Anaphylaxis can occur as a result of an immune-mediated reaction or direct non-immunemediated reaction. Immunologic anaphylaxis occurs following an initial sensitization. A second exposure generates an immune-mediated (most commonly IgE-mediated) reaction resulting in the release of inflammatory mediators from mast cells and basophils. Common perioperative medications/exposures causing immunologic anaphylaxis include neuromuscular blocking drugs (NMBDs), antibiotics, and latex.
Non-immunologic anaphylaxis occurs after the direct activation of mast cells and basophils, without immunologic involvement. This may occur on first exposure rather than requiring a prerequisite exposure for sensitization. Common examples include vancomycin, morphine, and cold temperature exposure. Any agent that can generate a non-immunologic reaction also has the potential to generate an immune-mediated reaction.
Relapse of anaphylaxis may occur up to 72 hours (median 11 hours) after the initial event, and has been reported in 1-20% of patients. The mechanism is not clearly understood, but may be caused by decreased plasma concentrations of anaphylaxis medications or a true immunologic phenomenon. After a severe hypersensitivity reaction, close observation for up to 72 hours in an ICU is strongly recommended.