Anaphylaxis – Diagnosis & Treatment
Cardinal Presentations / Presenting Problems, Critical Care / Resuscitation
- Anaphylaxis is a potentially life-threatening emergency that requires immediate diagnosis and treatment.
- The exact incidence of anaphylaxis is not known, but recent evidence suggests that it is increasing.
- There are approximately 1500 fatal cases of anaphylaxis in the United States per year.
- Anaphylaxis presents with a sudden onset of signs and symptoms, usually in more than one body system, within minutes to hours of exposure to a trigger.
Anaphylaxis is a clinical diagnosis and is highly likely when any one of the following three criteria is filled:
- Sudden onset of an illness (minutes to several hours) with involvement of the skin, mucosal tissue, or both (ie. generalized hives, itching or flushing, swollen lips-tongue-uvula) and at least one of the following:
- Respiratory compromise (ie. shortness of breath, wheeze, cough stridor, hypoxemia).
- Reduced BP or associated symptoms of end-organ dysfunction (ie. hypotonia [collapse], syncope, incontinence).
- Two or more of the following occurring rapidly (minutes to several hours) after exposure to a likely allergen or other trigger for that patient:
- Involvement of the skin-mucosal tissue (ie. generalized hives, itch-flush, swollen lips-tongue-uvula).
- Sudden respiratory compromise (ie. shortness of breath, wheeze, cough, stridor, hypoxemia).
- Sudden reduced BP or symptoms of end-organ dysfunction (ie. hypotonia [collapse], syncope, incontinence).
- Sudden gastrointestinal symptoms (ie. crampy abdominal pain, vomiting).
- Reduced BP after exposure to a known allergen for that patient (minutes to several hours):
- Infants and children: Low systolic BP (age specific) or greater than 30% decrease in systolic BP.
- Adults: Systolic BP of less than 90 mm Hg or greater than 30% decrease from baseline.
- Anaphylactic reactions often present as a combination of clinical characteristics, commonly affecting an array of organ systems:
- Skin (80% to 90% of episodes)
- Respiratory tract (70% of episodes)
- Gastrointestinal tract (30% to 45% of episodes)
- Cardiovascular (10% to 45% of episodes)
- Central nervous system (10% to 15% of episodes)
- Nasal congestion, sneezing, ocular itching, and tearing are also common complaints.
- Patients with laryngeal edema often complain of hoarseness, throat tightness, or stridor.
- Death from anaphylaxis usually results from asphyxiation due to upper or lower airway obstruction, or from cardiovascular collapse.
- Prompt assessment and treatment are critical in anaphylaxis, as respiratory or cardiac arrest and death can occur within minutes.
- The literature has shown that early administration of epinephrine improves patient outcomes and decreases the likelihood of death.
- Initial management:
- If applicable, remove the inciting cause (ie. stop infusion of a suspect medication).
- Administer epinephrine as early as possible.
- 0.3-0.5 mg IM, repeat every 5-15 minutes PRN.
- Consider and prepare for intubation.
- Airway edema can rapidly obscure visualization of the cords and necessitate a surgical airway.
- Intubate early if airway compromise is present.
- Basics: ABCs, obtain two large-bore IV catheters, initiate supplemental oxygen at 8-10 LPM via nasal prongs, place patient on cardiac monitors.
- Fluid resuscitation with 1-2 litres of normal saline rapid bolus.
- Place patient in recumbent position with lower extremities elevated.
- Anaphylaxis refractory to IM epinephrine:
- Start IV epinephrine drip at 1-5 mcg/min and titrate (use IV epinephrine with caution as dosing errors can cause myocardial ischemia/infarction).
- The addition of another vasopressor should be considered if the patient continues to be hypotensive despite maximal epinephrine and fluid resuscitation.
- Few case reports support the use of methylene blue, an inhibitor of nitric oxide synthase and guanylate cyclase.
- The efficacy and ideal dose of methylene blue is unknown, but a single bolus of 1 to 2 mg/kg given over 20 to 60 minutes has been used in cardiac surgery.
- Extracorporeal membrane oxygenation (ECMO): The decision to initiate ECMO should be considered early in patients unresponsive to traditional resuscitative measures, before irreversible ischemic acidosis develops.
