What is the recommended initial dose of epinephrine (adrenaline) for a patient with airway obstruction secondary to severe asthma?

Epinephrine Dosing for Severe Asthma with Airway Obstruction

For a patient with airway obstruction secondary to severe asthma, administer subcutaneous epinephrine (1:1000 concentration) at a dose of 0.01 mg/kg, up to a maximum of 0.3-0.5 mg, which can be repeated every 20 minutes for up to 3 doses. 1

Initial Dosing Algorithm

Adult Dosing (≥30 kg)

• Administer 0.3-0.5 mg (0.3-0.5 mL of 1:1000 solution) subcutaneously into the anterolateral thigh 1, 2
• Repeat every 20 minutes as needed for up to 3 doses 1
• The typical adult dose is 0.3 mg, with 0.5 mg reserved for more severe presentations 2

Pediatric Dosing (<30 kg)

• Administer 0.01 mg/kg subcutaneously, up to a maximum of 0.3 mg per injection 1, 2
• Repeat every 20 minutes for up to 3 doses as needed 1

Route and Site of Administration

The subcutaneous route into the anterolateral aspect of the mid-thigh is the preferred method for epinephrine administration in severe asthma. 1, 2

• The intramuscular route is equally acceptable and may provide faster absorption 2, 3
• Use a needle at least 1/2 to 5/8 inch long to ensure proper delivery 2
• Do not administer repeated injections at the same site, as vasoconstriction may cause tissue necrosis 2
• Avoid injection into buttocks, digits, hands, or feet 2

Critical Context: When to Use Epinephrine in Asthma

Epinephrine should be reserved for severe asthma exacerbations that are not responding adequately to first-line therapy with inhaled beta-agonists. 1

Indications for Epinephrine Use

• Severe airway obstruction with peak expiratory flow <40% predicted 1
• Life-threatening features present (silent chest, cyanosis, feeble respiratory effort, bradycardia, hypotension, exhaustion, confusion) 1
• Inadequate response to initial nebulized beta-agonist therapy 1
• Inability to deliver nebulized therapy effectively 1

Important Limitation

There is no proven advantage of systemic epinephrine therapy over aerosol beta-agonists in most cases of acute asthma. 1 Research demonstrates that in patients with severe airway obstruction (peak flow <120 L/min or <25% predicted), parenteral epinephrine was superior to aerosol epinephrine, but selective beta-2 agonists remain the preferred first-line treatment 4.

Monitoring and Safety Considerations

Monitor patients closely for cardiovascular effects, including increased heart rate, myocardial irritability, and increased oxygen demand. 1

• Epinephrine is well-tolerated even in patients >35 years of age, despite its nonselective adrenergic properties 1
• Inspect the solution before administration; do not use if colored, cloudy, or contains particulate matter 2
• Monitor clinically for reaction severity and cardiac effects with repeat doses titrated to effect 2
• Measure peak expiratory flow 15-30 minutes after administration to assess response 1

Concurrent Essential Therapies

Epinephrine is an adjunct to, not a replacement for, standard asthma therapy. 1

Must Continue Simultaneously:

• High-dose nebulized selective beta-2 agonists (albuterol 5 mg or terbutaline 10 mg) every 20 minutes for 3 doses 1
• Systemic corticosteroids (prednisolone 30-60 mg orally or IV hydrocortisone 200 mg) administered immediately 1
• Oxygen therapy to maintain SpO2 >90% (>95% in pregnant women and patients with heart disease) 1
• Ipratropium bromide (0.5 mg nebulized) added to beta-agonist for life-threatening features 1

Alternative: Terbutaline

Terbutaline 0.25 mg subcutaneously can be used as an alternative to epinephrine, repeated every 20 minutes for up to 3 doses. 1

• Terbutaline has more selective beta-2 activity compared to epinephrine's nonselective adrenergic effects 1
• However, there is no proven advantage of systemic therapy over aerosol beta-agonists 1

Common Pitfalls to Avoid

• Do not use the 1:10,000 concentration intended for IV use in cardiac arrest 1 - this is a critical medication error that can lead to underdosing
• Do not delay or withhold nebulized selective beta-2 agonists - these remain the cornerstone of acute asthma treatment 1
• Do not give epinephrine intravenously in conscious patients with asthma - the IV route is reserved for anaphylactic shock with appropriate dilution (0.05-0.1 mg of 1:10,000) 1
• Do not administer sedatives - these are contraindicated in asthma exacerbations 1
• Do not give antibiotics unless bacterial infection is documented 1

Decision Point: Hospital Admission

Patients requiring epinephrine for severe asthma should be referred to the hospital immediately. 1

Criteria supporting this decision include:

• Any life-threatening features present 1
• Peak expiratory flow <33% predicted after initial treatment 1
• Features of severe attack persisting after initial treatment 1
• Patients requiring parenteral therapy are at higher risk and need intensive monitoring 1