Anaphylaxis: Difference between revisions

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==Definition==
==Background==
*'''Acute, life-threatening, systemic allergic reaction''' involving multiple organ systems
*IgE-mediated (type I hypersensitivity) in most cases; can also be non-IgE mediated (anaphylactoid)
*'''Biphasic reaction''' occurs in '''5-20%''' of cases (recurrence 1-72 hours after initial reaction, usually within 8-10 hours)<ref>Lee S, et al. Biphasic anaphylaxis: review of incidence, clinical predictors, and observation recommendations. ''Immunol Allergy Clin North Am''. 2015;35(2):313-326. PMID 25841553</ref>
*Epinephrine is the ONLY first-line treatment — delays in administration increase mortality


===Common Triggers===
*Foods (most common overall): peanuts, tree nuts, shellfish, fish, milk, eggs, wheat, soy
*Medications: antibiotics (penicillin, cephalosporins), NSAIDs, neuromuscular blocking agents
*Insect stings: Hymenoptera (bees, wasps, hornets, fire ants)
*Latex
*'''Exercise-induced anaphylaxis''' (sometimes food-dependent)
*Idiopathic (~20% — no identifiable trigger)


Usually defined as severe multi-system allergic reaction.
==Clinical Features==
*Onset: minutes to hours after exposure (usually within 30 minutes)
*Skin/mucosal (90%): urticaria, flushing, angioedema, pruritus
*Respiratory (70%): laryngeal edema, stridor, bronchospasm, wheezing, dyspnea
*Cardiovascular (45%): [[hypotension]], [[tachycardia]], distributive [[shock]], syncope, cardiac arrest
*GI (45%): nausea, vomiting, abdominal cramps, diarrhea
*'''Neurologic''': anxiety, dizziness, altered mental status
*'''Anaphylaxis can occur WITHOUT skin findings''' (~10-20% of cases)


Key features include one or several of:
===Diagnostic Criteria (Any ONE of Three)===
*Criterion 1: Acute onset with skin/mucosal involvement AND respiratory compromise OR hypotension
*Criterion 2: Two or more systems involved rapidly after likely allergen: skin, respiratory, cardiovascular, GI
*Criterion 3: Hypotension after exposure to known allergen (SBP <90 or >30% decrease from baseline)


1) Airway swelling: visible or audible as stridor
==Differential Diagnosis==
*[[Angioedema]] (hereditary or ACE-inhibitor — no urticaria)
*Vasovagal syncope (bradycardia; no urticaria/wheezing)
*[[Asthma]] exacerbation
*[[Urticaria]] alone (without systemic involvement)
*Carcinoid syndrome, mastocytosis, scombroid fish poisoning
*[[Anxiety]] / panic attack
*[[Vocal cord dysfunction]]


2) Bronchospasm: causing wheeze
==Evaluation==
*'''Anaphylaxis is a clinical diagnosis''' — do NOT delay treatment for labs
*Serum tryptase: elevated supports diagnosis (draw within 1-3 hours of onset)
**Normal tryptase does NOT exclude anaphylaxis
**Useful for postmortem diagnosis and distinguishing from other causes
*Monitor: continuous ECG, pulse oximetry, blood pressure
*Consider: CBC, BMP, troponin (Kounis syndrome — allergic MI)


3) Hypotension: collapse, dizziness, confusion
==Management==
===Epinephrine (Cornerstone of Treatment)===
*Epinephrine 0.3-0.5 mg (1:1,000) IM in anterolateral thigh (vastus lateralis)
**Pediatric: 0.01 mg/kg (max 0.3 mg) IM
**Repeat every 5-15 minutes as needed
**'''Do NOT delay''' — there are NO absolute contraindications to epinephrine in anaphylaxis
*If refractory or in shock:
**Epinephrine infusion: 0.1-0.5 mcg/kg/min IV (mix 1 mg in 250 mL NS = 4 mcg/mL)
**IV epinephrine bolus (only for cardiac arrest or refractory shock): 0.1 mg of 1:10,000 IV
*IM > SC (faster absorption; SC absorption unreliable in shock)


