Anaesthesia (7) Flashcards
Inhalation agents
Sevoflurane, Isoflurane, Desflurane, Nitrous oxide, Xenon
IV agents
Propofol, Etomidate, Barbiturates, Ketamine
Ideal physical properties of inhalation agent
Non-flammable, stable with materials (e.g. plastic), long shelf life, environmentally friends, easy and cheap to manufacture
Ideal biological properties of inhalation agent
Pleasant to inhale (non-irritant), fast onset, high potency, minimal effects to other systems, no biotransformation, non-toxic to theatre personnel
Balanced anaesthesia triangle
- Unconsciousness
- Analgesia
- Muscle relaxation
Balanced anaesthesia
Usually combination of agents used, safer than large dose single agent, maximises benefit of individual agent, minimises adverse effects
Measuring anaesthetic potency - IV
MAC (Minimum Alveolar Concentration), Cp50
Producing unconciousness
- Meyer Overton theory
- Related to lipid solubility
- Pertubation of lipid membranes
- Common mechanism of action
- Now shown to be false (lipid membrane effect reproduced by small changes in temp in vitro, differing effects stereoisomers, large molecular weight compounds less potent than predicted)
How do anaesthetics work?
Modulate activity of transmitter-gated ion channels
Anaesthetics have positive effect on which gated ion channels?
GABAa and Strychine-sesntive glycine
Anaesthetics have negative effect on which gated ion channels?
5HT3, neuronal nicotinic and glutamate NMDA/AMPA
Inhalation agents
Solubility in blood determines onset/offset, low solubility=fast equilibrium, fast onset and quick recovery
Highly fat soluble GA
Given for long time accumulates in fat leading to ‘hangover’ effect for hours
IV agents
Quick onset, short duration (redistribution)
Adverse effects (general)
Vasodilation, decreased cardiac contractility, affect organ perfusion
