During a witnessed cardiac arrest secondary to anaphylaxis, is intramuscular epinephrine beneficial if the patient is already pulseless and EMTs are on scene?

Intramuscular Epinephrine in Anaphylaxis-Induced Cardiac Arrest

Once a patient with anaphylaxis progresses to pulseless cardiac arrest, you must immediately abandon intramuscular epinephrine and switch to standard ACLS protocols with intravenous/intraosseous epinephrine at cardiac arrest dosing (1 mg of 1:10,000 every 3-5 minutes). 1

The Critical Distinction: Before vs. After Cardiac Arrest

Pre-Arrest Anaphylaxis Management

• Intramuscular epinephrine 0.3-0.5 mg (1:1000 concentration) into the anterolateral thigh is the first-line treatment for anaphylaxis with signs of systemic reaction, hypotension, airway swelling, or difficulty breathing. 1
• This IM route produces rapid peak plasma concentrations and is preferred due to ease of administration, effectiveness, and safety in the perfusing patient. 1
• Repeat every 5-15 minutes as needed if symptoms persist. 1, 2

Once Cardiac Arrest Occurs

• The moment the patient becomes pulseless, standard BLS and ACLS protocols take absolute priority, with immediate administration of IV/IO epinephrine at cardiac arrest dosing. 1
• The dose becomes 1 mg IV/IO (1:10,000 concentration) every 3-5 minutes during ongoing resuscitation. 1, 3, 4
• Intramuscular epinephrine is not appropriate for cardiac arrest because absorption is unpredictable in the low-flow state, the dose is insufficient, and peripheral perfusion is compromised. 4

Why IM Epinephrine Fails in Cardiac Arrest

The physiologic rationale is straightforward:

• During cardiac arrest, peripheral perfusion essentially ceases, making intramuscular absorption unreliable and inadequate. 4
• The 0.3-0.5 mg IM dose used for anaphylaxis is only 30-50% of the 1 mg dose required for cardiac arrest. 1, 3
• Even if absorbed, the delayed and unpredictable pharmacokinetics cannot provide the immediate systemic delivery needed during pulseless arrest. 4

The Witnessed Arrest Scenario: Your Specific Question

If EMTs witness a patient arrest from anaphylaxis on scene:

• Do not give IM epinephrine once the patient is pulseless. 1, 4
• Immediately begin high-quality CPR and establish IV/IO access. 1
• Administer 1 mg of epinephrine 1:10,000 IV/IO as soon as vascular access is obtained, then every 3-5 minutes. 1, 3
• Continue standard ACLS algorithms including airway management, which is particularly critical given the potential for laryngeal edema in anaphylaxis. 1

The evidence is unequivocal: There are no randomized controlled trials supporting alternative treatment algorithms for anaphylaxis-induced cardiac arrest, and the cornerstone of management is standard BLS and ACLS with early IV/IO epinephrine. 1

Common Pitfalls and How to Avoid Them

Concentration Confusion (A Potentially Lethal Error)

• The 1:1000 concentration (1 mg/mL) used for IM anaphylaxis is ten times more concentrated than the 1:10,000 formulation (0.1 mg/mL) required for IV cardiac arrest dosing. 4, 5
• Giving 1:1000 IV can cause severe iatrogenic cardiac complications including transient severe systolic dysfunction, myocardial ischemia, and lethal arrhythmias. 5, 6, 7
• Hospitals should stock clearly labeled, pre-filled syringes that differentiate IM (1:1000) from IV/IO (1:10,000) epinephrine. 4, 5

Delaying the Transition

• Do not continue IM dosing once cardiac arrest develops, even if you "just gave" an IM dose seconds before the arrest. 4, 2
• The transition must be immediate—standard resuscitative measures and prompt IV/IO epinephrine take priority over continued IM administration. 1, 4

Inadequate Dosing in Refractory Cases

• Some cases of anaphylaxis-induced cardiac arrest may be refractory to standard management despite prompt recognition and treatment. 8
• If patients present with potentially fatal symptoms or progress to cardiac arrest within minutes, consider more aggressive IV epinephrine dosing: start with 1-3 mg IV slowly over 3 minutes, followed by 3-5 mg over 3 minutes, then 4-10 mg/min infusion. 3
• One case series reported that patients may progress to cardiac arrest within minutes despite prompt management, with a 2.5% cardiac arrest rate among anaphylaxis cases presenting with shock. 8

Adjunctive Therapies (Secondary to Epinephrine)

While epinephrine is being administered:

• Aggressive IV fluid resuscitation with 1-2 liters of normal saline rapidly in adults (20 mL/kg boluses in children) is mandatory, as anaphylactic shock can cause up to 37% loss of circulating blood volume. 1, 2
• Secure the airway early if laryngeal edema is present—planning for surgical airway may be necessary. 1

Important caveat: There is no proven benefit from antihistamines, inhaled beta-agonists, or IV corticosteroids during anaphylaxis-induced cardiac arrest. 1 These are second-line therapies that should never delay epinephrine administration. 2, 9

Special Considerations

Beta-Blocker Therapy

• Patients on beta-blockers may have refractory hypotension despite epinephrine. 3
• Consider glucagon 1-5 mg IV over 5 minutes followed by infusion at 5-15 mcg/min. 3, 2

Post-Arrest Management

• If return of spontaneous circulation (ROSC) is achieved, IV epinephrine infusion at 5-15 mcg/min may be considered for post-arrest shock. 1
• Close hemodynamic monitoring is mandatory as cardiovascular status can change rapidly. 1, 3

The Bottom Line Algorithm

For witnessed anaphylaxis arrest on scene with EMTs:

1. Patient still has pulse/blood pressure → IM epinephrine 0.3-0.5 mg (1:1000) into thigh, repeat every 5-15 minutes 1

2. Patient becomes pulseless → STOP IM dosing, begin CPR, establish IV/IO access, give 1 mg epinephrine (1:10,000) IV/IO every 3-5 minutes 1, 3, 4

3. Refractory arrest → Consider higher IV doses (1-3 mg initially, escalating to infusion) 3

4. ROSC achieved → Consider epinephrine infusion 5-15 mcg/min for persistent shock 1

The evidence is clear: intramuscular epinephrine has no role once cardiac arrest occurs, regardless of the underlying cause being anaphylaxis. 1, 4