Which anaesthetic gas is contraindicated in the presence of pneumothorax ?
**Core Concept**
The question tests the understanding of **anaesthetic gases** and their effects on **pneumothorax**, a condition where air leaks into the space between the lung and chest wall. The correct answer relies on knowledge of gas exchange and lung expansion.
**Why the Correct Answer is Right**
The correct answer is related to the fact that certain anaesthetic gases can expand the **pneumothorax**, worsening the condition. Specifically, gases that support combustion or are highly soluble in blood can exacerbate the issue. **Nitrous oxide** is known to expand air-filled spaces, making it a poor choice in cases of pneumothorax.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it is not typically associated with worsening pneumothorax.
**Option B:** Incorrect as it does not significantly expand air-filled spaces.
**Option C:** Incorrect because, although it has its drawbacks, it is not the most directly contraindicated in pneumothorax.
**Clinical Pearl / High-Yield Fact**
Remember, **nitrous oxide** can expand air-filled spaces, making it crucial to avoid its use in patients with pneumothorax to prevent further lung collapse. This is a key point for anaesthesia safety.
**Correct Answer:** D. Nitrous oxide.