Images obtained by a CT scan generally appear on a monitor as shades of gray. Because these structures resemble each other without contrast, a contrast agent is injected intravenously (in the vein) to highlight the structures that need to be better visualized. The contrast is iodine-based and is introduced using a power injector that allows a controlled amount at a controlled rate. Complications can arise with CT contrast injections despite safety precautions.
Allergic Reaction
One common complication of CT contrast is an allergic reaction. When contrast is injected into the vein, an allergic reaction can occur ranging from mild to severe. A mild allergic reaction manifests as itching, hives, sneezing or congestion. These symptoms are easily treated with an antihistamine. The more severe reaction manifests as difficulty breathing, swelling of the throat, low blood pressure and rapid or thready pulse; it is treated by an antihistamine or epinephrine injection. This type of reaction can be fatal if not treated immediately
Extravasation
Extravasation is the term given when fluid such as CT contrast gets into the surrounding tissues rather than the vein during an injection. This is painful to the patient and also decreases the image quality. Extravasation can occur because of the improper placement of the IV or a fragile vein that is unable to withstand the pressure of the injection of the contrast. Mild cases of extravasation create redness and swelling of the surrounding tissues that can be treated with a cold or warm compress. Severe cases of extravasation lead to a severe breakdown or even rupturing of the skin that may have to be repaired by plastic surgery. To avoid or at least reduce the extravasation, make sure the patient has a patent IV site and that the technologist monitors the contrast as it is injected.
Decreased Kidney Function
A patient with decreased kidney function is not a good candidate for a CT scan with contrast. With poor kidney function, the kidneys are not eliminating the waste produced by the body efficiently, and any additional fluid for the kidneys to filter can result in kidney failure. The best way to detect decreased kidney function is with a quick blood test called a creatinine test. If the creatinine is elevated or the glomerular filtration rate is below a certain level, injecting the patient with CT contrast could harm her.
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