Adjunctive Treatments (non-lifesaving)
- Epinephrine is first-line treatment for anaphylaxis, and there is no known equivalent substitute.
- None of these medications should be used as the initial treatment or as the sole treatment, because they do not relieve upper or lower respiratory tract obstruction, hypotension, or shock:
- H1 antihistamines: ie. diphenhydramine 25-50 mg IV over 5 minutes q4-6 hours PRN (maximum dose of 400 mg per 24 hours).
- H2 antihistamines: ie. famotidine 20 mg IV over at least 2 minutes.
- Bronchodilators: ie. nebulized salbutamol.
- Corticosteroids: ie. IV methylprednisolone.
- Beta blockers: thought to be associated with higher risk for severe anaphylaxis.
- Give glucagon 1-5 mg IV administered over 5 minutes, followed by an infusion of 5-15 mcg/min in patients on beta-blockers with refractory anaphylaxis.
- Monoamine oxidase inhibitors and tricyclic antidepressants: extend the duration of action of epinephrine.
Criteria For Transfer To Another Facility
- Dependent on resource availability.
Criteria For Close Observation And/or Consult
- All patients with suspected anaphylaxis should be closely monitored as above.
- Additional help should be called as needed (ie. involvement of ICU, anesthesia).
Criteria For Safe Discharge Home
- All patients with anaphylaxis should be observed until symptoms have completely resolved.
- Admission or observation is recommended for patients who do not respond promptly to IM epinephrine, require >1 dose of epinephrine, or received epinephrine only after a significant delay (>60 minutes), as these features may be risk factors for a biphasic response.
- All patients should be sent home with:
- An anaphylaxis emergency plan.
- At least one epinephrine auto-injector or a prescription for two epinephrine auto-injectors.
- Printed information about anaphylaxis and its treatment.
- Documented advice to follow up with an allergist, with a referral if possible.
Simons, F. E., Ardusso, L. E., Bilò, M. B., Dimov, V., Ebisawa, M., El-Gamal, Y. M., & Worm, M. (2012). 2012 Update: World Allergy Organization Guidelines for the assessment and management of anaphylaxis. Current Opinion in Allergy and Immunology, 12(4):389-99.
Campbell, R.L., Li, J.T., Nicklas, R.A., & Sadosty, A. (2014). Emergency department diagnosis and treatment of anaphylaxis: a practice parameter. Annals of Allergy, Asthma and Immunology, 113(6):599-608.
Sheikh, A., Shehata, Y.A., Brown, S.G., & Simons, F.E. (2009). Adrenaline for the treatment of anaphylaxis: cochrane systematic review. Allergy, 64(2):204.
Sampson, H.A., Mendelson, L., & Rosen, J.P. (1992). Fatal and near-fatal anaphylactic reactions to food in children and adolescents. New England Journal of Medicine, 327(6):380.
White, J.L., Greger, K.C., Lee, S., Kahoud, R.J., Li, J.T., Lohse, C.M., & Campbell, R.L. (2018). Patients taking beta-blockers do not require increased doses of epinephrine for anaphylaxis. Journal of Allergy and Clinical Immunology: In Practice, 6(5):1553.
Thomas, M., & Crawford, I. (2015). Best evidence topic report. Glucagon infusion in refractory anaphylactic shock in patients on beta-blockers. Emergency Medicine Journal, 22(4):272.
UpToDate: Anaphylaxis: Emergency treatment.
Rosen’s Emergency Medicine: Concepts and Clinical Practice, Chapter 109, 1418-1429.e2 (Allergy, Hypersensitivity & Anaphylaxis).
The purpose of this document is to provide health care professionals with key facts and recommendations for the diagnosis and treatment of patients in the emergency department. This summary was produced by the BC Emergency Medicine Network and uses the best available knowledge at the time of publication. However, healthcare professionals should continue to use their own judgment and take into consideration context, resources and other relevant factors. The BC Emergency Medicine Network is not liable for any damages, claims, liabilities, costs or obligations arising from the use of this document including loss or damages arising from any claims made by a third party. The BC Emergency Medicine Network also assumes no responsibility or liability for changes made to this document without its consent.
Last Updated Feb 17, 2022
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