Why does computed tomography (CT) contrast cause a burning sensation?

Why CT Contrast Causes a Burning Sensation

The burning sensation experienced during CT contrast injection is primarily due to the high osmolality and chemical properties of iodinated contrast media, which stimulate pain receptors as the contrast rapidly enters the bloodstream.

Physiological Mechanisms of the Burning Sensation

• The burning sensation is a normal physiologic reaction to iodinated contrast media (ICM) and is distinct from allergic or hypersensitivity reactions 1
• The sensation is more pronounced with high-concentration contrast media (370 mgI/mL) compared to medium-concentration contrast media (300 mgI/mL), with significantly higher heat sensation scores reported by patients receiving higher concentration agents 2
• The rapid injection of contrast material causes a localized warming effect as it enters the bloodstream, which activates temperature-sensitive nerve endings 2
• The sensation is typically described as a feeling of warmth or heat that spreads from the injection site through the body, often concentrated in the face, throat, and genital/rectal regions where there is increased vascularity 3

Factors That Influence Burning Sensation Intensity

• Injection rate: Faster injection rates (e.g., 4 mL/s vs. 1 mL/s) typically cause more intense burning sensations 2
• Contrast concentration: Higher iodine concentration contrast media produce stronger heat sensations than lower concentration agents 2
• Temperature of contrast: Extrinsic warming of contrast media to body temperature (37°C) may reduce adverse reactions with high-viscosity agents (iopamidol 370) but doesn't significantly affect reactions with lower viscosity agents (iopamidol 300) 4
• Hydration status: Although dehydration is often thought to increase adverse reactions, research shows that hydration status does not significantly affect the incidence of contrast-related sensations 5
• Patient age: Younger patients report more intense sensations and have higher rates of both physiologic and allergic-like reactions to contrast media 5

Distinguishing Normal Burning from Adverse Reactions

• The burning sensation is considered a normal physiologic response and not an adverse reaction 3
• True adverse reactions to contrast media range from 0.2% to 0.7% with modern low-osmolality contrast media (LOCM) 1
• Severe, life-threatening reactions such as anaphylaxis occur in approximately 0.1% of patients receiving iodinated contrast material 1
• Common symptoms of mild adverse reactions include itching, hives, and nausea, which are distinct from the normal burning sensation 3
• Patients should be informed before the procedure that they may experience a warm sensation or metallic taste during contrast injection to reduce anxiety 3

Risk Reduction Strategies

• Using low-osmolality contrast media (LOCM) instead of high-osmolality contrast media (HOCM) has significantly reduced the incidence of adverse reactions 1
• For high-viscosity contrast agents (like iopamidol 370), warming the contrast to body temperature (37°C) before injection can reduce extravasation rates and overall adverse events 4
• Using the smallest amount of contrast material necessary for diagnostic quality can help minimize both the burning sensation and potential adverse reactions 3
• Ensuring adequate hydration before the procedure is generally recommended, although research suggests it may not significantly affect the burning sensation specifically 5
• Premedication with corticosteroids and antihistamines is not indicated for the normal burning sensation but may be considered for patients with history of moderate to severe allergic-like reactions 1

Important Considerations for Special Populations

• Patients with renal insufficiency are at increased risk for contrast-induced nephropathy, which is the third most common cause of acute renal failure among hospitalized patients 1
• Patients with diabetes mellitus, pre-existing renal insufficiency, congestive heart failure, or recent contrast exposure have significantly increased risk of contrast-induced nephropathy 1
• Severe anaphylactic reactions to contrast material occur in 0.04% to 0.22% of procedures and can be life-threatening, requiring immediate treatment 1
• The risk of radiation-induced malignancy from CT scans is small but real, with approximately 0.4% of all cancers in the United States potentially attributable to radiation from CT studies 1

The burning sensation experienced during CT contrast injection is a normal physiologic response that should be distinguished from true adverse reactions. Understanding the mechanisms behind this sensation can help healthcare providers better prepare patients for what to expect during contrast-enhanced CT examinations.