Anaphylaxis

Definition

• Highly likely when ANY ONE of the following criteria is fulfilled:
• Criterion 1 (90% of pts)
• Acute onset of an illness involving the skin, mucosal tissue, or both AND at least one of the following:
• Respiratory compromise
• Reduced BP or associated symptoms (syncope, dizziness)
• Criterion 2 (10-20% of pts)
• TWO OR MORE of the following that that occur rapidly after exposure to a LIKELY allergen for that pt
• Involvement of the skin-mucosal tissue (hives, swollen lips-tongue-uvula)
• Respiratory compromise
• Reduced BP or associated symptoms
• Persistent GI symptoms (vomiting, diarrhea, crampy abd pain)
• Criterion 3
• Reduced BP after exposure to a KNOWN allergy for that pt (minutes to hours):
• Adults
• Systolic < 90 or > 30% from baseline
• Peds
• Less than 70 mmHg from 1 month up to 1 year
• Less than (70 mmHg + [2 x age]) from 1 to 10 years
• Less than 90 mmHg from 11 to 17 years

DDX

• Generalized urticaria
• Angioedema
• Asthma exacerbation
• Anxiety attack
• MI
• Scombroidosis
• Other forms of shock

Presentation

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

==Treatment ==

• Epinephrine 1:1000 IM 0.3-0.5mg (0.3-05mL) Q5-15min
• Always IM initially
• Start epinephrine infusion 1:10,000 2-10µg/min if inadequate response to IM
• PEDS
• IM - 0.01mg/kg/dose (max 0.5mg)
• IV infusion - 0.05-1 mcg/kg/min
• Oxygen
• NS bolus
• If unresponsive to Epi must assume pt to be severely intravascularly depleted
• Supine positioning
• Glucagon 1-2mg IV over 5 min, followed by infusion of 5-15µg/min (if on B-blocker AND unresponsive to epi)
• 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
• Methylprednisolone 125 mg IV
• Three day PO course (biphasic reaction always occurs within 72hrs)

Course

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

Disposition

• Admit: Severe and moderate (especially if symptoms did not respond promptly to epi)
• Home: Anaphylaxis that responded promptly after ED observation
• Send home with an epi autoinjector!

Sources

• Tintinalli
• 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.