What is the recommended emergency management for a patient with suspected anaphylaxis, including intramuscular epinephrine dosing, positioning, isotonic crystalloid resuscitation, adjunct antihistamines and corticosteroids, refractory intravenous epinephrine administration, bronchodilators, and monitoring?

Emergency Management of Anaphylaxis

Immediate First-Line Treatment: Intramuscular Epinephrine

Administer intramuscular epinephrine immediately into the anterolateral mid-thigh as soon as anaphylaxis is recognized—this is the only intervention proven to prevent death and must never be delayed. 1, 2

Dosing Protocol

• Adults and adolescents ≥30 kg: 0.3–0.5 mg of 1:1000 (1 mg/mL) epinephrine IM 1, 3, 2
• Children <30 kg: 0.01 mg/kg IM (maximum 0.3 mg) 1, 2
• Injection site: Mid-outer thigh (vastus lateralis)—achieves peak plasma concentration in 8±2 minutes versus 34±14 minutes with subcutaneous administration 1, 2
• Repeat dosing: Every 5–15 minutes if symptoms persist or recur; approximately 10–20% of patients require multiple doses 1, 2

Critical Timing Consideration

Delayed epinephrine administration is directly associated with anaphylaxis fatalities—inject epinephrine before any other intervention, including IV access or antihistamines. 1, 2

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Patient Positioning and Immediate Supportive Care

• Position supine with legs elevated (unless respiratory distress or vomiting present, then position for comfort) 1, 3
• Never allow the patient to stand, walk, or run—sudden postural changes can precipitate cardiovascular collapse 1
• Activate emergency medical services immediately while treating 2
• Administer supplemental oxygen at 6–8 L/min for any respiratory symptoms 1, 2

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Aggressive Fluid Resuscitation

Establish IV access immediately and administer isotonic crystalloid (normal saline or lactated Ringer's) rapidly to counteract vasodilation and capillary leak. 1, 3

Fluid Dosing

• Adults: 5–10 mL/kg in the first 5 minutes (approximately 1–2 L total); up to 20–30 mL/kg may be required 1, 3
• Children: Up to 30 mL/kg in the first hour 1, 2
• Grade II reactions: Initial bolus 0.5 L 1
• Grade III reactions: Initial bolus 1 L, repeat as needed based on clinical response 1

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Intravenous Epinephrine for Refractory Anaphylaxis

When shock persists despite multiple IM epinephrine doses and adequate fluid resuscitation, IV epinephrine is reasonable in a monitored setting. 4, 1

IV Bolus Dosing

• Adults: 50–100 μg (0.05–0.1 mg) of 1:10,000 concentration (0.1 mg/mL) administered slowly 4, 1, 3
• Children: 1 μg/kg IV bolus, titrated to response 1, 3
• Repeat every 5–15 minutes as needed 1

IV Infusion for Persistent Shock

• Epinephrine infusion: 0.05–0.1 μg/kg/min (approximately 1–4 μg/min in adults, maximum 10 μg/min) 4, 1, 3
• Titrate to hemodynamic response with continuous cardiac monitoring 1

Critical Safety Warning

Use only 1:10,000 concentration (0.1 mg/mL) for IV administration—the 1:1000 concentration used for IM injection can cause fatal arrhythmias if given IV. 1, 3 Continuous cardiac monitoring is mandatory during IV epinephrine administration. 1

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Adjunctive Medications (Second-Line Only—Never Delay Epinephrine)

Antihistamines and corticosteroids provide no acute benefit in anaphylaxis and must never be administered before or in place of epinephrine. 1, 3

H1-Antihistamines (for urticaria/itching only)

• Diphenhydramine: 25–50 mg IV/IM (or 1–2 mg/kg in children, maximum 50 mg) 1, 3, 2
• Alternative: Cetirizine 10 mg orally (less sedating) 1
• Does NOT relieve: Airway obstruction, bronchospasm, gastrointestinal symptoms, or shock 1

H2-Antihistamines (minimal evidence of benefit)

• Ranitidine: 50 mg IV in adults (1 mg/kg in children) 1, 3
• Alternative: Famotidine 20 mg IV if ranitidine unavailable 3
• Combination H1 + H2 may provide superior symptom control for cutaneous manifestations 3

Corticosteroids (no acute benefit, weak evidence for biphasic prevention)