== ==
===Adjunctive Therapies===
*IV fluids: aggressive NS bolus (1-2L in adults; 20 mL/kg in children) — distributive shock with massive third-spacing
*Albuterol 2.5-5 mg nebulized for bronchospasm (does not replace epinephrine)
*'''H1 antihistamine''': diphenhydramine 25-50 mg IV (treats urticaria/pruritus; does NOT treat life-threatening features)
*H2 antihistamine: famotidine 20 mg IV (adjunctive)
*Corticosteroids: methylprednisolone 125 mg IV or prednisone 1 mg/kg PO
**Theoretical benefit in preventing biphasic reaction (limited evidence)
**'''Do NOT rely on steroids as primary treatment''' (slow onset: 4-6 hours)
*Glucagon 1-5 mg IV for patients on beta-blockers (resistant to epinephrine)


===Refractory Anaphylaxis===
*Epinephrine infusion + aggressive volume resuscitation
*Vasopressin 1-2 units IV bolus for refractory hypotension
*Glucagon for beta-blocker use
*Consider methylene blue 1-2 mg/kg IV for refractory vasoplegia
*Secure airway early if airway edema progressing (may require surgical airway)


==Treatment ==
==Disposition==
*Observe minimum 4-6 hours after last dose of epinephrine (biphasic reaction monitoring)
*Extended observation (8-24 hours) if:
**Severe initial reaction (hypotension, intubation)
**History of biphasic reactions
**Delayed presentation
**Poor access to medical care
*Discharge with:
**Epinephrine auto-injector prescription (EpiPen or equivalent) — prescribe 2 devices
**Antihistamine (diphenhydramine or cetirizine) for 3 days
**Prednisone 40-60 mg PO daily × 3-5 days
**Allergist referral
**'''Written anaphylaxis action plan'''
**Strict avoidance of trigger
**'''Return precautions''': return immediately if symptoms recur


==See Also==
*[[Angioedema]]
*[[Urticaria]]
*[[Asthma]]
*[[Shock]]
*[[Epinephrine]]


Initial management targeted to life-saving measures
==References==
<references/>
*Lieberman P, et al. Anaphylaxis — a practice parameter update 2015. ''Ann Allergy Asthma Immunol''. 2015;115(5):341-384. PMID 26505932
*Cardona V, et al. World Allergy Organization anaphylaxis guidance 2020. ''World Allergy Organ J''. 2020;13(10):100472. PMID 33204386
*Simons FER, et al. World Allergy Organization guidelines for the assessment and management of anaphylaxis. ''World Allergy Organ J''. 2011;4(2):13-37. PMID 23268454
*Shaker MS, et al. Anaphylaxis — a 2020 practice parameter update. ''J Allergy Clin Immunol''. 2020;145(4):1082-1123. PMID 32001253


Cease any infusions of drugs, contrast, colloids
[[Category:Allergy and Immunology]]
 
[[Category:Critical Care]]
1) Epinephrine: always IM initially (see below)
 
    -IM 0.3-0.5mg Q5-15min
 
    -Epi infusion if slow response
 
    -try Glucagon if on B-blocker
 
2) IV access and NS bolus
 
3) secure airway early if threatened
 
 
Secondary management (largely symptom control)
 
4) Nebulised B-agonist for wheeze
 
5) Antihistamines (H1 & H2)
 
    -only once haemodyn stable
 
6) Corticosteroid
 
 
==Epinephrine==
 
 
(1:1,000;  1mg = 1mL)
 
*IM (lateral thigh)  =  0.3-0.5mg Q5-15min
 
(Peds = 10 mcg/kg/dose)
 
SEVERE: consider infusion, iv push is hazardous
 
IV: 5-15 mcg/min
 
(Peds = 0.05-1 mcg/kg/min)
 
