What is the recommended emergency management for a patient with suspected anaphylaxis, including intramuscular epinephrine dosing, positioning, supplemental oxygen, airway support, intravenous crystalloid resuscitation, adjunct antihistamine and corticosteroid therapy, repeat dosing criteria, observation duration, and prescription of an epinephrine auto‑injector?

Anaphylaxis Emergency Management Guidelines

Immediate First-Line Treatment: Intramuscular Epinephrine

Administer intramuscular epinephrine immediately upon recognition of anaphylaxis—this is the only first-line treatment and delays in administration are directly associated with increased mortality. 1, 2

Dosing Protocol

• Adults and adolescents >50 kg: 0.3-0.5 mg of 1:1000 (1 mg/mL) concentration 3, 1, 2
• Prepubertal children: 0.01 mg/kg (maximum 0.3 mg) 3, 1, 2
• Injection site: Mid-outer thigh (vastus lateralis muscle)—this route achieves peak plasma levels in 8±2 minutes compared to 34±14 minutes with subcutaneous administration 3, 4

Repeat Dosing Criteria

• Repeat every 5-15 minutes if symptoms persist or recur 3, 1, 2
• Approximately 6-19% of patients require a second dose 2
• After 3 intramuscular doses without response, consider epinephrine infusion at 0.05-0.1 μg/kg/min 4

The intramuscular route into the anterolateral thigh is superior to subcutaneous or deltoid injection because it achieves faster and higher plasma concentrations. 4 There are no absolute contraindications to epinephrine use in anaphylaxis, even in elderly patients with cardiac disease. 4

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Patient Positioning

Place the patient supine with lower extremities elevated unless respiratory distress or vomiting is present. 1, 2, 4

• Never allow the patient to stand, walk, or run—this can precipitate cardiovascular collapse 1
• If respiratory distress or vomiting occurs, position for comfort rather than strict supine 1
• In pregnant women, perform left uterine displacement to avoid aortocaval compression 4

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Supplemental Oxygen and Airway Management

• Administer supplemental oxygen at 6-8 L/min for all patients with respiratory symptoms or those receiving multiple epinephrine doses 3, 2, 4
• Establish and maintain airway patency 2
• Consider endotracheal intubation or cricothyrotomy if airway obstruction is imminent 2

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Intravenous Crystalloid Resuscitation

Establish IV access immediately and administer aggressive fluid resuscitation to combat vasodilation and capillary leak. 4

Fluid Bolus Protocol

• Adults: 5-10 mL/kg in first 5 minutes (1-2 L total), up to 20-30 mL/kg based on response 2, 4
• Children: Up to 30 mL/kg in the first hour 2
• Initial bolus for Grade II reactions: 0.5 L crystalloid 4
• Initial bolus for Grade III reactions: 1 L crystalloid 4
• Repeat boluses as needed for persistent hypotension 4

Use normal saline or lactated Ringer's solution. 4 Fluid resuscitation is imperative and should be administered early with the first epinephrine dose for patients with cardiovascular involvement. 3

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Adjunct Medications (ONLY After Epinephrine)

H1 Antihistamines

• Diphenhydramine 25-50 mg IV or chlorphenamine 10 mg IV for adults 4
• Pediatric dosing: 1-2 mg/kg (maximum 50 mg) 4
• Use oral liquid formulations when possible—absorbed more rapidly than tablets 1
• Critical caveat: Antihistamines treat only cutaneous symptoms and do NOT prevent or reverse cardiovascular collapse or airway obstruction 4

H2 Antihistamines

• Ranitidine 50 mg IV for adults (adjunctive therapy) 4

Corticosteroids

• Methylprednisolone 1-2 mg/kg/day IV every 6 hours or hydrocortisone 200 mg IV 4
• Important limitation: Corticosteroids have no proven role in acute treatment due to slow onset of action 3
• They are NOT reliable interventions to prevent biphasic anaphylaxis 3

