Contrast Media and Reactions

Contrast Media and Reactions Indian Medical PG Question 1: Drug of choice for beta antagonist toxicity is?

• A. Adrenaline
• B. Glucagon (Correct Answer)
• C. ACE inhibitors
• D. Dopamine

Contrast Media and Reactions Explanation: ***Glucagon*** - **Glucagon** is the drug of choice for **beta-blocker overdose** because it bypasses the beta-adrenergic receptors and directly activates **adenylate cyclase** to increase intracellular cAMP [1]. - This action leads to increased heart rate and myocardial contractility, counteracting the cardiac depression caused by beta-blockers [1]. *Adrenaline* - **Adrenaline** (epinephrine) is a beta-agonist, but its effects are blunted in severe **beta-blocker overdose** due to **competitive antagonism** at beta receptors. - While it can be used for its alpha-agonist effects to increase blood pressure, its efficacy in reversing profound bradycardia and myocardial depression may be limited. *ACE inhibitors* - **ACE inhibitors** are used in the management of hypertension and heart failure, primarily by reducing **angiotensin II** formation and inhibiting **bradykinin** degradation. - They have no direct role in reversing the immediate cardiovascular effects of **beta-antagonist toxicity**. *Dopamine* - **Dopamine** is a **catecholamine** with dose-dependent effects, including positive inotropy and chronotropy at higher doses, but it relies on **adrenergic receptor activation**. - Its effects can be attenuated in **beta-blocker overdose**, similar to adrenaline, making it less effective than glucagon as first-line therapy.

Contrast Media and Reactions Indian Medical PG Question 2: First line therapy in anaphylactic shock is:

• A. Epinephrine .5 ml of 1:1000 IM (Correct Answer)
• B. Atropine 3 mg intravenously
• C. Adenosine 12 mg intravenously
• D. Epinephrine 1 ml of 1:10000 intravenously

Contrast Media and Reactions Explanation: ***Epinephrine .5 ml of 1:1000 IM*** - **Epinephrine** is the **first-line treatment** for anaphylaxis due to its alpha-1 agonist effects (vasoconstriction, which increases blood pressure) and beta-2 agonist effects (bronchodilation, which improves breathing). [1] - The recommended dose and concentration for intramuscular administration in adults is **0.3-0.5 mg (0.3-0.5 mL of 1:1000 solution) IM**, repeated every 5-15 minutes as needed. *Atropine 3 mg intravenously* - **Atropine** is an anticholinergic medication used to treat **bradycardia** or organophosphate poisoning, not anaphylaxis. [4] - It does not address the widespread vasaodilation or bronchoconstriction seen in anaphylactic shock. *Adenosine 12 mg intravenously* - **Adenosine** is an antiarrhythmic drug primarily used to convert **supraventricular tachycardia (SVT)** to normal sinus rhythm. [3] - It has no role in the management of anaphylactic shock. *Epinephrine 1 ml of 1:10000 intravenously* - While epinephrine is the correct drug, **intravenous administration** of epinephrine 1:10,000 is typically reserved for **cardiac arrest** [2] or in cases of severe, refractory anaphylaxis under expert care, and carries a higher risk of adverse effects. - The initial and preferred route for anaphylaxis is **intramuscular**, as it provides rapid absorption with lower risks compared to IM administration.

Contrast Media and Reactions Indian Medical PG Question 3: Which of the following contrast agents is PREFERRED in a patient with renal dysfunction for the prevention of contrast-induced nephropathy?

• A. Iso-osmolar contrast (Correct Answer)
• B. High osmolar contrast
• C. Ionic contrast
• D. Low osmolar contrast

