acute asthma

---

severity grading

Severity	Key features
Moderate	Talks in sentences · RR increased · HR 100–120 · SpO2 90–95% · PEF 50–75% best · pCO2 normal
Severe	Talks in words · RR > 25 · HR > 120 · SpO2 < 90% · PEF 25–50% best · pCO2 normal (ominous if rising) · accessory muscle use, agitation
Life-threatening	Unable to speak · bradycardia · SpO2 < 90% · PEF < 25% best · pCO2 elevated · silent chest, cyanosis, confusion, exhaustion
Near-fatal	Requiring mechanical ventilation · respiratory arrest

---

ED management

all severities

1. Salbutamol — 5 mg nebulised q20min ×3 (or MDI 4–8 puffs via spacer q20min in moderate). Continuous nebulisation if severe
2. Systemic corticosteroids — give within first hour:
   • Prednisone 40–50 mg PO (if tolerating oral)
   • Methylprednisolone 40–60 mg IV or hydrocortisone 200 mg IV (if unable to take PO or life-threatening)
   • Alternative: dexamethasone 12–16 mg PO/IV once daily × 1–2 days (similar efficacy, better adherence)
3. Supplemental O2 — target SpO2 93–95% (avoid hyperoxia)

moderate, severe, or life-threatening — add:

4. Ipratropium — 250 µg nebulised q20min ×3 (first hour only; no benefit beyond 3 doses)
5. IV magnesium sulphate — 2 g (8 mmol) over 20 min; single dose for life-threatening or poor response to initial bronchodilators (3Mg, 2013)
6. Consider IV salbutamol infusion if poor response to nebulised therapy (5–20 µg/min, titrate; cardiac monitoring)

refractory / near-fatal:

7. Epinephrine — 0.3–0.5 mg IM (1:1000) if anaphylaxis suspected or peri-arrest
8. NIV — may be trialled cautiously; high failure rate in severe asthma
9. Intubation — see below

---

intubation considerations

Intubation in acute asthma carries high risk — delayed if possible but never delayed too long.

• Indications: respiratory arrest, refractory hypoxaemia, obtundation, haemodynamic collapse
• Preoxygenation: BiPAP is commonly used; consider early if trajectory is toward intubation
• Ketamine for induction (bronchodilator properties; 1–2 mg/kg IV)
• Use the largest ETT that fits (reduces resistance)
• Post-intubation: low RR (8–10/min), long expiratory time (I:E ≥ 1:4–5), low tidal volume (6–8 mL/kg), plateau pressure < 30 cmH2O, tolerate permissive hypercapnoea
• Danger: auto-PEEP and dynamic hyperinflation → hypotension post-intubation. Disconnect from ventilator briefly if haemodynamic collapse (decompress trapped air)
• Prognosis: immediate mortality for mechanically ventilated severe asthma is very low with appropriate ventilator strategy — do not delay intubation when indicated

---

disposition

discharge criteria (from ED)

• PEF > 60–70% predicted or personal best
• SpO2 ≥ 94% on room air
• Clinically improved, able to use inhaler
• Observed ≥ 1 hour after last bronchodilator

discharge plan

• Prednisone 40–50 mg PO daily × 5–7 days (no taper needed for ≤ 7 days)
• ICS — start or increase; prescribe ICS-formoterol if not already on it
• Written action plan — review or provide
• Follow-up within 2–7 days
• Review triggers — what caused this exacerbation?

admit if:

• Persistent SpO2 < 92% or PEF < 40% after treatment
• Any life-threatening features
• Prior near-fatal exacerbation
• Unable to be reassessed in follow-up
• Presenting overnight (symptoms may relapse)

---

what NOT to do

• Aminophylline IV — no evidence of benefit over standard bronchodilators; arrhythmia risk
• Chest X-ray routinely — only if pneumothorax, pneumonia, or alternate diagnosis suspected
• Sedate an agitated asthmatic — agitation is hypoxia/hypercapnoea until proven otherwise
• Send home without ICS — every ED visit for asthma is a failure of preventive therapy
• Delay steroids — greatest benefit when given within 1 hour of presentation