Anaesthesia | Pain | Step I: Inhalational Analgesics

Step I: Inhalational Analgesics
Session Overview
Description
This session explains the use of analgesia provided by the inhalational route. It concentrates on the use of nitrous oxide and oxygen mixtures.

Learning Objectives
By the end of this session you will be able to:

• Describe the types of clinical scenarios where inhalational analgesia may be useful
• Describe the equipment required to deliver inhalational analgesia
• Outline the basic principles of the mechanism of action of Entonox
• Describe the pharmacokinetics of Entonox
• Identify the side effects and contraindications associated with the use of Entonox
• Recognize the risks associated with occupational exposure

In modern anaesthetic practice, the term ‘inhalational analgesia' refers almost exclusively to the use of a mixture of nitrous oxide (N2O) and oxygen (O2). This can be delivered from a Boyle’s machine, or is marketed in the UK in pre-mixed cylinders by BOC under the trade name 'Entonox'.

Much less commonly, low concentrations of volatile anaesthetic agents in a carrier gas can be used as inhalational analgesics. Historically, trichloroethylene and methoxyflurane have been used, and some more recent work has been done on Isonox (0.2 % isoflurane in Entonox) and Isodesox (1 % desflurane, 0.25 % isoflurane and 60 % O2 in nitrogen).

This session will concentrate on Entonox and will cover:

• Equipment required
• Clinical uses of Entonox
• Pharmacokinetics and mechanisms of action
• Side effects and contraindications