Pulmonary · Topic 10 of 28

Acute Severe Asthma

Pulmonary · obstructive lung disease

Acute Severe Asthma

Albuterol plus ipratropium, oxygen to 93–95%, steroids within an hour, IV magnesium if refractory — and fear a silent chest or a normal PaCO₂.

Key numbers

Prednisone 40–50 mg within the first hourpred 40–50 mg × 5–7 d

Silent chest or drowsiness: life-threateningPEF < 50%, SpO₂ < 92%

Normal or rising PaCO₂ is ominousPaCO₂ ≥ 40 mmHg

Magnesium 2 g IV over 20 minutesMg 2 g IV over 20 min

01 · Look forSilent chest or drowsiness: life-threatening

Severe: cannot speak, drink or lie down, RR > 30, SpO₂ < 92%, PEF < 50%, quiet chest. Drowsiness, confusion, cyanosis or a silent chest are life-threatening — transfer to the ICU.

02 · Look forNormal or rising PaCO₂ is ominous

PaCO₂ is usually low (< 40 mmHg) in an attack; a normal or rising PaCO₂ (especially > 45) with fatigue or somnolence signals respiratory failure — prepare for ventilatory support.

03 · GiveMagnesium 2 g IV over 20 minutes

For severe attacks not responding to initial bronchodilators and steroids, or with persistent hypoxemia, give a single dose of IV magnesium sulfate 2 g over 20 minutes; it reduces admissions. Nebulized magnesium does not help.

Causes & risk factors

Why it happens

Red flags for fatal asthmaRisk of fatal asthma: near-fatal asthma needing intubation, hospitalization or ED visits in the past year, current or recent oral steroids, no ICS, SABA overuse (> 1 canister/month), psychiatric illness, food allergy.

Presentation

What you'll see

Pulsus paradoxus > 15 mmHg: severe attackImpending respiratory failure combines altered consciousness, cyanosis, pulsus paradoxus > 15 mmHg, SpO₂ < 90%, PaO₂ < 60 and PaCO₂ > 45 mmHg; expiration is prolonged (I:E ≥ 1:3).

Diagnosis & monitoring

Work-up

Intubate for PaCO₂ > 60 or falling consciousnessNIV evidence is weak; if tried, never in agitated patients, and never sedate to allow NIV. Intubate for PaCO₂ > 60 mmHg, decreasing consciousness, excessive secretions, or no clear improvement after 1 hour of NIV.

Discharge once PEF exceeds 70%Reassess symptoms, SpO₂ and PEF at 1 hour. Discharge when mild criteria hold 1–2 hours after the last SABA, SpO₂ ≥ 92% on room air, PEF > 70%, and home support is adequate.

Do right now

In this order

First moves

Silent chest or drowsiness: life-threateningPEF < 50%, SpO₂ < 92%

→

Albuterol every 20 minutes, plus ipratropium

→

Titrate oxygen to SpO₂ 93–95%

→

Prednisone 40–50 mg within the first hourpred 40–50 mg × 5–7 d

→

Magnesium 2 g IV over 20 minutesMg 2 g IV over 20 min

Why each step

Silent chest or drowsiness: life-threateningSevere: cannot speak, drink or lie down, RR > 30, SpO₂ < 92%, PEF < 50%, quiet chest. Drowsiness, confusion, cyanosis or a silent chest are life-threatening — transfer to the ICU.

Albuterol every 20 minutes, plus ipratropiumGive albuterol by MDI and spacer (4–10 puffs) or nebulizer (2.5–5 mg) every 20 minutes for the first hour; add ipratropium for moderate–severe attacks. MDI with spacer works as well as a nebulizer.

Titrate oxygen to SpO₂ 93–95%Give oxygen when SpO₂ is < 92%, titrated to 93–95% in adults (92–95% acceptable); controlled oxygen gives better physiological outcomes than 100% oxygen. Oximetry may overestimate saturation in dark skin.

Prednisone 40–50 mg within the first hourGive systemic corticosteroids within 1 hour for all but the mildest attacks: prednisone or prednisolone 40–50 mg daily for 5–7 days in adults; oral equals IV, and no taper is needed.

