advice
- No sedatives
- Monitor potassium (salbutamol lowers it)
Work A–E — assess and act as you go
The diagnoses you must not miss
tap to open eachWhat points toward it, what would rule it in, and how to manage it.
Any life-threatening feature; a rising or normal PaCO₂; exhaustion.
PEF, SpO₂, ABG.
Maximal treatment, IV magnesium, senior and ITU now; intubation by an experienced anaesthetist.
Sudden deterioration, unilateral reduced breath sounds, tracheal deviation.
CXR or lung ultrasound; tension is a clinical diagnosis.
Tension → needle decompression then chest drain. See the pneumothorax page.
Wheeze with urticaria, angioedema, hypotension after a trigger.
Clinical.
IM adrenaline. See the anaphylaxis page.
Investigate — what to order, when, and what it tells you
test with a question in mindPEF
SpO₂ / ABG
Bloods
CXR
How the plan comes together
disposition · handoverhome
PEF above 75% best/predicted 1 h after initial treatment (or stable after admission), good inhaler technique checked.
Prednisolone for at least 5 days, review inhaled steroids (preventer), written personalised asthma action plan, GP review within 2 working days.
admit / ITU
Any life-threatening feature, severe features persisting after initial treatment, previous near-fatal attack, pregnancy, presenting at night, or poor social support.
Hand over: PEF trend, treatments and times, gas, response.
Grade every attack with a PEF and SpO₂, and fear the patient who becomes quiet. Before discharge, check inhaler technique and make sure they have a preventer: most asthma deaths are in people who weren't on enough inhaled steroid. Nicely done getting here.
Clerking template
copy or downloadAcute asthma — documentation structure
A structure and prompt list to help you document and think systematically. It is not a completeness check and cannot guarantee nothing is missed — use your trust's own proforma, your seniors, and your clinical judgement.
Test yourself
active recallCover the answer, say it out loud, then reveal. Retrieval beats re-reading.
0 / 10 knownFrequently asked questions
quick answersWhat are the red flags for acute asthma?
- PEF below 33% best/predicted — think life-threatening
- SpO₂ below 92% — think life-threatening
- Silent chest, cyanosis, poor effort — think life-threatening
- Exhaustion, confusion, arrhythmia, hypotension — think life-threatening
- Normal or raised PaCO₂ — think near-fatal — ITU
- Previous ITU admission / ventilation — think high-risk patient
- Tracheal deviation, absent breath sounds — think pneumothorax
What is the initial management of acute asthma?
- Oxygen — to SpO₂ 94–98%
- Salbutamol 5 mg nebulised — oxygen-driven; back-to-back if severe
- Ipratropium 500 micrograms — nebulised, 4–6 hourly, in severe or life-threatening attacks
- Steroids — prednisolone 40–50 mg daily for at least 5 days, or IV hydrocortisone 100 mg 6-hourly if unable to swallow
- IV magnesium sulfate — 1.2–2 g over 20 min for severe/life-threatening attacks not responding
- Senior + ITU — life-threatening/near-fatal features, or not improving
Always alongside senior support and your local guideline.
What diagnoses must you not miss in acute asthma?
- Life-threatening / near-fatal asthma — silent chest · rising CO₂
- Pneumothorax — sudden worse · unilateral
- Anaphylaxis (mimic/trigger) — wheeze + rash/swelling
Open each one in the must-not-miss section for what points toward it, how to rule it in, and how to manage it.
What investigations should a junior doctor order for acute asthma?
- PEF — Severity and response, as % of best or predicted.
- SpO₂ / ABG — If SpO₂ below 92% or life-threatening features.
- Bloods — Salbutamol causes hypokalaemia.
- CXR — Suspected pneumothorax/consolidation, life-threatening attack, or poor response.
Admit or discharge: how is the plan decided for acute asthma?
- Home — PEF above 75% best/predicted 1 h after initial treatment (or stable after admission), good inhaler technique checked.
- Admit / itu — Any life-threatening feature, severe features persisting after initial treatment, previous near-fatal attack, pregnancy, presenting at night, or poor social support.
Is there a clerking template for acute asthma?
Yes — there is a free clerking template for acute asthma on this page, structured as presenting complaint, red flags asked, history, examination (A–E), investigations, differentials, plan and escalation. You can copy it or download it as a Word document. Jump to the template.
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