Contrast Media and Pharmacology Flashcards

A 68-year-old patient with type 2 diabetes is scheduled for a contrast-enhanced CT of the abdomen. The patient's medication list includes Metformin. Their most recent lab results show an eGFR of 50 mL/min/1.73 m². Based on the Canadian Association of Radiologists (CAR) guidelines, what is the most appropriate action regarding the Metformin?

Answer: Proceed with the scan and instruct the patient to continue taking Metformin as prescribed.

According to the Canadian Association of Radiologists (CAR) guidelines, for patients with an estimated Glomerular Filtration Rate (eGFR) greater than 30 mL/min/1.73 m², it is not necessary to discontinue Metformin before or after the administration of iodinated contrast media. The patient's eGFR of 50 mL/min/1.73 m² is well above this threshold, indicating a low risk of contrast-associated acute kidney injury that could lead to lactic acidosis.

Which property of an iodinated contrast agent is the primary determinant of its potential to cause immediate, dose-dependent, non-allergic adverse effects such as a heat sensation, discomfort, and nausea?

Answer: Osmolality

Osmolality refers to the concentration of particles dissolved in a fluid. High-osmolality contrast media (HOCM) have a much higher concentration of particles than blood plasma, causing a rapid shift of fluid into the vascular space. This shift is responsible for many of the chemotoxic, non-allergic reactions like sensations of heat, pain at the injection site, and nausea. Low-osmolality (LOCM) and iso-osmolar (IOCM) agents were developed to minimize these effects.

During a power injection of iodinated contrast for a CT scan, the patient complains of sudden, sharp pain and swelling at the IV site. The MRT immediately stops the injection and suspects extravasation. What is the most appropriate initial management step?

Answer: Elevate the affected limb and apply a cold compress.

The standard initial management for contrast media extravasation is to stop the injection, elevate the affected limb to reduce hydrostatic pressure, and apply cold compresses. A cold compress causes vasoconstriction, which helps to limit the spread of the extravasated contrast and reduce inflammation and pain. Warm compresses might be used later to enhance absorption but are not the recommended initial step.

A patient develops urticaria (hives), pruritus (itching), and mild bronchospasm minutes after receiving intravenous iodinated contrast media. This type of reaction is best classified as:

Answer: Idiosyncratic (Anaphylactoid)

This constellation of symptoms—hives, itching, and bronchospasm—is characteristic of an idiosyncratic, or anaphylactoid, reaction. These reactions are not dose-dependent and resemble a true allergic reaction (anaphylaxis) but are not typically mediated by IgE antibodies. Chemotoxic reactions are dose-dependent effects like heat or nausea. Vasovagal reactions involve a drop in heart rate and blood pressure. Pyrogenic reactions are caused by contaminants and result in fever.

A patient experiences a severe anaphylactoid reaction to contrast media, characterized by profound hypotension and severe bronchospasm. Which of the following is the first-line emergency medication that should be administered?

Answer: Epinephrine (Adrenaline)

For a severe anaphylactoid reaction with life-threatening symptoms like severe bronchospasm and hypotension, intramuscular (IM) epinephrine is the first-line treatment. Epinephrine is a potent bronchodilator and vasoconstrictor that counteracts the most dangerous effects of the reaction. Diphenhydramine (an antihistamine) is a secondary treatment, while atropine is used for bradycardia and furosemide is a diuretic.

To minimize the risk of contrast-associated acute kidney injury (CA-AKI) in a high-risk outpatient, which of the following laboratory values is the most important to assess before administering intravenous iodinated contrast?

Answer: Estimated Glomerular Filtration Rate (eGFR)

The estimated Glomerular Filtration Rate (eGFR) is the most accurate and reliable measure of kidney function used to stratify the risk of CA-AKI. While serum creatinine is used to calculate eGFR, the eGFR itself accounts for variables like age, sex, and race, providing a more comprehensive assessment. Canadian guidelines use eGFR thresholds (e.g., <30 mL/min/1.73 m²) to identify high-risk patients who may require specific precautions. BUN, INR, and hematocrit are not primary indicators of renal function for this purpose.