Anaphylaxis

This page is for adult patients. For pediatric patients, see:Anaphylaxis (peds).

Background

• Type I hypersensitivity reaction that is either severe in nature or having two or more organ systems involved.
• Clinically Anaphylaxis and its treatment is virtually identical whether it is the traditional IgE dependent anaphylaxis reaction (vast majority), or the IgE independent anaphylactoid reaction
• Precipitants
  • Food (most common)
  • Medications
  • Insect stings
  • Latex
  • Aerobic exercise
  • Idiopathic (rare)

Clinical Features

Raised urticaria

Angioedema of tongue

Angioedema of face.

• Cutaneous symptoms (90%)
  • Hives
  • Angioedema
  • Itching
  • Morbilliform rash
• Respiratory symptoms (70%)
  • Wheezing
  • Shortness of breath
  • Throat itching or tightness
  • Hoarseness
  • Stridor
  • Hypoxia, cyanosis
• Gastrointestinal symptoms (40%)
  • Abdominal pain
  • Nausea, vomiting
  • Diarrhea
• Cardiovascular symptoms (35%)
  • Hypotension
  • Chest pain
  • Palpitations
• Central Nervous System
  • Uneasiness
  • Altered mental status
  • Headache, dizziness, confusion
  • Syncope

Expected Course

Uniphasic (80-90%)

• Symptoms peak within 30 minutes to 1 hour after onset, resolve within 30 minutes to 1 hour of receiving treatment

Biphasic (10-20%)

Biphasic reactions are rare and can occur anywhere from 10 minutes up to six days after an initial reaction.

• Uniphasic response, followed by asymptomatic period of hour or more, then return of symptoms
• The second phase does not necessarily resemble the first!
• More likely with a severe initial presentation or repeated epinephrine doses. Additionally hypotension, widened pulse pressure, unknown trigger, and drug trigger in children
• Little evidence to support the use of discharge steroids to prevent a biphasic reaction
• 0.4% of patients with anaphylaxis had a rebound event while in the ED

Differential Diagnosis

Acute allergic reaction

• Allergic reaction/urticaria
• Anaphylaxis
• Angioedema
• Anxiety attack
• Asthma exacerbation
• Carcinoid syndrome
• Cold urticaria
• Contrast induced allergic reaction
• Scombroid
• Shock
• Transfusion reaction

Shock

• Cardiogenic
  • Acute valvular Regurgitation/VSD
  • CHF
  • Dysrhythmia
  • ACS
  • Myocardial Contusion
  • Myocarditis
  • Drug toxicity (e.g. beta blocker, CCB, or bupropion OD)
• Obstructive
  • Air embolism
  • Aortic Stenosis
  • Cardiac Tamponade
  • PE
  • Tension pneumothorax
• Distributive
  • Adrenal crisis
  • Anaphylaxis
  • Neurogenic shock
  • Sepsis
  • Toxicologic
• Hypovolemic
  • Severe dehydration
  • Hemorrhagic shock (traumatic and non-traumatic)

Erythematous rash

• Positive Nikolsky’s sign
  • Febrile
    • Staphylococcal scalded skin syndrome (children)
    • Toxic epidermal necrolysis/SJS (adults)
  • Afebrile
    • Toxic epidermal necrolysis
• Negative Nikolsky’s sign
  • Febrile
    • Toxic shock syndrome
    • Kawasaki disease
    • Scarlet fever
    • DRESS syndrome
    • Cellulitis
    • Acute generalized exanthematous pustulosis
  • Afebrile
    • Alcohol intoxication
    • Anaphylaxis
    • Cellulitis
    • Dermatitis (multiple types)
    • Drug rash
    • Erysipelas
    • Erythema multiforme
    • Exfoliative erythroderma
    • Scombroid
    • Vancomycin infusion reaction

Evaluation

Anaphylaxis is highly likely when ANY ONE of the following criteria is fulfilled

Criterion 1 (90% of patients)

