Acute Asthma

Severity is classified by PEFR, SpO₂, RR, HR and ability to speak. Life-threatening features require immediate ITU involvement. Never underestimate acute asthma — it kills.

BTS/SIGN Asthma Guideline

The pathway

1 · Assess severity

Moderate: PEFR 50–75%, speaking in phrases
Severe: PEFR 33–50%, RR >25, HR >110, unable to complete sentences
Life-threatening: PEFR <33%, SpO₂ <92%, silent chest, cyanosis, confusion, bradycardia

2 · O₂

High-flow O₂ via face mask. Target SpO₂ 94–98%. Drive nebs with O₂.

3 · Salbutamol nebuliser

2.5–5mg via oxygen-driven nebuliser. Can be given back-to-back in severe/life-threatening.

4 · Ipratropium bromide

500mcg nebulised. Add to salbutamol in acute severe and life-threatening asthma.

5 · Systemic steroids

Prednisolone 40–50mg PO or hydrocortisone 100mg IV. Give within 1 hour. Continue 5 days minimum.

6 · IV magnesium sulphate

1.2–2g over 20 minutes IV. For life-threatening or severe not responding to initial treatment.

7 · Reassess PEFR

At 15–30 minutes. If <50% and not improving — escalate to ITU.

8 · Discharge criteria

PEFR >75% for 1 hour, stable SpO₂, inhaler technique checked, prednisolone 5 days, GP follow-up 2 working days.

Drugs

Drug	Dose	Route	Notes
Salbutamol	2.5–5mg	Nebulised	O₂-driven. Can repeat back-to-back in life-threatening.
Ipratropium	500mcg	Nebulised	Add in acute severe. Q4–6h after initial dose.
Prednisolone	40–50mg	PO	Or hydrocortisone 100mg IV if can't swallow. 5 days.
Magnesium sulphate	1.2–2g	IV	Over 20 minutes. Single dose.
Hydrocortisone	100mg	IV	Use if unable to take oral steroids.

When to escalate

PEFR <33% (life-threatening),SpO₂ <92% despite high-flow O₂,Silent chest,Exhaustion, confusion, reduced conscious level,No improvement at 15–30 minutes,PaCO₂ normal or rising (pre-arrest sign)

Reference: BTS/SIGN British Guideline on Management of Asthma 2019 (updated 2023)

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