An anaphylactic reaction or anaphylaxis is an exaggerated immunological response to a substance to which an individual has become sensitised. When the patient is in contact with the substance, histamine, serotonin, tryptase and other vasoactive substances are released from basophils and mast cells. Anaphylactoid reactions are clinically indistinguishable from anaphylaxis, but are mediated by the drug or substance directly, and not by sensitised IgE antibodies. The commonest features are cardiovascular. Not all signs occur in every patient - one feature may be more obvious than others.
Reactions range from minor to life-threatening.
An awake patient will have a range of symptoms, but the diagnosis is more difficult in an anaesthetised patient. Suspect anaphylaxis in an anaesthetised patient who suddenly becomes hypotensive or develops broncho-spsm, particularly if this follows administration of a drug or fluid. Latex allergy may be delayed in onset, sometimes taking up to 60 minutes to occur. Hypotension and cardiovascular collapse. Tachycardia, arrhythmias, ECG may show ischaemic changes.