Prevention of Contrast Reactions — MCQs
Which contrast agent is not used for CT scans?
AMPLE history involved all except?
Which of the following indicates radiograph contrast induced nephropathy?
All of the following forces are involved in antigen-antibody reactions, except:
Which of the following inhalational anaesthetic agent can cause hepatitis on repeated use?
What mechanism explains the pathogenesis of Jarisch-Herxheimer reaction in patients treated for syphilis?
Which immunoglobulin is known to be heat-labile?
A patient with acute history of blistering and denudation involving >30% BSA along with erosions of the lips with hemorrhagic crusting and other mucosa for few days. What is the most common triggering factor?
Rectified spirit is NOT used as preservative in case of:
Which of the following is a feature of antemortem burns?
Prevention of Contrast Reactions Indian Medical PG Practice Questions and MCQs
Question 1: Which contrast agent is not used for CT scans?
- A. CO2 (Correct Answer)
- B. Iodinated high-osmolality contrast media
- C. Barium compounds
- D. Gadolinium-based contrast agents
Explanation: ***CO2*** - **CO2** (carbon dioxide) is **not used as a contrast agent in CT scans**. - CO2 is primarily used in **angiography** (especially for peripheral vessels in patients with iodine allergy or renal insufficiency) where it acts as a negative contrast agent. - In CT, CO2 would appear as air/gas density and create artifacts rather than providing diagnostic enhancement, making it unsuitable for routine CT imaging. *Iodinated high-osmolality contrast media* - These are **iodinated contrast agents** that contain iodine atoms which strongly attenuate X-rays, making them highly effective for **CT imaging**. - High-osmolality contrast media (HOCM) like **diatrizoate** and **iothalamate** were the standard CT contrast agents historically. - They have largely been replaced by **low-osmolality** and **iso-osmolality** agents due to higher incidence of **adverse reactions**, but they are still used for CT scans. *Barium compounds* - **Barium sulfate** suspensions are widely used as **oral or rectal contrast agents** for CT imaging of the gastrointestinal tract. - Barium has high atomic number and effectively attenuates X-rays, making the **GI lumen clearly visible** on CT scans. - Used in **CT enterography**, **CT colonography**, and routine **abdominal/pelvic CT** protocols. *Gadolinium-based contrast agents* - **Gadolinium-based contrast agents (GBCAs)** are primarily designed for **MRI** due to their **paramagnetic properties**. - However, gadolinium DOES attenuate X-rays and can be used **off-label for CT** in patients with **severe iodine allergy** or **contraindications to iodinated contrast**. - While less effective than iodinated agents for CT (requiring higher doses), gadolinium-enhanced CT is a recognized alternative in special clinical circumstances.
Question 2: AMPLE history involved all except?
- A. Last meal
- B. Pregnancy
- C. Personal history (Correct Answer)
- D. Allergy
Explanation: ***Personal history*** - The "P" in **AMPLE** stands for **Past medical history**, not Personal history. Personal history (social history) is a broader category that includes elements like smoking, alcohol use, and occupation, which are not specifically covered by the AMIPLE acronym. - While personal history is important for overall patient assessment, it is not a direct component of the focused **AMPLE** mnemonic used in emergency and critical care settings. *Last meal* - The "L" in **AMPLE** stands for **Last meal** (or Last oral intake). - This information is crucial for assessing aspiration risk, especially before procedures or surgery, and understanding metabolic status. *Pregnancy* - The "P" in **AMPLE** stands for **Past medical history or Pregnancy**. - For female patients of reproductive age, identifying pregnancy status is critical for medication administration, imaging decisions, and overall management. *Allergy* - The "A" in **AMPLE** stands for **Allergies**. - Knowing a patient's allergies is fundamental to prevent adverse reactions to medications, foods, and environmental factors during treatment.
Question 3: Which of the following indicates radiograph contrast induced nephropathy?
- A. Decreased urine output
- B. Increased bilirubin
- C. Increased creatinine levels (Correct Answer)
- D. Decreased bilirubin
Explanation: ***Increased creatinine levels*** - **Contrast-induced nephropathy (CIN)** is defined as an abrupt increase in **serum creatinine** following the intravascular administration of contrast material [1]. - A typical increase is defined as an absolute increase in serum creatinine of at least 0.3 mg/dL (26.5 µmol/L) or a 50% relative increase from baseline within 48-72 hours. *Decreased urine output* - While a **decreased urine output** (oliguria) can be a symptom of acute kidney injury, it is not the primary diagnostic criterion for **contrast-induced nephropathy**. - The diagnosis of CIN relies more specifically on changes in **renal function markers** like creatinine, rather than just urine volume [1]. *Increased bilirubin* - **Increased bilirubin** levels typically indicate **liver dysfunction** or **hemolysis**, not necessarily kidney injury. - There is no direct causal link between contrast media administration and elevated bilirubin as a marker of acute kidney damage. *Decreased bilirubin* - **Decreased bilirubin** levels are not associated with any form of organ damage and generally hold no clinical significance. - This finding would not indicate **contrast-induced nephropathy** or any other common pathology.
