A girl was brought to the emergency in unconscious state with history of faintness in bathroom showing cherry red discoloration. She was declared dead. The bathroom was a poorly ventilated room with a newly installed geyser. Blood toxicology reports shows high concentration of irrespirable gas. What could be this gas?

1. A

   CO

2. B

   CO2

3. C

   Hydrogen sulphide

4. D

   Methane

Appeared in: INI-CET EXAM -2025

Explanation

• Carbon Monoxide (CO) is produced by incomplete combustion of carbon-containing fuels, a common risk with faulty or poorly ventilated heating appliances like geysers.
• CO has an affinity for hemoglobin over 200 times that of oxygen, forming stable carboxyhemoglobin (COHb).
• This binding prevents oxygen from being transported to the tissues, causing severe systemic hypoxia.
• The resulting carboxyhemoglobin is bright red, leading to the classic post-mortem sign of cherry-red skin and mucous membranes.

Why Other Options Were Wrong

• Option B: Carbon dioxide (CO2) is a simple asphyxiant that displaces oxygen. It causes hypercapnia and respiratory acidosis, leading to cyanosis (bluish discoloration of the skin), not cherry-red discoloration.
• Option C: Hydrogen sulphide (H2S) poisoning is characterized by a distinct 'rotten egg' smell, which was not mentioned. It inhibits cellular respiration but does not cause cherry-red skin.
• Option D: Methane is a non-toxic simple asphyxiant that displaces oxygen. It does not have a characteristic color sign and would lead to symptoms of oxygen deprivation, resulting in pallor or cyanosis.

Related Visual

• Visual 1: Diagram: A visual showing a hemoglobin molecule, illustrating how a Carbon Monoxide molecule binds to the iron center, blocking the much larger Oxygen molecule from attaching. This clarifies the concept of competitive binding.
• Visual 2: Clinical Photo: An image depicting the characteristic cherry-red livor mortis on the skin of a patient with fatal CO poisoning. This reinforces the key diagnostic sign mentioned in the question.

Clinical Relevance

• Nursing practice connection: Prioritize focused assessment, early escalation, and real-time monitoring when managing Identification of toxic gas based on clinical signs and environmental context in acute care settings.
• Nurses must recognize that early symptoms of CO poisoning (headache, nausea, dizziness) mimic the flu, leading to misdiagnosis. A high index of suspicion is crucial, especially when environmental clues are present.
• The immediate nursing intervention for suspected CO poisoning is to remove the person from the source and administer 100% high-flow oxygen via a non-rebreather mask to displace CO from hemoglobin and shorten its half-life.
• Patient education on prevention is a key nursing role. This includes advising on the importance of proper ventilation for fuel-burning appliances and the installation of carbon monoxide detectors in homes.

How to Approach the Question

• First, identify the key clinical sign in the scenario. Here, the most specific and unusual finding is 'cherry red discoloration'.
• Next, analyze the environmental context provided: 'poorly ventilated room' and 'newly installed geyser'. This points to a potential source of toxic gas from incomplete combustion.
• Connect the key sign to the context. Ask yourself, 'Which toxic gas produced by incomplete combustion causes cherry-red skin?'
• Evaluate the options based on this connection. Recall or deduce the classic signs of poisoning for each gas.
• CO poisoning is famously associated with cherry-red skin due to carboxyhemoglobin. CO2, Methane, and H2S cause different signs (cyanosis, asphyxia, rotten egg smell).
• Select the option that perfectly matches both the clinical sign and the environmental source.

Concept Tested & Keywords

• Concept Tested: Identification of toxic gas based on clinical signs and environmental context.
• Stem keywords: unconscious, cherry red discoloration, poorly ventilated room, geyser, irrespirable gas
• Lead-in keywords: What could be this gas?
• Clinical cues: The cue 'cherry red discoloration' is a pathognomonic sign for carbon monoxide poisoning.
• Clinical cues: The context of a 'poorly ventilated room with a newly installed geyser' points towards a source of incomplete combustion.

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