CAMRT Contrast Media and Pharmacology Questions and Answers 2 — Questions and Answers
Question 1: A patient with a history of mild contrast reaction (hives) is scheduled for contrast CT. What protocol is recommended?
- Cancel the examination
- Proceed without contrast
- Premedicate with corticosteroids and antihistamines (Correct answer)
- Use gadolinium instead
Correct answer: Premedicate with corticosteroids and antihistamines
Premedication reduces the risk of repeat reaction for patients with mild prior reactions.
Typical regimen: prednisone 50 mg at 13, 7, and 1 hour before, plus diphenhydramine 50 mg one hour before the procedure.
Question 2: What is the primary mechanism by which iodinated contrast enhances CT images?
- Increases magnetic susceptibility
- Emits radiation detected by CT detectors
- Attenuates X-rays due to iodine high atomic number (Correct answer)
- Causes tissue fluorescence
Correct answer: Attenuates X-rays due to iodine high atomic number
Iodine (Z=53) causes significant X-ray attenuation through photoelectric absorption.
Iodine K-edge at 33.2 keV falls within the diagnostic CT energy range, making it exceptionally efficient at absorbing X-rays.
Question 3: Which lab value must be checked before giving iodinated contrast to a diabetic patient on metformin?
- Blood glucose
- Complete blood count
- Estimated glomerular filtration rate (eGFR) (Correct answer)
- Liver function tests
Correct answer: Estimated glomerular filtration rate (eGFR)
eGFR is checked because contrast-induced kidney injury could impair metformin clearance, risking lactic acidosis.
If eGFR is 30 or above, metformin can continue. Below 30, metformin is withheld for 48 hours post-contrast until kidney function is confirmed stable.
Question 4: What is the osmolality classification of iohexol (Omnipaque)?
- High-osmolality
- Low-osmolality with fewer adverse reactions than HOCM (Correct answer)
- Iso-osmolality for intrathecal use only
- Ultra-low-osmolality for paediatric use
Correct answer: Low-osmolality with fewer adverse reactions than HOCM
Iohexol is a non-ionic, low-osmolality contrast medium with significantly fewer adverse reactions.
Osmolality is approximately 600-800 mOsm/kg, versus 1500-2000 for high-osmolality ionic agents. LOCM agents have essentially replaced HOCM in Canadian practice.
Question 5: A patient develops bronchospasm during contrast-enhanced CT. What is the first-line treatment?
- IV diphenhydramine
- Subcutaneous epinephrine
- Nebulized salbutamol (Correct answer)
- IV atropine
Correct answer: Nebulized salbutamol
Nebulized salbutamol directly relaxes bronchial smooth muscle for isolated bronchospasm.
Salbutamol 2.5 mg via nebulizer is first-line for bronchospasm without hypotension. If accompanied by anaphylaxis signs, intramuscular epinephrine becomes first-line.
Question 6: What is the recommended maximum contrast volume for a patient with eGFR of 35 mL/min?
- No contrast should be administered
- Volume should not exceed the eGFR value (35 mL) (Correct answer)
- Standard volumes without restriction
- Reduce to 50% of standard dose
Correct answer: Volume should not exceed the eGFR value (35 mL)
The contrast volume-to-eGFR ratio guideline limits volume in mL to the eGFR value.
Additional measures include adequate IV hydration and avoiding nephrotoxic medications. Patients with eGFR below 30 require careful risk-benefit analysis.
CAMRT Contrast Media and Pharmacology Questions and Answers 2
A patient with a history of mild contrast reaction (hives) is scheduled for contrast CT.
What protocol is recommended?