Question 4: All of the following forces are involved in antigen-antibody reactions, except:
- A. Electrostatic bond
- B. Hydrogen bond
- C. Covalent bond (Correct Answer)
- D. Van der Waals forces
Explanation: ***Covalent bond*** - **Covalent bonds** are strong, irreversible bonds that involve the sharing of electrons between atoms. - Antigen-antibody interactions are predominantly **non-covalent** and reversible, allowing for dynamic binding and release. *Vander Waal's forces* - **Van der Waals forces** are weak attractive forces that arise from temporary fluctuations in electron distribution, creating transient dipoles. - They are crucial in antigen-antibody binding, especially when the molecules are in **close proximity**, contributing to overall affinity. *Electrostatic bond* - **Electrostatic (ionic) bonds** occur between oppositely charged groups on the antigen and antibody surfaces. - These interactions are significant for **initial recognition** and overall binding stability, particularly at appropriate pH levels. *Hydrogen bond* - **Hydrogen bonds** form between a hydrogen atom covalently linked to an electronegative atom (like oxygen or nitrogen) and another electronegative atom. - They play a vital role in the **specificity and strength** of antigen-antibody interactions by providing numerous weak, directional contacts.
Question 5: Which of the following inhalational anaesthetic agent can cause hepatitis on repeated use?
- A. Sevoflurane
- B. Halothane (Correct Answer)
- C. Ether
- D. Isoflurane
Explanation: ***Halothane*** - Halothane is known to cause **halothane hepatitis** (also known as halothane-induced liver injury), a rare but severe form of liver damage, particularly on **repeated exposure**. - This is due to the **metabolism of halothane** in the liver, which can produce reactive intermediates that lead to immune-mediated liver cell necrosis. *Sevoflurane* - Sevoflurane is generally considered to have a **low incidence of liver toxicity** and is preferred in patients with pre-existing liver disease. - While it can be metabolized to fluoride ions, the clinical significance of this in terms of liver damage is considered to be minimal compared to halothane. *Ether* - **Diethlyl ether** is an older anesthetic agent that is no longer commonly used due to its flammability and slower induction/recovery times. - While it can cause some hepatic dysfunction, it is not primarily associated with the severe, immune-mediated hepatitis seen with halothane. *Isoflurane* - Isoflurane is an ether-based anesthetic with a much **lower metabolism** rate than halothane. - This reduced metabolism contributes to its **lower potential for liver toxicity** compared to halothane, making it a safer option for patients with liver concerns.
Question 6: What mechanism explains the pathogenesis of Jarisch-Herxheimer reaction in patients treated for syphilis?
- A. Massive release of treponemal endotoxins
- B. Inflammatory response to rapid spirochete lysis (Correct Answer)
- C. Autoimmune reaction triggered by treatment
- D. Allergic reaction to penicillin
Explanation: The Jarisch-Herxheimer reaction (JHR) is primarily caused by the rapid destruction of a large number of spirochetes, leading to the release of lipoproteins and other antigenic substances. This release triggers an acute systemic inflammatory response, manifesting as fever, chills, headache, and myalgias. While bacteria do release toxins, Treponema pallidum, the causative agent of syphilis, is a spirochete and does not produce classical endotoxins (which are typically associated with gram-negative bacteria) [1]. The inflammatory mediators are released from the host in response to the rapid breakdown of the spirochetes themselves, not pre-formed endotoxins. JHR is an acute reaction that occurs shortly after the initiation of antibiotic therapy and resolves spontaneously, which is not characteristic of a prolonged autoimmune disease. There is no evidence to suggest that the body produces antibodies against its own tissues as a result of syphilis treatment in JHR. An allergic reaction to penicillin would typically present with hives, pruritus, bronchospasm, or anaphylaxis, and would persist with repeated doses of the drug. The Jarisch-Herxheimer reaction is distinct from an allergic reaction; it is a predictable inflammatory response to spirochete killing and can occur even with non-penicillin therapies for syphilis. **References:** [1] 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. 63-64.
Question 7: Which immunoglobulin is known to be heat-labile?
- A. IgA
- B. IgG
- C. IgM (Correct Answer)
- D. IgE
Explanation: ***IgM*** - **IgM** is known for its **heat lability** and is readily denatured at 56°C within a few minutes. - This characteristic is due to its **pentameric structure** held together by disulfide bonds and J chains, which are sensitive to thermal denaturation. - Heat lability of IgM is clinically important in complement fixation tests and other laboratory assays where heat inactivation is performed. - IgM is the first antibody produced in primary immune response and its heat sensitivity distinguishes it from other immunoglobulins. *IgA* - **IgA** exists in monomeric (serum) and dimeric (secretory) forms and shows moderate stability to heat. - Secretory IgA is relatively stable as it needs to function in harsh mucosal environments, though not as heat-resistant as IgG. - Does not exhibit the pronounced heat lability characteristic of IgM. *IgG* - **IgG** is the most stable immunoglobulin and is highly resistant to heat denaturation. - Can withstand temperatures up to 60-70°C without significant loss of activity. - Its monomeric structure with strong intramolecular bonds provides exceptional thermal stability. - Most abundant antibody in serum and has the longest half-life. *IgE* - **IgE** is actually quite stable to heat and can withstand 56°C for extended periods. - While it has a short half-life in serum (2-3 days), this is due to receptor binding rather than heat instability. - Important in type I hypersensitivity reactions and parasitic infections. - Does not show the characteristic heat lability that defines IgM.
