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About 3% of patients who receive nonionic, lower-osmolality monomeric contrast media (LOCM) will experience a contrast reaction, though the vast majority of reactions are mild and require no treatment. However, about 1 in 1600 (0.06%) of patients receiving LOCM will need treatment for a reaction and a severe life-threatening reaction occurs with about 1 in 2500 patient injections (0.04%). Key to treating a contrast reaction is recognition of the type of reaction. Patient manifestations of reactions can be generally divided into 3 main categories: the uncomfortable patient; the subdued, poorly responsive patient; and, the anxious and agitated patient. In general, the more quickly a contrast reaction is recognized, correctly diagnosed and treated, the better the result-with less medication. Therefore, the goals of management should include early detection, the necessary multitasking to understand the type of reaction, and initiation of appropriate treatment as soon as possible.
This article reviews some mechanisms of reactions, the clinical presentations of the various reactions, and outlines an approach and recommended medications for dealing specifically with each reaction type.
Mechanism of contrast allergy
The exact causal mechanism of contrast- induced anaphylactic reactions is still debated. From his extensive research, Elliot Lasser1 has proposed a mechanism in which the large contrastcontaining molecule causes an overload effect on the antigen-binding sites on immunoglobulin E (IgE) of mast cells and basophils and does not bind directly to an antigen-specific site. This effect varies with the particular contrast medium. Since the immunoglobulin binding is nonspecific, the resultant reaction depends on the quantity of circulating IgE and mast cells at the time the contrast medium is administered. This nonspecific binding helps explain why patients with strong allergic history are at particular risk and why prior exposure to the contrast agent is not necessary for a reaction to occur.
Other considerations are that direct contact of the contrast agent with the endothelium of blood vessels may activate Factor XII; this substance in turn activates kallikrein; kallikrein activates bradykinin; bradykinin activates prostaglandin and the leucotrienes. 1,2 Leucotrienes are similar in their action to histamine, but are multifold more potent and not blocked by antihistamines. Bradykinin can mimic all the significant pathophysiological effects of histamine but is far more potent and, again, this sequence of events would not...