Toxicology and Overdose Management — MCQs
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A 7-year-old girl's parents report a history of fever, for which she was treated with paracetamol, following which the fever subsided. Later, she developed seizures and altered sensorium. Urine examination revealed oxalate crystals on microscopy. Blood anion gap and osmolality were increased. The diagnosis is:
A patient with salicylic acid poisoning has the following arterial blood gas analysis report: pH is 7.12 , PCO2 is 18 mm Hg HCO3– is 12 mmol/L. The resulting acid-base abnormality can be best labelled
Cafe coronary commonly occurs when a person is:
A 50-year-old male with a history of chronic alcoholism presents with altered sensorium and signs of portal hypertension. What is the most appropriate initial management step?
Which of the following laboratory findings is most consistent with a diagnosis of carbon monoxide poisoning?
A 45-year-old woman presents with shortness of breath and cyanosis. Arterial blood gas shows a low oxygen saturation despite a normal PaO2. What is the most likely diagnosis?
Which of the following conditions is MOST characteristically associated with central cyanosis?
A 45-year-old man with a history of alcohol dependence is found unconscious with pinpoint pupils and respiratory depression. What is the most appropriate immediate intervention?
A patient presents with pinpoint pupils, respiratory depression, and coma. Which poison is most likely responsible?
A 40-year-old male presents with altered mental status and metabolic acidosis. His blood tests show a high anion gap and osmolar gap. Which poison would you suspect?
Toxicology and Overdose Management Indian Medical PG Practice Questions and MCQs
Question 151: A 7-year-old girl's parents report a history of fever, for which she was treated with paracetamol, following which the fever subsided. Later, she developed seizures and altered sensorium. Urine examination revealed oxalate crystals on microscopy. Blood anion gap and osmolality were increased. The diagnosis is:
- A. Ethylene glycol (Correct Answer)
- B. Lactic acidosis
- C. Renal tubular acidosis
- D. Paracetamol poisoning
Explanation: ***Ethylene glycol*** - The presence of **calcium oxalate crystals** in urine, along with a high **anion gap metabolic acidosis** and **increased osmolality**, are classic signs of ethylene glycol poisoning [2]. - Initial symptoms can be vague, but progression to **seizures** and altered sensorium indicates severe toxicity affecting the central nervous system and kidneys [2]. *Lactic acidosis* - While lactic acidosis can cause an **increased anion gap**, it does not typically present with **oxalate crystals** in the urine [1]. - It's a common finding in many critical conditions but doesn't explain the full clinical picture, especially the specific urinary findings. *Renal tubular acidosis* - This condition involves a defect in renal acid excretion or bicarbonate reabsorption, leading to **normal anion gap metabolic acidosis**, not an elevated one. - It is not associated with **oxalate crystals** or acute neurological deterioration like seizures. *Paracetamol poisoning* - Paracetamol overdose primarily causes **hepatotoxicity** and, in severe cases, renal failure, but does not typically lead to **oxalate crystalluria** or an **increased osmolal gap** like ethylene glycol. - The patient was treated with paracetamol for fever, but the subsequent severe symptoms are inconsistent with paracetamol directly causing the described findings.
Question 152: A patient with salicylic acid poisoning has the following arterial blood gas analysis report: pH is 7.12 , PCO2 is 18 mm Hg HCO3– is 12 mmol/L. The resulting acid-base abnormality can be best labelled
- A. Metabolic acidosis with respiratory alkalosis (Correct Answer)
- B. Metabolic acidosis
- C. Metabolic acidosis with respiratory acidosis
- D. Respiratory acidosis with metabolic alkalosis
Explanation: ***Metabolic acidosis with respiratory alkalosis*** - The **low pH (7.12)** indicates academia, while the **low HCO3– (12 mmol/L)** points to a **primary metabolic acidosis** [1]. - The **low PCO2 (18 mm Hg)** suggests a **compensatory respiratory alkalosis**, as the body attempts to blow off CO2 to raise pH [1]. *Metabolic acidosis* - While there is a **primary metabolic acidosis (low HCO3–)**, this option fails to recognize the **compensatory respiratory response (low PCO2)** [1]. - In salicylic acid poisoning, both a metabolic acidosis and a respiratory alkalosis (due to direct stimulation of the respiratory center) typically occur together [2]. *Metabolic acidosis with respiratory acidosis* - This option incorrectly identifies a **respiratory acidosis**, which would be characterized by a **high PCO2** [3]. - Salicylate poisoning causes **respiratory stimulation**, leading to a **low PCO2** (respiratory alkalosis), not acidosis [2]. *Respiratory acidosis with metabolic alkalosis* - This option is incorrect because the **low pH** clearly indicates acidosis, not alkalosis [3]. - Additionally, the **low PCO2** indicates respiratory alkalosis, not acidosis, and the **low HCO3–** indicates metabolic acidosis, not alkalosis.
