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allergy.anaphylaxis.v1PRODUCTION
allergy.anaphylaxis.v1

Anaphylaxis (acute resuscitation)

allergyacuteadultpediatric
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Encounter flow

11/12 authored

Canonical 12-phase frame with authored status for this dossier.

Current phase

Frame

Detailed

Confirm acute multisystem hypersensitivity scope; exclude isolated urticaria, vasovagal, panic, ACE-i angioedema (Sampson 2006 NIAID criteria)

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Advance rule
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Advance when

multisystem involvement OR known trigger + airway/circulatory compromise (WAO 2020)

Patient inputs (13)

Tachycardia + relative bradycardia (paradoxical) on epinephrine (WAO 2020)

Tachypnea + accessory muscle use signals severe bronchospasm / impending failure (EAACI 2014)

Minutes-to-hours onset; alpha-gal delayed 3-6h; biphasic 1-72h (AAAAI/ACAAI 2020)

Asthma is single largest risk factor for fatal anaphylaxis (Pumphrey 2000)

Beta-blockade attenuates epinephrine response; glucagon adjunct indicated (AAAAI/ACAAI 2020)

Food / drug / venom / latex exposure window anchors phenotype + duration of monitoring (WAO 2020)

Distributive shock; SBP <90 (adult) or age-adjusted threshold defines circulatory criterion (Sampson 2006 NIAID)

SpO2 <92% triggers high-flow O2 + early airway escalation (NICE 2020)

ACEi predisposes to refractory hypotension + bradykinin angioedema mimic (WAO 2020)

Left lateral tilt; epinephrine still first-line; obstetric escalation (Simons JACI 2011)

Peak 1-2h post onset confirms mast-cell activation; baseline >11.4 ng/mL prompts mastocytosis workup (NICE 2020)

Rules in distributive shock + sepsis mimic; trend on resuscitation (WAO 2020)

Pediatric weight-based dosing (epi 0.01 mg/kg IM, NS 20 mL/kg) per AAAAI/ACAAI 2020

* = hard-required. Engine cannot meaningfully run until these are filled.

Severity triggers (7)

7 need judgement
  • informationallife_threateningno_response_to_2_im_epi — WAO 2020
    Persistent hypotension, airway oedema, or bronchospasm despite >=2 IM epinephrine doses (5-15 min apart) plus 1-2 L crystalloid (AAAAI/ACAAI 2020)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationallife_threateningstridor_progressive_airway_edema — Pumphrey 2000
    Stridor, voice change, tongue/laryngeal swelling progressing despite IM epi (WAO 2020)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationallife_threateningcardiac_arrest_from_anaphylaxis — AHA 2024
    PEA / asystole during anaphylactic shock (AHA 2024)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalseverebiphasic_reaction_within_72h — AAAAI 2020
    Recurrence of anaphylaxis features 1-72 h after initial resolution (typical 4-12 h) per AAAAI/ACAAI 2020
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalseverebeta_blocker_refractory_shock — AAAAI 2020
    Refractory hypotension in patient on beta-blocker or ACE-inhibitor despite epi + IVF (AAAAI/ACAAI 2020)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalseverepregnancy_anaphylaxis — Simons 2011
    Anaphylaxis in pregnant patient (any trimester) per Simons JACI 2011
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalmoderatemast_cell_activation_baseline_elevated — NICE 2020
    Acute tryptase >11.4 ng/mL OR persistent elevation 24 h - 2 weeks after event (NICE 2020)
    Trigger could not be auto-evaluated — needs clinician judgement.