Magnesium 2 g IV over 20 minutesFor severe attacks not responding to initial bronchodilators and steroids, or with persistent hypoxemia, give a single dose of IV magnesium sulfate 2 g over 20 minutes; it reduces admissions. Nebulized magnesium does not help.

Management

Orders

Ventilate slowly: low rate, high flowIf intubated, use volume assist-control with a low rate, high inspiratory flow (> 80 L/min) to lengthen exhalation, tidal volume 6–8 mL/kg ideal body weight, and accept hypercapnia to limit auto-PEEP.

Intubate with ketamine; avoid prolonged paralysisKetamine can be used for intubation by clinicians familiar with it; avoid routine neuromuscular blockade, which combined with corticosteroids can cause prolonged neuromuscular weakness.

Epinephrine first only if anaphylaxisIf the attack is part of anaphylaxis, give IM (or intranasal) epinephrine first; epinephrine is not routine for asthma without anaphylaxis.

Discharge on ICS-formoterol, never SABA aloneEvery patient leaves on ICS-containing treatment — preferably ICS-formoterol maintenance-and-reliever therapy (age ≥ 12) — with an action plan, inhaler teaching and follow-up within 2–7 days; SABA-only treatment is no longer recommended.

Red flags & don'ts

Avoid harm

Post-intubation hypotension: disconnect to release auto-PEEP complicationBreath stacking after intubation raises intrathoracic pressure and causes hypotension; disconnect the ventilator to let the patient exhale, then resume at a slower rate — and consider tension pneumothorax.

No sedatives in the nonintubated patient avoidSedatives, anxiolytics and hypnotics must be avoided during an asthma attack: respiratory depression from these drugs has been linked to avoidable asthma deaths.

No aminophylline, no routine antibiotics avoidIV aminophylline and theophylline are not recommended (poor efficacy, serious toxicity), and antibiotics are given only with strong evidence of infection such as fever, purulent sputum or pneumonia on imaging.

Moderate or severe acute asthma?

Commonly confused

Speech and posture	Talks in phrases, prefers sitting
Respiratory rate	Increased but ≤ 30/min
SpO₂ on room air	≥ 92%
PEF	50–70% of best or predicted
Chest	Expiratory wheeze

More detail

Reference

Show 6 reference facts

Before attributing distress to asthma, consider anaphylaxis, inducible laryngeal obstruction, pneumothorax, pneumonia, heart failure and pulmonary embolism.

Moderate attack (GINA): talks in phrases, prefers sitting, RR increased but ≤ 30/min, accessory muscle use, expiratory wheeze, SpO₂ ≥ 92% on room air, PEF 50–70% of best or predicted.

Arterial blood gases are not routine: obtain them when PEF or FEV1 is < 50% predicted or the patient is not responding or deteriorating; chest radiographs only for suspected complications.

High-dose SABA can cause tachycardia, hypokalemia, arrhythmias and lactic acidosis with hyperventilation, which can be mistaken for worsening asthma.

With permissive hypercapnia, a slow sodium bicarbonate infusion can be considered if pH falls below 7.10, aiming for pH 7.20–7.25; reduce tidal volume if plateau pressure exceeds 30–35 cmH₂O.

Heliox has no routine role but may be considered for severe attacks unresponsive to standard therapy; inhaled anesthetics (sevoflurane, isoflurane) bronchodilate in status asthmaticus but are poorly studied.

Pearl

A tiring patient with asthma and a “normal” PaCO₂ is not improving — the patient is running out of strength.

Sources · GINA 2026 Global Strategy for Asthma Management and Prevention (Strategy Report, Chapter 9) · GINA 2026 Summary Guide for Asthma Management and Prevention (Figure 9) · Merck Manual Professional — Treatment of Acute Asthma Exacerbations · Merck Manual Professional — Asthma · Merck Manual Professional — Overview of Mechanical Ventilation · Weingart S. EMCrit 16 — Coding Asthmatic, DOPES and Finger Thoracostomy · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).