Managing Anaphylaxis

How is anaphylaxis diagnosed?

Diagnostic criteria for anaphylaxis are difficult to outline, due to the wide range of signs and symptoms and a lack of reliable or timely laboratory testing.^1,4

Diagnosis of anaphylaxis during the acute episode is typically based on clinical signs and symptoms.⁷

Anaphylaxis may be likely if a patient has sudden onset (minutes to hours) of:¹

• skin and/or mucosal symptoms (e.g., hives, itching, flushing, angioedema) AND at least one of the following:
  • respiratory symptoms (e.g., shortness of breath, wheezing, cough, hypoxemia)
  • low blood pressure
  • symptoms of end organ damage (collapse, syncope)

OR

• Two or more of the following after exposure to a SUSPECTED allergen/trigger:
• skin and/or mucosal symptoms (e.g., hives, itching, flushing, angioedema)
• respiratory symptoms (e.g., shortness of breath, wheezing, cough, hypoxemia)
• low blood pressure or end organ damage (collapse, syncope)
• gastrointestinal symptoms (e.g., abdominal pain and cramping, vomiting)

OR

• low systolic blood pressure (<90 mmHg [adults]) or >30% drop in BP (adults or children) after a KNOWN allergen exposure

How are anaphylaxis symptoms classified?

Mild¹⁰

Moderate¹⁰

Severe^10,*

erythema

hives

angioedema

chest or throat tightness

dyspnea, wheezing, stridor (high pitched wheezing; more common in children than adults)

nausea, vomiting, abdominal pain

dizziness

diaphoresis

cyanosis, oxygen saturation ≤92%

hypotension

confusion, loss of consciousness

incontinence

*Risk factors for severe and/or fatal anaphylaxis include cardiovascular disease, asthma, older age, and coexisting comorbid conditions.¹

What is the role of epinephrine?

Use intramuscular (IM) epinephrine first-line to treat anaphylaxis, injecting into the anterolateral thigh (upper front of thigh, toward the side, away from the middle) [Evidence Level C]. Dose is 0.01 mg/kg up to a max of 0.5 mg (adults) or 0.3 mg (children).^1,7 

Repeat doses as needed every five to 15 minutes for continuing symptoms.^1,7,12

What is important to know about biphasic anaphylaxis?

Biphasic anaphylaxis is a recurrence of anaphylaxis symptoms (with no further exposure to causative trigger) beginning an hour or more after an asymptomatic period.^1,12

Up to about 20% of patients who experience anaphylaxis may experience a repeat episode within about 72 hours.^1,4,6 Most occur within six to twelve hours.¹²

There are not good predictors of which patients have these recurrent episodes of anaphylaxis. Consider the following as possible indicators of an increased risk for these recurrent episodes of anaphylaxis:^1,6

Consider longer observation periods for patients with severe anaphylaxis or those who require more than one dose of epinephrine to monitor for recurrent episodes of anaphylaxis.^1,6

What is the role of antihistamines?

Do NOT rely on antihistamines to prevent biphasic anaphylaxis.^1,11

Do NOT use antihistamines as a substitute for epinephrine.^1,6,12 Antihistamines:^1,6

It is NOT necessary to use antihistamines WITH epinephrine. When treating anaphylaxis, consider ADDING an antihistamine AFTER epinephrine to ease cutaneous symptoms (i.e., itching associated with urticaria, flushing).^1,6,12 

What is the role of steroids?

Do NOT rely on steroids to prevent biphasic anaphylaxis.^1,6,11

Do NOT use steroids as a substitute for epinephrine.¹² Steroids:^1,6

When treating anaphylaxis, the addition of steroids AFTER epinephrine may be considered as optional or adjunctive therapy in patients with asthma or recent steroid use (due to potentially suppressed HPA axis).^6,11,12

Dexamethasone (orally) or methylprednisolone (intravenously) are examples of steroids used in anaphylaxis protocols.²

What is the role of antihistamines/
steroids as premedication?

Follow your institution’s protocols when considering premedicating patients with antihistamines and/or steroids to prevent hypersensitivity reactions with:¹

What is the role of beta-agonist therapy during anaphylaxis?

For patients who experience bronchospasm during anaphylaxis, inhaled beta-agonist therapy can be added on
(e.g., albuterol [US]; salbutamol [Canada]).^7,8,12

Some protocols also add ipratropium 0.5 mg inhaled by nebulizer.^5,9

What follow-up is appropriate for patients who experience anaphylaxis?

Ensure patients are prescribed epinephrine auto-injectors.^4,6 Some data indicate only 63% of kids diagnosed with anaphylaxis in the emergency department are prescribed epinephrine at discharge.⁴

Educate all patients who experience anaphylaxis about:^1,6

Refer patients to an allergist.¹

Talk to patients about thresholds for care.¹ For example:^1,4

Ensure patients have an allergy and anaphylaxis plan.³ These can be personalized for patients: