Anaphylaxis

Background

Definition

Highly likely when ANY ONE of the following criteria is fulfilled:

1. Criterion 1 (90% of pts)
   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 BP or associated symptoms (syncope, dizziness)
2. 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 pt
      1. Involvement of the skin-mucosal tissue (hives, swollen lips-tongue-uvula)
      2. Respiratory compromise
      3. Reduced BP or associated symptoms
      4. Persistent GI symptoms (vomiting, diarrhea, crampy abd pain)
3. Criterion 3
   1. Reduced BP after exposure to a KNOWN allergy for that pt (minutes to hours):
      1. Adults
         1. Systolic < 90 or > 30% from baseline
      2. Peds
         1. Less than 70 mmHg from 1 month up to 1 year
         2. Less than (70 mmHg + [2 x age]) from 1 to 10 years
         3. Less than 90 mmHg from 11 to 17 years

Course

1. Uniphasic (80-90%)
   1. Symptoms peak within 30min-1hr after onset, resolves within 30min-1hr of receiving Tx
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 epi
      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

DDX

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

Diagnosis

Presentation

• Cutaneous symptoms - 90%
• Respiratory symptoms - 70%
• GI symptoms - 40%
• Cardiovascular symptoms - 35%

Treatment

1. Epinephrine 1:1000 IM 0.3-0.5mg (0.3-0.5mL) Q5-15min
   1. Give as soon as possible
   2. Always IM initially
   3. Start epinephrine infusion 1:10,000 2-10µg/min if inadequate response to IM
   4. Peds
      1. IM - 0.01mg/kg/dose (max 0.5mg)
      2. IV infusion - 0.05-1 mcg/kg/min
2. Oxygen
   1. Consider intubation if e/o airway edema
3. NS bolus
   1. If unresponsive to Epi assume distributive shock (give NS 1-2L)
4. Glucagon 1-2mg IV over 5 min followed by infusion of 5-15µg/min
   1. If on B-blocker AND unresponsive to epi
5. Also consider:
   1. Albuterol: For bronchospasm resistant to IM epinephrine
   2. Antihistamines
      1. 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 peds)
      2. Three day PO course (biphasic reaction always occurs within 72hrs)

Disposition

1. Admit: Severe and moderate (especially if symptoms did not respond promptly to epi)
2. Home: Symptom-free for at least 4hr
   1. Send home with an epi autoinjector!

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 Reviews2008, 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.
• Tintinalli's Emergency Medicine