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Recommended regimen

Acute anaphylaxis bundle — epi-first per WAO 2020
axis: anaphylaxis_acute_resuscitationstep 1 - Step 1 — IM epinephrine immediately on recognition (Simons JACI 2011)
Selected step "Step 1 — IM epinephrine immediately on recognition (Simons JACI 2011)" — Any criterion for anaphylaxis met per Sampson 2006 NIAID (sudden multisystem reaction OR known trigger + airway/breathing/circulation compromise OR hypotension after exposure)
  • epinephrine
    first line
    alpha_beta_agonist
    Adult 0.3-0.5 mg (0.3-0.5 mL of 1:1000); pediatric 0.01 mg/kg (max 0.3 mg) per AAAAI/ACAAI 2020 • IM lateral thigh (vastus lateralis) per Simons JACI 2011 • Repeat q5-15 min PRN until response (WAO 2020) (max: 0.5 mg per single IM dose adult; 3 doses before considering IV infusion (AAAAI/ACAAI 2020))
    triggers: anaphylaxis_recognised
    Only mortality-reducing intervention; IM lateral thigh > deltoid > SC; never delay for steroids/antihistamines (Resus Council UK 2021, JTF 2023, GA²LEN 2024)
    rxcui 3992

ed playbook — drug actions (8)

  1. 1. epinephrine
    Adult 0.3-0.5 mg IM (1:1000); pediatric 0.01 mg/kg (max 0.3 mg) per AAAAI/ACAAI 2020 • IM lateral thigh (Simons JACI 2011) • Repeat q5-15 min PRN (WAO 2020)
    trigger: Anaphylaxis recognised (Sampson 2006 criteria)
    Only mortality-reducing intervention; never delay for IV access or other meds (Simons JACI 2011)
  2. 2. oxygen
    8-10 L/min NRB or titrate (NICE 2020) • inhaled • continuous
    trigger: SpO2 <92% or any airway involvement (NICE 2020)
    High-flow O2 supports ventilation while epi acts (WAO 2020)
  3. 3. normal_saline
    Adult 1-2 L bolus; pediatric 20 mL/kg (AAAAI/ACAAI 2020) • IV • Repeat x 2-3 PRN
    trigger: Hypotension or persistent shock after first IM epi (WAO 2020)
    Distributive shock with massive vascular leak; supine + legs raised (EAACI 2014)
  4. 4. epinephrine infusion
    0.05-0.5 mcg/kg/min titrated (WAO 2020) • IV • continuous
    trigger: Refractory after >=2 IM doses + 1-2 L IVF (AAAAI/ACAAI 2020)
    JTF 2023 / WAO 2020 — preferred over IV bolus to avoid arrhythmia
  5. 5. diphenhydramine + famotidine
    Diphen 25-50 mg + famotidine 20 mg (AAAAI/ACAAI 2020) • IV/IM/PO • q6-12h x 24-48 h
    trigger: Cutaneous symptoms after hemodynamic stabilisation (WAO 2020)
    H1+H2 dual blockade for urticaria/pruritus only (Lin Ann Emerg Med 2000)
  6. 6. methylprednisolone
    125 mg IV (adult); 1-2 mg/kg pediatric (AAAAI/ACAAI 2020) • IV • q6h x 24 h
    trigger: Refractory bronchospasm, asthmatic phenotype, or biphasic-risk inpatient (AAAAI/ACAAI 2020)
    No proven biphasic prevention; reserve for refractory / asthma overlap (JTF 2023)
  7. 7. albuterol
    2.5-5 mg nebulised (AAAAI/ACAAI 2020) • inhaled • q20 min x 3 then q1-4 h
    trigger: Persistent bronchospasm despite IM epi (WAO 2020)
    Adjunct beta2 bronchodilation (EAACI 2014)
  8. 8. glucagon
    1-5 mg IV bolus then 5-15 mcg/min infusion (AAAAI/ACAAI 2020) • IV • Bolus + infusion
    trigger: Beta-blocker on board with refractory hypotension (AAAAI/ACAAI 2020)
    cAMP rescue when beta-receptor blocked (JTF 2023)

Auto-drafted A&P note

ed

Subjective

- Possible entry pathways: Urticaria + angioedema after exposure (Sampson 2006 NIAID criteria); Stridor / throat tightness (WAO 2020 airway criterion); Acute dyspnea / wheeze (EAACI 2014 respiratory criterion).

Objective

- No vitals, labs, or imaging entered for this encounter.

Assessment

**Anaphylaxis (acute resuscitation)** (allergy.anaphylaxis.v1).
Phenotype framing: Distinguish anaphylaxis from severe asthma, septic shock, ACS, vasovagal, scombroid, HAE, ACEi-AE, mastocytosis flare (WAO 2020)
Scope: Confirm acute multisystem hypersensitivity scope; exclude isolated urticaria, vasovagal, panic, ACE-i angioedema (Sampson 2006 NIAID criteria)

No severity triggers fired against current inputs.

