How can cumulative radiation dose be estimated?
What commonly ordered CT scan delivers the highest dose of ionizing radiation?
What are the risk factors for contrast-related allergic reactions?
How can the potential for contrast-induced nephropathy be minimized?
For an acutely ill patient whose illness is one snapshot in time, one must not lose sight of the cumulative risks of short- and long-term adverse effects of modern imaging. These may be due to contrast administration, ionizing radiation, and the possibility of incidental findings generating additional studies.
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 can occur when oral contrast material is administered to a patient with achalasia or other significant risk factor for aspiration, especially when contrast material is administered while the patient is supine. Although inert, when aspirated into the lungs, barium is permanent. Barium becomes concentrated as it passes through the GI tract and can 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. It is important to remember that although gastrografin will be reabsorbed, it can 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 106-1 and 106-2).
Table 106-1 Conditions Associated with Adverse Reactions to Contrast Material |Favorite Table|Download (.pdf)
Table 106-1 Conditions Associated with Adverse Reactions to Contrast Material
|Risk factors for contrast-acquired renal failure|
- Preexisting renal insufficiency
- Diabetes alone, and diabetic nephropathy, especially > Cr 1.5 mg/dL, or 60 ml/minute/1.73 m2
- Acutely rising Cr
- Concurrent use of vasoconstrictive (nonsteroidal anti-inflammatory medications), nephrotoxic medications (aminoglycosides), and volume-depleting agents such as diuretics
- States of reduced perfusion such as hypotension, hypovolemia, cirrhosis, and congestive heart failure
- Age > 70, hypertension, anemia, female gender, multiple comorbidities
- Urgent procedures
- Large volume contrast load
|Risk factors for contrast-related allergy reactions|
- Previous anaphylaxis to contrast material
- Multiple medication allergies, including ...