• Acute onset of an illness involving the skin, mucosal tissue, or both AND at least one of the following:
  • Respiratory Compromise
  • Reduced blood pressure or associated symptoms (Syncope, Dizziness)

Criterion 2 (10-20% of patients)

• TWO OR MORE of the following that occur rapidly after exposure to a LIKELY allergen for that patient
  • Involvement of the skin-mucosal tissue (hives, swollen lips-tongue-uvula)
  • Respiratory compromise
  • Hypotension or associated symptoms
  • Persistent gastrointestinal symptoms: (vomiting, diarrhea, crampy abdominal pain)

Criterion 3

• Hypotension after exposure to a KNOWN allergy for that patient (minutes to hours):
  • Adults: systolic blood pressure (SBP) <90 mmHg or >30% reduction from baseline
  • Pediatrics
    • 1 month - 1 year: SBP <70 mmHg
    • 1 year - 10 years: SBP <(70 mmHg + [2 x age])
    • 11 years - 17 years: SBP <90 mmHg

Management

• Epinephrine
  • 1:1000 IM 0.3 - 0.5mg (0.3 - 0.5mL) every 5 - 15 minutes
  • Give as soon as possible
  • Always IM initially
  • If response to IM is inadequate: give epinephrine infusion 1:10,000 2 - 10 µg/min
  • How to make a quick epinephrine drip: Take your code-cart epinephrine (it does not matter if it is 1:1,000 or 1:10,000) and inject 1mg into a liter bag of NS. Final concentration is 1mcg/ml. Run at 1cc/min and titrate to effect.
• Pediatric: Epinephrine 1:1000 0.01mg/kg (max 0.5mg) IM every 5 to 15 minutes
  • IV infusion: 0.05 - 1 mcg/kg/min
• Supplemental oxygen
  • Consider endotracheal intubation if airway edema present
• Normal saline bolus
  • If unresponsive to epinephrine assume distributive shock and give 1 - 2 liters of normal saline
• Also consider
  • Albuterol for bronchospasm resistant to IM epinephrine
  • Antihistamines (for symptom control AFTER hemodynamically stable)
    • Diphenhydramine: 25 to 50mg IV (1mg/kg in children)
    • Ranitidine: 50mg IV (0.5mg/kg in children) (has been found to improve urticaria but not angioedema at 2 hours)
    • AVOID promethazine as this can worsen hypotension
  • Glucocorticoid
    • MAY blunt biphasic reaction although little evidence to support usage
    • Methylprednisolone: 125mg IV (2mg/kg in children)
    • Dexamethasone: 10mg IV or PO (0.6mg/kg in children)
  • Glucagon
    • 1 - 5mg IV over 5 minutes followed by infusion of 5 - 15 µg/min
    • If taking beta-blocker AND unresponsive to epinephrine
  • Consider adding additional pressor support if persistent hypotension present
    • For example: vasopressin 2-8 units for persistent refractory shock (case series only)
    • Norepinephrine 0.05 to 0.5 mcg/kg per minute

Disposition

Admit

• Severe and moderate presentations, especially if symptoms did not respond promptly to epinephrine or required repeat dosing
• Labs that may be requested by allergist/admitting team if uncertain diagnosis
  • Histamine level - serum elevation 30-60 min following anaphylaxis, window easily missed
  • Tryptase - peaks at 2-4 hrs, remains elevated 6-12 hrs

Discharge

• Consider discharge after 1 hour observation, if no severe symptoms and no repeat epinephrine doses (AAAAI recommendations)
  • NPV of 1-hour observation was 95%, with NPV for biphasic anaphylaxis after >6 hours of observation of 97.3%
• Send home with an epinephrine autoinjector! (Epi-Pen)
  • Up to 6% of the people with anaphylaxis have a repeat ED visit for anaphylaxis within 7 days

See Also

• Allergic Reaction
• Angioedema