 
NB: Cardiac Arrest adult dose: 1mg of 1:10,000 IVP
 
 
==Glucagon==
 
 
consider if not responsive to Epi, esp if on B-blocker
 
1-5mg iv over 5min
 
then infusion, start at 5mcg/min & titrate to BP
 
(Peds = 0.02-0.1 mg/kg stat, max. 1mg)
 
 
==Source ==
 
 
2/6/06  DONALDSON (adapted from Tintinalli)
 
Brown SGA, Mullins RJ and Gold MS, Anaphylaxis: diagnosis and management, MJA 2006; 185: 283–289 
 
Ewan PW, ABC of allergies – Anaphylaxis, BMJ 1998; 316: 1442-1445
 
Simons FER, Gu X, Simons KJ, Epinephrine absorption in adults: Intramuscular versus subcutaneous injection, J Allergy Clin Immunol 2001;108:871-3
 
Lieberman P et al, The diagnosis and management of anaphyalxis: An updated practice parameter, J Allergy Clin Immunol 2005;115;3:S483-S523
 
Sheikh A, Shehata YA, Brown SGA, Simons FER. Adrenaline (epinephrine) for the treatment of anaphylaxis with and without shock.Cochrane Database of Systematic Reviews2008, Issue 4. Art. No.: CD006312. DOI:10.1002/14651858.CD006312.pub2.
 
 
 
 
 
[[Category:Airway/Resus]]

Latest revision as of 09:23, 22 March 2026

Background

  • Acute, life-threatening, systemic allergic reaction involving multiple organ systems
  • IgE-mediated (type I hypersensitivity) in most cases; can also be non-IgE mediated (anaphylactoid)
  • Biphasic reaction occurs in 5-20% of cases (recurrence 1-72 hours after initial reaction, usually within 8-10 hours)[1]
  • Epinephrine is the ONLY first-line treatment — delays in administration increase mortality

Common Triggers

  • Foods (most common overall): peanuts, tree nuts, shellfish, fish, milk, eggs, wheat, soy
  • Medications: antibiotics (penicillin, cephalosporins), NSAIDs, neuromuscular blocking agents
  • Insect stings: Hymenoptera (bees, wasps, hornets, fire ants)
  • Latex
  • Exercise-induced anaphylaxis (sometimes food-dependent)
  • Idiopathic (~20% — no identifiable trigger)

Clinical Features

  • Onset: minutes to hours after exposure (usually within 30 minutes)
  • Skin/mucosal (90%): urticaria, flushing, angioedema, pruritus
  • Respiratory (70%): laryngeal edema, stridor, bronchospasm, wheezing, dyspnea
  • Cardiovascular (45%): hypotension, tachycardia, distributive shock, syncope, cardiac arrest
  • GI (45%): nausea, vomiting, abdominal cramps, diarrhea
  • Neurologic: anxiety, dizziness, altered mental status
  • Anaphylaxis can occur WITHOUT skin findings (~10-20% of cases)

Diagnostic Criteria (Any ONE of Three)

  • Criterion 1: Acute onset with skin/mucosal involvement AND respiratory compromise OR hypotension
  • Criterion 2: Two or more systems involved rapidly after likely allergen: skin, respiratory, cardiovascular, GI
  • Criterion 3: Hypotension after exposure to known allergen (SBP <90 or >30% decrease from baseline)

Differential Diagnosis

  • Angioedema (hereditary or ACE-inhibitor — no urticaria)
  • Vasovagal syncope (bradycardia; no urticaria/wheezing)
  • Asthma exacerbation
  • Urticaria alone (without systemic involvement)
  • Carcinoid syndrome, mastocytosis, scombroid fish poisoning
  • Anxiety / panic attack
  • Vocal cord dysfunction