Plan

Regimen axis: **Acute anaphylaxis bundle — epi-first per WAO 2020** — step "Step 1 — IM epinephrine immediately on recognition (Simons JACI 2011)".
1. epinephrine Adult 0.3-0.5 mg (0.3-0.5 mL of 1:1000); pediatric 0.01 mg/kg (max 0.3 mg) per AAAAI/ACAAI 2020 IM lateral thigh (vastus lateralis) per Simons JACI 2011 Repeat q5-15 min PRN until response (WAO 2020) (alpha_beta_agonist, first line) — Only mortality-reducing intervention; IM lateral thigh > deltoid > SC; never delay for steroids/antihistamines (Resus Council UK 2021, JTF 2023, GA²LEN 2024)

Setting playbook (ed) — Reverse anaphylaxis with immediate IM epinephrine, secure airway/breathing/circulation, observe for biphasic reaction, dispense epi-pen + action plan + allergist referral (AAAAI/ACAAI 2020)
2. epinephrine Adult 0.3-0.5 mg IM (1:1000); pediatric 0.01 mg/kg (max 0.3 mg) per AAAAI/ACAAI 2020 IM lateral thigh (Simons JACI 2011) Repeat q5-15 min PRN (WAO 2020) — Anaphylaxis recognised (Sampson 2006 criteria) (Only mortality-reducing intervention; never delay for IV access or other meds (Simons JACI 2011))
3. oxygen 8-10 L/min NRB or titrate (NICE 2020) inhaled continuous — SpO2 <92% or any airway involvement (NICE 2020) (High-flow O2 supports ventilation while epi acts (WAO 2020))
4. normal_saline Adult 1-2 L bolus; pediatric 20 mL/kg (AAAAI/ACAAI 2020) IV Repeat x 2-3 PRN — Hypotension or persistent shock after first IM epi (WAO 2020) (Distributive shock with massive vascular leak; supine + legs raised (EAACI 2014))
5. epinephrine infusion 0.05-0.5 mcg/kg/min titrated (WAO 2020) IV continuous — Refractory after >=2 IM doses + 1-2 L IVF (AAAAI/ACAAI 2020) (JTF 2023 / WAO 2020 — preferred over IV bolus to avoid arrhythmia)
6. diphenhydramine + famotidine Diphen 25-50 mg + famotidine 20 mg (AAAAI/ACAAI 2020) IV/IM/PO q6-12h x 24-48 h — Cutaneous symptoms after hemodynamic stabilisation (WAO 2020) (H1+H2 dual blockade for urticaria/pruritus only (Lin Ann Emerg Med 2000))
7. methylprednisolone 125 mg IV (adult); 1-2 mg/kg pediatric (AAAAI/ACAAI 2020) IV q6h x 24 h — Refractory bronchospasm, asthmatic phenotype, or biphasic-risk inpatient (AAAAI/ACAAI 2020) (No proven biphasic prevention; reserve for refractory / asthma overlap (JTF 2023))
8. albuterol 2.5-5 mg nebulised (AAAAI/ACAAI 2020) inhaled q20 min x 3 then q1-4 h — Persistent bronchospasm despite IM epi (WAO 2020) (Adjunct beta2 bronchodilation (EAACI 2014))
9. glucagon 1-5 mg IV bolus then 5-15 mcg/min infusion (AAAAI/ACAAI 2020) IV Bolus + infusion — Beta-blocker on board with refractory hypotension (AAAAI/ACAAI 2020) (cAMP rescue when beta-receptor blocked (JTF 2023))

Non-pharmacologic actions:
- Supine + legs raised; left lateral tilt if pregnant 2nd/3rd trimester (WAO 2020; Simons JACI 2011)
- Remove ongoing trigger (stop infusion, remove stinger, discontinue offending drug) per EAACI 2014
- Two large-bore IV access (NICE 2020)
- Continuous cardiac + SpO2 + capnography (NICE 2020)
- Early airway escalation: prepare for fibreoptic intubation if stridor/laryngeal oedema — do not delay (Pumphrey 2000)
- Cardiac arrest from anaphylaxis: high-quality CPR + IV epi 1 mg q3-5 min + IVF (AHA 2024)

