54-year-old female with a documented prior moderate hypersensitivity reaction to iodinated contrast media, premedicated with prednisone 50mg PO the night before and the morning of a contrast-enhanced CT angiogram for suspected pulmonary embolism. During infusion of iohexol 350 mg I/mL she develops diffuse urticaria, audible expiratory wheezing, stridor, and rapidly progressive hypoxemia.
Acute Resuscitation Milestones & Priorities
Clinical phases and key interventions encountered in this emergency module:
Anaphylaxis treatment follows epinephrine-first, antihistamines-second, steroids-third; prophylaxis does not confer acute reversal.
Breakthrough reactions during premedicated contrast studies must be treated on their own merits, not by repeating the failed regimen.
Iodinated contrast cross-reactivity is high (25-60%); switch to a different imaging modality rather than a different molecule.
Biphasic anaphylaxis occurs in up to 20% of cases; intubated patients warrant a minimum of 12-24 hours of monitored observation.
Skin testing after anaphylaxis must be deferred 4-6 weeks to avoid false negatives from mast-cell mediator depletion.
Future imaging strategies should consider non-contrast modalities, MRI with gadolinium (different cross-reactivity profile), or formal desensitization.
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