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Allergic Reaction / Anaphylaxis

Category: Medical Sources: raw/protocols/nm-sop-guidelines-treatment-2022.pdf; UCLA EMT Ultimate Study Guide (2026) Last updated: 2026-05-06

Overview

Anaphylaxis is a severe, systemic allergic reaction involving multiple organ systems — primarily the airway, respiratory tract, and cardiovascular system. It is a life-threatening emergency requiring immediate epinephrine. Allergic reactions exist on a spectrum from localized (hives, localized swelling) to anaphylaxis (systemic involvement with airway compromise or cardiovascular collapse).

The EMT-B must distinguish between a simple allergic reaction (localized skin findings without systemic involvement) and anaphylaxis (systemic involvement — airway, breathing, or circulation compromised). Epinephrine is only indicated when systemic involvement is present.

Key Points

  • Anaphylaxis triggers: insect stings, food (peanuts, shellfish, tree nuts, dairy), medications (penicillin, NSAIDs), latex, contrast dye, exercise, idiopathic
  • Three system involvement criterion for epinephrine: Respiratory compromise (wheeze, stridor, dyspnea) OR cardiovascular compromise (hypotension, tachycardia, syncope) OR both — localized hives alone do NOT trigger epinephrine
  • "Silent chest" is ominous in anaphylaxis — bronchospasm so severe that no air moves, producing no wheeze
  • Patient may have their own EpiPen — this can be used; document time and dose
  • Epinephrine may need to be repeated; effect is short-lived (15–20 minutes)
  • Even if patient appears to improve with epinephrine, all anaphylaxis patients must be transported — biphasic reactions occur in up to 20% of cases (second wave of symptoms hours later)

Assessment Relevance

History (history-taking): - SAMPLE: Known allergies, allergen exposure (what, when, how much), prior anaphylaxis, prior EpiPen use, medications (antihistamines, steroids taken pre-arrival may blunt presentation), last meal - OPQRST: Onset (typically rapid — minutes after exposure), what provoked it, symptoms

Physical exam (secondary-assessment): - Airway: Stridor (upper airway edema), hoarseness, drooling, difficulty swallowing - Breathing: Wheezing (bronchospasm), decreased/absent breath sounds, SpO2, respiratory rate/effort - Circulation: BP, pulse rate and quality, skin color, capillary refill, diaphoresis - Skin: Urticaria (hives), angioedema (facial/lip/tongue swelling), flushing, pallor - GI: Nausea, vomiting, abdominal cramping (systemic involvement even without respiratory compromise)

Priority indicators: stridor, inability to speak, silent chest, hypotension, loss of consciousness

Procedures

  1. Scene size-up (scene-size-up): identify trigger if visible (bee sting site, food container); remove stinger by scraping (not pinching)
  2. Primary assessment (primary-assessment): assess airway (stridor?), breathing (wheeze, SpO2), circulation (BP, pulse)
  3. Determine: localized reaction vs. systemic anaphylaxis
  4. If systemic involvement (airway compromise, respiratory distress, or cardiovascular collapse):
  5. Administer epinephrine IM — see epinephrine-auto-injector
  6. Apply high-flow oxygen via NRB mask — see oxygen-administration
  7. Request ALS intercept immediately
  8. Position: supine with legs elevated if hypotensive; sitting upright if respiratory distress
  9. Transport — do not delay for reassessment
  10. Reassess (reassessment) every 5 minutes; may need to repeat epinephrine
  11. Monitor for biphasic reaction

NM Protocol Notes

From NM EMS Treatment Guidelines (2022):

EMT-B and First Responder scope: - EPINEPHRINE 1:1,000 (1 mg/mL) — IM, lateral thigh - Adult: 0.3 mg IM using pre-measured pre-filled device (EpiPen) or 0.3 mL dose-limiting syringe - Pediatric: 0.01 mg/kg IM using pre-measured pre-filled pediatric device; not to exceed adult dose - May be repeated every 5–15 minutes if signs of anaphylaxis and hypoperfusion persist - Cardiac monitoring required at all levels for all patients receiving epinephrine - For insect bites: remove stinger with scraping motion; do not pinch the stinger with tweezers

Additional ALS medications (not EMT-B scope — for context/ALS intercept): - ALBUTEROL 5.0 mg nebulized (or Duo Neb 2.5mg Albuterol + 0.5mg Ipratropium) or LEVALBUTEROL 0.63–1.25 mg — for bronchospasm - IPRATROPIUM 0.5 mg — adjunct bronchodilator - Large bore IV/IO isotonic solution — titrate to maintain adequate perfusion - DIPHENHYDRAMINE (Benadryl): - Adult: 25–50 mg slow IV/IO at 1 mL/min or deep IM - Pediatric: 1 mg/kg slow IV/IO or deep IM (max 50 mg) - SOLUMEDROL (methylprednisolone): Adult 125 mg IV/IO; Pediatric 1–2 mg/kg IV/IO (max 125 mg) OR DEXAMETHASONE: Adult 10 mg IV/IO/IM; Pediatric 0.6 mg/kg (max 10 mg) - For cardiovascular collapse with hypotension (paramedic only): IV epinephrine drip; EPINEPHRINE 1:10,000 mini-bolus