AVOID / contraindication checks:
- Epinephrine iv only in cardiac arrest or icu monitored infusion (WAO 2020)
- Avoid cimetidine with beta blockers anaphylaxis (AAAAI/ACAAI 2020)
- Do not substitute antihistamine or steroid for epinephrine (Simons JACI 2011)

Monitoring

Regimen monitoring:
- continuous telemetry min 4-6h post stable (NICE 2020)
- q15min vitals during epi infusion (WAO 2020)
- tryptase at 1-2h and baseline 24h to 2wk (NICE 2020)

Setting (ed) monitoring:
- q5-15 min vitals through resuscitation; q15 min during epi infusion (WAO 2020)
- Continuous telemetry minimum 4-6 h after last symptom (NICE 2020)
- Acute tryptase 1-2 h post-onset; baseline tryptase 24 h - 2 weeks if elevated (NICE 2020)
- Repeat ECG if Kounis suspected (WAO 2020)

Follow-up plan: 2x epi auto-injectors + written action plan + allergist referral 4-6 weeks; medical-alert bracelet; venom immunotherapy referral if hymenoptera (AAAAI/ACAAI 2020; EAACI 2014)
- Close-out criterion: auto-injectors prescribed, action plan signed, allergist referral placed (NICE 2020)

Monitoring phase: Continuous telemetry, q15min vitals during epi infusion; tryptase follow-up baseline at 24h-2 weeks if elevated acutely (NICE 2020)

Disposition

Current setting: ed — Reverse anaphylaxis with immediate IM epinephrine, secure airway/breathing/circulation, observe for biphasic reaction, dispense epi-pen + action plan + allergist referral (AAAAI/ACAAI 2020)

Disposition criteria:
- Discharge home: mild reaction (skin only or skin + GI), responded to single IM epi dose, asymptomatic >=4 h, two epi auto-injectors prescribed, written action plan + allergist referral, return precautions reviewed (NICE 2020)
- Extended observation >=12 h: required >=2 epi doses, biphasic risk factors (severe initial reaction, drug trigger, beta-blocker, asthma), or delayed presentation (AAAAI/ACAAI 2020)
- Admit / ICU: refractory shock, IV epi infusion required, intubated, persistent biphasic-recurrence risk (WAO 2020)

Escalation triggers (move to higher acuity):
- No response to 2 IM epi doses → IV epi infusion + ICU (WAO 2020)
- Stridor / progressive airway oedema → emergent intubation (Pumphrey 2000)
- Cardiopulmonary arrest → ACLS with IV epi + aggressive volume (AHA 2024)
- Recurrent (biphasic) reaction → re-treat from Step 1 + extend observation (AAAAI/ACAAI 2020)

Patient Action Plan

**Anaphylaxis emergency action plan (WAO 2020; AAAAI/ACAAI 2020)**
Personalised values: known_triggers, epi_pen_strength, asthma_inhaler, beta_blocker_on_board.

**No reaction — stable / trigger avoidance (WAO 2020)** (green):
Triggers:
- No symptoms after exposure or distance from known trigger (WAO 2020)
- No skin, breathing, GI, or circulatory symptoms (Sampson 2006)
Actions:
- Carry TWO epinephrine auto-injectors at all times (AAAAI/ACAAI 2020)
- Avoid known triggers; read food labels; communicate allergy at restaurants and clinics (EAACI 2014)
- Wear medical-alert identification (WAO 2020)
- Keep allergist follow-up appointments (NICE 2020)
- Keep asthma controller therapy current if applicable (Pumphrey 2000)

**Mild reaction — skin or mild GI only (Sampson 2006 Grade 1-2)** (yellow):
Triggers:
- Hives / itching only (Sampson 2006 Grade 1)
- Mild lip / face swelling without breathing change (WAO 2020)
- Mild abdominal cramps / one episode of vomiting (Sampson 2006)
- No throat tightness, no breathing difficulty, no dizziness (WAO 2020)
Actions:
- Take an antihistamine (cetirizine 10 mg or diphenhydramine 25-50 mg) per AAAAI/ACAAI 2020
- Watch closely for ANY of: throat tightness, voice change, hard time breathing, dizziness, fainting, severe abdominal pain, repeated vomiting (WAO 2020)
- Have epinephrine ready in your hand (AAAAI/ACAAI 2020)
- Call provider OR go to ED if any new symptom develops (NICE 2020)
Contact provider when:
- Symptoms not resolving within 1 hour (NICE 2020)
- Any new chest, throat, or breathing symptom (WAO 2020)
- Reaction worsening despite antihistamine (AAAAI/ACAAI 2020)

**Anaphylaxis — give epinephrine NOW, then call 911 (AAAAI/ACAAI 2020)** (red):
Triggers:
- ANY of: trouble breathing, wheeze, throat tightness, voice hoarse / muffled (Sampson 2006 criterion 1)
- Hives PLUS any breathing or stomach symptom after a trigger (Sampson 2006 criterion 2)
- Lightheaded, faint, or pale / clammy (WAO 2020 circulatory)
- Repetitive vomiting + skin symptoms (Sampson 2006)
- Sudden collapse after exposure (WAO 2020)
- Past severe reaction + any symptom now after re-exposure (AAAAI/ACAAI 2020)
Actions:
- INJECT epinephrine auto-injector into the OUTER MIDDLE THIGH right now (through clothing if needed). Hold for 3 seconds. (Simons JACI 2011)
- CALL 911 / emergency services immediately, even if you feel better — biphasic reaction can occur 1-72 hours later. (AAAAI/ACAAI 2020)
- Lie flat with legs raised (or left side if pregnant or vomiting). Do NOT stand up suddenly. (WAO 2020)
- Use second epinephrine auto-injector after 5-15 min if symptoms persist or return. (AAAAI/ACAAI 2020)
- Use rescue inhaler (albuterol 4-8 puffs) for wheeze AFTER giving epinephrine, not instead. (WAO 2020)
- Bring used auto-injectors to the hospital. (NICE 2020)
Contact provider when:
- Always call 911 — anaphylaxis requires hospital observation even if symptoms resolve quickly (NICE 2020)

Earlier-Return Triggers

Return-precaution thresholds (watch for):
- [LIFE_THREATENING] Persistent hypotension, airway oedema, or bronchospasm despite >=2 IM epinephrine doses (5-15 min apart) plus 1-2 L crystalloid (AAAAI/ACAAI 2020)
- [LIFE_THREATENING] Stridor, voice change, tongue/laryngeal swelling progressing despite IM epi (WAO 2020)
- [LIFE_THREATENING] PEA / asystole during anaphylactic shock (AHA 2024)

Citations

- Resuscitation Council UK 2021 Adult Advanced Life Support + JTF/AAAAI/ACAAI Anaphylaxis Practice Parameter Update (Shaker JACI 2020; reaffirmed 2023) + 2024 GA²LEN consensus on anaphylaxis definition (Cardona JACI 2025) + WAO 2020 Anaphylaxis Guidance (Cardona WAO J 2020) + EAACI 2021 + 2024 AHA focused update on cardiac arrest from anaphylaxis [PMID:32001253](https://pubmed.ncbi.nlm.nih.gov/32001253/)
- Cited evidence (PMID 33204386) [PMID:33204386](https://pubmed.ncbi.nlm.nih.gov/33204386/)

Last reconciled with current guidelines: 2026-05-12.
References
  • Resuscitation Council UK 2021 Adult Advanced Life Support + JTF/AAAAI/ACAAI Anaphylaxis Practice Parameter Update (Shaker JACI 2020; reaffirmed 2023) + 2024 GA²LEN consensus on anaphylaxis definition (Cardona JACI 2025) + WAO 2020 Anaphylaxis Guidance (Cardona WAO J 2020) + EAACI 2021 + 2024 AHA focused update on cardiac arrest from anaphylaxis — PMID:32001253
  • Cited evidence (PMID 33204386) — PMID:33204386