Anaphylaxis should be considered in the differential diagnosis when any one of the three main criteria list below occurs in a patient:
1. Acute onset of an illness (minutes to hours) with involvement of the skin, mucoasal tissue, or both (e.g., generalized hives, pruritus and or flushing, swollen lips/tongue/uvula and at least one of the following:
a.) respiratory compromise – dyspnea, wheeze-bronchospasm, stridor, reduced peakflow, hypoxemia
b.) reduced blood pressure or associated symptoms of end-organ dysfunction – hypotonia, collapse, syncope, incontinence
2. Two or more of the following that occur rapidly after exposure to a likely allergen for that patient (minutes to several hours)
a.) involvement of the skin and/or mucosal tissue
b.) respiratory compromise (e.g., dyspnea, wheezing-bronchospasm, stridor, reduced peak flow, hypoxemia)
c.) reduced blood pressure or associated symptoms of end-organ dysfunction (e.g. hypotonia, collapse, syncope, incontinence)
d.) persistent gastrointestinal symptoms
3. Reduced blood pressure after exposure to known allergen for that patient
a.) infants and children; low systolic blood pressure (age specific) or > 30% decrease in systolic blood pressure
b.) adults: systolic blood pressure < 90 mmHg or > 30% decrease from the patient’s baseline
(adapted from Avoiding Common Errors in the Emergency Department, p. 73)
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