Question 8: A patient with acute history of blistering and denudation involving >30% BSA along with erosions of the lips with hemorrhagic crusting and other mucosa for few days. What is the most common triggering factor?
- A. Drug induced (Correct Answer)
- B. Viral infection
- C. Idiopathic
- D. Bacterial infection
Explanation: ***Drug induced*** - **Toxic epidermal necrolysis (TEN)**, characterized by blistering and denudation of >30% body surface area and mucosal involvement, is most commonly triggered by **drugs**, such as sulfonamides, antiepileptics, allopurinol, and NSAIDs. - The rapid onset and severe presentation are highly suggestive of an adverse drug reaction. *Viral infection* - While viruses can trigger some mucocutaneous reactions, severe widespread necrosis and denudation like in TEN are not typically **direct viral effects**. - **Herpes simplex virus (HSV)** can cause erythema multiforme, which is less severe and extensive than TEN. *Idiopathic* - While some cases of severe cutaneous adverse reactions can be idiopathic, the vast majority of **TEN cases have an identifiable trigger**, with drugs being the leading cause. - Attributing it to an unknown cause would be less precise given the common association with medications. *Bacterial infection* - Bacterial infections, such as **Staphylococcal scalded skin syndrome (SSSS)**, can cause blistering and desquamation, but it primarily affects children and involves a superficial epidermal split, rather than the full-thickness necrosis seen in TEN. - SSSS typically spares the **mucous membranes**, unlike the prominent mucosal involvement described in the patient.
Question 9: Rectified spirit is NOT used as preservative in case of:
- A. Phenol (Correct Answer)
- B. Cyanide
- C. Alphos
- D. Insecticides
Explanation: ***Phenol*** - Rectified spirit is **NOT used** for preserving specimens containing **phenol** because phenol is a **volatile poison**. - When mixed with alcohol, phenol can **evaporate** or undergo chemical interactions, leading to loss of the poison and inaccurate toxicological analysis. - Due to this **chemical incompatibility**, phenol specimens should be preserved by **refrigeration without chemical preservatives** or in specific non-alcoholic media. *Cyanide* - Rectified spirit is commonly used as a preservative for specimens involving **cyanide** poisoning cases. - It helps in preventing putrefaction while the specimen is awaiting toxicological analysis. *Alphos* - **Alphos** (aluminum phosphide) poisoning cases often require tissue or organ preservation. - Rectified spirit can be used to preserve tissues, facilitating subsequent analysis for phosphine gas or its metabolites. *Insecticides* - In cases involving **insecticide** poisoning, rectified spirit is a standard preservative for biological samples. - It helps maintain the integrity of the sample, allowing for accurate detection and quantification of various insecticide compounds.
Question 10: Which of the following is a feature of antemortem burns?
- A. Pugilistic attitude
- B. Bleeding present
- C. Absence of vital reaction
- D. Soot in airways (from smoke inhalation) (Correct Answer)
Explanation: ***Soot in airways (from smoke inhalation)*** - The presence of **soot in airways** is the **most specific and reliable indicator** that the individual was **breathing at the time of the fire**, confirming an **antemortem burn**. - This indicates **smoke inhalation while alive** and is considered the **gold standard feature** for distinguishing antemortem from postmortem burns in forensic medicine. - Found on autopsy examination of the respiratory tract (trachea, bronchi, and lungs). *Pugilistic attitude* - This characteristic boxer-like posture results from **heat-induced muscle contraction** due to **coagulation and shortening of muscle proteins** when exposed to high temperatures. - It occurs in **both antemortem and postmortem burns**, making it **non-specific** for timing of burns. - Therefore, it cannot be used to determine whether burns occurred before or after death. *Absence of vital reaction* - **Absence of vital reaction** is a feature of **postmortem burns**, not antemortem burns. - **Antemortem burns** show **vital reaction signs** including inflammatory infiltration, vesicle/blister formation with fluid, hyperemia, and tissue response to injury. - The presence of vital reaction confirms the person was alive when burned. *Bleeding present* - While bleeding theoretically suggests antemortem injury (requires active circulation), **external bleeding is not a reliable or specific feature** used in forensic practice to diagnose antemortem burns. - Burns typically cause **coagulation of blood vessels** (heat seals vessels), making significant bleeding uncommon. - **Vital reaction signs** (inflammation, blisters) are the standard indicators used, not bleeding per se.
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