Multisystem anaphylaxis with urticaria, asthma, edema, and cardiovascular collapse leads to an obvious diagnosis. However, if symptoms are restricted to a single system such as angio-edema or cardiovascular collapse, the diagnosis may be difficult or not considered. Cases have been described where anaphylaxis was suspected only after the fifth episode of cardiovascular collapse. Anaphylaxis may only be considered as a cause of cardiovascular collapse when removal of drapes or clothing has revealed erythema or urticaria.
Many diseases simulate an allergic response and may mimic anaphylaxis. Distinction from 'cardiac' causes of cardiovascular collapse may be assisted by a lowered venous pressure, vasodilatation, and supraventricular tachycardia as the predominant rhythm in anaphylactic shock. While a volume deficit may occur in hypotension due to cardiac causes, the volume deficit in anaphylaxis is usually greater. Vasovagal reactions after parenteral drug administration, particularly dental block with local anesthesia, are commonly misdiagnosed as anaphylaxis. Initial bradycardia, the rapid return of a strong pulse without treatment, and hyperventilation are important in the diagnosis.
The distinction between anaphylactic bronchospasm and allergic asthma is semantic only. The presence of airway obstruction and tension pneumothorax must be rapidly excluded in the patient who is difficult to inflate after respiratory arrest. 'Factitious' allergic emergencies have been described. Angioneurotic edema may be mimicked by venous or lymphatic obstruction, particularly in head and neck surgery.
The cardinal signs that anaphylaxis is likely to be severe are rapid onset, dyspnea, stridor, facial swelling, and/or hypotension. Clinical features
The clinical effects of mediator release have variable clinical expression relating to the mediator released, the mechanisms, the quantity, the timing, and the reactivity, number, and state of the receptors. In general, smooth muscle cells are affected, producing bronchoconstriction in the airway, vasodilatation in peripheral blood vessels, increased capillary permeability, and increased secretion of exocrine glands. This leads to the clinical manifestations shown in Table,,,,,?.
Table 2 Clinical features of anaphylaxis
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