Indocyanine Green (ICG) is a sterile, water-soluble tricarbocyanine dye. When administered intravenously, the dye rapidly enters the bloodstream and binds primarily to plasma proteins, such as albumin. This characteristic allows it to remain confined within the vascular system for a short period, helping medical professionals visualize structures and assess function in real time.
The Role of Indocyanine Green in Diagnostics
ICG fluoresces brightly when exposed to near-infrared light. This property makes it an effective tool for visualizing blood flow and specific tissues during diagnostic tests. The dye is used extensively in ophthalmology for angiography, allowing detailed visualization of the choroidal circulation beneath the retina.
Beyond eye imaging, ICG is also used to assess liver function, as the dye is cleared exclusively by the liver into the bile with a short half-life of roughly three to four minutes. Surgeons use the dye to guide procedures, such as mapping lymphatic pathways or delineating tumors.
Common and Expected Adverse Reactions
A minor percentage of individuals may experience transient discomfort immediately following the injection, often including a temporary feeling of warmth or flushing throughout the body. Localized reactions at the injection site, such as mild pain, redness, or temporary discoloration, have also been reported.
Some patients may experience non-specific symptoms like nausea or a headache. These symptoms are typically short-lived and resolve without the need for medical intervention.
Severe Hypersensitivity and Systemic Risks
Severe adverse reactions, particularly hypersensitivity responses, are a possibility that requires immediate attention. The most serious reaction is anaphylaxis, an acute and potentially life-threatening allergic response that occurs rarely. The overall incidence of severe adverse reactions is estimated to be very low, with some studies reporting a rate around 0.05%.
Symptoms of an anaphylactic reaction can develop rapidly and include severe respiratory distress, such as difficulty breathing or laryngospasm. Patients may also show signs of angioedema, which is significant swelling of the face, tongue, lips, or throat. A sudden and significant drop in blood pressure, known as hypotension, is a serious systemic risk that can occur, sometimes requiring vasopressor support.
Other severe signs include widespread rash, urticaria, or hives. Deaths from anaphylaxis have been reported following ICG administration, underscoring the necessity of close patient monitoring. Medical staff must be prepared with appropriate agents, such as epinephrine and corticosteroids, to manage these rare but severe events.
Patient Risk Factors and Contraindications
A documented history of hypersensitivity or allergic reaction to the dye itself is a primary contraindication. Because ICG contains a small percentage of sodium iodide, a history of allergy to iodides is also a primary risk factor.
Patients with severe hepatic impairment should be treated with caution, as the liver is solely responsible for clearing ICG from the body. Furthermore, patients with uremia, a condition involving high levels of waste products in the blood, are also advised against ICG administration.