What are the diagnostic criteria and treatment for anaphylaxis?

Diagnosis and Treatment of Anaphylaxis

Anaphylaxis is diagnosed when any one of three established clinical criteria is fulfilled, and immediate administration of intramuscular epinephrine is the first-line treatment for all cases of anaphylaxis. 1

Diagnostic Criteria for Anaphylaxis

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

Criterion 1

• Acute onset of illness (minutes to several hours) with involvement of skin/mucosal tissue (generalized hives, itching, flushing, swollen lips-tongue-uvula)
• AND at least one of:
  • Respiratory compromise (shortness of breath, wheeze, cough, stridor, hypoxemia)
  • Reduced blood pressure or symptoms of end-organ dysfunction (hypotonia, collapse, incontinence)

Criterion 2

• Two or more of the following occurring rapidly after exposure to a likely allergen:
  • Skin/mucosal involvement (hives, itch, flush, swollen lips-tongue-uvula)
  • Respiratory compromise (dyspnea, wheeze, stridor, hypoxemia)
  • Reduced blood pressure or associated symptoms (hypotonia, syncope, incontinence)
  • Persistent gastrointestinal symptoms (crampy abdominal pain, vomiting)

Criterion 3

• Reduced blood pressure after exposure to known allergen:
  • Adults: systolic BP <90 mmHg or >30% decrease from baseline
  • Infants/children: age-specific low systolic BP or >30% decrease from baseline
    • <70 mmHg (1 month to 1 year)
    • <70 mmHg + (2 × age) (1-10 years)
    • <90 mmHg (11-17 years) 1

Important Clinical Considerations

• Skin manifestations are present in most cases but may be absent in up to 20% of anaphylaxis cases 1, 2
• Respiratory symptoms occur in up to 70% of cases 1
• Cardiovascular symptoms occur in up to 35% of cases 1
• Gastrointestinal symptoms occur in up to 40% of cases 1
• Children more commonly present with respiratory symptoms than hypotension 1
• Adults more commonly present with cardiovascular symptoms 2

Time Course and Patterns

• Anaphylaxis typically develops rapidly (minutes to hours) after allergen exposure
• Reactions may follow three patterns:
  • Uniphasic: resolves within minutes to hours without recurrence
  • Biphasic: recurrence of symptoms after initial resolution (typically around 8 hours, but can occur up to 72 hours later) in approximately 4-5% of cases
  • Protracted: prolonged symptoms lasting up to 32 hours despite treatment 1

Treatment Algorithm

Immediate Management

1. Administer epinephrine intramuscularly into lateral thigh (first-line treatment) 3, 4, 5

   • Adult dose: 0.3-0.5 mg
   • Pediatric dose: 0.01 mg/kg (maximum 0.3 mg)
   • May repeat every 5-15 minutes if needed

2. Position patient supine with legs elevated (unless respiratory distress requires sitting)

3. Establish IV access and administer fluid resuscitation for hypotension

   • Crystalloids initially (1-2 L rapidly in adults)
   • Consider colloids for severe shock 4

4. Provide supplemental oxygen if needed

5. Additional medications:

   • H₁-antihistamines for cutaneous symptoms (not a substitute for epinephrine) 5
   • Glucocorticoids to prevent protracted or biphasic reactions 4
   • Inhaled beta-2 agonists for persistent bronchospasm 4
   • Consider vasopressors for refractory hypotension 2

For Severe or Refractory Cases

• If inadequate response to IM epinephrine, initiate IV epinephrine infusion 4, 2
• Consider vasopressors if hypotension persists despite epinephrine 2

Post-Acute Management

• Observe patient for at least 4-6 hours after symptom resolution (longer if severe reaction) 1, 2
• Refer to allergist for:
  • Confirmation of trigger
  • Risk assessment
  • Education on avoidance measures
  • Prescription for epinephrine autoinjector
  • Consideration of immunotherapy if appropriate 4, 2

Common Pitfalls to Avoid

1. Delayed epinephrine administration - Epinephrine is the first-line treatment and should not be delayed in favor of antihistamines or steroids 5

2. Failure to recognize anaphylaxis without skin manifestations - Remember that up to 20% of cases may not have urticaria or other skin symptoms 1, 2

3. Dismissing isolated hypotension after allergen exposure - This alone can fulfill criterion 3 for anaphylaxis 1

4. Discharging patients too early - Observe for at least 4 hours due to risk of biphasic reactions 1, 2

5. Confusing anaphylaxis with vasovagal reactions - In vasovagal reactions, urticaria is absent, heart rate is typically bradycardic, and skin is cool and pale 1

6. Relying on antihistamines alone - While helpful for mild symptoms, they cannot prevent or treat the life-threatening aspects of anaphylaxis 5