Features range from mild skin rashes to severe urticaria, hypotension, broncho-spasm, abdominal pain, diarrhoea, a 'feeling of impending doom' and cardiovascular collapse. Initial hypotension is largely related to profound vasodilation, which is followed by leakage of intravascular fluid into the interstitium. Cardiac depression (thought to be caused by circulating inflammatory mediators) may also contribute to hypotension. The cardiovascular effects are exacerbated by aortocaval compression.
Features usually occur within a few seconds or minutes of exposure to the allergen. In Caesarean section in latex allergic subjects, anaphylaxis typically occurs 10-15 minutes after induction of anaesthesia and once surgery has started, since the most provocative stimulus is exposure via mucous membranes.
Since clinical features may develop at a time of great physiological change, e.g. during Caesarean section or during/after delivery, it may be difficult to assess the situation and determine what has happened. Administration of many different drugs together or within a short time is common and this may hinder the diagnosis (and is suspected of increasing the risk of a reaction).
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