spotlight 3 pp. Intravenous Contrast Media Overview

Intravenous Contrast Media (ICM)

• ICMs are commonly used to enhance radiologic imaging, introduced in the 1950s.
• They have a generally good safety record, with adverse effects often mild and self-limiting.
• However, severe, life-threatening reactions are possible.

Classification of ICMs

• ICMs are classified based on modifications of a 2,4,6-tri-iodinated benzene ring.
• They can be ionic monomers (e.g., Renografin, Hypaque, Conray), with a higher osmolality, and are associated with a higher risk of adverse effects.
• Or they can be non-ionic monomers (e.g., Omnipaque, Isovue, Optiray, Ultravist), considered agents of choice due to their lower adverse effects, less chemotoxicity, and less tissue damage. Non-ionic monomers are more costly than ionic monomers.

Osmolality

• Osmolality is related to the chemical structure of ICMs.
• High-osmolality ICMs have a greater risk of adverse reactions.
• Low-osmolality ICMs are generally preferred due to less adverse events.

Osmotic Effects

• ICMs can cause transient decreases in renal blood flow and glomerular filtration rate (GFR).

ICM Reactions: Pathogenesis

• ICM reactions can involve direct cellular toxicity, enzyme induction, and activation of the complement, fibrinolytic, kinin, and other systems.
• Reactions are classified as idiosyncratic or nonidiosyncratic.

Idiosyncratic Reactions

• Idiosyncratic reactions occur within 20 minutes of injection and are independent of the dose administered.
• They're not true hypersensitivity reactions, as they do not involve IgE antibodies.
• They are common in individuals with a history of prior ICM reactions, asthma, or other allergies.

Idiosyncratic Reaction Symptoms

• Symptoms can include hives, pruritus, nausea, vomiting, diaphoresis, facial swelling, hypertension or hypotension (severe), tachycardia or bradycardia, arrhythmias, syncope, seizures, bronchospasm, and pulmonary edema.
• In severe cases, death is possible.

Nonidiosyncratic Reactions

• Nonidiosyncratic reactions can be delayed, appearing 30 minutes to 7 days after injection.
• They may resemble flu-like symptoms.
• Caution is required during pregnancy as ICMs may cross the placenta.

Contrast-Induced Nephropathy (CIN)

• CIN is a complication that can occur after ICM use.
• It's characterized by an increase in serum creatinine levels indicative of kidney damage.
• Risk factors include pre-existing renal issues, CHF (heart failure), and use of NSAIDs or aminoglycosides.

Management Considerations

• Patient history and physical assessment are crucial before administration.
• Advanced life support equipment and drugs should be readily available.
• Nonidiosyncratic reactions should be treated as necessary.
• For severe idiosyncratic reactions, monitor vital signs, provide cardiovascular support, and manage the airway and ventilation as needed.
• Antihistamines (H1 and H2 blockers) may be used; IV fluids should be iso-osmolar (e.g., normal saline, lactated Ringer's solution).

Prevention Strategies for CIN and Adverse Reactions

• Adequate hydration, antioxidants, and theophylline may be useful adjuncts.

Fluorescence-Guided Surgery

• Fluorescence-guided surgery helps improve tissue visibility during minimally invasive procedures.
• This technique is used in sentinel lymph node mapping, tumor detection, and visualization of vital structures.
• An intraoperative IV dye is often used.

Indocyanine Green (ICG)

• ICG is a nonspecific contrast agent used in the near-infrared region.
• Administration is preoperatively or intraoperatively.
• Visualization times range from 1 to 30 minutes.
• Dosage is dependent on the procedure, but adult dosage is 5 mg and pediatric is 2.5 mg.

Methylene Blue (MB)

• MB is another contrast agent with absorption in the near infrared region.
• Dose ranges from 0.25 to 2 mg/kg IV and can be administered as an infusion up to 3 mg/kg/hr, administered slowly.
• Avoid use in G6PD deficiency and be cautious of hepatic/renal impairment. It is contraindicated with most antidepressants.

Adverse Effects

• Methylene blue can have adverse effects, including fatal serotonin toxicity (in patients on antidepressants), hemolysis, hypersensitivity reactions, hypertension, reduced perfusion, and others.

Oximetry Interference

• IV dyes can interfere with oximetry, potentially leading to inaccurate oxygen saturation measurements.