Contrast Media and Reactions Explanation: ***Iso-osmolar contrast*** - **Iso-osmolar contrast agents** (e.g., iodixanol) have an osmolality of ~290 mOsm/kg, which is identical to that of plasma. - **This is the PREFERRED choice** in patients with renal dysfunction as multiple studies demonstrate the lowest risk of contrast-induced nephropathy (CIN). - The iso-osmolar formulation minimizes osmotic stress on renal tubules and reduces the risk of acute kidney injury. - **Current guidelines recommend iso-osmolar agents as first-line** in high-risk patients with pre-existing renal impairment. *Low osmolar contrast* - **Low osmolar contrast agents** have osmolality of 600-900 mOsm/kg, which is significantly lower than high osmolar agents but still 2-3 times higher than plasma. - While **acceptable and safer than high osmolar agents**, they are not as optimal as iso-osmolar contrast for patients with renal dysfunction. - These agents are widely used and represent a reasonable alternative when iso-osmolar agents are not available. *High osmolar contrast* - **High osmolar contrast agents** have osmolality >1400 mOsm/kg (about 5 times that of plasma). - They carry the **highest risk of contrast-induced nephropathy** due to severe osmotic load and direct tubular toxicity. - **Contraindicated or strongly avoided** in patients with pre-existing renal dysfunction. *Ionic contrast* - **Ionic contrast** refers to the chemical structure (dissociates into ions) rather than osmolality. - Can be either high or low osmolar—the ionic nature alone does not determine renal safety. - The critical factor for nephrotoxicity prevention is osmolality, not ionic charge.

Contrast Media and Reactions Indian Medical PG Question 4: A cardiovascular parameter helpful in diagnosis of anaphylaxis during anaesthesia:

• A. Bradycardia
• B. Dysrhythmia
• C. Increased peripheral vascular resistance
• D. Hypotension (Correct Answer)

Contrast Media and Reactions Explanation: ***Hypotension*** - **Hypotension** is a hallmark cardiovascular sign of anaphylaxis, occurring due to widespread **vasodilation** and increased vascular permeability. - This symptom is often profound and unresponsive to initial fluid resuscitation due to the ongoing systemic release of inflammatory mediators. *Bradycardia* - While bradycardia can occur in some rare cases of anaphylaxis (e.g., **vasovagal response**), **tachycardia** is the more common cardiac response due to compensatory mechanisms. - It is not a primary or consistent indicator of anaphylaxis, making it less helpful for diagnosis in this context. *Dysrhythmia* - **Dysrhythmias** can occur during anaphylaxis due to myocardial ischemia or electrolyte imbalances, but they are not a direct or consistent diagnostic feature. - Their presence often reflects severe compromise or co-existing conditions rather than being a primary anaphylactic sign. *Increased peripheral vascular resistance* - Anaphylaxis is characterized by a significant **decrease in peripheral vascular resistance** due to mast cell and basophil degranulation releasing vasodilatory mediators like histamine. - Therefore, an increase in peripheral vascular resistance would contradict the pathophysiology of anaphylaxis.

Contrast Media and Reactions Indian Medical PG Question 5: Which of the following is NOT a characteristic feature of anaphylactic shock?

• A. Angioedema
• B. Urticarial rash
• C. Pedal edema (Correct Answer)
• D. Flushing

Contrast Media and Reactions Explanation: ***Pedal edema*** - While **edema** can occur in anaphylaxis due to increased vascular permeability, **pedal edema** (swelling primarily in the lower extremities) is not a defining characteristic or a primary life-threatening feature of anaphylactic shock. - Anaphylactic shock primarily manifests with systemic symptoms like **hypotension**, **bronchospasm**, and widespread **urticaria** or **angioedema**, rather than isolated peripheral swelling [1], [3]. *Angioedema* - **Angioedema** is a common and often serious feature of anaphylaxis, involving swelling of deeper layers of the skin and mucous membranes [1]. - It can affect the **lips**, **face**, **throat**, and **airway**, potentially leading to airway obstruction [3]. *Urticarial rash* - An **urticarial rash**, or **hives**, is a hallmark cutaneous manifestation of anaphylaxis, characterized by itchy red welts [2]. - It is caused by the release of histamine and other mediators that increase capillary permeability, leading to fluid leakage into the skin [2], [3]. *Flushing* - **Flushing** is a common early symptom of anaphylaxis, characterized by sudden redness and warmth of the skin [1]. - It results from widespread **vasodilation** caused by mediator release, such as histamine [3].

