Induction Agents

What is an induction agent?

Induction agents are drugs used to induce and maintain general anaesthesia. Usually the term induction agent refers to the intravenous agents described below, however it is possible to do a gas induction using a volatile anaesthetic agent as well, so they can also technically be included as induction agents.

Objectives of this section

  • Recall the pertinent chemical, pharmacokinetic and pharmacological properties of PropofolKetamineThiopentoneEtomidate and Midazolam
  • Compare and contrast the properties of these drugs and their clinical uses in anaesthetic practice
  • Use this knowledge and understanding to select an appropriate induction agent for various clinical scenarios


  • The most commonly used agent
  • Usually a 10mg/ml lipid emulsion
  • Well tolerated, and contrary to popular believe, it can be given to patients with an egg allergy, because the constituent in propofol is from the yolk, and the allergens are in the egg white



  • NB. Thiopentone can be used as an IV infusion for Cerebral Protection, but for the purposes of Anaesthesia is only used as an induction bolus. 



  • Note that while midazolam is a benzodiazepine, it can also be used as an induction agent
  • It is also commonly used as a pre-medication and anxiolytic

Summary PDF

Created on By unicyclemedic

Induction Agents

Test your knowledge of Induction Agents

1 / 15

Which of the following would be an appropriate volume of 1% Propofol to induce anaesthesia in a 21-year-old 80kg male ASA-1 patient undergoing an elective circumcision?

2 / 15

Which statement regarding Ketamine is correct?

3 / 15

Which statement regarding Thiopentone is incorrect?

4 / 15

Which of the following induction agents has analgesic activity?

5 / 15

Which of the following Induction Agents is presented in Propylene Glycol?

6 / 15

A 34-year old ASA1 lady is listed for a hysteroscopy and change of mirena coil as day surgery. Is it likely to be a very quick and uncomplicated procedure (around 15 minutes) and so the plan is to use a supraglottic airway device. Which induction agent would be most appropriate in this instance?

7 / 15

Which of the following induction agents is the most potent?

8 / 15

Which of the following is not true of Midazolam?

9 / 15

GABAA receptors are ionotropic, while GABAB receptors are metabotropic. Which of the following agents' mechanism of action is not related to potentiation of GABAA receptors?

10 / 15

The ENT team list a 3-year-old male ASA1 for emergency extraction of foreign body from the auditory canal. Last time this happened, he became very distressed in the anaesthetic room on attempting to site a peripheral cannula and the parents are keen that this can be avoided today.

What would be the most appropriate way to induce anaesthesia?

11 / 15

Which of the following statements regarding Propofol is incorrect?

12 / 15

A 73-year-old female is listed for an emergency laparotomy for presentation highly suspicious for bowel ischaemia. She is clinically septic with observations as follows: HR 128, BP 83/42, T 38.4, RR 28, SpO2 95% on 40% Venturi.

On arrival in the anaesthetic room, an arterial line is sited in addition to a central line for initiation of noradrenaline infusion.

What is the most appropriate induction agent for this patient?

13 / 15

The 'Classical' RSI is performed with suxamethonium and which induction agent?

14 / 15

Which agent inhibits 11β-hydroxylase and 17α-hydroxylase in the biosynthetic pathway to form cortisol and aldosterone?

15 / 15

Which of the following agents is metabolised by esterases?

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The average score is 71%


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