Epinephrine IV drip

Concept Link

Anaphylaxis causes distributive shock — the same mechanism covered in shock-physiology. The vasodilation and maldistribution of blood flow described there explains why epinephrine works: it reverses vasodilation (alpha-1) and supports cardiac output (beta-1/beta-2). (paramedic only): Consider 0.5 mcg/kg/min when cardiovascular collapse present despite repeated IM epinephrine doses + at least 60 mL/kg IV fluid boluses

NREMT Relevance

Common NREMT question angles: - The three criteria for epinephrine: systemic involvement (airway, breathing, or cardiovascular) — localized hives alone are NOT sufficient - EpiPen sites: lateral thigh (preferred), outer thigh — can administer through clothing - Epinephrine 1:1,000 vs. 1:10,000 — the auto-injector contains 1:1,000 (IM use); 1:10,000 is IV use (ALS) - Adult dose 0.3 mg, pediatric dose 0.15 mg (EpiPen Jr) or 0.01 mg/kg - All anaphylaxis patients must be transported (biphasic reaction risk) - Stinger removal: scraping not pinching

NREMT Differentiators

Anaphylaxis vs. Asthma vs. Septic Shock

Feature Anaphylaxis Asthma (Severe) Septic Shock
Cause Allergen exposure Bronchoconstriction (trigger or no trigger) Infection (bacteria)
Onset Rapid (minutes) Variable (minutes to hours) Gradual (hours to days)
Skin Hives, flushing, angioedema Pale, diaphoretic Warm, flushed (early); mottled (late)
Airway Stridor (upper), wheeze (lower) Wheeze (lower only) No stridor; wheeze uncommon
BP Low (distributive shock) Normal until late Low (distributive shock)
Temperature Normal or low Normal Fever (or hypothermia in severe sepsis)
First-line Tx Epinephrine IM Albuterol IV fluids + transport
Epi indicated? YES — always Only if severe/refractory NO

KEY DIFFERENTIATOR — Anaphylaxis: Hives + wheeze + hypotension after allergen exposure = anaphylaxis. Epinephrine is the ONLY first-line treatment. Antihistamines (Benadryl) and steroids are adjuncts — they DO NOT replace epinephrine.

KEY DIFFERENTIATOR — Asthma vs. Anaphylaxis: If the patient is wheezing AND has hives/angioedema/hypotension, it's anaphylaxis — give epinephrine, NOT albuterol first. Albuterol is an adjunct in anaphylaxis (for bronchospasm), not the primary treatment.

Epinephrine Decision Tree

Patient has wheeze / stridor / dyspnea OR hypotension / tachycardia / syncope?
       |
      YES → Systemic involvement → GIVE EPINEPHRINE
       |
       NO → Localized reaction (hives only) → NO epinephrine; monitor

Localized reaction (NO epinephrine): - Hives, itching, flushing — confined to skin - No airway compromise, no breathing difficulty, no BP change - Treatment: diphenhydramine (ALS/online med control), transport and monitor for progression

Anaphylaxis (GIVE epinephrine): - Respiratory: wheeze, stridor, dyspnea, silent chest - Cardiovascular: hypotension, weak/fast pulse, syncope - GI alone (vomiting, cramping) with allergen exposure = give epinephrine (systemic involvement)

Epinephrine Key Facts

Detail Value
Concentration (auto-injector) 1:1,000 (1 mg/mL) — IM only
Adult dose 0.3 mg IM
Pediatric dose 0.15 mg IM (EpiPen Jr) or 0.01 mg/kg
Injection site Lateral thigh (vastus lateralis)
Can inject through clothing? YES
Duration of effect 15–20 minutes
Can repeat? Yes — every 5–15 min if symptoms persist
1:10,000 — what's it for? IV use — ALS/paramedic only, NOT auto-injector

NREMT TRAP — 1:1,000 vs 1:10,000: Auto-injector = 1:1,000 = IM. Never confuse with 1:10,000 which is the IV concentration. The NREMT will test this.

Biphasic Reaction

A biphasic reaction is a second wave of anaphylaxis occurring 1–72 hours after the initial reaction, even after the patient appears to have recovered.

  • Incidence: ~20% of anaphylaxis patients
  • All anaphylaxis patients must be transported — even if they feel fine after epinephrine
  • Patient refusal: document thoroughly; emphasize the biphasic risk; AMA if they insist

NREMT RULE: The patient feels better after their EpiPen — do you still transport? YES, always. Biphasic reaction can be fatal. No exceptions.

Positioning in Anaphylaxis

Presentation Position
Hypotension without respiratory distress Supine, legs elevated (Trendelenburg)
Respiratory distress Upright (sitting)
Unconscious / unresponsive Supine — manage airway

Sources

  • raw/protocols/nm-sop-guidelines-treatment-2022.pdf — Allergic Reaction/Anaphylaxis protocol (p. 33–34)