Question 153: Cafe coronary commonly occurs when a person is:
- A. Eating meat
- B. Intoxicated (Correct Answer)
- C. Eating fish
- D. Eating fatty food
Explanation: ***Intoxicated*** - **Intoxication**, particularly with alcohol, impairs the **gag reflex** and **swallowing coordination**, increasing the risk of aspiration and airway obstruction [1]. - Reduced awareness and slowed reactions due to intoxication make it difficult for an individual to clear their airway effectively if food becomes lodged, leading to a "cafe coronary" [1]. *Eating meat* - While meat can be a common culprit in cafe coronary incidents due to its **fibrous texture** and potential for large boluses, it's not the primary underlying condition [1], [2]. - The act of eating meat itself does not inherently cause the impaired protective reflexes seen in cafe coronary. *Eating fish* - Fish typically presents a relatively **low risk** for airway obstruction compared to other foods, as it is generally softer and breaks down more easily. - Although bones can be an issue, the specific "cafe coronary" scenario refers to significant airway obstruction by a bolus, not usually associated with typical fish consumption [2]. *Eating fatty food* - Eating fatty foods primarily relates to **digestive issues** or cardiovascular risk, not typically to acute airway obstruction. - Fatty foods do not inherently impair swallowing reflexes or significantly increase the risk of aspiration in the same way intoxication does.
Question 154: A 50-year-old male with a history of chronic alcoholism presents with altered sensorium and signs of portal hypertension. What is the most appropriate initial management step?
- A. Perform upper gastrointestinal endoscopy (UGIE)
- B. Administer chlordiazepoxide
- C. Administer thiamine
- D. Administer lactulose (Correct Answer)
Explanation: ***Administer lactulose*** - The patient's presentation with altered sensorium and chronic alcoholism, coupled with signs of portal hypertension, strongly suggests **hepatic encephalopathy**. [1] - **Lactulose** is the most appropriate initial management step because it helps to reduce ammonia absorption from the gut by acidifying the colon and acting as an osmotic laxative, thereby improving neurological function. [1] *Perform upper gastrointestinal endoscopy (UGIE)* - While **portal hypertension** can lead to varices and bleeding, an UGIE is an invasive procedure and not the immediate priority for a patient presenting with altered sensorium due to suspected hepatic encephalopathy. - UGIE would be indicated if there were active **gastrointestinal bleeding** (e.g., hematemesis, melena) or hemodynamic instability, which are not explicitly mentioned as the primary concern. *Administer chlordiazepoxide* - **Chlordiazepoxide** is a benzodiazepine used to treat **alcohol withdrawal syndrome** (delirium tremens), which can also cause altered mental status. - However, given the signs of portal hypertension, **hepatic encephalopathy** is a more likely cause of altered sensorium, and benzodiazepines can worsen it by precipifying sedation. *Administer thiamine* - **Thiamine** administration is crucial in chronic alcoholics to prevent and treat **Wernicke-Korsakoff syndrome**, which can cause altered mental status, ophthalmoplegia, and ataxia. [2] - While important in all chronic alcoholics, addressing the potentially life-threatening ammonia toxicity in **hepatic encephalopathy** with lactulose takes precedence in the immediate management of altered sensorium.
Question 155: Which of the following laboratory findings is most consistent with a diagnosis of carbon monoxide poisoning?
