## Core Concept
The question tests knowledge of anaesthetic agents and their effects on blood pressure, specifically in patients with hypertension. Understanding the pharmacological profiles of various anaesthetic agents is crucial for safe administration, especially in patients with pre-existing conditions like hypertension.

## Why the Correct Answer is Right
Ketamine can increase blood pressure and heart rate due to its sympathomimetic effects, which are primarily mediated through the release of catecholamines (adrenaline and noradrenaline) and to some extent through direct stimulation of the sympathetic nervous system. This increase in sympathetic activity can be problematic in patients with hypertension, as it may lead to a significant rise in blood pressure, potentially causing cardiovascular complications.

## Why Each Wrong Option is Incorrect
* **Option A:** Propofol generally causes a decrease in blood pressure due to vasodilation and a decrease in cardiac output. It is not specifically contraindicated in hypertension and can be used carefully.
* **Option B:** Thiopentone (thiopental) also decreases blood pressure, mainly through vasodilation and a decrease in cardiac output. It's not contraindicated in hypertension.
* **Option D:** Midazolam has minimal effects on blood pressure and cardiac output, making it a relatively safe choice for patients with hypertension.

## Clinical Pearl / High-Yield Fact
A key point to remember is that ketamine can be particularly risky in patients with hypertension or cardiovascular disease due to its potential to increase blood pressure and heart rate. Conversely, propofol and thiopental are often considered safer in this context because they tend to decrease blood pressure.

## Correct Answer: C. Ketamine.