Acute asthma and COPD exacerbations

Acute Severe Asthma: Emergency Management

Acute severe asthma is an immediate medical emergency. Severity classification dictates the aggressiveness of pharmacological escalation and monitoring.

Severity Stratification in Acute Asthma

• Mild to Moderate: Speaks in phrases, heart rate $100-120\text{ bpm}$, respiratory rate $< 25\text{ breaths/min}$, oxygen saturation $\ge 94\%$, PEF $50-75\%$ predicted.
• Severe: Cannot complete sentences in one breath, accessory muscle use, respiratory rate $> 25\text{ breaths/min}$, heart rate $> 110\text{ bpm}$, oxygen saturation $< 93\%$, PEF $33-50\%$ predicted.
• Life-Threatening: Silent chest on auscultation, cyanosis, feeble respiratory effort, bradycardia or dysrhythmia, hypotension, exhaustion, altered conscious state, PEF $< 33\%$ predicted, or a normal/elevated arterial $\text{PaCO}_2$ ($> 42\text{ mmHg}$). In a hyperventilating patient, a 'normal' $\text{PaCO}_2$ signals respiratory muscle fatigue and impending respiratory arrest.

Emergency Pharmacological Protocol

• Acute adult asthma oxygen: Give oxygen if SpO2 is below 92% and titrate to 92–96%. Patients at risk of hypercapnic respiratory failure need a target such as 88–92% and blood-gas monitoring. Uncontrolled high oxygen concentrations are not universally harmless.

1. Inhaled Bronchodilators: Administer salbutamol ($5\text{ mg}$) plus ipratropium bromide ($500\ \mu\text{g}$) nebulised back-to-back using oxygen at $6-8\text{ L/min}$, or salbutamol 12 puffs via a pressurized metered-dose inhaler (pMDI) with a large-volume spacer (giving 1 puff per 4 tidal breaths) every 15 to 20 minutes for the first hour.
2. Systemic Corticosteroids: Initiate oral prednisolone $50\text{ mg}$ immediately. If the patient is vomiting, unable to swallow, or in extremis, administer intravenous hydrocortisone $100\text{ mg}$ every 6 hours. Systemic steroids accelerate resolution of airway mucosal oedema and reduce relapse rates.
3. Intravenous Magnesium Sulfate: For patients presenting with severe or life-threatening features refractory to initial bronchodilator therapy, infuse intravenous magnesium sulfate $2\text{ g}$ ($8.4\text{ mmol}$) in $100\text{ mL}$ normal saline over 20 minutes. Magnesium induces bronchial smooth muscle relaxation through calcium channel antagonism.
4. Intravenous Salbutamol and Aminophylline: Reserved strictly for intensive care settings under continuous invasive hemodynamic monitoring when intubation is imminent. Intravenous salbutamol carries significant risks of severe lactic acidosis, hypokalaemia, and tachyarrhythmias.

Acute Exacerbation of COPD (AECOPD)

An acute exacerbation of COPD is an acute worsening of baseline respiratory symptoms (dyspnoea, cough, sputum volume, and sputum purulence) beyond normal day-to-day variations that warrants a change in regular medication.

Controlled Oxygen Delivery

Excess oxygen can worsen CO2 retention in COPD, largely through V/Q changes and the Haldane effect, with altered ventilation also contributing. It is not simply loss of a hypoxic drive. Titrate to the prescribed target and obtain blood gases when indicated; acute asthma can also develop ventilatory failure and should not receive indiscriminate oxygen.

• Delivery System: Use 24% or 28% Venturi masks or low-flow nasal cannulae at $1-2\text{ L/min}$. Monitor arterial blood gases (ABG) at baseline and repeat within 30 to 60 minutes after initiating or adjusting oxygen therapy.

Pharmacological Escalation

• Bronchodilators: Nebulised salbutamol ($2.5-5\text{ mg}$) and ipratropium bromide ($500\ \mu\text{g}$) driven by compressed air (never unmonitored oxygen; if oxygen is required, bleed low-flow oxygen via nasal prongs at $2\text{ L/min}$ beneath the air-driven nebuliser mask).
• Systemic Corticosteroids: Oral prednisolone $30-50\text{ mg}$ once daily for 5 days. Extended courses offer no additional benefit and increase risks of hyperglycemia, secondary infection, and prolonged hospital stays.
• Antimicrobial Therapy: Prescribed based on the Anthonisen criteria when patients exhibit increased sputum purulence plus either increased sputum volume or increased dyspnoea. First-line oral therapy per Australian Therapeutic Guidelines is amoxicillin $500\text{ mg}$ every 8 hours or doxycycline $100\text{ mg}$ every 12 hours for 5 days.

Non-Invasive Ventilation (NIV / BiPAP)

Non-invasive bilevel positive airway pressure ventilation is the standard of care for acute hypercapnic respiratory failure complicating AECOPD. NIV reduces work of breathing, improves alveolar ventilation, lowers intubation rates by over 60%, and significantly reduces inpatient mortality.

• Arterial Blood Gas: Criteria for Initiating NIV in AECOPD: Persistent respiratory acidosis ($\text{pH} < 7.35$ and $\text{PaCO}_2 > 45\text{ mmHg}$) despite 60 minutes of optimal medical therapy
• Clinical Signs: Criteria for Initiating NIV in AECOPD: Moderate-to-severe dyspnoea with tachypnoea ($\text{RR} > 25\text{ breaths/min}$), accessory muscle use, or abdominal paradox
• Settings Protocol: Criteria for Initiating NIV in AECOPD: Inspiratory Positive Airway Pressure (IPAP) started at $10-12\text{ cmH}_2\text{O}$; Expiratory Positive Airway Pressure (EPAP) at $4-5\text{ cmH}_2\text{O}$
• Contraindications: Criteria for Initiating NIV in AECOPD: Cardiac or respiratory arrest, severe hemodynamic instability, facial burns/trauma, impaired consciousness/inability to protect airway, active vomiting, massive upper GI bleed

Primary references (checked 7 October 2026): Australian Asthma Handbook.