**Question:** Intravenous anaesthetics are all except-

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

**Core Concept:**
Intravenous anesthetics are a group of drugs used for inducing and maintaining general anesthesia. These drugs are administered intravenously and interact with the central nervous system to produce a loss of consciousness, muscle relaxation, and other anesthetic effects.

**Why the Correct Answer is Right:**
The correct answer, option D (Midazolam), is an exception because it is primarily used for sedation and amnesia rather than general anesthesia. Midazolam is a benzodiazepine, which binds to specific sites on the gamma-aminobutyric acid (GABA) receptors and enhances the inhibitory neurotransmission, leading to sedation and amnesia.

**Why Each Wrong Option is Incorrect:**

A. Propofol (Option A) is a short-acting intravenous anesthetic that is commonly used for induction of general anesthesia. It acts as a GABA agonist and enhances the inhibitory neurotransmission, leading to rapid induction of anesthesia and rapid recovery.

B. Ketamine (Option B) is a dissociative anesthetic that works by inhibiting NMDA (N-methyl-D-aspartate) receptors, leading to a dissociative anesthetic effect. While it can be used for general anesthesia, it is not typically considered as a primary agent for inducing general anesthesia.

C. Thiopentone (Option C) is a barbiturate, a type of intravenous anesthetic drug. Barbiturates act as central nervous system depressants, producing a decrease in neuronal excitability, which leads to loss of consciousness and muscle relaxation.

**Clinical Pearl:**

Intravenous anesthesia involves a combination of drugs tailored to the patient's condition, age, and procedure duration. Choosing the correct agent and appropriate depth of anesthesia is crucial for patient safety and optimal surgical conditions. Knowledge of the pharmacological properties of these drugs is essential for effective management of patients undergoing surgery.