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

Epinephrine

1. 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
   4. How to make a quick epi drip: Take your code-cart epi (it doesn't matter if it's 1:1,000 or 1:10,000) and inject 1mg into a liter bag of NS. Final concentration is 1mcg/ml. Run at 1cc/hr and titrate to effect.
2. Pediatric: Epinephrine 1:1000 0.01 mg/kg (max 0.5mg) IM every 5 to 15 minutes
   1. 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

Glucagon

• 1 - 2mg IV over 5 minutes followed by infusion of 5 - 15 µg/min
• If taking beta-blocker AND unresponsive to epinephrine

Also consider

Albuterol

• for bronchospasm resistant to IM epinephrine

Antihistamines

• only for sympton control (hives, itching) AFTER hemodynamically stable

Diphenhydramine

• 25 to 50 mg IV

Ranitidine

• 50 mg IV (minimal evidence to support this)

Glucocorticoid

• MAY blunt biphasic reaction although little evidence to support usage
• Methylprednisolone: *125 mg IV (2mg/kg in children)
• Dexamethasone: 10mg IV or PO (0.6mg/kg in children)

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

• Admit: Severe and moderate, especially if symptoms did not respond promptly to epinephrine
• Discharge: Symptom-free for at least 4 hours and mild initial presentation
  • 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

Biphasic Reaction

• More likely with a severe initial presentation, hypotension, and recurrent epinephrine dosing requirements in the emergency department
• 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

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.