Oxygen therapy, HFNC and NIV

Acute severe and life-threatening asthma

Reviewed Nov 2026·2 references
New· views rounded down, updated weekly

Grade severity quickly (PEF, speech, RR, HR, SpO2, PaCO2). Give oxygen-driven salbutamol, ipratropium and steroids at once; add IV magnesium; a normal or rising PaCO2 is a danger sign; intubate early and ventilate to avoid breath stacking.

At the bedside

Timed steps
  1. 1

    Grade severity

    0 min

    Acute severe: PEF 33-50% predicted/best, RR ≥ 25, HR ≥ 110, cannot complete sentences. Life-threatening: PEF < 33%, SpO2 < 92%, PaO2 < 60 mmHg (8 kPa), normal PaCO2 (35-45 mmHg), silent chest, cyanosis, poor effort, arrhythmia, exhaustion, altered consciousness, hypotension. Near-fatal: raised PaCO2.

  2. 2

    Oxygen

    0 min

    Target SpO2 93-95%.

  3. 3

    Bronchodilators

    0-5 min

    Salbutamol 5 mg nebulised with oxygen, repeated every 15-30 min (or continuous 5-10 mg/h); add ipratropium 500 mcg every 4-6 h in severe/life-threatening attacks.

  4. 4

    Steroids

    0-60 min

    Prednisolone 40-50 mg orally (or hydrocortisone 100 mg IV every 6 h); continue ≥ 5 days.

  5. 5

    IV magnesium

    Poor response

    1.2-2 g IV over 20 min, single dose.

  6. 6

    Senior / ICU

    Still poor

    Consider IV aminophylline (senior decision), IV salbutamol only if inhaled therapy cannot be used; ketamine infusion as bridge; ABG for rising PaCO2.

  7. 7

    When

    Intubate

    Exhaustion, falling GCS, rising PaCO2 with acidosis, arrest. Use ketamine induction, large tube (≥ 8.0), most experienced operator.

  8. 8

    Avoid breath stacking

    Ventilate

    Low rate 8-12, Vt 6-8 mL/kg PBW, short Ti, high inspiratory flow, I:E ≥ 1:4, accept PaCO2 rise (permissive hypercapnia, pH > 7.2), plateau < 30, measure intrinsic PEEP. If hypotension: disconnect and compress the chest gently.

First-line bronchodilator

Salbutamol (albuterol)

Nebulised
Dose
5 mg every 15-30 min, or continuous 5-10 mg/h
Preparation
5 mg/2.5 mL respule (or 1 mL of 5 mg/mL + 3 mL NS)

Add-on in severe attacks

Ipratropium bromide

Nebulised
Dose
500 mcg every 4-6 h

Severe attack not responding

Magnesium sulfate

IV over 20 min
Dose
1.2-2 g single dose
Preparation
2 g = 4 mL of 50% in 100 mL NS over 20 min

Systemic steroid

Prednisolone / hydrocortisone

Oral / IV
Dose
Prednisolone 40-50 mg daily ≥ 5 days, or hydrocortisone 100 mg IV 6-hourly

Senior-only add-on

Aminophylline

IV
Dose
5 mg/kg over 20 min (omit if on theophylline), then 0.5 mg/kg/h
Worked example
60 kg: 300 mg in 100 mL NS over 20 min, then 30 mg/h
Red flag · call your senior now
Normal PaCO2 in an asthma attack means fatigue: life-threatening.
Red flag
Silent chest, cyanosis, confusion, bradycardia, hypotension.
Red flag
Hypotension after intubation: dynamic hyperinflation or tension pneumothorax.
Pitfall
Sedating an agitated hypoxic asthmatic on the ward.
Pitfall
Under-dosing steroids or delaying them.
Pitfall
Treating with high respiratory rate on the ventilator (breath stacking, barotrauma, cardiac arrest).
Pearl
Measure intrinsic PEEP with an end-expiratory hold; plateau pressure < 30 cmH2O and auto-PEEP < 10 cmH2O are reasonable targets.

References

  1. 1

    British Thoracic Society / Scottish Intercollegiate Guidelines Network. British guideline on the management of asthma (SIGN 158), 2019, amended 2024: management of acute asthma

  2. 2

    Global Initiative for Asthma. Global strategy for asthma management and prevention (current report)

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NIV and CPAP beyond COPD

Educational reference for trained clinicians. Check doses against your hospital protocol and the patient in front of you.