Patient Care, Safety, and Radiopharmaceutical/Contrast Considerations
Pre-scan assessment
Confirm identity with two identifiers, review the order and clinical question, and screen for pregnancy, prior contrast reactions, asthma, renal disease, diabetes, and metformin use. Establish IV access appropriate for the planned injection rate; an 18–20 G antecubital IV is typical for CTA. Document baseline vital signs when contrast or sedation is planned, and explain the procedure to reduce motion and anxiety.
Iodinated contrast
Most modern agents are low-osmolar. Renal risk is estimated with eGFR, not creatinine alone. ACR guidance: at eGFR ≥30, iodinated contrast can generally be given without withholding metformin; at eGFR <30, weigh benefit versus risk and consider hydration. Premedication (for example, prednisone 50 mg PO at 13, 7, and 1 hour plus diphenhydramine 50 mg PO 1 hour before) is for prior moderate or severe reactions, not routine allergy.
Reactions and extravasation
Classify reactions: mild (flushing, urticaria), moderate (vomiting, bronchospasm), and severe/anaphylactoid (hypotension, laryngeal edema, arrest). Treat severe reactions with epinephrine, oxygen, IV fluids, and call for help. For extravasation, stop the injection, elevate the limb, apply a cold compress (warm for some agents), document, and monitor.
Traps
Questions mix immediate versus delayed reactions, confuse creatinine with eGFR, and imply metformin must always be stopped. Pregnancy should be asked about, but do not delay emergent life-saving scans.
Rule of thumb
eGFR <30 signals high risk: proceed only if the study is necessary, and document the risk-benefit discussion. The classic 13-7-1 hour steroid schedule is a common exam answer.