Inhalational anaesthetic agents

[Ref: SH4:p42; BH1:p47]

Overview

History

1840s - Discovery of anaesthetic properties of diethyl ether, nitrous oxide, and chloroform

1930s - Fluorination of molecules decreased flammability and toxicity

1950s - First fluorinated agent (fluroxene) introduced

Introduction for clinical use

• 1951 - Fluroxene
• 1956 - Halothane
• 1960 - Methoxyflurane
• 1973 - Enflurane
• 1981 - Isoflurane
• 1992 - Desflurane
• 1994 - Sevoflurane

Balanced anaesthesia

• Hypnosis
• Analgesia
• Muscle relaxation

Ideal properties of anaesthetic agent

Clinical usage

• Low blood:gas coefficient
  * Fast onset
  * Fast recovery
  * Fast adjustment
• Non-irritant and pleasant smell
• Adequate potency
  * Allow for high FiO2

Side-effects

• Minimal and predictable respiratory and CVS effect
• No systemic toxicity
• CNS effect reversible and non-excitatory
• No metabolism

Stability

• Stable in light, heat, and alkali
• Stable in soda lime and non corrosive
• Not inflammable or explosive
• Cheap and good shelf life
• Easy to manufacture
• No environmental impact
• Low latent heat of vapourisation