PHAR1101 Lecture 5: Lecture 5
Lecture 5- Impact of Anaesthesia
Modern anaesthesia
Anxiolysis
Analgesia
Hypnosis
Muscle relaxation
Timeline
Approx. 1000 BC
Opium 3200 BC
Alcohol 3200 BC
Hashish 1200 BC
Joseph Priestley 1775
"I had discovered an air five or six times as good as common air."
Horace Wells
Successfully self-experiments with nitrous oxide anaesthesia, but struggles to
demonstrate his new interventions to the public at Massachusetts General Hospital
Boston
General rules
The higher the oil-gas partition coefficient, the higher the potency of the
anaesthetic
The lower the blood-gas partition coefficient, the faster are onset of
anaesthetic effect and recovery
The unit MAC (minimum alveolar concentration)
o1 MAC= dose at which 50% of subjects do not react to skin incisions
oUsed to describe the potency of a volatile anaesthetic agent and to
guide the clinical user
Property N20
Physical Colourless
Non-flammable
Boiling point -88 degrees
Blood/gas partition coefficient 0.47
Oil/gas partition coefficient 1.4
Metabolism 0.004%
MAC 105% theoretical
1272 by Raymundus Lulus and 154o analgesic properties first described by Paracelsus
1846 T G Morton demonstrated the first successful anaesthetic with ether at
Massachusetts general hospital in Boston
Strong Ether
Property Diethylether
Boiling point 35 degrees
Blood/gas partition coefficient 12
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Oil/gas partition coefficient 65
MAC 1.9%
Chloroform Pur
Property Chloroform
Blood/gas partition coefficient 10
Oil/gas partition coefficient 260
MAC 0.5%
First used by James Young Simpson 8.11.1847
2 months later 1st anaesthesia related death
1853: Queen Victoria gives birth to her 8th son Leopold under the influence of
chloroform
Drug Blood: gas Oil: gas MAC Induction/recovery
Halothane 2.4 220 0.8 Medium
Enflurane 1.9 98 0.7 Medium
Isoflurane 1.4 92 1.2 Medium
Sevoflurane 0.6 52 2.1 Fast
Desflurane 0.4 23 6.1 Fast
Intravenous Anaesthetics
Thiopental
First used by 1934 by Lundi and Waters, last barbiturate in anaesthesia
Advantage: fast onset (20 seconds), short duration of action (via
redistribution)
Disadvantage: unstable solution, strongly alkaline, repeated doses will lead to
accumulation in fatty tissue, cardiovascular and respiratory depression
Propofol
Discovered 1977
Most commonly used intravenous anaesthetic in Australia
Advantage:
oFast onset (approx. 60 seconds)
oFast metabolism (liver)
oIdeal for sedation and induction/maintenance for general anaesthesia
Disadvantage:
oPainful injection
oCardiovascular and respiratory depression
Ketamine
Discovered 1942
NMDA receptor antagonist
Produces dissociative anaesthesia (analgesia with only moderate hypnosis)
Advantage:
Fast onset
Very low respiratory depression
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High cardiovascular stability (sympathomimetic)
oIdeal "field anaesthetic"
Disadvantage:
Increases intracranial pressure
Hallucinations
nightmares
Inhalational or iv anaesthesia: just two different option
Onset of iv anaesthetics generally more predictable and shorter
Recovery after cessation of administration is generally longer for iv agents
Lecture 6 - Morphine and Quest for Perfect Pain Control
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