Contrast Media and Reactions Indian Medical PG Question 6: Which of the following statements about contrast in radiography is true:

• A. Gadolinium cannot cross an intact blood brain barrier
• B. Iohexol is a high osmolar contrast media
• C. Non-ionic contrast agents are always high osmolar
• D. Ionic monomers have three iodine atoms per two particles in solution (Correct Answer)

Contrast Media and Reactions Explanation: ***Ionic monomers have three iodine atoms per two particles in solution*** - **Ionic monomeric contrast agents** (e.g., diatrizoate, iothalamate) dissociate in solution, producing **two particles** (one cation and one anion containing three iodine atoms) per molecule. - This dissociation results in a **high osmolality** compared to non-ionic agents, as osmolality is determined by the number of particles in solution. *Gadolinium cannot cross an intact blood brain barrier* - This statement is **FALSE** - **Gadolinium-based contrast agents CAN cross the blood-brain barrier when it is compromised**. - They are used in MRI precisely because they extravasate into tissues where the **blood-brain barrier is disrupted**, such as in tumors, inflammation, or infections. - However, they do **not cross an intact BBB** due to their size and hydrophilicity. *Iohexol is a high osmolar contrast media* - **Iohexol** is a **non-ionic, low osmolality contrast medium** (LOCM). - Its non-ionic nature means it does not dissociate in solution, leading to a significantly lower osmolality compared to older ionic agents. *Non-ionic contrast agents are always high osmolar* - **Non-ionic contrast agents** are characterized by their molecular structure which **does not dissociate into ions** in solution. - This property makes them **low osmolar** or **iso-osmolar**, meaning they have fewer particles in solution compared to ionic agents, thereby reducing osmolality.

Contrast Media and Reactions Indian Medical PG Question 7: Serum sickness is mediated by which type of hypersensitivity?

• A. Type II
• B. Type IV
• C. Type III (Correct Answer)
• D. Type I

Contrast Media and Reactions Explanation: ***Type III*** - Serum sickness is a classic example of a **Type III hypersensitivity reaction**, characterized by the formation of **immune complexes** [1], [2]. - These immune complexes deposit in various tissues (e.g., blood vessels, joints, kidneys), leading to inflammation and tissue damage [3]. *Type II* - **Type II hypersensitivity** involves antibodies (IgG or IgM) binding directly to antigens on the surface of cells or in the extracellular matrix, leading to cell lysis or dysfunction. - Examples include **hemolytic transfusion reactions** or autoimmune hemolytic anemia, which are distinct from serum sickness. *Type IV* - **Type IV hypersensitivity** is a **delayed-type hypersensitivity (DTH)** reaction mediated by T cells rather than antibodies. - It typically manifests 24-72 hours after antigen exposure and is seen in conditions like **contact dermatitis** or tuberculosis skin tests. *Type I* - **Type I hypersensitivity** is an immediate reaction mediated by **IgE antibodies** binding to mast cells and basophils, leading to the release of inflammatory mediators upon re-exposure to an allergen. - Examples include **anaphylaxis** or allergic rhinitis, which have a rapid onset and different underlying mechanisms compared to serum sickness. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 214-215. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 172-173. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 215-216.

Contrast Media and Reactions Indian Medical PG Question 8: A 28-year-old male patient presents with colicky abdominal pain along with vomiting. X-ray abdomen shows:

• A. Pseudo-obstruction
• B. Cancer colon
• C. Small bowel obstruction (Correct Answer)
• D. Paralytic ileus

Contrast Media and Reactions Explanation: ***Small bowel obstruction*** - The X-ray image shows multiple **dilated loops of small bowel** with **air-fluid levels** and prominent **valvulae conniventes** (herringbone pattern), which are classic signs of small bowel obstruction. - The clinical presentation of **colicky abdominal pain** and **vomiting** is highly consistent with a small bowel obstruction. *Pseudo-obstruction* - Pseudo-obstruction, or Ogilvie's syndrome, primarily affects the **large bowel**, leading to colonic dilation without a mechanical obstruction. - While it can cause abdominal pain and vomiting, the X-ray findings would typically show marked dilation of the colon rather than predominantly small bowel loops. *Cancer colon* - Colon cancer, if it causes obstruction, typically presents as a **large bowel obstruction**, with colonic dilation proximal to the tumor. - While severe cases could lead to cecal dilation and subsequent small bowel obstruction, the primary radiographic findings would focus on the colon. *Paralytic ileus* - Paralytic ileus, or adynamic ileus, involves generalized bowel dilation (both small and large bowel) due to **impaired peristalsis**, without mechanical obstruction. - Although it causes abdominal pain and vomiting, it usually presents with more continuous, less colicky pain, and the X-ray often shows gas in the colon, which is typically absent or minimal in a complete small bowel obstruction.

