6.1 Contrast Reactions & Contrast-Induced Nephropathy

Contrast Reactions & Contrast-Induced Nephropathy

Iodinated contrast is how coronary arteries become visible and how two different emergencies start. The ARRT Cardiac-Interventional outline groups them under Patient Care 1.H.1: allergy-type reactions graded mild, moderate, and severe; adverse effects that include nephrotoxicity and physiologic responses of the airway, hemodynamics, and central nervous system (CNS); and the treatments and medications used to prevent or reverse those events. This section uses American College of Radiology (ACR)-style mild/moderate/severe categories as a teaching framework. That is a clinical scaffold, not a claim that ARRT copied ACR wording onto the CI exam.

Quick Answer: Stop the injection, call for help, give oxygen, and treat anaphylaxis with physician-directed epinephrine. A warm flush is not hives. Contrast-induced acute kidney injury (CI-AKI), still commonly called contrast-induced nephropathy (CIN), is a creatinine rise prevented with hydration and less volume, not with steroids.

Two mechanisms, not one iodine allergy

Allergic-like (anaphylactoid) reactions look like allergy: urticaria, pruritus, bronchospasm, laryngeal edema, and anaphylaxis. They are often not classic immunoglobulin E (IgE) anaphylaxis and can occur on first exposure. A prior iodinated-contrast reaction is the history that actually changes risk. Shellfish or povidone-iodine skin-prep allergy is not a reliable cross-reaction.

Physiologic (chemotoxic) reactions come from osmolality, chemotoxicity, and the injection itself: warmth, metallic taste, nausea, pain at the site, bradycardia with hypotension (vasovagal), transient hypertension, arrhythmia, and, rarely, seizure. Airway, hemodynamic, and CNS signs can appear in either pathway. Classify by the pattern, not by a single number on the monitor.

Allergy type: mild, moderate, severe

Mild. Limited urticaria or pruritus, limited cutaneous edema, a scratchy throat without dyspnea, sneezing or nasal congestion. The patient speaks in full sentences. Blood pressure and saturation are stable. Observe with the intravenous (IV) line still in and with repeat vital signs. An H1 antihistamine such as diphenhydramine may be given for bothersome hives. Mild is not a synonym for ignore: mild reactions can escalate.

Moderate. Diffuse urticaria, facial edema without frank respiratory failure, throat tightness or hoarseness, and bronchospasm or wheezing with little or no hypoxia. Stop further contrast. Apply oxygen. Give an antihistamine. Give a nebulized beta-agonist (albuterol) for wheeze. Notify the physician and the circulating registered nurse (RN) now. Do not wait for hypotension before you treat moderate airway findings. Draw up epinephrine so it is in the room if the reaction climbs.

Severe (anaphylaxis). Hypotension, hypoxia, laryngeal edema with stridor, diffuse erythema with shock, or cardiovascular collapse. This is a resuscitation. Stop the injection. Call for help or a code. High-flow oxygen. Epinephrine is first-line: typically 0.3 mg intramuscular (IM) of 1 mg/mL (1:1000) in the lateral thigh, or a carefully diluted IV epinephrine bolus or infusion under physician direction. Give isotonic IV fluid for hypotension. Suction and airway equipment belong on the table, not in a locked closet. Repeat IM epinephrine if shock persists while the team prepares IV therapy.

Adverse physiologic responses: airway, hemodynamic, CNS

Airway. A brief cough or chest warmth after a left coronary injection is often chemotoxic. Stridor, facial swelling, and hypoxic wheeze are allergic-like until proven otherwise and need epinephrine, not reassurance.

Hemodynamic. A vasovagal response is bradycardia plus hypotension, often after pain, a sheath, or a contrast bolus. Stop the stimulus, flatten the table or use Trendelenburg if the airway is protected, give IV fluids, and give atropine as ordered (commonly 0.5 mg IV, repeatable toward a typical 3 mg ACLS-style ceiling). Anaphylactic shock is usually hypotension with tachycardia (or a relative tachycardia) plus skin or airway findings. Atropine is the wrong first drug for that pattern. Isolated hypertensive spikes after a painful stick or a catecholamine surge are treated by stopping the stimulus, confirming the cuff is not cycling on a restrained arm, and using a physician-directed vasodilator only if the pressure is a true hypertensive emergency.

