Radiologic Procedures, Contrast Media, and Interventional Care
Radiologic Procedures
Know each modality's hazards
CT: contrast timing and orals, radiation dose, aspiration risk with oral contrast, and extravasation with power injection. MRI: absolute emphasis on safety screening - implants, aneurysm clips, pacemakers, cochlear implants, foreign bodies, tattoos and permanent makeup, and loose ferromagnetic items. Know the difference between MR-safe, MR-conditional, and MR-unsafe labeling, the four safety zones, hearing protection, sedation and claustrophobia management, and burn risk from conducting loops of wire or monitoring cable. Fluoroscopy: patient cooperation, aspiration during barium studies, and skin dose with long cases. Interventional radiology: pre-procedure INR and platelets, consent, sedation monitoring, and post-procedure access-site care. Nuclear medicine: radiopharmaceutical handling, and teaching the patient that they are a temporary radiation source.
Traps: confusing sedation-related hypoventilation with an allergic reaction; assuming a patient's self-report of a safe prior MRI means screening is complete; forgetting that the most dangerous complication after femoral arterial access - retroperitoneal hemorrhage - can present with back or flank pain and a falling hematocrit with no visible swelling at the site; and missing a vasovagal response (bradycardia, hypotension, diaphoresis, pallor) that needs recumbency and fluids, not epinephrine.
Worked example: 45 minutes after a femoral angiogram the patient reports back pain, is pale, and the heart rate has climbed from 72 to 108. The site looks clean. Treat this as a possible retroperitoneal bleed: hold pressure, get vitals and stat hemoglobin, notify the provider, and prepare for fluids or transfusion.
Rule of thumb: after arterial access, check site, distal pulses, color, warmth, sensation, and motion at set intervals, and take any new back or flank pain seriously.
Contrast Media
Two reaction families, one grading scale
Iodinated agents differ by ionicity and osmolality (high-osmolar ionic, low-osmolar nonionic, iso-osmolar). Lower osmolality generally means fewer chemotoxic effects such as warmth, nausea, and discomfort, but it does not eliminate anaphylactoid risk. Chemotoxic reactions are dose- and osmolality-related (flushing, nausea, arrhythmia); anaphylactoid reactions are idiosyncratic and histamine-mediated (urticaria, bronchospasm, hypotension) and can occur on first exposure.
Treat by severity, not by symptom count: isolated hives get an antihistamine and observation; bronchospasm or hypotension gets oxygen, IV fluids, and epinephrine 0.3–0.5 mg IM (1:1000) in the adult, repeated as needed. IV push epinephrine is a classic wrong answer. Premedication regimens such as prednisone 50 mg PO at 13, 7, and 1 hour plus diphenhydramine reduce but never abolish breakthrough reactions.
Also know: contrast-associated AKI risk factors and hydration, gadolinium and nephrogenic systemic fibrosis (highest with group I linear agents in severe renal impairment), barium versus water-soluble iodinated oral contrast when perforation is suspected, and extravasation management - stop the injection, aspirate through the cannula, remove it, elevate, apply cold (warm for vasoconstrictors), document, and arrange follow-up reassessment.
Traps: treating shellfish or seafood allergy as a contraindication (iodine is not the allergen); assuming a prior reaction plus premedication makes rechallenge risk-free; mistaking a delayed maculopapular rash for anaphylaxis; and using barium in a patient with suspected bowel perforation.
Rule of thumb: the drug follows the severity - antihistamine for skin only, epinephrine for airway or blood pressure.