- A. Increased PaCO2 and decreased pH
- B. Decreased PaO2 with normal oxygen saturation
- C. Normal PaO2 with decreased oxygen saturation (Correct Answer)
- D. Decreased PaCO2 with normal PaO2
Explanation: ***Normal PaO2 with decreased oxygen saturation*** - Carbon monoxide (CO) binds to hemoglobin with an affinity 200-250 times greater than oxygen, forming **carboxyhemoglobin (COHb)** [2]. This reduces the **oxygen-carrying capacity** of the blood and shifts the oxygen dissociation curve to the left, but it does **not affect the partial pressure of oxygen (PaO2)** dissolved in the plasma [1]. - The pulse oximeter, which typically measures oxygen saturation, will show a falsely high reading because it cannot differentiate between oxyhemoglobin and carboxyhemoglobin, but actual **oxygen saturation is decreased**. *Increased PaCO2 and decreased pH* - This pattern suggests **respiratory acidosis**, which is not a direct or primary finding of carbon monoxide poisoning. - While severe CO poisoning can lead to lactic acidosis, an increase in PaCO2 points to impaired ventilation, not specifically CO toxicity [3]. *Decreased PaO2 with normal oxygen saturation* - A decreased PaO2 with normal oxygen saturation is a contradictory finding and not physiologically consistent, as oxygen saturation is directly dependent on PaO2. - This pattern would indicate a measurement error or a highly unusual physiological state, neither of which is characteristic of CO poisoning. *Decreased PaCO2 with normal PaO2* - This suggests **respiratory alkalosis**, often due to hyperventilation. - While patients with CO poisoning may hyperventilate due to hypoxia, this ABG pattern is not the defining laboratory finding for CO poisoning, and **PaO2 would remain normal** until very late stages.
Question 156: A 45-year-old woman presents with shortness of breath and cyanosis. Arterial blood gas shows a low oxygen saturation despite a normal PaO2. What is the most likely diagnosis?
- A. Pulmonary embolism
- B. Carbon monoxide poisoning (Correct Answer)
- C. Asthma
- D. Pneumonia
Explanation: ***Carbon monoxide poisoning*** - **Carbon monoxide** binds to **hemoglobin** with a much higher affinity than oxygen, forming **carboxyhemoglobin (COHb)**, which prevents oxygen transport [1]. - This leads to a low-oxygen saturation reading by pulse oximetry, even when the **partial pressure of oxygen (PaO2)** in the blood is normal, because the PaO2 measures dissolved oxygen, not oxygen bound to hemoglobin [1], [2]. - Furthermore, CO causes a leftward shift of the oxyhemoglobin dissociation curve affecting the offloading of oxygen from hemoglobin to the tissue [1], [2]. *Pulmonary embolism* - A **pulmonary embolism** typically causes **hypoxemia** and a low **PaO2** due to ventilation-perfusion mismatch, which contradicts the normal PaO2 in this case. - While it can cause shortness of breath and cyanosis, the **ABG** findings of **normal PaO2** despite **low oxygen saturation** are not characteristic. *Asthma* - **Asthma** involves **bronchoconstriction** and airflow obstruction, leading to **hypoxemia** and a **low PaO2** in severe cases. - It would not typically present with a normal PaO2 alongside a significantly desaturated pulse oximeter reading, as the PaO2 directly reflects the amount of dissolved oxygen in the blood. *Pneumonia* - **Pneumonia** causes impaired gas exchange due to inflammation and fluid in the alveoli, resulting in **hypoxemia** and a **low PaO2**. - The coexistence of **normal PaO2** with **low oxygen saturation** points away from pneumonia, as the primary issue in pneumonia is usually a failure to oxygenate the blood effectively, thus lowering PaO2.
Question 157: Which of the following conditions is MOST characteristically associated with central cyanosis?
- A. Pulmonary embolism
- B. Severe anemia
- C. Congestive heart failure
- D. Methemoglobinemia (Correct Answer)
Explanation: ***Methemoglobinemia*** - This condition involves the oxidation of hemoglobin to **methemoglobin**, which cannot bind oxygen effectively and gives blood a characteristic **chocolate-brown color**. [1], [3] - Even with normal oxygen levels, the presence of **deoxygenated methemoglobin** leads to a striking **central cyanosis** that is often out of proportion to oxygen saturation. [1] *Pulmonary embolism* - While a large pulmonary embolism can cause hypoxemia and peripheral cyanosis, **central cyanosis** is not its most characteristic or earliest sign. - The primary mechanism is **ventilation-perfusion mismatch**, which can lead to desaturation but often presents with dyspnea before profound cyanosis. *Severe anemia* - In severe anemia, there is a **reduced amount of hemoglobin** available to become deoxygenated, even if oxygen transport is inadequate. [2] - Patients with severe anemia are often **pale** rather than cyanotic because the absolute amount of deoxygenated hemoglobin required to produce cyanosis (typically 5 g/dL) is not met. *Congestive heart failure* - Severe heart failure can lead to **peripheral cyanosis** due to poor perfusion and increased oxygen extraction in the tissues. - **Central cyanosis** may occur in decompensated heart failure with significant pulmonary edema causing hypoxemia, but it is not the most uniquely characteristic initial sign compared to methemoglobinemia.