CNS. Transient headache or dizziness after a large or high-osmolality load can be chemotoxic. Seizure, a dense focal deficit, or sudden unresponsiveness is not just contrast warmth. Support airway, breathing, and circulation, stop the injection, and consider hypoxia, air embolism, and stroke (section 6.3).

Treatment and medications: types, indications, contraindications

Epinephrine. Indication: progressing moderate or severe anaphylaxis with airway, breathing, or hypotensive features. In this setting the contraindication is relative. Known coronary disease does not withhold epinephrine from true anaphylaxis; the untreated reaction kills faster than a directed catecholamine dose. The CI technologist does not independently push IV epinephrine. You open the crash cart, draw as directed, and document the time.

Antihistamines (H1 blockers such as diphenhydramine; some protocols add an H2 blocker). Indication: urticaria and pruritus. They do not reverse shock or laryngeal edema. Cautions: urinary retention, narrow-angle glaucoma, and excess sedation in the elderly.

Corticosteroids (prednisone, methylprednisolone, hydrocortisone). They do not rescue the next five minutes of anaphylaxis. Their CI-relevant job is premedication and possible late-phase modulation. An IV steroid is often added in severe reactions as an adjunct, never as a substitute for epinephrine. A single emergency dose is not withheld for hyperglycemia or infection, but steroids are not a just-in-case push before every injection.

Albuterol. Indication: bronchospasm with adequate blood pressure. If the patient is crashing, epinephrine covers both bronchospasm and shock.

Premedication for prior reactors — timing matters

Elective protocols combine a steroid plus an antihistamine, and the clock is measured in hours:

• A common 13-hour oral schedule: prednisone 50 mg at 13 hours, 7 hours, and 1 hour before contrast, plus diphenhydramine 50 mg one hour before.
• An alternate: methylprednisolone 32 mg at 12 hours and 2 hours, plus an antihistamine.

Accelerated IV regimens (for example hydrocortisone plus diphenhydramine) are used when a case cannot wait 12 hours; they are less well proven. Premedication reduces recurrent-reaction risk; it does not erase it. Breakthrough reactions still occur.

STEMI trap: premedication does not make a true ST-elevation myocardial infarction (STEMI) wait 13 hours. Reperfuse. Staff the room with epinephrine, airway gear, and a full crash cart. Document the prior reaction and the physician's decision.

Nephrotoxicity: CIN / CI-AKI

CIN/CI-AKI is a rise in serum creatinine after iodinated contrast — teaching ranges often cite an increase of about 0.3–0.5 mg/dL or a 25–50% relative rise within 48–72 hours — once other causes of acute kidney injury are considered. This is chemotoxic nephrotoxicity, not an allergy.

Risk: chronic kidney disease (CKD) is the dominant risk. Add dehydration, high contrast volume, diabetes, shock or hypotension, decompensated heart failure, and stacked contrast loads (computed tomography plus PCI in one day). Delayed anuria with livedo and eosinophilia after catheter scraping of a diseased aorta is cholesterol embolization, a different disease.

Prevention: periprocedural isotonic saline when the patient can tolerate volume; minimize contrast volume (dilute injections, intravascular imaging instead of extra cine, staged PCI); consider iso-osmolar contrast media (IOCM) such as iodixanol in high-risk CKD per operator preference. Stop other nephrotoxins as ordered. N-acetylcysteine is not a reliable substitute for hydration. Bicarbonate protocols are laboratory-specific and never replace saline.

Trap: giving a steroid for the kidneys confuses allergy prophylaxis with nephroprotection. Steroids do not prevent CIN.

Scenario and exam traps

A 62-year-old with a prior hive-only reaction completes a 13-hour steroid-plus-antihistamine protocol for elective angiography. After the first left coronary injection he has diffuse hives and throat tightness with SpO2 94%. That is moderate. Stop contrast, oxygen, antihistamine, prepare epinephrine. If systolic pressure then falls to 72 mm Hg with hypoxia, the case has become severe anaphylaxis — IM epinephrine now, not another diphenhydramine dose.

Traps: warmth and nausea are physiologic, not automatically anaphylaxis. Mild hives can progress. Premedication is hours, not diphenhydramine in holding five minutes ago. Emergency PCI is not postponed for an elective 13-hour prep. CIN is a creatinine story, prevented mainly by hydration and less volume.