**Question:** Intravenous anaesthetic causing suppression of steroid synthesis:

A. Propofol
B. Thiopentone
C. Ketamine
D. Sevoflurane

**Core Concept:**
The question is testing our understanding of the pharmacological effects of intravenous anaesthetics on the hypothalamic-pituitary-adrenal axis, which is responsible for the production of steroid hormones like cortisol and aldosterone. Steroid hormones play a crucial role in maintaining homeostasis and regulating various physiological processes in the body.

**Why the Correct Answer is Right:**
The correct answer, **D. Sevoflurane**, is a volatile anaesthetic commonly used for general anaesthesia. Sevoflurane targets the hypothalamic-pituitary-adrenal axis by inhibiting the release of corticotropin-releasing hormone (CRH) from the hypothalamus, and adrenocorticotropic hormone (ACTH) from the pituitary gland. This suppression of CRH and ACTH leads to a decrease in cortisol and aldosterone production by the adrenal glands, resulting in the observed suppression of steroid synthesis.

**Why Each Wrong Option is Incorrect:**

A. **Propofol (Option A)** is a short-acting intravenous anaesthetic, widely used for induction and maintenance of anaesthesia. Although propofol can suppress the hypothalamic-pituitary-adrenal axis, its effect is less pronounced compared to sevoflurane.

B. **Thiopentone (Option B)** is another intravenous anaesthetic used for induction of general anaesthesia. Thiopentone also suppresses the hypothalamic-pituitary-adrenal axis, but its clinical significance is less compared to sevoflurane.

C. **Ketamine (Option C)** is a dissociative anaesthetic agent, primarily used for induction and maintenance of general anaesthesia. While ketamine has some effect on the hypothalamic-pituitary-adrenal axis, the clinical significance is less compared to sevoflurane.

**Clinical Pearl:**
Due to its potent and sustained suppression of the hypothalamic-pituitary-adrenal axis, sevoflurane is contraindicated in patients with pre-existing adrenal insufficiency, as it can exacerbate the condition.

**Why the Correct Answer is Right:**
Sevoflurane is a potent inhibitor of the hypothalamic-pituitary-adrenal axis, which is why it is rightly chosen as the correct answer. In contrast, the other options have lesser effects on the same axis, and thus are less likely to suppress steroid synthesis.