Anaphylaxis

Definition

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

Criterion 1 (90% of patients)

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

Criterion 2 (10-20% of pts)

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

Criterion 3

1. Hypotension after exposure to a KNOWN allergy for that patient (minutes to hours):
   1. Adults: systolic blood pressure (SBP) <90 mmHg or >30% reduction from baseline
   2. Pediatrics
      1. 1 month - 1 year: SBP <70 mmHg
      2. 1 year - 10 years: SBP <(70 mmHg + [2 x age])
      3. 11 years - 17 years: SBP <90 mmHg

Differential Diagnosis

1. Generalized urticaria
2. Angioedema
3. Asthma exacerbation
4. Anxiety attack
5. Acute Coronary Syndromes
6. Scombroidosis
7. Other forms of shock

Presentation

• Cutaneous symptoms: 90%
• Respiratory symptoms: 70%
• Gastrointestinal symptoms: 40%
• Cardiovascular symptoms: 35%

Treatment

1. Epinephrine 1:1000 IM 0.3 - 0.5mg (0.3 - 0.5mL) every 5 - 15 minutes
   1. Give as soon as possible
   2. Always IM initially
   3. If response to IM is inadequate: give epinephrine infusion 1:10,000 2 - 10 µg/min
2. Pediatric:Epinephrine 1:1000 IM 0.01 mg/kg (max 0.5mg) every 5 to 15 minutes
   1. IV infusion: 0.05 - 1 mcg/kg/min
3. Supplemental oxygen
   1. Consider endotracheal intubation if airway edema present
4. Normal saline bolus
   1. If unresponsive to [[Epi]|epinephrine] assume distributive shock and give 1 - 2 liters of normal saline
5. Glucagon 1 - 2mg IV over 5 minutes followed by infusion of 5 - 15 µg/min
   1. If taking beta-blocker AND unresponsive to epinephrine
6. Also consider:
   1. Albuterol: for bronchospasm resistant to IM epinephrine
   2. Antihistamines: only for sympton control (hives, itching) AFTER hemodynamically stable
      1. Diphenhydramine 25 to 50 mg IV
      2. Ranitidine 50 mg IV (minimal evidence to support this)
   3. Glucocorticoid: MAY blunt biphasic reaction
      1. Methylprednisolone 125 mg IV (2mg/kg in children)
      2. Three days oral steroid: biphasic reaction always occurs within 72 hours

Course

1. Uniphasic (80-90%)
   1. Symptoms peak within 30 minutes to 1 hour after onset, resolve within 30 minutes to 1 hour of receiving treatment
2. Biphasic (10-20%)
   1. Uniphasic response, followed by asymptomatic period of hour or more, then return of symptoms
   2. The second phase does not necessarily resemble the first!
   3. Possible risk factors
      1. Severe initial symptoms
      2. Late administration of epineprhine
      3. Delayed resolution of initial symptoms
   4. Little evidence that glucocorticoids blunt a biphasic presentation
3. Protracted (case reports)
   1. Lasts hours to days without resolving completely

Disposition

1. Admit: Severe and moderate, especially if symptoms did not respond promptly to epinephrine
2. Home: Symptom-free for at least 4 hours
   1. Send home with an epinephrine autoinjector! (Epi-Pen, Auvi-Q, etc)

See Also

• Allergic Reaction
• Angioedema (Upper Airway)

Sources

• 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 Reviews 2008, Issue 4. Art. No.: CD006312. DOI:10.1002/14651858.CD006312.pub2
• Second symposium on the definition and management of anaphylaxis: summary report--Second National Institute of Allergy and Infectious Disease/Food Allergy and Anaphylaxis Network symposium.