Evaluation

  • Anaphylaxis is a clinical diagnosis — do NOT delay treatment for labs
  • Serum tryptase: elevated supports diagnosis (draw within 1-3 hours of onset)
    • Normal tryptase does NOT exclude anaphylaxis
    • Useful for postmortem diagnosis and distinguishing from other causes
  • Monitor: continuous ECG, pulse oximetry, blood pressure
  • Consider: CBC, BMP, troponin (Kounis syndrome — allergic MI)

Management

Epinephrine (Cornerstone of Treatment)

  • Epinephrine 0.3-0.5 mg (1:1,000) IM in anterolateral thigh (vastus lateralis)
    • Pediatric: 0.01 mg/kg (max 0.3 mg) IM
    • Repeat every 5-15 minutes as needed
    • Do NOT delay — there are NO absolute contraindications to epinephrine in anaphylaxis
  • If refractory or in shock:
    • Epinephrine infusion: 0.1-0.5 mcg/kg/min IV (mix 1 mg in 250 mL NS = 4 mcg/mL)
    • IV epinephrine bolus (only for cardiac arrest or refractory shock): 0.1 mg of 1:10,000 IV
  • IM > SC (faster absorption; SC absorption unreliable in shock)

Adjunctive Therapies

  • IV fluids: aggressive NS bolus (1-2L in adults; 20 mL/kg in children) — distributive shock with massive third-spacing
  • Albuterol 2.5-5 mg nebulized for bronchospasm (does not replace epinephrine)
  • H1 antihistamine: diphenhydramine 25-50 mg IV (treats urticaria/pruritus; does NOT treat life-threatening features)
  • H2 antihistamine: famotidine 20 mg IV (adjunctive)
  • Corticosteroids: methylprednisolone 125 mg IV or prednisone 1 mg/kg PO
    • Theoretical benefit in preventing biphasic reaction (limited evidence)
    • Do NOT rely on steroids as primary treatment (slow onset: 4-6 hours)
  • Glucagon 1-5 mg IV for patients on beta-blockers (resistant to epinephrine)

Refractory Anaphylaxis

  • Epinephrine infusion + aggressive volume resuscitation
  • Vasopressin 1-2 units IV bolus for refractory hypotension
  • Glucagon for beta-blocker use
  • Consider methylene blue 1-2 mg/kg IV for refractory vasoplegia
  • Secure airway early if airway edema progressing (may require surgical airway)

Disposition

  • Observe minimum 4-6 hours after last dose of epinephrine (biphasic reaction monitoring)
  • Extended observation (8-24 hours) if:
    • Severe initial reaction (hypotension, intubation)
    • History of biphasic reactions
    • Delayed presentation
    • Poor access to medical care
  • Discharge with:
    • Epinephrine auto-injector prescription (EpiPen or equivalent) — prescribe 2 devices
    • Antihistamine (diphenhydramine or cetirizine) for 3 days
    • Prednisone 40-60 mg PO daily × 3-5 days
    • Allergist referral
    • Written anaphylaxis action plan
    • Strict avoidance of trigger
    • Return precautions: return immediately if symptoms recur

See Also

References

  1. ↑ Lee S, et al. Biphasic anaphylaxis: review of incidence, clinical predictors, and observation recommendations. Immunol Allergy Clin North Am. 2015;35(2):313-326. PMID 25841553
  • Lieberman P, et al. Anaphylaxis — a practice parameter update 2015. Ann Allergy Asthma Immunol. 2015;115(5):341-384. PMID 26505932
  • Cardona V, et al. World Allergy Organization anaphylaxis guidance 2020. World Allergy Organ J. 2020;13(10):100472. PMID 33204386
  • Simons FER, et al. World Allergy Organization guidelines for the assessment and management of anaphylaxis. World Allergy Organ J. 2011;4(2):13-37. PMID 23268454
  • Shaker MS, et al. Anaphylaxis — a 2020 practice parameter update. J Allergy Clin Immunol. 2020;145(4):1082-1123. PMID 32001253
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