General Anaesthetics Notes

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Lecture 13 General anaesthetics

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Examples o Injection/Intravenous Anaesthetics
? Thipentone
? Propofol (better than above)
? Etomidate
? Midazolam (sedative)
? Ketamine (dissociative anaesthetic) o Inhalation anesthetics
? Nitrous oxide
? Isoflurane, desflurane, sevoflurane (halothane) Effects o Loss of consciousness (not asleep) o Analgesia (many, but not all, produce pain relief) o Muscle relaxation (important in surgery) o Associated with loss of reflexes Stages of anaesthesia (occur with increasing drug in brain) o STAGE 1- ANALGESIA
? Drowsiness (not yet unconscious) o STAGE 2- EXCITEMENT
? Loss of consciousness
? Respiration is irregular, patient is thrashing (unwanted)
? Need to get through this stage as quickly as possible o STAGE 3- SURGICAL ANAESTHESIA
? Regular respiration
? Decline in muscle tone
? Loss of reflexes (planes o STAGE 4- MEDULLARY PARALYSIS
? Too much general anaesthetic
? Stop breathing=death Drug combinations o Premedication- sedative o Rapid induction- propofol, thiopental (anaesthesia induced) o Maintenance of anaesthesia- isoflurane, nitrous oxide o Analgesic supplement- opiate (give during anaesthesia to stop pain going to spinal cord that causes adaptation which would cause pain after surgery) o Muscle relaxant- NMJ blocking agent e.g. atracurium o Muscarinic antagonist- Atropine (operations could increase secretion as PSNS stimulate, so atropine) o (Anticholinesterase) Mechanisms of action (not certain) o No structure activity relationship o No obvious receptor they would all bind to o Unitary theory
? Lipid theories

* Membrane expansion o GA dissolves into lipid membrane and expands lipid

* Membrane fluidity

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