**Question:** Anaesthesia given to dog:

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

**Correct Answer:** A. Propofol

**Core Concept:** Anaesthesia in dogs is a complex process that involves depressing the central nervous system to achieve surgical immobility and amnesia. Different anaesthetic agents target different pathways in the central nervous system to achieve this effect.

**Why the Correct Answer is Right:** Propofol (diprivan) is a short-acting intravenous anaesthetic agent, which is commonly used for induction of anaesthesia in dogs. It selectively inhibits gamma-aminobutyric acid (GABA) receptors in the brain, leading to depression of the central nervous system and achieving surgical immobility and amnesia. Propofol is characterized by a rapid onset, short duration, and minimal cardiovascular effects, making it suitable for use in dogs.

**Why Each Wrong Option is Incorrect:**

B. Ketamine: Ketamine is a dissociative anaesthetic agent that primarily works on the NMDA receptors in the central nervous system, leading to sensory dissociation and peripheral vasoconstriction. While ketamine is used in some cases, Propofol is generally preferred due to its less cardiovascular impact and shorter duration.

C. Thiopentone: Thiopentone is an intravenous barbiturate anaesthetic agent that depresses the central nervous system through GABA receptors, similar to Propofol. However, it is typically less commonly used than Propofol due to its longer duration and potential cardiovascular effects.

D. Althesin: Althesin is an older anaesthetic agent that consists of a mixture of thiopentone and hyoscine (scopolamine), which also targets GABA receptors. It is less commonly used than Propofol due to its longer duration and potential side effects.

**Clinical Pearls:**

In clinical practice, the choice of anaesthetic agent depends on the specific surgical procedure, patient's health status, and the preferences of the veterinary surgeon or anaesthesiologist. Propofol is a popular choice due to its rapid onset, short duration, and minimal cardiovascular effects. However, it is essential to consider the individual patient's condition and surgical requirements when selecting the most appropriate anaesthetic agent.