• Methylprednisolone: 1–2 mg/kg IV every 6 hours (typically 40 mg IV every 6 hours for 70 kg adult) 1, 3
• Alternative: Hydrocortisone 200 mg IV (adults) or 100 mg IV (children 6–12 years) 1, 3
• Onset of action: 4–6 hours—provides no immediate benefit 1, 3
• Evidence: Does NOT reliably prevent biphasic reactions despite common use 1, 3

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Management of Persistent Bronchospasm

• Nebulized albuterol: 2.5–5 mg in 3 mL saline for bronchospasm unresponsive to epinephrine 1, 3, 2
• Does NOT treat: Airway edema or cardiovascular collapse 1
• Consider only after epinephrine has been administered 1

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Special Populations and Refractory Cases

Patients on Beta-Blockers

For patients on beta-blockers with anaphylaxis refractory to epinephrine and fluids, administer glucagon. 1, 3

• Adult dose: 1–5 mg IV over 5 minutes, followed by infusion at 5–15 μg/min 1, 3
• Pediatric dose: 20–30 μg/kg (maximum 1 mg) IV over 5 minutes 1, 3
• Warning: Rapid glucagon administration can induce vomiting 1

Alternative Vasopressors for Persistent Hypotension

• Norepinephrine, vasopressin, phenylephrine, dopamine, or metaraminol may be used when hypotension persists despite epinephrine and fluids 1, 3
• Titrate to restore blood pressure with continuous hemodynamic monitoring 1

Airway Management

• Prepare for emergency cricothyroidotomy or tracheostomy if severe oropharyngeal/laryngeal edema develops—conventional intubation may be impossible 4, 1, 2
• Refer to a provider with advanced airway expertise immediately 4, 2

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Observation and Monitoring

All patients must be observed for a minimum of 4–6 hours in a facility equipped to manage anaphylaxis, even if symptoms resolve after a single epinephrine dose. 1, 2

Extended Observation or Admission Required For:

• >1 epinephrine dose (strongest predictor of biphasic reaction) 1
• Severe initial presentation (hypotension, respiratory compromise, cardiovascular instability) 1
• Wide pulse pressure at presentation 1
• Unknown trigger 1
• Drug trigger in children 1
• Coexisting asthma, especially poorly controlled 1, 2
• Adolescents/young adults with peanut or tree-nut allergy 1, 2
• Refractory or protracted symptoms 1

Biphasic Reaction Risk

• Biphasic anaphylaxis occurs in 1–20% of cases, typically around 8 hours after initial reaction but can appear up to 72 hours later 1
• Number needed to monitor (NNM): 13 patients who required multiple epinephrine doses to detect one biphasic reaction 1

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Mast Cell Tryptase Sampling

• First sample: 1 hour after reaction onset 1
• Second sample: 2–4 hours after onset 1
• Baseline sample: At least 24 hours post-reaction for comparison 1
• Clearly label each sample with collection time and date 3

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Mandatory Discharge Requirements

Every patient discharged after anaphylaxis must receive: 1, 2

• Two epinephrine autoinjectors (0.15 mg for 10–25 kg; 0.3 mg for ≥25 kg) with hands-on training 1, 2
• Written, personalized anaphylaxis emergency action plan detailing symptoms, triggers, and epinephrine use 1, 2
• Education about biphasic reaction risk and clear instructions to return immediately if symptoms recur 1
• Plan for monitoring autoinjector expiration dates 1
• Referral to an allergist for follow-up within 1–2 weeks 1, 2

Optional Discharge Medications (NOT substitutes for epinephrine)

• Prednisone: 1 mg/kg daily (maximum 60–80 mg) for 2–3 days 3
• H1-antihistamine for 2–3 days 3
• H2-antihistamine twice daily for 2–3 days 3

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Critical Pitfalls to Avoid

• Do NOT delay IM epinephrine while establishing IV access—IM injection achieves therapeutic levels faster 1, 2
• Do NOT use subcutaneous epinephrine—onset is too slow (34 minutes vs. 8 minutes IM) 1, 5
• Do NOT rely on antihistamines or corticosteroids as primary treatment—they provide no acute benefit 1, 3
• Do NOT discharge patients solely on symptom resolution—biphasic reactions may develop hours later 1
• There are NO absolute contraindications to epinephrine in anaphylaxis, even in elderly patients with cardiovascular disease—the risk of death from anaphylaxis outweighs any epinephrine-related risk 1, 6