Contrast Media and Reactions Indian Medical PG Question 9: Enhancement in CT contrast is due to -

• A. Iodine (Correct Answer)
• B. Gadolinium
• C. Mercury
• D. Silver

Contrast Media and Reactions Explanation: ***Iodine*** - **Iodine-based contrast agents** are commonly used in CT scans to enhance the visualization of blood vessels, organs, and certain lesions due to their **high atomic number** and ability to absorb X-rays. - The degree of enhancement observed on a CT image is directly proportional to the concentration of **iodine** in the tissue or blood. *Gadolinium* - **Gadolinium-based contrast agents** are predominantly used in **Magnetic Resonance Imaging (MRI)**, not CT scans. - Gadolinium works by altering the **magnetic properties** of water molecules in tissues, thereby improving MRI signal intensity. *Mercury* - **Mercury** is a highly toxic heavy metal and is **not used as a contrast agent** in any imaging modality due to its severe health risks. - While historically used in some medical applications, it has been replaced by safer alternatives. *Silver* - **Silver** is not used as a contrast agent in medical imaging; it has no suitable properties for enhancing images in CT or other common modalities. - It is known for its **antimicrobial properties** and is sometimes used in wound dressings.

Contrast Media and Reactions Indian Medical PG Question 10: In a child, non-functioning kidney is best diagnosed by

• A. Creatinine clearance
• B. Ultrasonography
• C. IVU
• D. DTPA renogram (Correct Answer)

Contrast Media and Reactions Explanation: ***DTPA renogram*** - A **DTPA renogram** (diethylene triamine pentaacetic acid scan) is a nuclear medicine study that assesses **renal blood flow** and **glomerular filtration rate (GFR)**. - It is highly effective in determining if a kidney is non-functioning because it directly measures the **uptake and excretion of a radiotracer** by the kidney, providing quantitative data on its functional capacity. *Creatinine clearance* - **Creatinine clearance** is a measure of overall kidney function, reflecting the GFR of **both kidneys combined**. - It cannot specifically identify a non-functioning individual kidney, as the other kidney might compensate for the non-functioning one, leading to a near-normal overall creatinine clearance. *Ultrasonography* - **Ultrasonography** is excellent for evaluating **renal anatomy**, such as size, shape, and presence of cysts, hydronephrosis, or stones. - While it can show structural abnormalities, it provides limited direct information about the **functional status** of the kidney, and a structurally normal kidney can still be non-functional. *IVU (Intravenous Urography)* - **Intravenous Urography (IVU)** uses contrast dye injected intravenously to visualize the kidneys, ureters, and bladder, assessing both anatomy and some aspects of function. - If a kidney is non-functioning, it would show **no uptake or excretion of the contrast dye**, but IVU involves radiation exposure and nephrotoxic contrast, making DTPA renogram often preferred in children for functional assessment.

Contrast Media and Reactions Flashcard 1 of 7

Question: _____ monomers (Advantage) form better images in IVP and have anticoagulant property

Answer: Ionic

Contrast Media and Reactions Flashcard 2 of 7

Question: _____ has Iodine: particle ratio of 3:1

Answer: Non-ionic monomer

Contrast Media and Reactions Flashcard 3 of 7

Question: _____ has osmolarity of 300 mOsm (Iso-osmolar).

Answer: Non-ionic Dimer

Contrast Media and Reactions Flashcard 4 of 7

Question: Iodinated Contrast media: _____ monomer has Iodine: particle ratio of 3:2.

Answer: Ionic

Contrast Media and Reactions Flashcard 5 of 7

Question: Iodinated contrast media: While, _____ has only 1 particle and ionic has 2 charged particles.

Answer: non-ionic

Contrast Media and Reactions Flashcard 6 of 7

Question: iodinated contrast medias can be classified as _____, monomers or dimers

Answer: Ionic and non-ionic

Contrast Media and Reactions Flashcard 7 of 7

Question: Gadolinium contrast for MRI is contraindicated in _____ and chronic renal disease

Answer: pregnancy