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INTRODUCTION

Key Clinical Questions

  • image How do you estimate cumulative radiation dose and risk?

  • image What is the latest theory about contrast-induced nephropathy?

  • image What are the risk factors for contrast-related allergic reactions?

  • image What are the risks associated with gadolinium-based contrast materials?

One must not lose sight of the potential risks of short- and long-term adverse effects of modern imaging for an acutely ill patient whose hospitalization is one snapshot in time. There are risks associated with contrast administration, ionizing radiation, and the possibility of incidental findings generating additional studies.

CONTRAST MATERIALS

ORAL CONTRAST

Contrast materials may be administered intravenously, orally, rectally, and for problem solving, through a variety of support lines and tubes. The selection of a specific oral contrast agent is based on the risk for aspiration versus the risk for extravasation of the contrast material. Catastrophic aspiration requiring ICU admission may occur when oral contrast material is administered to a patient with achalasia or other significant risk factors for aspiration, especially while the patient is supine. Although inert, barium is permanent when aspirated into the lungs. Barium becomes concentrated as it passes through the GI tract and may contribute to constipation and obstipation, particularly at the concentrations administered for x-ray and fluoroscopic examinations. Gastrografin is more commonly used when there is concern for extravasation into mediastinum or peritoneal cavity. Although gastrografin will be reabsorbed, it may cause pulmonary edema due to its hypertonicity. Gastrografin contains iodine and should not be used in patients with a known iodine allergy, as a small amount is absorbed in the GI tract. Specialized contrast agents may also be used for purposes such as distending the bowel without obscuring mucosal enhancement.

IODINATED INTRAVENOUS CONTRAST

Low-osmolar nonionic contrast agents are almost universally used in current practice due to their reduced risk of fluid shifts and allergic reaction. In a labile patient, these risks may not be warranted for the increase in diagnostic information provided by the contrast enhancement. This is best determined in consultation with the radiologist, to explore how crucial the intravenous contrast is for the clinical question at hand (Tables 113-1 and 113-2).

TABLE 113-1Conditions Associated with Adverse Reactions to Contrast Material

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