FFinalistSouthampton · 2027
Acute care
AKT · Acute care/Cardiac & respiratory

Acute asthma (severe/life-threatening)

Acute bronchoconstriction + airway inflammation

Overview

A potentially fatal asthma exacerbation. Severity is graded (moderate / acute severe / life-threatening) on objective signs — and the dangerous trap is the SILENT chest and a normalising CO2, which signal exhaustion, not improvement.

Recognise

  • Acute severe: PEF 33–50% best/predicted, RR ≥25, HR ≥110, cannot complete sentences
  • Life-threatening: PEF <33%, SpO2 <92%, SILENT chest, cyanosis, exhaustion, bradycardia/hypotension, altered consciousness
  • Near-fatal: raised PaCO2 / needing ventilation

Red flags

  • A SILENT chest, exhaustion, normal or rising CO2, or SpO2 <92% = life-threatening → seek ICU

Differentials & how to tell them apart

Acute exacerbation of COPDolder smoker, chronic airflow limitation, CO2 retainer
Acute pulmonary oedemacrackles, raised JVP, cardiac history, frothy sputum
Anaphylaxistrigger, urticaria/angioedema, hypotension
Inhaled foreign body / upper-airway obstructionstridor, sudden onset

Investigations

PEF, SpO2, ABG (a normalising/rising PaCO2 is ominous), CXR if complications suspected.

Management

O2 to 94–98% + nebulised salbutamol/ipratropium + steroids; escalate with IV magnesium

  1. 1High-flow O2 (94–98%), back-to-back nebulised salbutamol + ipratropium, early steroids (prednisolone PO or hydrocortisone IV).Gate: Life-threatening features (silent chest, exhaustion, rising CO2, SpO2 <92%) → IV magnesium sulfate + urgent ICU/anaesthetics
  2. 2Senior/ICU review; consider IV salbutamol/aminophylline; ventilation if deteriorating.
Oxygen (target 94–98%) — high-flow
Salbutamol (back-to-back/nebulised) + ipratropium — bronchodilators, O2-driven nebs
Steroids (oral prednisolone or IV hydrocortisone) — early
IV magnesium sulfate — severe/life-threatening not responding

Key points

A rising or "normal" PaCO2 in an exhausted asthmatic is a pre-terminal sign, not reassurance. The silent chest means too little air movement to wheeze.

Monitor & prognosis

PEF, SpO2, serial ABG, RR/HR; response to nebs; ICU threshold.

Good with prompt treatment; near-fatal attacks flag high future risk.

Source: BTS/SIGN (now NICE/BTS/SIGN) asthma guideline