Anaesthesia Flashcards
Give 3 examples of inhalational anaesthetic agents
Give 2 IV
Inhalational: - Nitrous oxide - Isoflurane - Sevoflurane IV: - Propofol - Ketamine
What is the general theory behind anaesthesia?
Principal anaesthetic agent plus adjuvant drugs
What is regional anaesthesia?
Affects larger regions of the body by blocking transmission between that region and the spinal cord
What is local anaesthesia?
Affects small region via peripheral nerve block
Where does general anaesthesia act in terms of anatomical locations?
- Reticular activating system
- Brainstem
- Spinal cord
List 4 molecular targets of anaesthetic agents
- GABA chloride channels
- Glycine chloride channels
- Nicotinic ACh receptors
- NMDA receptors
What is the mechanism of action of Propofol?
Binding to which other channel works exactly the same way?
Acts via GABA chloride channels - bind to channel and increase its sensitivity to GABA - in turn increases chloride currents so cell is hyperpolarised - less excitable
Glycine chloride channels
What is the theory behind targeting nicotinic ACh receptors in anaesthesia?
Inhibiting nACh receptors reduces excitatory currents - contributes to amnesia and analgesia
What is the mechanism of action of nitrous oxide and ketamine?
Bind to glutamate NMDA receptors, which reduces calcium currents and therefore reduces neurotransmission
In terms of pharmacodynamics, what is the mechanism of action of anaesthetic agents which bind to inhibitory ligand-gated channels (GABA/glycine)?
(Mention potency and efficacy)
They are positive allosteric modulators - they decrease the EC50, meaning less GABA/glycine needs to bind in order to exert the same level of effect
Therefore there is increased ligand potency and efficacy
In terms of pharmacodynamics, what is the mechanism of action of anaesthetic agents which bind to excitatory ligand-gated ion channels?
(Mention potency and efficacy)
Non-competitive allosteric antagonism -
once agent binds, receptor is inactivated. Therefore fewer receptors available for binding, so decreased efficacy.
BUT affinity for the unbound receptors is still just as high - no change in potency.
Therefore potency (i.e. EC50) is unchanged but efficacy decreases
How are the inhalational anaesthetic agents administered?
Volatile liquids at room temperature - vaporised and mixed with “carrier” of O2/air/nitrous oxide
Breathed in via mask
What is the MAC?
Minimum alveolar concentration - alveolar concentration at which 50% of patients fail to move to a surgical stimulus
How is MAC linked to potency?
The lower the MAC, the more potent the agent is -
MAC is related to lipid solubility, and the higher the lipid solubility, the more potent the anaesthetic
What is the normal MAC dose needed?
1.2 - 1.5
