**Question:** A 25 year old male is undergoing incision and drainage of an abscess under general anaesthesia with spontaneous respiration. The most efficient anaesthetic circuit is:

A. Total intravenous anaesthesia (TIVA) using propofol and remifentanil
B. Sevoflurane in oxygen and air
C. Desflurane in oxygen and air
D. Alfaxalone and medetomidine

**Correct Answer: B. Sevoflurane in oxygen and air**

**Core Concept:**
In this scenario, the patient is undergoing an operation under general anaesthesia but maintains spontaneous respiration. This indicates that the patient will require a balanced anaesthetic technique, where both intravenous and inhalational agents are used, to achieve a balance between depth and stability of anaesthesia, maintain spontaneous ventilation, and minimize the risk of respiratory depression.

**Why the Correct Answer is Right:**
A balanced anaesthetic technique is recommended for patients undergoing surgery with spontaneous ventilation to maintain a stable depth of anaesthesia while allowing spontaneous breathing. Sevoflurane in oxygen and air (Option B) is chosen for the following reasons:

1. Sevoflurane: A potent inhalational anaesthetic agent with a rapid onset and offset of action, making it suitable for short procedures like incision and drainage of an abscess.
2. Oxygen and air: Provides adequate oxygenation and ventilation while minimizing the risk of hypoxia and hypercapnia, which can be detrimental for the patient.

**Why Other Options are Incorrect:**

A. TIVA (Total intravenous anaesthesia) with propofol and remifentanil (Option A) is less suitable because:
- Propofol is a short-acting anaesthetic agent, which may cause a rapid onset and offset of action, potentially leading to a less stable depth of anaesthesia.
- Remifentanil is a potent opioid analgesic that can cause respiratory depression, which is not desired in a patient with spontaneous ventilation.

C. Desflurane in oxygen and air (Option C) is less suitable because:
- Desflurane is a newer agent with a shorter half-life, which may lead to a less stable depth of anaesthesia and more rapid onset and offset of action compared to sevoflurane.

D. Alfaxalone and medetomidine (Option D) is less suitable because:
- Alfaxalone is a newer agent with a shorter half-life, which may cause less stable depth of anaesthesia and more rapid onset and offset of action compared to sevoflurane.
- Medetomidine is a short-acting alpha-2 agonist used for sedation and analgesia, not anaesthesia induction.

**Clinical Pearls:**

1. A balanced anaesthesia technique with a combination of inhalational and intravenous agents is essential for patients with spontaneous ventilation.
2. Sevoflurane is a suitable choice due to its balanced properties between stability, rapid onset and offset, and minimal respiratory depression.
3. Adjunct