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Table 1.  

Epidemiology of Anaphylaxis in Emergency Departments

Table 2.  

'Epidemiology' of Prescription of Epinephrine

Table 3.  

Blood Systolic Pressure Values Indicating Hypotension

Table 4.  

Temporal Iinvolvement of Various Organs During Acute Anaphylactic Episodes in Paediatrics

Table 5.  

Perception of the Frequency of Anaphylaxis by Allergists vs. Nonallergists

Anaphylaxis in the Emergency Department: A Paediatric Perspective: Biphasic Anaphylaxis


Biphasic Anaphylaxis

Treatment of an acute anaphylactic episode must keep in view the possibility of biphasic anaphylaxis, which can develop after as many as 20% of anaphylactic reactions. The biphasic reaction can be less severe than, equally severe as, or more severe than the initial reaction, ranging from mild symptoms to a fatality.

Biphasic reactions happen in up to one-third of patients who have had fatal or near-fatal reactions. These patients seem to have fully recovered when severe bronchospasm suddenly recurs; the recurrence is typically more refractory to standard therapy and often requires intubation and mechanical ventilation.[62] Predicting such recurrences is not easy. The more severe the anaphylactic reaction, the more probable is a recurrence: although the absolute number of patients requiring more than one epinephrine injection is similar for each degree of severity, the number of patients requiring several epinephrine injections increases significantly with increased symptom severity.[63] The interval between the first anaphylactic reaction and the subsequent fatal or near-fatal anaphylactic episode can be between 2 and 72 h (mean 6-10 h), and no specific symptom is predictive of recurrence. Systemic corticosteroids are unable to prevent recurrence.[64] Even though up to 20% anaphylactic reactions are followed by a biphasic reaction, 97% of patients are discharged from the ED after an acute episode of anaphylaxis, particularly when they are of lower social level.[50] This may reflect economic and social considerations, but it seems too high a proportion of the episodes. No specific protocols have been established, but a 24-h admission after an anaphylactic attack would seem reasonable.[65] A recent article[66] reviews retrospective and prospective studies on the incidence of biphasic reactions, the clinical characteristics that may suggest that a reaction will develop into a biphasic reaction, and the recommendations for observation periods after an anaphylactic reaction.

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