Question 158: A 45-year-old man with a history of alcohol dependence is found unconscious with pinpoint pupils and respiratory depression. What is the most appropriate immediate intervention?
- A. Naloxone administration (Correct Answer)
- B. Flumazenil administration
- C. Thiamine administration
- D. Intravenous fluids
Explanation: ***Naloxone administration*** - The combination of **pinpoint pupils**, **respiratory depression**, and unconsciousness, especially in a patient with a history of **alcohol dependence** (which can mask or coexist with opioid use), is highly suggestive of **opioid overdose** [1], [2]. - **Naloxone** is a specific **opioid antagonist** that rapidly reverses the effects of opioid-induced respiratory depression [4]. *Flumazenil administration* - **Flumazenil** is an antagonist for **benzodiazepine overdose** [4]. - While benzodiazepines can cause respiratory depression and altered mental status, they typically do not cause **pinpoint pupils**. *Thiamine administration* - **Thiamine** (vitamin B1) is essential for patients with **alcohol dependence** to prevent or treat **Wernicke-Korsakoff syndrome** [3]. - While important in this patient population, it is not the immediate life-saving intervention for acute respiratory depression and unconsciousness. *Intravenous fluids* - **Intravenous fluids** are used to address dehydration, hypovolemia, or to facilitate drug excretion, and may be part of supportive care. - However, they do not directly reverse **respiratory depression** or address the underlying cause of unconsciousness in an opioid overdose.
Question 159: A patient presents with pinpoint pupils, respiratory depression, and coma. Which poison is most likely responsible?
- A. Opioids (Correct Answer)
- B. Barbiturates
- C. Organophosphates
- D. Cyanide
Explanation: ***Opioids*** - This constellation of symptoms—**pinpoint pupils**, **respiratory depression**, and **coma** (the classic triad)—is characteristic of severe opioid overdose [1], [2]. - Opioids act on mu-opioid receptors in the central nervous system, leading to suppression of respiratory drive and altered mental status [1], [3]. *Barbiturates* - While barbiturate overdose can cause **respiratory depression** and **coma**, it typically causes **dilated or normal pupils**, not pinpoint pupils. - Barbiturates primarily enhance the effects of GABA, leading to generalized CNS depression. *Organophosphates* - Organophosphate poisoning causes a **cholinergic crisis**, which includes pinpoint pupils (**miosis**), but also presents with symptoms like **salivation**, **lacrimation**, **urination**, **defecation**, **gastrointestinal upset**, and **emesis** (SLUDGE syndrome), which are not mentioned. - These agents inhibit acetylcholinesterase, leading to an overstimulation of cholinergic receptors. *Cyanide* - Cyanide poisoning primarily affects cellular respiration, leading to **lactic acidosis**, **coma**, and **cardiovascular collapse**. - **Pinpoint pupils** are not a typical feature; instead, pupils may be dilated or normal, and the patient may have a characteristic **"bitter almond" breath** odor.
Question 160: A 40-year-old male presents with altered mental status and metabolic acidosis. His blood tests show a high anion gap and osmolar gap. Which poison would you suspect?
- A. Methanol (Correct Answer)
- B. Ethanol
- C. Isopropanol
- D. Benzene
Explanation: ***Methanol*** - **Methanol** poisoning typically leads to a **high anion gap metabolic acidosis** due to the accumulation of formic acid, which is a toxic metabolite [1], [2]. - It also causes a **high osmolar gap** because methanol itself is an osmotically active substance in the bloodstream [1], [3]. *Ethanol* - While ethanol can cause a high osmolar gap, it generally does **not cause a high anion gap metabolic acidosis** unless consumed in extremely large quantities or in conjunction with other conditions like alcoholic ketoacidosis. - **Ethanol** metabolism primarily leads to the production of acetate, which does not contribute significantly to an elevated anion gap. *Isopropanol* - Isopropanol poisoning commonly results in a **high osmolar gap** due to the presence of isopropanol in the blood and its metabolite, acetone [1]. - However, it typically causes **ketosis without acidosis** or only a mild metabolic acidosis, as acetone is not a strong acid. *Benzene* - **Benzene** exposure is primarily associated with **bone marrow suppression** (aplastic anemia, leukemia) and neurological effects, not with significant metabolic acidosis or a high osmolar gap in acute overdose. - Its toxic effects are distinct from those seen with alcohol-based poisonings.
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General Principles of Toxicology
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