Inhaled Beta-2 Agonists

• Albuterol nebulizer or MDI for persistent bronchospasm or lower respiratory symptoms (chest tightness, wheezing, shortness of breath) after initial epinephrine 3, 2

Never administer antihistamines or corticosteroids before or instead of epinephrine—this is a common and potentially fatal error. 1, 2

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Management of Refractory Anaphylaxis

For patients unresponsive to 3 intramuscular epinephrine doses:

Epinephrine Infusion

• Preparation: Add 1 mg (1 mL) of 1:1000 epinephrine to 250 mL D5W (concentration 4.0 μg/mL) 4
• Infusion rate: 0.05-0.1 μg/kg/min (or 1-4 μg/min in adults, increasing to maximum 10 μg/min) 4

Alternative Vasopressors

• Dopamine infusion for persistent hypotension despite epinephrine and fluids 1
• Consider norepinephrine, vasopressin, phenylephrine, or metaraminol 4

Special Populations

• Patients on beta-blockers: Administer glucagon 1-5 mg IV over 5 minutes, followed by 5-15 mcg/min infusion titrated to response 1, 4

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Observation Duration and Disposition

All patients must be transferred to an emergency department for observation, preferably by EMS vehicle. 1, 2

Minimum Observation Period

• Standard cases: 4-6 hours minimum after symptom resolution 1, 2, 4
• Extended observation or admission indicated for:
  • Severe anaphylaxis (Grade III-IV reactions) 4
  • Requirement of >1 dose of epinephrine 3, 2
  • History of biphasic reactions 2
  • Wide pulse pressure, unknown trigger, or drug trigger in children 3

Biphasic Anaphylaxis Risk

Biphasic anaphylaxis (recurrence after appropriate treatment) occurs in a subset of patients. 3 Predictors include severity of initial presentation, administration of multiple epinephrine doses, wide pulse pressure, unknown trigger, and skin/mucosal signs. 3 Extended observation in a setting capable of managing anaphylaxis is essential for high-risk patients. 3

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Discharge Planning: Epinephrine Auto-Injector Prescription

Before discharge, prescribe two epinephrine autoinjectors with hands-on training in proper use. 1, 2, 4

Autoinjector Dosing

• 0.1 mg: Infants >7.5 kg (where available) 4
• 0.15 mg: Children weighing 10-25 kg 4
• 0.3 mg: Individuals weighing ≥25 kg 4

Additional Discharge Requirements

• Provide a written, personalized anaphylaxis emergency action plan that includes common symptoms/signs, clear instructions for epinephrine use, and list of known triggers 1, 4
• Educate on biphasic reaction risk and when to re-administer epinephrine 2
• Refer to an allergist for trigger identification and long-term management 1, 2
• Establish a plan for monitoring autoinjector expiration dates 4

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High-Risk Populations Requiring Heightened Vigilance

The following groups are at increased risk for severe or fatal anaphylaxis and require epinephrine autoinjector prescriptions with heightened vigilance:

• Adolescents and young adults 1, 2
• Patients with coexisting asthma, especially severe or poorly controlled 1, 2
• Previous history of anaphylaxis 1
• Peanut/tree nut allergies 1
• Food allergy combined with asthma 4

Consider prescribing epinephrine autoinjectors for all patients with IgE-mediated food allergies, even without prior anaphylaxis. 4

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Critical Pitfalls to Avoid

• Delaying epinephrine administration while waiting for help or establishing IV access—this is directly associated with anaphylaxis fatalities 1, 2, 4
• Administering antihistamines or corticosteroids before epinephrine 2
• Using subcutaneous route or arm injection site instead of intramuscular thigh 2
• Waiting to "see if symptoms improve" before giving epinephrine 2
• Allowing the patient to stand or walk during treatment 1
• Failing to prescribe two epinephrine autoinjectors at discharge 1, 4

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Optional: Mast Cell Tryptase Sampling

For diagnostic confirmation and future risk stratification:

• First sample: 1 hour after reaction onset 4
• Second sample: 2-4 hours after onset 4
• Baseline sample: At least 24 hours post-reaction for comparison 4