Intravenous Contrast Media Overview M 3 Spotlight

Intravenous Contrast Media (ICM)

• Introduced in the 1950s, ICMs are commonly prescribed drugs.
• They enhance radiologic imaging.
• ICMs generally have a good safety record, with adverse effects often mild and self-limiting, but severe, life-threatening reactions are possible.
• ICMs are classified based on modifications of a 2,4,6-tri-iodinated benzene ring.

Osmolality

• Osmolality is related to chemical structure.
• High-osmolar ICMs (Renografin, Hypaque, Conray) have a higher risk of adverse effects.
• Low-osmolar ICMs (Omnipaque, Isovue, Optiray, Ultravist) are preferred due to fewer adverse events and less chemotoxicity. They are more costly but less damaging to tissue if extravasated.

Osmotic Effects

• ICMs can transiently decrease renal blood flow and glomerular filtration rate (GFR).
• ICMs can have a dehydrating effect.

ICM Reactions

• ICM reactions can stem from direct cellular toxicity, enzyme induction, or activation of complement, fibrinolytic, kinin, or other systems.
• Reactions are classified as idiosyncratic or nonidiosyncratic.
• Contrast-induced nephropathy (CIN) is a possible complication.

Idiosyncratic Reactions

• These reactions happen within 20 minutes of injection, independent of the dose.
• They aren't true hypersensitivity reactions (no IgE antibodies involved).
• They're common in patients with prior ICM reactions, asthma, or allergies.
• Recurrence isn't guaranteed.

Symptoms of Idiosyncratic Reactions

• Skin reactions (hives, pruritus).
• Gastrointestinal issues (nausea, vomiting).
• Sweating (diaphoresis).
• Cardiovascular problems (high or low blood pressure, tachycardia or bradycardia, arrhythmias, syncope, seizures).
• Severe cases can lead to death.
• Respiratory distress (bronchospasm, pulmonary edema).

Nonidiosyncratic Reactions

• These reactions can be delayed (30 minutes to 7 days after injection).
• They may resemble flu-like symptoms.
• They are of concern in pregnancy as the ICM can cross the placenta.
• ICMs may be mutagenic, and nonionic agents are favored for administration.

Nonidiosyncratic Cardiovascular Reactions

• ICMs can affect the myocardium directly.
• Vasovagal reactions are possible, often leading to angina or syncope.
• There is a heightened risk of peripheral vasodilation, hypotension, ventricular arrhythmias and cardiac arrest.
• High-osmolar fluids with ICM can also lead to hypertension and pulmonary edema.

Other Nonidiosyncratic Reactions

• Possible reactions include neuropathy, polyarthropathy, site reactions from extravasation, tissue damage, compartment syndrome.
• Other reactions include metallic taste, nausea, vomiting, constipation, pruritus, syncope and depression.
• ICMs can exacerbate existing cardiac conditions, arrhythmias, pheochromocytoma, sickle cell anemia, hyperthyroidism, and myasthenia gravis.

Contrast-Induced Nephropathy (CIN)

• CIN involves a significant elevation in creatinine (>50% baseline) and up to 25% of patients experience sustained renal insufficiency / oliguria.
• Pre-existing renal insufficiency significantly increases CIN risk.
• Other factors increasing risk include CHF, aging, the use of NSAIDs or aminoglycosides, repeated injections and large doses of ICM.
• Contributing factors include high ICM viscosity, high osmolarity, dehydration, and underlying tubular damage.

Management Considerations

• Pre-operative assessments are crucial, and equipment and drugs for managing emergencies should be readily available.
• For non-idiosyncratic reactions, treatment is focused on symptoms.
• For moderate or severe reactions including anaphylaxis or severe cardiovascular compromise/failure, airway, breathing and circulation must be managed promptly. Antihistamines (H1 and H2 blockers), epinephrine, corticosteroids and IV fluids to correct hypotension are crucial.

Management Considerations for CIN

• Adequate hydration, supportive treatment and measures directed at restoring volume and electrolyte balance are imperative.
• The use of specific therapies like antioxidants and the adjustment of factors that increase CIN risk, are necessary.

Management Considerations: Prevention

• Prevention strategies include considering corticosteroids, especially after a patient has suffered a prior severe reaction.
• Other prevention measures, such as lower-level support, for prevention include the administration of antihistamines before and after the procedure.

Contrast Media in Specific Procedures

• Fluorescence-guided surgery uses fluorescent contrast agents to enhance visibility in minimally invasive procedures like sentinel lymph node mapping, tumor detection, visualization of vital structures and tissue perfusion.

Indocyanine Green (ICG)

• ICG is a nonspecific contrast agent used in the near-infrared region.
• It has an absorption/emission at 800-850 nm.
• A 25 mg vial of sterile green powder is reconstituted, and used within 6 hours.
• Hypersensitivity reactions such as hives are possible, and antihistamines, corticosteroids, and epinephrine might be required.
• Anaphylaxis is also a possible severe adverse reaction.

Indigo Carmine

• Indigo Carmine is a nonspecific contrast agent in the near infrared region.
• It has uses like cystoscopy for ureteral injury and flow assessments, and in obstetrics for amniotic fluid leak assessment.
• It is administered intravenously or intramuscularly.
• Half-life is 4-5 minutes, and dose is 5 mL.
• Pregnancy safety is not fully established.

Methylene Blue (MB)

• MB is another nonspecific contrast agent, used in near-infrared region with absorption/emission around 700 nm, with less tissue penetration than ICG.
• Common formulations include ampules and prefilled syringes.
• It is incompatible with normal saline and must be diluted in 50mL of D5W before administration.
• Important to avoid in patients with G6PD deficiency, severe hepatic or renal impairment.
• Black box warning for fetal harm exists.

Methylene Blue Adverse Reactions

• A potent adverse effect of MB is fatal serotonin toxicity in patients taking antidepressants.
• Hemolysis, hypersensitivity reactions, hypertension, angina, and reduced perfusion are also possible.

Oximetry Interference

• IV dyes interfere with oximetry readings.
• Pulse and cerebral oximetry are affected by dyes that impact red and infrared wavelength absorption ratios, leading to falsely low oxygenation readings.
• This is particularly concerning with the use of methylene blue.